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Document And Entity Information - USD ($)	12 Months Ended
Document And Entity Information - USD ($)	Dec. 31, 2011	Feb. 21, 2012	Jun. 30, 2011
Document And Entity Information [Abstract]
Document Type	10-K
Document Period End Date	Dec. 31, 2011
Document Fiscal Year Focus	2011
Document Fiscal Period Focus	FY
Entity Registrant Name	BOSTON PROPERTIES INC
Amendment Flag	false
Entity Central Index Key	0001037540
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		148,280,022
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes
Entity Public Float			$ 15,296,908,315

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2011	Dec. 31, 2010
ASSETS
Real estate, at cost	$ 13,389,472	$ 12,764,935
Less: accumulated depreciation	(2,642,986)	(2,323,818)
Total real estate	10,746,486	10,441,117
Cash and cash equivalents	1,823,208	478,948
Cash held in escrows	40,332	308,031
Investments in securities	9,548	8,732
Tenant and other receivables (net of allowance for doubtful accounts of $1,766 and $2,081, respectively)	79,838	60,813
Related party notes receivable	280,442	270,000
Interest receivable from related party notes receivable	89,854	69,005
Accrued rental income (net of allowance of $2,515 and $3,116, respectively)	522,675	442,683
Deferred charges, net	445,403	436,019
Prepaid expenses and other assets	75,458	65,663
Investments in unconsolidated joint ventures	669,722	767,252
Total assets	14,782,966	13,348,263
Liabilities:
Mortgage notes payable, net	3,123,267	3,047,586
Unsecured senior notes (net of discount of $9,814 and $8,402, respectively)	3,865,186	3,016,598
Unsecured exchangeable senior notes (net of discount of $3,462 and $8,249, respectively)	1,715,685	1,721,817
Unsecured line of credit
Accounts payable and accrued expenses	155,139	161,592
Dividends and distributions payable	91,901	81,031
Accrued interest payable	69,105	62,327
Other liabilities	293,515	237,467
Total liabilities	9,313,798	8,328,418
Commitments and contingencies
Noncontrolling interest:
Redeemable preferred units of the Operating Partnership	55,652	55,652
Equity:
Excess stock, $.01 par value, 150,000,000 shares authorized, none issued or outstanding
Preferred stock, $.01 par value, 50,000,000 shares authorized, none issued or outstanding
Common stock, $.01 par value, 250,000,000 shares authorized, 148,186,511 and 140,278,005 issued and 148,107,611 and 140,199,105 outstanding at December 31, 2011 and 2010, respectively	1,481	1,402
Additional paid-in capital	4,936,457	4,417,162
Dividends in excess of earnings	(53,080)	(24,763)
Treasury common stock at cost, 78,900 shares at December 31, 2011 and 2010	(2,722)	(2,722)
Accumulated other comprehensive loss	(16,138)	(18,436)
Total stockholders' equity attributable to Boston Properties, Inc.	4,865,998	4,372,643
Noncontrolling interests:
Common units of the Operating Partnership	548,581	592,164
Property partnerships	(1,063)	(614)
Total equity	5,413,516	4,964,193
Total liabilities and equity	$ 14,782,966	$ 13,348,263

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2011	Dec. 31, 2010
Consolidated Balance Sheets [Abstract]
Tenant and other receivables, allowance for doubtful accounts	$ 1,766	$ 2,081
Accrued rental income, allowance	2,515	3,116
Unsecured senior notes, discount	9,814	8,402
Unsecured exchangeable senior notes, discount	$ 3,462	$ 8,249
Excess stock, par value	$ 0.01	$ 0.01
Excess stock, shares authorized	150,000,000	150,000,000
Excess stock, shares issued	0	0
Excess stock, shares outstanding	0	0
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares issued	148,186,511	140,278,005
Common stock, shares outstanding	148,107,611	140,199,105
Treasury common stock at cost, shares	78,900	78,900

Consolidated Statements Of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Revenue
Base rent	$ 1,407,070	$ 1,231,564	$ 1,185,431
Recoveries from tenants	201,395	180,719	200,899
Parking and other	83,097	64,490	66,597
Total rental revenue	1,691,562	1,476,773	1,452,927
Hotel revenue	34,529	32,800	30,385
Development and management services	33,435	41,231	34,878
Total revenue	1,759,526	1,550,804	1,518,190
Expenses
Rental	593,977	501,694	501,799
Hotel	26,128	25,153	23,966
General and administrative	81,442	79,658	75,447
Acquisition costs	155	2,614
Suspension of development		(7,200)	27,766
Depreciation and amortization	439,184	338,371	321,681
Total expenses	1,140,886	940,290	950,659
Operating income	618,640	610,514	567,531
Other income (expense)
Income from unconsolidated joint ventures	85,896	36,774	12,058
Interest and other income	5,358	7,332	4,059
Gains (losses) from investments in securities	(443)	935	2,434
Interest expense	(394,131)	(378,079)	(322,833)
Losses from early extinguishments of debt	(1,494)	(89,883)	(510)
Income from continuing operations	313,826	187,593	262,739
Gains on sales of real estate		2,734	11,760
Net income	313,826	190,327	274,499
Net income attributable to noncontrolling interests
Noncontrolling interests in property partnerships	(1,558)	(3,464)	(2,778)
Noncontrolling interest-redeemable preferred units of the Operating Partnership	(3,339)	(3,343)	(3,594)
Noncontrolling interest-common units of the Operating Partnership	(36,250)	(24,099)	(35,534)
Noncontrolling interest in gains on sales of real estate - common units of the Operating Partnership		(349)	(1,579)
Net income attributable to Boston Properties, Inc.	$ 272,679	$ 159,072	$ 231,014
Basic earnings per common share attributable to Boston Properties, Inc.:
Net income	$ 1.87	$ 1.14	$ 1.76
Weighted average number of common shares outstanding	145,693	139,440	131,050
Diluted earnings per common share attributable to Boston Properties, Inc.:
Net income	$ 1.86	$ 1.14	$ 1.76
Weighted average number of common and common equivalent shares outstanding	146,218	140,057	131,512

Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Consolidated Statements Of Comprehensive Income [Abstract]
Net income	$ 313,826	$ 190,327	$ 274,499
Other comprehensive income:
Net effective portion of interest rate contracts		421
Amortization of interest rate contracts	2,595	3,408	2,904
Other comprehensive income	2,595	3,829	2,904
Comprehensive income	316,421	194,156	277,403
Net income attributable to noncontrolling interests	(41,147)	(31,255)	(43,485)
Comprehensive income attributable to noncontrolling interests	(297)	(487)	(390)
Comprehensive income attributable to Boston Properties, Inc.	$ 274,977	$ 162,414	$ 233,528

Consolidated Statements Of Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-In Capital [Member]	Earnings (Dividends) In Excess Of Dividends (Earnings) [Member]	Treasury Stock, At cost [Member]	Accumulated Other Comprehensive Loss [Member]	Noncontrolling Interests [Member]	Total
Equity, value at Dec. 31, 2008	$ 1,212	$ 3,559,841	$ 154,953	$ (2,722)	$ (24,291)	$ 570,112	$ 4,259,105
Equity, shares at Dec. 31, 2008	121,181,000
Conversion of operating partnership units to Common Stock, shares	139,000
Conversion of operating partnership units to Common Stock, value	$ 1	3,969				(3,970)
Reallocation of noncontrolling interest		(42,490)				42,490
Allocated net income for the year			231,014			39,891	270,905
Dividends/distributions declared			(290,534)			(46,574)	(337,108)
Sale of Common Stock, net of offering costs, shares	17,250,000
Sale of Common Stock, net of offering costs, value	$ 173	841,737					841,910
Shares issued pursuant to stock purchase plan, shares	12,000
Shares issued pursuant to stock purchase plan, value		620					620
Net activity from stock option and incentive plan, shares	298,000
Net activity from stock option and incentive plan, value	$ 3	10,002				24,725	34,730
Distributions to noncontrolling interests in property partnerships						(4,007)	(4,007)
Amortization of interest rate contracts					2,514	390	2,904
Equity, value at Dec. 31, 2009	$ 1,389	4,373,679	95,433	(2,722)	(21,777)	623,057	5,069,059
Equity, shares at Dec. 31, 2009	138,880,000
Conversion of operating partnership units to Common Stock, shares	592,000
Conversion of operating partnership units to Common Stock, value	$ 6	17,176				(17,182)
Reallocation of noncontrolling interest		20,176				(20,176)
Allocated net income for the year			159,072			27,912	186,984
Dividends/distributions declared			(279,268)			(42,570)	(321,838)
Shares issued pursuant to stock purchase plan, shares	9,000
Shares issued pursuant to stock purchase plan, value		630					630
Net activity from stock option and incentive plan, shares	718,000
Net activity from stock option and incentive plan, value	$ 7	25,038				29,770	54,815
Acquisition of noncontrolling interest in property partnership		(19,098)				(6,384)	(25,482)
Acquisition of equity component of exchangeable senior notes		(439)					(439)
Distributions to noncontrolling interests in property partnerships						(3,365)	(3,365)
Effective portion of interest rate contracts					367	54	421
Amortization of interest rate contracts					2,974	434	3,408
Equity, value at Dec. 31, 2010	$ 1,402	4,417,162	(24,763)	(2,722)	(18,436)	591,550	$ 4,964,193
Equity, shares at Dec. 31, 2010	140,199,000						140,199,105
Conversion of operating partnership units to Common Stock, shares	2,919,000
Conversion of operating partnership units to Common Stock, value	$ 29	85,469				(85,498)
Reallocation of noncontrolling interest		(23,073)				23,073
Allocated net income for the year			272,679			37,808	$ 310,487
Dividends/distributions declared			(300,996)			(39,132)	(340,128)
Sale of Common Stock, net of offering costs, shares	4,660,000
Sale of Common Stock, net of offering costs, value	$ 47	438,990					439,037
Shares issued pursuant to stock purchase plan, shares	6,000
Shares issued pursuant to stock purchase plan, value		620					620
Net activity from stock option and incentive plan, shares	324,000
Net activity from stock option and incentive plan, value	$ 3	17,289				21,427	38,719
Distributions to noncontrolling interests in property partnerships						(2,007)	(2,007)
Amortization of interest rate contracts					2,298	297	2,595
Equity, value at Dec. 31, 2011	$ 1,481	$ 4,936,457	$ (53,080)	$ (2,722)	$ (16,138)	$ 547,518	$ 5,413,516
Equity, shares at Dec. 31, 2011	148,108,000						148,107,611

Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash flows from operating activities:
Net income	$ 313,826	$ 190,327	$ 274,499
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	439,184	338,371	321,681
Non-cash compensation expense	29,672	32,852	26,636
Income from unconsolidated joint ventures	(85,896)	(36,774)	(12,058)
Distributions of net cash flow from operations of unconsolidated joint ventures	39,851	16,734	12,676
Losses (gains) on investments in securities	443	(935)	(2,434)
Non-cash portion of interest expense	54,962	56,174	55,664
Settlement of accreted debt discount on repurchases of unsecured exchangeable senior notes	(5,601)	(17,555)
Losses from early extinguishments of debt	1,494	12,211	10
Suspension of development		(7,200)	27,766
Non-cash rental revenue			(3,600)
Gains on sales of real estate		(2,734)	(11,760)
Change in assets and liabilities:
Cash held in escrows	(9,801)	(8,664)	103
Tenant and other receivables, net	(19,396)	(5,115)	1,844
Accrued rental income, net	(79,992)	(79,562)	(46,410)
Prepaid expenses and other assets	(39,213)	3,239	4,717
Accounts payable and accrued expenses	6,660	(32,839)	14,848
Accrued interest payable	6,778	(13,731)	8,926
Other liabilities	6,569	(9,393)	(9,452)
Tenant leasing costs	(53,212)	(59,513)	(46,280)
Total adjustments	292,502	185,566	342,877
Net cash provided by operating activities	606,328	375,893	617,376
Cash flows from investing activities:
Acquisitions of real estate	(112,180)	(394,363)	(3,664)
Construction in process	(271,856)	(321,978)	(371,958)
Building and other capital improvements	(61,961)	(20,683)	(28,630)
Tenant improvements	(76,320)	(113,495)	(38,592)
Proceeds from land transaction	43,887
Proceeds from mortgage loan released from (placed in) escrow	267,500	(267,500)
Deposit on real estate released from (placed in) escrow	10,000	(10,000)
Acquisition of note receivable		(22,500)
Issuance of notes receivable	(10,442)
Capital contributions to unconsolidated joint ventures	(17,970)	(62,806)	(11,015)
Capital distributions from unconsolidated joint ventures	140,505	49,902	3,180
Investments in securities, net	(1,259)	2,149	4,078
Net cash used in investing activities	(90,096)	(1,161,274)	(446,601)
Cash flows from financing activities:
Proceeds from mortgage notes payable	1,178,306	268,964	107,929
Repayments of mortgage notes payable	(1,251,841)	(730,191)	(125,238)
Proceeds from unsecured senior notes	848,019	1,542,947	699,517
Repurchases of unsecured senior notes		(700,000)
Repurchases of unsecured exchangeable senior notes	(44,586)	(218,592)
Repurchase of equity component of unsecured exchangeable senior notes		(439)
Repayments of unsecured line of credit			(100,000)
Repayment of note payable			(25,000)
Deferred financing costs	(15,970)	(16,353)	(9,849)
Deposit on mortgage loan financing	(14,500)
Returned deposit on mortgage loan financing	14,500
Net proceeds from ATM stock issuances	439,037
Proceeds from equity transactions	9,667	22,593	850,624
Dividends and distributions	(332,597)	(324,686)	(357,328)
Acquisition of noncontrolling interest in property partnership		(25,482)
Distributions to noncontrolling interests in property partnerships	(2,007)	(3,365)	(4,007)
Net cash provided by (used in) financing activities	828,028	(184,604)	1,036,648
Net increase (decrease) in cash and cash equivalents	1,344,260	(969,985)	1,207,423
Cash and cash equivalents, beginning of the year	478,948	1,448,933	241,510
Cash and cash equivalents, end of the year	1,823,208	478,948	1,448,933
Supplemental disclosures:
Cash paid for interest	386,170	394,172	307,059
Interest capitalized	48,178	40,981	48,816
Non-cash investing and financing activities:
Additions to real estate included in accounts payable	10,767	3,693	36,789
Mortgage notes payable assumed in connection with the acquisition of real estate	143,900	843,104
Note receivable converted to real estate		22,500
Dividends and distributions declared but not paid	91,901	81,031	80,536
Conversions of noncontrolling interests to Stockholders' Equity	85,498	17,182	3,970
Issuance of restricted securities to employees and directors	$ 25,087	$ 19,222	$ 22,964

Organization And Basis Of Presentation

12 Months Ended

Dec. 31, 2011

Organization And Basis Of Presentation [Abstract]

Organization And Basis Of Presentation

Organization and Basis of Presentation

Organization

Boston Properties, Inc. (the "Company"), a Delaware corporation, is a self-administered and self-managed real estate investment trust ("REIT"). The Company is the sole general partner of Boston Properties Limited Partnership (the "Operating Partnership") and at December 31, 2011 owned an approximate 88.3% (86.2% at December 31, 2010) general and limited partnership interest in the Operating Partnership. Partnership interests in the Operating Partnership are denominated as "common units of partnership interest" (also referred to as "OP Units"), "long term incentive units of partnership interest" (also referred to as "LTIP Units") or "preferred units of partnership interest" (also referred to as "Preferred Units"). In addition, in February 2008 and February 2011, the Company issued LTIP Units in connection with the granting to employees of outperformance awards (also referred to as "2008 OPP Units" and "2011 OPP Units," respectively). Because the rights, preferences and privileges of 2008 OPP Units and 2011 OPP Units differ from other LTIP Units granted to employees as part of the annual compensation process, unless specifically noted otherwise, all references to LTIP Units exclude 2008 OPP Units and 2011 OPP Units. On February 5, 2011, the measurement period for the Company's 2008 OPP Unit awards expired and the Company's total return to shareholders ("TRS") was not sufficient for employees to earn and therefore become eligible to vest in any of the 2008 OPP Unit awards. Accordingly, all 2008 OPP Unit awards were automatically forfeited (See Note 17).

Unless specifically noted otherwise, all references to OP Units exclude units held by the Company. A holder of an OP Unit may present such OP Unit to the Operating Partnership for redemption at any time (subject to restrictions agreed upon at the time of issuance of OP Units to particular holders that may restrict such redemption right for a period of time, generally one year from issuance). Upon presentation of an OP Unit for redemption, the Operating Partnership must redeem such OP Unit for cash equal to the then value of a share of common stock of the Company ("Common Stock"). In lieu of a cash redemption, the Company may elect to acquire such OP Unit for one share of Common Stock. Because the number of shares of Common Stock outstanding at all times equals the number of OP Units that the Company owns, one share of Common Stock is generally the economic equivalent of one OP Unit, and the quarterly distribution that may be paid to the holder of an OP Unit equals the quarterly dividend that may be paid to the holder of a share of Common Stock. An LTIP Unit is generally the economic equivalent of a share of restricted common stock of the Company. LTIP Units, whether vested or not, will receive the same quarterly per unit distributions as OP Units, which equal per share dividends on Common Stock (See Note 17).

At December 31, 2011, there was one series of Preferred Units outstanding (i.e., Series Two Preferred Units). The Series Two Preferred Units bear a distribution that is set in accordance with an amendment to the partnership agreement of the Operating Partnership. Preferred Units may also be converted into OP Units at the election of the holder thereof or the Operating Partnership in accordance with the amendment to the partnership agreement (See Note 11).

All references to the Company refer to Boston Properties, Inc. and its consolidated subsidiaries, including the Operating Partnership, collectively, unless the context otherwise requires.

Properties

At December 31, 2011, the Company owned or had interests in a portfolio of 153 commercial real estate properties (the "Properties") aggregating approximately 42.2 million net rentable square feet, including seven properties under construction totaling approximately 2.6 million net rentable square feet. In addition, the Company had structured parking for approximately 44,528 vehicles containing approximately 15.1 million square feet. At December 31, 2011, the Properties consist of:

•

146 office properties, including 128 Class A office properties (including six properties under construction) and 18 Office/Technical properties;

•

one hotel;

•

three retail properties; and

•

three residential properties (including one property under construction).

The Company owns or controls undeveloped land parcels totaling approximately 510.5 acres. In addition, the Company has a noncontrolling interest in the Boston Properties Office Value-Added Fund, L.P. (the "Value-Added Fund"), which is a strategic partnership with two institutional investors through which the Company has pursued the acquisition of value-added investments in assets within its existing markets. The Company's investments through the Value-Added Fund are not included in its portfolio information or any other portfolio level statistics. At December 31, 2011, the Value-Added Fund had investments in 24 buildings comprised of an office property in Chelmsford, Massachusetts and office complexes in Mountain View, California.

The Company considers Class A office properties to be centrally located buildings that are professionally managed and maintained, that attract high-quality tenants and command upper-tier rental rates, and that are modern structures or have been modernized to compete with newer buildings. The Company considers Office/Technical properties to be properties that support office, research and development, laboratory and other technical uses. The Company's definitions of Class A Office and Office/Technical properties may be different than those used by other companies. Net rentable square feet amounts are unaudited.

Basis of Presentation

Boston Properties, Inc. does not have any other significant assets, liabilities or operations, other than its investment in the Operating Partnership, nor does it have employees of its own. The Operating Partnership, not Boston Properties, Inc., executes all significant business relationships. All majority-owned subsidiaries and affiliates over which the Company has financial and operating control and variable interest entities ("VIE"s) in which the Company has determined it is the primary beneficiary are included in the consolidated financial statements. All significant intercompany balances and transactions have been eliminated in consolidation. The Company accounts for all other unconsolidated joint ventures using the equity method of accounting. Accordingly, the Company's share of the earnings of these joint ventures and companies is included in consolidated net income.

- Definition

The entire disclosure for organization, consolidation and basis of presentation of financial statements disclosure.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
-Number 51
-Paragraph 2-6
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Name Statement of Position (SOP)
-Publisher AICPA
-Number 94-6
-Paragraph 10
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef
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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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+ Details

Summary Of Significant Accounting Policies

12 Months Ended

Dec. 31, 2011

Summary Of Significant Accounting Policies [Abstract]

Summary Of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Real Estate

Upon acquisitions of real estate, the Company assesses the fair value of acquired tangible and intangible assets (including land, buildings, tenant improvements, "above-" and "below-market" leases, leasing and assumed financing origination costs, acquired in-place leases, other identified intangible assets and assumed liabilities, and allocates the purchase price to the acquired assets and assumed liabilities, including land at appraised value and buildings as if vacant. The Company assesses and considers fair value based on estimated cash flow projections that utilize discount and/or capitalization rates that it deems appropriate, as well as available market information. Estimates of future cash flows are based on a number of factors including the historical operating results, known and anticipated trends, and market and economic conditions. The fair value of the tangible assets of an acquired property considers the value of the property as if it were vacant. The Company also considers an allocation of purchase price of other acquired intangibles, including acquired in-place leases that may have a customer relationship intangible value, including (but not limited to) the nature and extent of the existing relationship with the tenants, the tenant's credit quality and expectations of lease renewals. Based on its acquisitions to date, the Company's allocation to customer relationship intangible assets has been immaterial.

The Company records acquired "above-" and "below-market" leases at their fair values (using a discount rate which reflects the risks associated with the leases acquired) equal to the difference between (1) the contractual amounts to be paid pursuant to each in-place lease and (2) management's estimate of fair market lease rates for each corresponding in-place lease, measured over a period equal to the remaining term of the lease for above-market leases and the initial term plus the term of any below-market fixed rate renewal options for below- market leases. Other intangible assets acquired include amounts for in-place lease values that are based on the Company's evaluation of the specific characteristics of each tenant's lease. Factors to be considered include estimates of carrying costs during hypothetical expected lease-up periods considering current market conditions, and costs to execute similar leases. In estimating carrying costs, the Company includes real estate taxes, insurance and other operating expenses and estimates of lost rentals at market rates during the expected lease-up periods, depending on local market conditions. In estimating costs to execute similar leases, the Company considers leasing commissions, legal and other related expenses.

Management reviews its long-lived assets used in operations for impairment following the end of each quarter and when there is an event or change in circumstances that indicates an impairment in value. An impairment loss is recognized if the carrying amount of its assets is not recoverable and exceeds its fair value. If such criteria are present, an impairment loss is recognized based on the excess of the carrying amount of the asset over its fair value. The evaluation of anticipated cash flows is highly subjective and is based in part on assumptions regarding future occupancy, rental rates and capital requirements that could differ materially from actual results in future periods. Since cash flows on properties considered to be "long-lived assets to be held and used" are considered on an undiscounted basis to determine whether an asset has been impaired, the Company's established strategy of holding properties over the long term directly decreases the likelihood of recording an impairment loss. If the Company's strategy changes or market conditions otherwise dictate an earlier sale date, an impairment loss may be recognized and such loss could be material. If the Company determines that impairment has occurred, the affected assets must be reduced to their fair value.

ASC 360 (formerly known as SFAS No. 144) requires that qualifying assets and liabilities and the results of operations that have been sold, or otherwise qualify as "held for sale," be presented as discontinued operations in all periods presented if the property operations are expected to be eliminated and the Company will not have significant continuing involvement following the sale. The components of the property's net income that is reflected as discontinued operations include the net gain (or loss) upon the disposition of the property held for sale, operating results, depreciation and interest expense (if the property is subject to a secured loan). The Company generally considers assets to be "held for sale" when the transaction has been approved by the Board of Directors, or a committee thereof, and there are no known significant contingencies relating to the sale, such that the property sale within one year is considered probable. Following the classification of a property as "held for sale," no further depreciation is recorded on the assets, and the asset is written down to the lower of carrying value or fair market value.

Real estate is stated at depreciated cost. A variety of costs are incurred in the acquisition, development and leasing of properties. The cost of buildings and improvements includes the purchase price of property, legal fees and other acquisition costs. Effective January 1, 2009, the Company was required to expense costs that an acquirer incurs to effect a business combination such as legal, due diligence and other closing related costs. Costs directly related to the development of properties are capitalized. Capitalized development costs include interest, internal wages, property taxes, insurance, and other project costs incurred during the period of development. After the determination is made to capitalize a cost, it is allocated to the specific component of a project that is benefited. Determinations of when a development project commences and capitalization begins, and when a development project is substantially complete and held available for occupancy and capitalization must cease, involve a degree of judgment. The Company's capitalization policy on development properties is guided by guidance in ASC 835-20 "Capitalization of Interest" and ASC 970 "Real Estate – General" (formerly known as SFAS No. 34 "Capitalization of Interest Cost" and SFAS No. 67 "Accounting for Costs and the Initial Rental Operations of Real Estate Projects"). The costs of land and buildings under development include specifically identifiable costs. The capitalized costs include pre-construction costs necessary to the development of the property, development costs, construction costs, interest costs, real estate taxes, salaries and related costs and other costs incurred during the period of development. The Company begins the capitalization of costs during the pre-construction period, which it defines as activities that are necessary to the development of the property. The Company considers a construction project as substantially completed and held available for occupancy upon the completion of tenant improvements, but no later than one year from cessation of major construction activity. The Company ceases capitalization on the portion (1) substantially completed and (2) occupied or held available for occupancy, and capitalizes only those costs associated with the portion under construction, or if activities necessary for the development of the property have been suspended. Interest costs capitalized for the years ended December 31, 2011, 2010 and 2009 were $48.2 million, $41.0 million and $48.8 million, respectively. Salaries and related costs capitalized for the years ended December 31, 2011, 2010 and 2009 were $6.5 million, $6.2 million and $7.9 million, respectively.

Expenditures for repairs and maintenance are charged to operations as incurred. Significant betterments are capitalized. When assets are sold or retired, their costs and related accumulated depreciation are removed from the accounts with the resulting gains or losses reflected in net income or loss for the period.

The Company computes depreciation and amortization on properties using the straight-line method based on estimated useful asset lives. In accordance with ASC 805 (formerly known as SFAS No. 141(R)), the Company allocates the acquisition cost of real estate to land, building, tenant improvements, acquired "above-" and "below-market" leases, origination costs and acquired in-place leases based on an assessment of their fair value and depreciates or amortizes these assets (or liabilities) over their useful lives. The amortization of acquired "above-" and "below-market" leases and acquired in-place leases is recorded as an adjustment to revenue and depreciation and amortization, respectively, in the Consolidated Statements of Operations.

Depreciation is computed on a straight-line basis over the estimated useful lives of the assets as follows:


Land improvements		25 to 40 years
Buildings and improvements		10 to 40 years
Tenant improvements		Shorter of useful life or terms of related lease
Furniture, fixtures, and equipment		3 to 7 years

Cash and Cash Equivalents

Cash and cash equivalents consist of cash on hand and investments with maturities of three months or less from the date of purchase. The majority of the Company's cash and cash equivalents are held at major commercial banks which may at times exceed the Federal Deposit Insurance Corporation limit of $250,000. The Company has not experienced any losses to date on its invested cash.

Cash Held in Escrows

Escrows include amounts established pursuant to various agreements for security deposits, property taxes, insurance and other costs.

Investments in Securities

The Company accounts for investments in trading securities at fair value, with gains or losses resulting from changes in fair value recognized currently in earnings. The designation of trading securities is generally determined at acquisition. The Company maintains a deferred compensation plan that is designed to allow officers of the Company to defer a portion of their current income on a pre-tax basis and receive a tax-deferred return on these deferrals. The Company's obligation under the plan is that of an unsecured promise to pay the deferred compensation to the plan participants in the future. At December 31, 2011 and 2010, the Company has funded approximately $9.5 million and $8.7 million, respectively, into a separate account, which is not restricted as to its use. The Company recognized gains (losses) of approximately $(0.4) million, $0.9 million and $2.2 million on its investments in the account associated with the Company's deferred compensation plan during the years ended December 31, 2011, 2010 and 2009, respectively.

Tenant and other receivables

Tenant and other accounts receivable, other than accrued rents receivable, are expected to be collected within one year.

Deferred Charges

Deferred charges include leasing costs and financing fees. Leasing costs include an allocation for acquired intangible in-place lease values and direct and incremental fees and costs incurred in the successful negotiation of leases, including brokerage, legal, internal leasing employee salaries and other costs which have been deferred and are being amortized on a straight-line basis over the terms of the respective leases. Internal leasing salaries and related costs capitalized for the years ended December 31, 2011, 2010 and 2009 were $4.4 million, $5.4 million and $3.3 million, respectively. External fees and costs incurred to obtain long-term financing have been deferred and are being amortized over the terms of the respective loans on a basis that approximates the effective interest method and are included with interest expense. Unamortized financing and leasing costs are charged to expense upon the early repayment or significant modification of the financing or upon the early termination of the lease, respectively. Fully amortized deferred charges are removed from the books upon the expiration of the lease or maturity of the debt.

Investments in Unconsolidated Joint Ventures

The Company consolidates variable interest entities in which it is considered to be the primary beneficiary. The primary beneficiary is defined by the entity having both of the following characteristics: (1) the power to direct the activities that, when taken together, most significantly impact the variable interest entity's performance, and (2) the obligation to absorb losses and right to receive the returns from the variable interest entity that would be significant to the variable interest entity. Except for ownership interests in variable interest entities for which the Company is the primary beneficiary, the Company accounts for its investments in joint ventures under the equity method of accounting because it exercises significant influence over, but does not control, these entities. The Company's judgment with respect to its level of influence or control of an entity involves the consideration of various factors including the form of the Company's ownership interest, its representation in the entity's governance, the size of its investment (including loans), estimates of future cash flows, its ability to participate in policy making decisions and the rights of the other investors to participate in the decision making process and to replace the Company as manager and/or liquidate the venture, if applicable. The Company's assessment of its influence or control over an entity affects the presentation of these investments in the Company's consolidated financial statements.

These investments are recorded initially at cost, as Investments in Unconsolidated Joint Ventures, and subsequently adjusted for equity in earnings and cash contributions and distributions. Any difference between the carrying amount of these investments on the balance sheet and the underlying equity in net assets is amortized as an adjustment to equity in earnings of unconsolidated joint ventures over the life of the related asset. Under the equity method of accounting, the net equity investment of the Company is reflected within the Consolidated Balance Sheets, and the Company's share of net income or loss from the joint ventures is included within the Consolidated Statements of Operations. The joint venture agreements may designate different percentage allocations among investors for profits and losses, however, the Company's recognition of joint venture income or loss generally follows the joint venture's distribution priorities, which may change upon the achievement of certain investment return thresholds. The Company may account for cash distributions in excess of its investment in an unconsolidated joint venture as income when the Company is not the general partner in a limited partnership and when the Company has neither the requirement nor the intent to provide financial support to the joint venture. The Company's investments in unconsolidated joint ventures are reviewed for impairment periodically and the Company records impairment charges when events or circumstances change indicating that a decline in the fair values below the carrying values has occurred and such decline is other-than-temporary. The ultimate realization of the investment in unconsolidated joint ventures is dependent on a number of factors, including the performance of each investment and market conditions. The Company will record an impairment charge if it determines that a decline in the value below the carrying value of an investment in an unconsolidated joint venture is other than temporary.

To the extent that the Company contributes assets to a joint venture, the Company's investment in the joint venture is recorded at the Company's cost basis in the assets that were contributed to the joint venture. To the extent that the Company's cost basis is different than the basis reflected at the joint venture level, the basis difference is amortized over the life of the related asset and included in the Company's share of equity in net income of the joint venture. In accordance with the provisions of ASC 970-323 "Investments—Equity Method and Joint Ventures" ("ASC 970-323") (formerly Statement of Position 78-9 "Accounting for Investments in Real Estate Ventures" ("SOP 78-9")), the Company will recognize gains on the contribution of real estate to joint ventures, relating solely to the outside partner's interest, to the extent the economic substance of the transaction is a sale.

Equity Offering Costs

Underwriting commissions and offering costs have been reflected as a reduction of additional paid-in capital.

Treasury Stock

The Company's share repurchases are reflected as treasury stock utilizing the cost method of accounting and are presented as a reduction to consolidated stockholders' equity.

Dividends

Earnings and profits, which determine the taxability of dividends to stockholders, will differ from income reported for financial reporting purposes due to the differences for federal income tax purposes in the treatment of gains on the sale of real property, revenue and expense recognition, compensation expense, and in the estimated useful lives and basis used to compute depreciation.

The tax treatment of common dividends per share for federal income tax purposes is as follows:


	For the year ended December 31,
	2011					2010					2009
	Per Share		%			Per Share		%			Per Share		%
Ordinary income	$	2.06		97.39	%	$	1.17		58.39	%	$	2.15		90.93	%
Capital gain income		0.05		2.61	%		—		—			—		—
Return of capital		—		—			0.83		41.61	%		0.21		9.07	%

Total	$	2.11		100.00	%	$	2.00		100.00	%	$	2.36		100.00	%

Revenue Recognition

Contractual rental revenue is reported on a straight-line basis over the terms of the respective leases. The impact of the straight-line rent adjustment increased revenue by approximately $77.0 million, $85.1 million and $42.2 million for the years ended December 31, 2011, 2010 and 2009, respectively, as the revenue recorded exceeded amounts billed. In accordance with ASC 805 (formerly SFAS No. 141(R)), the Company recognizes rental revenue of acquired in-place "above-" and "below-market" leases at their fair values over the terms of the respective leases. The impact of the acquired in-place "above-" and "below-market" leases increased revenue by approximately $10.8 million, $2.4 million and $4.2 million for the years ended December 31, 2011, 2010 and 2009, respectively. Accrued rental income, as reported on the Consolidated Balance Sheets, represents cumulative rental income earned in excess of rent payments received pursuant to the terms of the individual lease agreements. The Company maintains an allowance against accrued rental income for future potential tenant credit losses. The credit assessment is based on the estimated accrued rental income that is recoverable over the term of the lease. The Company also maintains an allowance for doubtful accounts for estimated losses resulting from the inability of tenants to make required rent payments. The computation of this allowance is based on the tenants' payment history and current credit status, as well as certain industry or geographic specific credit considerations. If the Company's estimates of collectability differ from the cash received, then the timing and amount of the Company's reported revenue could be impacted. The credit risk is mitigated by the high quality of the Company's existing tenant base, reviews of prospective tenants' risk profiles prior to lease execution and consistent monitoring of the Company's portfolio to identify potential problem tenants.

Recoveries from tenants, consisting of amounts due from tenants for common area maintenance, real estate taxes and other recoverable costs are recognized as revenue in the period during which the expenses are incurred. Tenant reimbursements are recognized and presented in accordance with guidance in ASC 605-45 "Principal Agent Considerations" ("ASC 605-45") (formerly known as Emerging Issues Task Force, or EITF, Issue 99-19 "Reporting Revenue Gross as a Principal versus Net as an Agent," or ("Issue 99-19")). ASC 605-45 requires that these reimbursements be recorded on a gross basis, as the Company is generally the primary obligor with respect to purchasing goods and services from third-party suppliers, has discretion in selecting the supplier and has credit risk. The Company also receives reimbursement of payroll and payroll related costs from third parties which the Company reflects on a net basis in accordance with ASC 605-45.

The Company's hotel revenues are derived from room rentals and other sources such as charges to guests for long-distance telephone service, fax machine use, movie and vending commissions, meeting and banquet room revenue and laundry services. Hotel revenues are recognized as earned.

The Company receives management and development fees from third parties. Property management fees are recorded and earned based on a percentage of collected rents at the properties under management, and not on a straight-line basis, because such fees are contingent upon the collection of rents. The Company reviews each development agreement and records development fees as earned depending on the risk associated with each project. Profit on development fees earned from joint venture projects is recognized as revenue to the extent of the third party partners' ownership interest.

Gains on sales of real estate are recognized pursuant to the provisions included in ASC 360-20 "Real Estate Sales" ("ASC 360-20") (formerly known as SFAS No. 66, "Accounting for Sales of Real Estate" ("SFAS No. 66")). The specific timing of a sale is measured against various criteria in ASC 360-20 related to the terms of the transaction and any continuing involvement in the form of management or financial assistance associated with the properties. If the sales criteria for the full accrual method are not met, the Company defers some or all of the gain recognition and accounts for the continued operations of the property by applying the finance, leasing, profit sharing, deposit, installment or cost recovery methods, as appropriate, until the sales criteria are met.

Ground Leases

The Company has non-cancelable ground lease obligations with various initial term expiration dates through 2068. The Company recognizes ground rent expense on a straight-line basis over the terms of the respective ground lease agreements. The future contractual minimum lease payments to be made by the Company as of December 31, 2011, under non-cancelable ground leases which expire on various dates through 2068, are as follows:


Years Ending December 31,	(in thousands)
2012	$	12,693
2013		12,908
2014		13,272
2015		13,595
2016		13,820
Thereafter		927,394

Earnings Per Share

Basic earnings per share ("EPS") is computed by dividing net income available to common shareholders, as adjusted for unallocated earnings (if any) of certain securities issued by the Operating Partnership, by the weighted average number of shares of Common Stock outstanding during the year. Diluted EPS reflects the potential dilution that could occur from shares issuable in connection with awards under stock-based compensation plans, including upon the exercise of stock options, and conversion of the noncontrolling interests in the Operating Partnership.

Fair Value of Financial Instruments

The carrying values of cash and cash equivalents, marketable securities, escrows, receivables, accounts payable, accrued expenses and other assets and liabilities are reasonable estimates of their fair values because of the short maturities of these instruments.

For purposes of financial reporting disclosures, the Company estimates the fair value of mortgage notes payable, unsecured senior notes and unsecured exchangeable senior notes. The Company discounts the spread between the future contractual interest payments and hypothetical future interest payments on mortgage debt and unsecured notes based on current market rates for similar securities. In determining the current market rates, the Company adds its estimates of market spreads to the quoted yields on federal government treasury securities with similar maturity dates to its debt. Because the Company's valuations of its financial instruments are based on these types of estimates, the actual fair values of its financial instruments may differ materially if the Company's estimates do not prove to be accurate. The following table presents the aggregate carrying value of the Company's indebtedness and the Company's corresponding estimate of fair value as of December 31, 2011 and December 31, 2010 (in thousands):


	December 31, 2011					December 31, 2010
	Carrying Amount			Estimated Fair Value		Carrying Amount			Estimated Fair Value
Mortgage notes payable	$	3,123,267		$	3,297,903	$	3,047,586		$	3,121,193
Unsecured senior notes		3,865,186			4,148,461		3,016,598			3,241,542
Unsecured exchangeable senior notes		1,715,685	(1)		1,904,115		1,721,817	(1)		1,929,291

Total	$	8,704,138		$	9,350,479	$	7,786,001		$	8,292,026

(1)	Includes the net impact of unamortized portion of imputed discounts under ASC 470-20 (formerly known as FSP No. APB 14-1) totaling approximately $54.5 million and $93.6 million at December 31, 2011 and 2010, respectively (See Note 8).

Derivative Instruments and Hedging Activities

Derivative instruments and hedging activities require management to make judgments on the nature of its derivatives and their effectiveness as hedges. These judgments determine if the changes in fair value of the derivative instruments are reported in the consolidated statements of operations as a component of net income or as a component of comprehensive income and as a component of equity on the consolidated balance sheets. While management believes its judgments are reasonable, a change in a derivative's effectiveness as a hedge could materially affect expenses, net income and equity. The Company accounts for the effective portion of changes in the fair value of a derivative in other comprehensive income (loss) and subsequently reclassifies the effective portion to earnings over the term that the hedged transaction affects earnings. The Company accounts for the ineffective portion of changes in the fair value of a derivative directly in earnings.

Income Taxes

The Company has elected to be treated as a REIT under Sections 856 through 860 of the Internal Revenue Code of 1986, as amended (the "Code"), commencing with its taxable year ended December 31, 1997. As a result, the Company generally will not be subject to federal corporate income tax on its taxable income that is distributed to its stockholders. A REIT is subject to a number of organizational and operational requirements, including a requirement that it currently distribute at least 90% of its annual taxable income. The Company's policy is to distribute at least 100% of its taxable income. Accordingly, the only provision for federal income taxes in the accompanying consolidated financial statements relates to the Company's consolidated taxable REIT subsidiaries. The Company's taxable REIT subsidiaries did not have significant tax provisions or deferred income tax items.

The Company owns a hotel property which is managed through a taxable REIT subsidiary. The hotel taxable REIT subsidiary, a wholly owned subsidiary of the Operating Partnership, is the lessee pursuant to the lease for the hotel property. As lessor, the Operating Partnership is entitled to a percentage of gross receipts from the hotel property. Marriott International, Inc. continues to manage the hotel property under the Marriott name and under terms of the existing management agreements. In connection with the restructuring, the revenue and expenses of the hotel property are being reflected in the Company's Consolidated Statements of Operations. The hotel taxable REIT subsidiary is subject to tax at the federal and state level and, accordingly, the Company has recorded a tax provision in the Company's Consolidated Statements of Operations for the years ended December 31, 2011, 2010 and 2009.

The net difference between the tax basis and the reported amounts of the Company's assets and liabilities is approximately $0.9 billion and $1.2 billion as of December 31, 2011 and 2010, respectively, which is primarily related to the difference in basis of contributed property and accrued rental income.

Certain entities included in the Company's consolidated financial statements are subject to certain state and local taxes. These taxes are recorded as operating expenses in the accompanying consolidated financial statements.

The following reconciles GAAP net income attributable to Boston Properties, Inc. to taxable income:


	For the year ended December 31,
	2011			2010			2009
	(in thousands)
Net income attributable to Boston Properties, Inc.	$	272,679		$	159,072		$	231,014
Straight-line rent adjustments		(77,422	)		(75,943	)		(38,287	)
Book/Tax differences from depreciation and amortization		117,675			67,362			61,366
Book/Tax differences on gains/losses from capital transactions		(38,443	)		(2,373	)		(10,111	)
Book/Tax differences from stock-based compensation		827			(1,957	)		15,966
Book/Tax differences on losses from early extinguishments of debt		40			6,448			—
Impairment loss on investments in unconsolidated joint ventures		—			—			6,374
Other book/tax differences, net		29,349			3,921			492

Taxable income	$	304,705		$	156,530		$	266,814

Stock-based employee compensation plans At December 31, 2011, the Company has a stock-based employee compensation plan. Effective January 1, 2005, the Company adopted early ASC 718 "Compensation – Stock Compensation" ("ASC 718") (formerly SFAS No. 123 (revised) ("SFAS No. 123R"), "Share-Based Payment"), which revised the fair value based method of accounting for share-based payment liabilities, forfeitures and modifications of stock-based awards and clarified previous guidance in several areas, including measuring fair value, classifying an award as equity or as a liability and attributing compensation cost to reporting periods.

Use of Estimates in the Preparation of Financial Statements

The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. These estimates include such items as depreciation and allowances for doubtful accounts. Actual results could differ from those estimates.

Real Estate

12 Months Ended

Dec. 31, 2011

Real Estate [Abstract]

Real Estate

3. Real Estate

Real estate consisted of the following at December 31 (in thousands):


	2011			2010
Land	$	2,356,522		$	2,216,768
Land held for future development		266,822			757,556
Buildings and improvements		8,658,468			7,602,704
Tenant improvements		1,262,616			1,090,462
Furniture, fixtures and equipment		26,359			24,043
Construction in progress		818,685			1,073,402

Total		13,389,472			12,764,935
Less: Accumulated depreciation		(2,642,986	)		(2,323,818	)

	$	10,746,486		$	10,441,117

Acquisitions

On February 1, 2011, the Company completed the acquisition of Bay Colony Corporate Center in Waltham, Massachusetts for an aggregate purchase price of approximately $185.0 million. The purchase price consisted of approximately $41.1 million of cash and the assumption of approximately $143.9 million of indebtedness. The assumed debt is a securitized senior mortgage loan that bears interest at a fixed rate of 6.53% per annum and matures on June 11, 2012. The loan requires interest-only payments with a balloon payment due at maturity. Bay Colony Corporate Center is an approximately 985,000 net rentable square foot, four-building Class A office park situated on a 58-acre site in Waltham, Massachusetts. The following table summarizes the allocation of the aggregate purchase price of Bay Colony Corporate Center at the date of acquisition (in thousands).


Land	$	18,769
Building and improvements		136,081
Tenant improvements		12,370
In-place lease intangibles		20,626
Above market rents		5,802
Below market rents		(3,332	)
Above market assumed debt adjustment		(5,316	)

Total aggregate purchase price	$	185,000
Less: Indebtedness assumed		(143,900	)

Net assets acquired	$	41,100

On November 22, 2011, the Company acquired 2440 West El Camino Real located in Mountain View, California for a net purchase price of approximately $71.1 million in cash. 2440 West El Camino Real is an approximately 140,000 net rentable square foot Class A office property. The following table summarizes the allocation of the aggregate purchase price of 2440 West El Camino Real at the date of acquisition (in thousands).


Land	$	16,741
Building and improvements		47,199
Tenant improvements		4,086
In-place lease intangibles		5,284
Above market rents		30
Below market rents		(2,260	)

Net assets acquired	$	71,080

The following table summarizes the estimated amortization of the acquired above-market lease intangibles (net of acquired below-market lease intangibles) and the acquired in-place lease intangibles for Bay Colony Corporate Center and 2440 West El Camino Real for each of the five succeeding years (in thousands).


	Acquired In-Place Lease Intangibles		Acquired Net Above-/(Below-) Market Lease Intangibles
2012	$	6,397	$	124
2013		4,647		(54	)
2014		3,576		(183	)
2015		2,539		(72	)
2016		1,171		41

Bay Colony Corporate Center contributed approximately $19.1 million of revenue and approximately $(11.8) million of earnings to the Company for the period from February 1, 2011 through December 31, 2011. 2440 West El Camino Real contributed approximately $0.8 million of revenue and approximately $0.2 million of earnings to the Company for the period from November 22, 2011 through December 31, 2011.

The accompanying unaudited pro forma information for the years ended December 31, 2011 and 2010 is presented as if the acquisition of (1) Bay Colony Corporate Center on February 1, 2011 and (2) 2440 West El Camino Real on November 22, 2011, had occurred on January 1, 2010. This unaudited pro forma information is based upon the historical consolidated financial statements and should be read in conjunction with the consolidated financial statements and notes thereto. This unaudited pro forma information does not purport to represent what the actual results of operations of the Company would have been had the above occurred, nor do they purport to predict the results of operations of future periods.


Pro Forma (Unaudited)	Year Ended December 31,
(in thousands, except per share data)	2011		2010
Total revenue	$	1,768,805	$	1,577,441
Income from continuing operations	$	315,457	$	180,957
Net income attributable to Boston Properties, Inc.	$	274,123	$	153,282
Basic earnings per share:
Net income per share attributable to Boston Properties, Inc.	$	1.88	$	1.10
Diluted earnings per share:
Net income per share attributable to Boston Properties, Inc.	$	1.87	$	1.09

Developments

On January 14, 2011, the Company placed in-service approximately 57% of the office component of its Atlantic Wharf development project located in Boston, Massachusetts. The office component is comprised of approximately 798,000 net rentable square feet. On November 15, 2011, the Company completed and fully placed in-service the office component of the development project.

On March 1, 2011, the Company placed in-service approximately 13% of the office component of its 2200 Pennsylvania Avenue development project located in Washington, DC. The office component is comprised of approximately 459,000 net rentable square feet. On August 17, 2011, the Company completed and fully placed in-service the office component of the development project.

On May 1, 2011, the Company placed in-service approximately 16% of its 510 Madison Avenue development project located in New York City. 510 Madison Avenue is an approximately 347,000 net rentable square foot Class A office property.

On May 11, 2011, the Company partially placed in-service the Residences on The Avenue, the residential component of its 2221 I Street, NW development project located in Washington, DC. The residential component is comprised of 335 apartment units and approximately 50,000 square feet of retail space. On July 13, 2011, the Company completed and fully placed in-service the residential component of the development project.

On May 24, 2011, the Company signed a lease with a law firm for approximately 184,000 square feet at 250 West 55th Street in New York City. In conjunction with the execution of the lease, the Company resumed development of the planned approximately 989,000 square foot Class A office project and commenced capitalization of interest.

On July 1, 2011, the Company completed and placed in-service 100% of The Lofts at Atlantic Wharf, the residential component of its Atlantic Wharf development project located in Boston, Massachusetts. The residential component is comprised of 86 apartment units and approximately 9,000 square feet of retail space.

On July 5, 2011, the Company commenced the redevelopment of 12310 Sunrise Valley Drive, a Class A office project with approximately 268,000 net rentable square feet located in Reston, Virginia. The Company will capitalize incremental costs during the redevelopment.

On July 14, 2011, the Company entered into a 15-year lease for 100% of a build-to-suit development project with approximately 190,000 net rentable square feet of Class A office space located on land owned by the Company at 17 Cambridge Center in Cambridge, Massachusetts. In conjunction with the execution of the lease, the Company has commenced construction of the project.

On December 19, 2011, the Company commenced construction of its Reston Town Center Residential project, a residential project comprised of 359 apartment units located in Reston, Virginia.

Dispositions

On May 23, 2011, the Company entered into a ground lease for 75 Ames Street, a vacant land parcel in Cambridge, Massachusetts located on the same site as the Company's Cambridge Center West Garage property and adjacent to the Company's Seven Cambridge Center property, with a third party. In addition, the Company entered into a development agreement to serve as project manager for a 250,000 square foot research laboratory building to be developed on the site at the ground lessee's expense and will also serve, upon completion of development, as property manager. The terms of the ground lease require the Company to form a condominium for the site upon completion of the development, at which time each party will subject their respective interests in the buildings and land to the condominium and will in turn be conveyed a condominium unit comprised of their respective building as well as an undivided ownership interest in the land. Gross proceeds to the Company are expected to total approximately $56.8 million, including $11.4 million in development fees for the Company's services. As of December 31, 2011, the Company has received approximately $48.9 million and anticipates receiving another $7.9 million in development fees through the third quarter of 2014. The cash received under the ground lease will initially be recognized as unearned revenue and recognized over the 99-year term of the ground lease. The Company will recognize approximately $459,000 per year in ground lease payments prior to the anticipated conveyance of the condominium interest in 2014. Upon completion of the development and conveyance of the condominium interest, the transaction and related remaining costs will be accounted for and recognized as a gain on sale of real estate in accordance with ASC 360-20 "Real Estate Sales."

On June 6, 2011, the Company terminated its agreement, dated April 21, 2011, to sell its Carnegie Center portfolio located in Princeton, New Jersey for approximately $468.0 million. Carnegie Center is a sixteen building Class A office park set on 560 acres and totaling more than 2.0 million net rentable square feet. Under the terms of the agreement, either party had the right to terminate the agreement at any time without any cost or payment to the other party.

- Definition

The entire disclosure for certain real estate investment financial statements, real estate investment trust operating support agreements, real estate owned, retail land sales, time share transactions, as well as other real estate related disclosures.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 57
-Paragraph 2
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph c
-Subparagraph Schedule III
-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 28
-Article 12

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 6
-Subparagraph a
-Article 5

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher OTS
-Name Federal Regulation (FR)
-Number Title 12
-Chapter V
-Section 563c.102
-Paragraph 11
-Subsection I
-LegacyDoc This is a non-GAAP reference that was included in the 2009 taxonomy. It will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
-Number 43
-Chapter 3
-Section A
-Paragraph 9
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 154
-Paragraph 22
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 67
-Paragraph 4, 5, 6, 7
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name FASB Interpretation (FIN)
-Number 46R
-Paragraph 23, 24
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Statement of Position (SOP)
-Number 01-6
-Paragraph 13
-Subparagraph f
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 15
-Paragraph 28
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Statement of Position (SOP)
-Number 75-2
-Paragraph 47, 51, 52
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Audit and Accounting Guide (AAG)
-Number AAG-DEP
-Chapter 11
-Paragraph 2, 6, 9-11, 18, 20
-IssueDate 2006-05-01
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Statement of Position (SOP)
-Number 04-2
-Paragraph 41, 63, 64
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 15: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 144
-Paragraph 7, 34
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 16: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 34
-Paragraph 9, 11, 12, 13, 14, 15, 21
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 17: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 66
-Paragraph 4, 5, 37, 50, 59, 65, 95, 97
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 18: http://www.xbrl.org/2003/role/presentationRef
-Publisher OTS
-Name Federal Regulation (FR)
-Number Title 12
-Chapter V
-Section 563c.102
-Paragraph 10
-Subparagraph a, b
-Subsection I
-LegacyDoc This is a non-GAAP reference that was included in the 2009 taxonomy. It will be removed from future versions of this taxonomy.

Reference 19: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 10
-Subparagraph 4
-Article 9

Reference 20: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 11
-Article 9

Reference 21: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 970
-SubTopic 360
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-28)
-URI http://asc.fasb.org/extlink&oid=6590653&loc=d3e638233-123024

+ Details

Deferred Charges

12 Months Ended

Dec. 31, 2011

Deferred Charges [Abstract]

Deferred Charges

Deferred Charges

Deferred charges consisted of the following at December 31, (in thousands):


	2011			2010
Leasing costs (and lease related intangibles)	$	598,352		$	558,620
Financing costs		85,554			89,680

		683,906			648,300
Less: Accumulated amortization		(238,503	)		(212,281	)

	$	445,403		$	436,019

Investments In Unconsolidated Joint Ventures

12 Months Ended

Dec. 31, 2011

Investments In Unconsolidated Joint Ventures [Abstract]

Investments In Unconsolidated Joint Ventures

5. Investments in Unconsolidated Joint Ventures

The investments in unconsolidated joint ventures consists of the following at December 31, 2011:


Entity	Properties	Nominal % Ownership
Square 407 Limited Partnership	Market Square North	50.0	%
The Metropolitan Square Associates LLC	Metropolitan Square	51.0	%
BP/CRF 901 New York Avenue LLC	901 New York Avenue	25.0	%(1)
WP Project Developer LLC	Wisconsin Place Land and Infrastructure	33.3	%(2)
RBP Joint VentureLLC	Eighth Avenue and 46thStreet	50.0	%(3)
Boston Properties Office Value-Added Fund, L.P.	300 Billerica Road and Mountain View Research and Technology Parks	37.6	%(1)(4)
Annapolis Junction NFM, LLC	Annapolis Junction	50.0	%(5)
767 Venture, LLC	The General Motors Building	60.0	%
2 GCT Venture LLC	Two Grand Central Tower	60.0	%(6)
540 Madison Venture LLC	540 Madison Avenue	60.0	%
125 West 55^thStreet Venture LLC	125 West 55^thStreet	60.0	%
500 North Capitol LLC	500 North Capitol Street, NW	30.0	%

(1)	The Company's economic ownership can increase based on the achievement of certain return thresholds.

(2)	The Company's wholly-owned entity that owns the office component of the project owns a 33.3% interest in the entity owning the land and infrastructure of the project.

(3)	This property is not in operation and consists of assembled land.

(4)	Represents the Company's effective ownership interest. The Company has a 25.0% interest in the 300 Billerica Road property and a 39.5% interest in the Mountain View Research and Technology Park properties.

(5)	Comprised of one building, one building under construction and two undeveloped land parcels.

(6)	The property was sold on October 25, 2011. As of December 31, 2011, the investment is comprised of working capital and a portion of the sale proceeds.

Certain of the Company's joint venture agreements include provisions whereby, at certain specified times, each partner has the right to initiate a purchase or sale of its interest in the joint ventures at an agreed upon fair value. Under these provisions, the Company is not compelled to purchase the interest of its outside joint venture partners.

The combined summarized financial information of the unconsolidated joint ventures is as follows (in thousands):


	December 31,
Balance Sheets	2011			2010
Real estate and development in process, net	$	4,542,594		$	5,028,851
Other assets		668,113			749,308

Total assets	$	5,210,707		$	5,778,159

Mortgage and Notes payable	$	2,988,894		$	3,151,220
Other liabilities		854,257			969,082
Members'/Partners' equity		1,367,556			1,657,857

Total liabilities and members'/partners' equity	$	5,210,707		$	5,778,159

Company's share of equity	$	799,479		$	924,235
Basis differential(1)		(129,757	)		(156,983	)

Carrying value of the Company's investments in unconsolidated joint ventures	$	669,722		$	767,252

(1)

This amount represents the aggregate difference between the Company's historical cost basis and the basis reflected at the joint venture level, which is typically amortized over the life of the related assets and liabilities. Basis differentials occur from impairment of investments and upon the transfer of assets that were previously owned by the Company into a joint venture. In addition, certain acquisition, transaction and other costs may not be reflected in the net assets at the joint venture level.


Statements of Operations	Year Ended December 31,
	2011			2010			2009
	(in thousands)
Total revenue(1)	$	589,294		$	607,915		$	595,533
Expenses
Operating		170,404			175,309			163,209
Depreciation and amortization		190,437			215,533			232,047

Total expenses		360,841			390,842			395,256

Operating income		228,453			217,073			200,277
Other income (expense)
Interest expense		(228,494	)		(235,723	)		(232,978	)
Gains from early extinguishments of debt		—			17,920			—
Loss on guarantee obligation		—			(3,800	)		—
Impairment losses		(40,468	)		—			(24,568	)

Net loss	$	(40,509	)	$	(4,530	)	$	(57,269	)

Company's share of net loss	$	(25,374	)	$	(5,691	)	$	(22,197	)
Impairment losses on investments		—			—			(9,385	)
Gain on sale of real estate		46,166			572			—
Basis differential		27,226			6,565			11,299
Elimination of inter-entity interest on partner loan		37,878			35,328			32,341

Income from unconsolidated joint ventures	$	85,896		$	36,774		$	12,058

(1)

Includes straight-line rent adjustments of $21.9 million, $24.5 million and $28.0 million for the years ended December 31, 2011, 2010 and 2009, respectively. Includes net "above" and "below" market rent adjustments of $120.3 million, $132.1 million and $157.5 million for the years ended December 31, 2011, 2010 and 2009, respectively.

On March 16, 2011, the Company's Value-Added Fund extended the maturity date by two months to May 31, 2011 of the mortgage loan collateralized by its Mountain View Technology Park property located in Mountain View, California totaling approximately $24.7 million. The mortgage loan bore interest at a variable rate equal to LIBOR plus 1.50% per annum and was scheduled to mature on March 31, 2011. On June 29, 2011, the Company's Value-Added Fund extended the maturity date to November 15, 2011. On November 22, 2011, the Company's Value-Added Fund refinanced the mortgage loan totaling approximately $24.6 million. The new mortgage loan totaling $20.0 million bears interest at a variable rate equal to LIBOR plus 2.50% per annum and matures on November 22, 2014. In connection with the loan refinancing, the unconsolidated joint venture repaid approximately $4.6 million of the previous mortgage loan utilizing existing cash reserves and the proceeds from a loan from the Company's Operating Partnership. The loan from the Company's Operating Partnership consists of an agreement to lend up to $6.0 million to the Value-Added Fund, of which approximately $3.7 million had been advanced as of December 31, 2011. The loan from the Company's Operating Partnership bears interest at a fixed rate of 10.0% per annum and matures on November 22, 2014.

On March 26, 2011, a joint venture in which the Company has a 30% interest removed from service and commenced the redevelopment of 500 North Capitol Street, NW located in Washington, DC. On January 18, 2011, the joint venture entered into a lease with a law firm for approximately 171,000 square feet of space. On October 14, 2011, the unconsolidated joint venture obtained construction financing totaling $107.0 million collateralized by the redevelopment project. The construction financing bears interest at a variable rate equal to LIBOR plus 1.65% per annum and matures on October 14, 2014 with two, one-year extension options, subject to certain conditions. At closing, approximately $33.3 million was drawn to fund the repayment of the existing mortgage loan totaling $22.0 million and approximately $11.3 million of previously incurred development costs.

On March 31, 2011, a joint venture in which the Company has a 50% interest refinanced its construction loan collateralized by Annapolis Junction located in Annapolis, Maryland. The construction loan totaling approximately $42.7 million bore interest at a variable rate equal to LIBOR plus 1.00% per annum and was scheduled to mature on September 12, 2011. The new mortgage loan totaling approximately $42.3 million bears interest at a variable rate equal to LIBOR plus 1.75% per annum and matures on March 31, 2018 with one, three-year extension option, subject to certain conditions.

On June 3, 2011, a joint venture in which the Company has a 50% interest amended its joint venture agreement to add a new development project to its Annapolis Junction property located in Annapolis, Maryland. The outside joint venture partner contributed the improved parcel of land and the Company contributed cash for its 50% interest. The development project is an approximately 120,000 net rentable square foot Class A office project. On November 17, 2011, the unconsolidated joint venture obtained construction financing totaling $19.0 million collateralized by the development project. The construction financing bears interest at a variable rate equal to LIBOR plus 1.65% per annum and matures on November 17, 2013 with two, one-year extension options, subject to certain conditions.

On June 28, 2011, the Company's Value-Added Fund modified the mortgage loan collateralized by its Mountain View Research Park property located in Mountain View, California. The mortgage loan totaling approximately $112.3 million bore interest at a variable rate equal to LIBOR plus 1.75% per annum and had matured on May 31, 2011. The new mortgage loan totaling $92.0 million bears interest at a variable rate equal to LIBOR plus 2.50% per annum and matures on May 31, 2014. In connection with the loan modification, the joint venture repaid approximately $20.3 million of the previous mortgage loan utilizing unfunded capital commitments from the joint venture's partners on a pro rata basis, existing cash reserves and the proceeds from a loan from the Company's Operating Partnership. The loan from the Company's Operating Partnership consists of an agreement to lend up to $12.0 million to the Company's Value-Added Fund, of which approximately $6.7 million had been advanced as of December 31, 2011. The loan from the Operating Partnership bears interest at a fixed rate of 10.0% per annum and matures on May 31, 2014.

On October 25, 2011, an unconsolidated joint venture in which the Company has a 60% interest completed the sale of Two Grand Central Tower located in New York City for approximately $401.0 million, including the assumption by the buyer of approximately $176.6 million of mortgage indebtedness. Net cash proceeds totaled approximately $210.0 million, of which the Company's share was approximately $126.0 million, after the payment of transaction costs of approximately $14.4 million. Two Grand Central Tower is an approximately 650,000 net rentable square foot Class A office tower. The unconsolidated joint venture's carrying value of the net assets of the property aggregated approximately $427.1 million. As a result, pursuant to the provisions of ASC 360 "Property, Plant and Equipment" ("ASC 360") (formerly known as SFAS No. 144 "Accounting for the Impairment or Disposal of Long Lived Assets"), the unconsolidated joint venture recognized a non-cash impairment loss and loss on sale of real estate aggregating approximately $40.5 million, which is equal to the difference between (1) the sale price less cost to sell and (2) the carrying value of the net assets of the property. Separately, the Company had previously recognized an impairment loss on its investment in the unconsolidated joint venture totaling approximately $74.3 million under the provisions of ASC 323 "Investments-Equity Method and Joint Ventures" ("ASC 323") (formerly known as Accounting Principles Board Opinion No. 18 "The Equity Method of Accounting for Investments in Common Stock" ("APB No. 18")). As a result, the Company recognized a gain on sale of real estate totaling approximately $46.2 million, which is included within income from unconsolidated joint ventures on the Company's consolidated statements of operations.

- Definition

The entire disclosure for equity investment, or group of investments, for which combined disclosure is appropriate, including: (a) the name of each investee and percentage of ownership of common stock, (b) accounting policies for investments in common stock, (c) difference between the amount at which the investment is carried and the amount of underlying equity in net assets and the accounting treatment of the difference, (d) the total fair value of each identified investment for which a market value is available, (e) summarized information as to assets, liabilities, and results of operations of the investees (for investments in unconsolidated subsidiaries, common stock of joint ventures, or other investments using the equity method), and (f) material effects of possible conversions, exercises, or contingent issuances of the investee. Other disclosures include (a) the names of any investee in which the investor owns 20 percent or more of the voting stock and investment is not accounted for using the equity method, and the reasons why not, and (b) the names of any investee in which the investor owns less than 20 percent of the voting stock and the investment is accounted for using the equity method, and the reasons why it is.

+ References + Details

Mortgage Notes Payable

12 Months Ended

Dec. 31, 2011

Mortgage Notes Payable [Abstract]

Mortgage Notes Payable

6. Mortgage Notes Payable

The Company had outstanding mortgage notes payable totaling approximately $3.1 billion and $3.0 billion as of December 31, 2011 and 2010, respectively, each collateralized by one or more buildings and related land included in real estate assets. The mortgage notes payable are generally due in monthly installments and mature at various dates through April 10, 2022.

Fixed rate mortgage notes payable totaled approximately $3.1 billion and $2.7 billion at December 31, 2011 and 2010, respectively, with contractual interest rates ranging from 4.75% to 9.93% per annum at December 31, 2011 and 5.55% to 7.75% per annum at December 31, 2010 (with weighted-averages of 5.75% and 6.18% at December 31, 2011 and 2010, respectively).

There were no variable rate mortgage loans at December 31, 2011. Variable rate mortgage notes payable (including construction loans payable) totaled approximately $317.5 million at December 31, 2010 with interest rates ranging from 0.30% to 2.20% above the London Interbank Offered Rate ("LIBOR")/Eurodollar. As of December 31, 2011 and 2010, the LIBOR rate was 0.30% and 0.26%, respectively. If market interest rates on the Company's variable rate debt outstanding at December 31, 2010 had been 100 basis points greater, total interest expense would have increased by approximately $3.2 million for the year ended December 31, 2010.

On January 12, 2011, the Company notified the master servicer of the $25.0 million non-recourse mortgage loan collateralized by its Montvale Center property located in Gaithersburg, Maryland that the cash flows generated from the property were insufficient to fund debt service payments and capital improvements necessary to lease and operate the property and that the Company was not prepared to fund any cash shortfalls. Accordingly, at the request of the Company, the loan has been placed with the special servicer. The Company is not current on making debt service payments and is currently in default. The Company is currently accruing interest at the default interest rate of 9.93% per annum. The net book value of the property at December 31, 2011 totaled approximately $8.3 million, which is less than the estimated fair value of the property (See Note 20).

On February 1, 2011, in connection with the Company's acquisition of Bay Colony Corporate Center in Waltham, Massachusetts, the Company assumed the mortgage loan collateralized by the property totaling approximately $143.9 million. The assumed debt is a securitized senior mortgage loan that requires interest-only payments with a balloon payment due at maturity. The assumed mortgage loan, which bears contractual interest at a fixed rate of 6.53% per annum and matures on June 11, 2012, was recorded at its fair value of approximately $149.2 million using an effective interest rate of 3.75% per annum.

On May 11, 2011, the Company refinanced at maturity its mortgage loan collateralized by its 601 Lexington Avenue property located in New York City totaling approximately $453.3 million utilizing the proceeds of a draw under its Unsecured Line of Credit, which borrowing was secured by a mortgage on the property. The mortgage loan bore interest at a fixed rate of 7.19% per annum.

On August 19, 2011, the Company obtained mortgage financing totaling $725.0 million collateralized by its 601 Lexington property. The mortgage loan bears interest at a fixed rate of 4.75% per annum and matures on April 10, 2022. Proceeds from the mortgage financing were used to repay the borrowing under the Company's Operating Partnership's Unsecured Line of Credit totaling approximately $453.3 million. The additional cash proceeds were used to refinance the $267.5 million mortgage loan collateralized by the Company's 510 Madison Avenue property located in New York City. In connection with the refinancing, the lien of the 510 Madison Avenue mortgage was spread to 601 Lexington Avenue and released from 510 Madison Avenue so that 510 Madison Avenue is no longer encumbered by any mortgage debt.

On November 9, 2011, the Company used available cash to repay the mortgage loan collateralized by its Reservoir Place property located in Waltham, Massachusetts totaling $50.0 million. The mortgage financing bore interest at a variable rate equal to Eurodollar plus 2.20% per annum and was scheduled to mature on July 30, 2014. There was no prepayment penalty. The Company recognized a loss from early extinguishment of debt totaling approximately $0.5 million consisting of the write-off of unamortized deferred financing costs.

On November 16, 2011, the Company terminated the construction loan facility collateralized by its Atlantic Wharf property located in Boston, Massachusetts totaling $192.5 million. The construction loan facility bore interest at a variable rate equal to LIBOR plus 3.00% per annum and was scheduled to mature on April 21, 2012 with two, one-year extension options, subject to certain conditions. The Company had not drawn any amounts under the facility. The Company recognized a loss from early extinguishment of debt totaling approximately $0.4 million consisting of the write-off of unamortized deferred financing costs.

Six mortgage loans totaling approximately $953.1 million at December 31, 2011 and six mortgage loans totaling approximately $883.4 million at December 31, 2010 have been accounted for at their fair values on the dates the mortgage loans were assumed. The impact of recording the mortgage loans at fair value resulted in a decrease to interest expense of approximately $9.2 million, $3.8 million and $4.1 million for the years ended December 31, 2011, 2010 and 2009, respectively. The cumulative liability related to the fair value adjustments was $23.8 million and $27.7 million at December 31, 2011 and 2010, respectively, and is included in mortgage notes payable in the Consolidated Balance Sheets.

Contractual aggregate principal payments of mortgage notes payable at December 31, 2011 are as follows:


	Principal Payments
	(in thousands)
2012	$	248,986
2013		103,209
2014		87,757
2015		26,182
2016		397,629
Thereafter		2,235,710

Total aggregate principal payments		3,099,473
Unamortized balance of historical fair value adjustments		23,794

Total carrying value of mortgage notes payable	$	3,123,267

Unsecured Senior Notes

12 Months Ended

Dec. 31, 2011

Unsecured Senior Notes [Abstract]

Unsecured Senior Notes

7. Unsecured Senior Notes

The following summarizes the unsecured senior notes outstanding as of December 31, 2011 (dollars in thousands):


	Coupon/ Stated Rate			Effective Rate(1)			Principal Amount			Maturity Date(2)
10 Year Unsecured Senior Notes		6.250	%		6.381	%	$	182,432		January 15, 2013
10 Year Unsecured Senior Notes		6.250	%		6.291	%		42,568		January 15, 2013
12 Year Unsecured Senior Notes		5.625	%		5.693	%		300,000		April 15, 2015
12 Year Unsecured Senior Notes		5.000	%		5.194	%		250,000		June 1, 2015
10 Year Unsecured Senior Notes		5.875	%		5.967	%		700,000		October 15, 2019
10 Year Unsecured Senior Notes		5.625	%		5.708	%		700,000		November 15, 2020
10 Year Unsecured Senior Notes		4.125	%		4.289	%		850,000		May 15, 2021
7 Year Unsecured Senior Notes		3.700	%		3.853	%		850,000		November 15, 2018

Total principal								3,875,000
Net unamortized discount								(9,814	)

Total							$	3,865,186

(1)	Yield on issuance date including the effects of discounts on the notes.

(2)	No principal amounts are due prior to maturity.

On November 10, 2011, the Company's Operating Partnership completed a public offering of $850.0 million in aggregate principal amount of its 3.700% unsecured senior notes due 2018. The notes were priced at 99.767% of the principal amount to yield an effective rate (including financing fees) of 3.853% to maturity. The notes will mature on November 15, 2018, unless earlier redeemed. The aggregate net proceeds from the offering were approximately $841.2 million after deducting underwriting discounts and transaction expenses.

The indenture relating to the unsecured senior notes contains certain financial restrictions and requirements, including (1) a leverage ratio not to exceed 60%, (2) a secured debt leverage ratio not to exceed 50%, (3) an interest coverage ratio of greater than 1.50, and (4) an unencumbered asset value of not less than 150% of unsecured debt. At December 31, 2011 and 2010, the Company was in compliance with each of these financial restrictions and requirements.

Unsecured Exchangeable Senior Notes

12 Months Ended

Dec. 31, 2011

Unsecured Exchangeable Senior Notes [Abstract]

Unsecured Exchangeable Senior Notes

8. Unsecured Exchangeable Senior Notes

The following summarizes the unsecured exchangeable senior notes outstanding as of December 31, 2011 (dollars in thousands):


	Coupon/ Stated Rate			Effective Rate(1)			Exchange Rate			Principal Amount			First Optional Redemption Date by Company	Maturity Date
3.625% Exchangeable Senior Notes		3.625	%		4.037	%		8.5051	(2)	$	747,500		N/A	February 15, 2014
2.875% Exchangeable Senior Notes		2.875	%		3.462	%		7.0430	(3)		576,194		February 20, 2012(4)	February 15, 2037
3.750% Exchangeable Senior Notes		3.750	%		3.787	%		10.0066	(5)		450,000		May 18, 2013(6)	May 15, 2036

Total principal											1,773,694
Net unamortized discount											(3,462	)
Adjustment for the equity component allocation, net of accumulated amortization											(54,547	)

Total										$	1,715,685

(1)	Yield on issuance date including the effects of discounts on the notes but excluding the effects of the adjustment for the equity component allocation.

(2)

The initial exchange rate is 8.5051 shares per $1,000 principal amount of the notes (or an initial exchange price of approximately $117.58 per share of Boston Properties, Inc.'s common stock). In addition, the Company entered into capped call transactions with affiliates of certain of the initial purchasers, which are intended to reduce the potential dilution upon future exchange of the notes. The capped call transactions were intended to increase the effective exchange price to the Company of the notes from $117.58 to approximately $137.17 per share (subject to adjustment), representing an overall effective premium of approximately 40% over the closing price on August 13, 2008 of $97.98 per share of Boston Properties, Inc.'s common stock. The net cost of the capped call transactions was approximately $44.4 million. As of December 31, 2011, the effective exchange price was $135.25 per share.

(3)

In connection with the special distribution of $5.98 per share of Boston Properties, Inc.'s common stock declared on December 17, 2007, the exchange rate was adjusted from 6.6090 to 7.0430 shares per $1,000 principal amount of notes effective as of December 31, 2007, resulting in an exchange price of approximately $141.98 per share of Boston Properties, Inc.'s common stock (See Note 20).

(4)

Holders may require the Operating Partnership to repurchase the notes for cash on February 15, 2012, 2017, 2022, 2027 and 2032 and at any time prior to their maturity upon a fundamental change, in each case at a price equal to 100% of the principal amount of the notes being repurchased plus any accrued and unpaid interest up to, but excluding, the repurchase date. The Operating Partnership repurchased/redeemed the notes for cash in February 2012 at a price equal to 100% of the principal amount of the notes being repurchased/redeemed plus any accrued and unpaid interest up to, but excluding, the repurchase/redemption date (See Note 20).

(5)

In connection with the special distribution of $5.98 per share of Boston Properties, Inc.'s common stock declared on December 17, 2007, the exchange rate was adjusted from 9.3900 to 10.0066 shares per $1,000 principal amount of notes effective as of December 31, 2007, resulting in an exchange price of approximately $99.93 per share of Boston Properties, Inc.'s common stock.

(6)

Holders may require the Operating Partnership to repurchase the notes for cash on May 18, 2013 and May 15, 2016, 2021, 2026 and 2031 and at any time prior to their maturity upon a fundamental change, in each case at a price equal to 100% of the principal amount of the notes being repurchased plus any accrued and unpaid interest up to, but excluding, the repurchase date.

ASC 470-20 (formerly known as FSP No. APB 14-1) requires the liability and equity components of convertible debt instruments that may be settled in cash upon conversion (including partial cash settlement) to be separately accounted for in a manner that reflects the issuer's nonconvertible debt borrowing rate. ASC 470-20 requires that the initial proceeds from the sale of the Operating Partnership's $862.5 million of 2.875% exchangeable senior notes due 2037, $450.0 million of 3.75% exchangeable senior notes due 2036 and $747.5 million of 3.625% exchangeable senior notes due 2014 be allocated between a liability component and an equity component in a manner that reflects interest expense at the interest rate of similar nonconvertible debt that could have been issued by the Operating Partnership at such time. The Company measured the fair value of the debt components of the 2.875%, 3.75% and 3.625% exchangeable senior notes for the periods presented based on effective interest rates of 5.630%, 5.958% and 6.555%, respectively. The aggregate carrying amount of the debt component was approximately $1.72 billion and $1.72 billion (net of the ASC 470-20 adjustment of approximately $54.5 million and $93.6 million) at December 31, 2011 and December 31, 2010, respectively. As a result, the Company attributed an aggregate of approximately $230.3 million of the proceeds to the equity component of the notes, which represents the excess proceeds received over the fair value of the notes at the date of issuance. The equity component of the notes has been reflected within Additional Paid-in Capital in the Consolidated Balance Sheets. The Company reclassified approximately $1.0 million of deferred financing costs to Additional Paid-in Capital, which represented the costs attributable to the equity components of the notes. The carrying amount of the equity component was approximately $202.5 million and $207.1 million at December 31, 2011 and December 31, 2010, respectively. The resulting debt discount will be amortized over the period during which the debt is expected to be outstanding (i.e., through the first optional redemption dates or, in the case of the 2014 notes, the maturity date) as additional non-cash interest expense. The additional non-cash interest expense attributable to each debt security will increase in subsequent reporting periods through the first optional redemption date (or, in the case of the 2014 notes, the maturity date) as the debt accretes to its par value over the same period. The aggregate contractual interest expense was approximately $66.3 million, $69.0 million and $74.4 million for the years ended December 31, 2011, 2010 and 2009, respectively. As a result of applying ASC 470-20, the Company reported additional non-cash interest expense of approximately $38.8 million, $38.3 million and $38.6 million for the years ended December 31, 2011, 2010 and 2009, respectively. ASC 470-20 requires companies to retrospectively apply the requirements of the pronouncement to all periods presented.

On November 9, 2011, the Company's Operating Partnership repurchased $50.0 million aggregate principal amount of its 2.875% exchangeable senior notes due 2037 for approximately $50.2 million. The repurchased notes had an aggregate carrying value of approximately $49.6 million at the time of repurchase resulting in the recognition of a loss on early extinguishment of debt of approximately $0.6 million during the year ended December 31, 2011. There remains an aggregate of approximately $576.2 million of these notes outstanding (See Note 20).

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

+ References + Details

Unsecured Line Of Credit	12 Months Ended
Unsecured Line Of Credit	Dec. 31, 2011
Unsecured Line Of Credit [Abstract]
Unsecured Line Of Credit	9. Unsecured Line of Credit On June 24, 2011, the Company's Operating Partnership amended and restated the revolving credit agreement governing the Company's Unsecured Line of Credit, which (1) reduced the total commitment from $1.0 billion to $750.0 million, (2) extended the maturity date from August 3, 2011 to June 24, 2014, with a provision for a one-year extension at the Company's option, subject to certain conditions and the payment of an extension fee equal to 0.20% of the total commitment then in effect, and (3) increased the per annum variable interest rates available, which resulted in an increase of the per annum variable interest rate on outstanding balances from Eurodollar plus 0.475% per annum to Eurodollar plus 1.225% per annum. Under the amended Unsecured Line of Credit, the Company may increase the total commitment to $1.0 billion, subject to syndication of the increase. In addition, a facility fee currently equal to an aggregate of 0.225% per annum of the total commitment is payable by the Company in equal quarterly installments. The interest rate and facility fee are subject to adjustment in the event of a change in the Operating Partnership's unsecured debt ratings. The Unsecured Line of Credit is a recourse obligation of the Company's Operating Partnership. The Unsecured Line of Credit contains a competitive bid option that allows banks that are part of the lender consortium to bid to make loan advances to the Company at a reduced interest rate. On May 11, 2011, the Company refinanced at maturity its mortgage loan collateralized by its 601 Lexington Avenue property located in New York City totaling approximately $453.3 million utilizing the proceeds of a draw under its Unsecured Line of Credit, which borrowing was secured by a mortgage on the property. On August 19, 2011, the Company used proceeds from the new mortgage financing on 601 Lexington Avenue to repay the borrowing under the Company's Operating Partnership's Unsecured Line of Credit (See Note 6). At December 31, 2011, there were no amounts outstanding on the Unsecured Line of Credit. The terms of the Unsecured Line of Credit require that the Company maintain a number of customary financial and other covenants on an ongoing basis, including: (1) a leverage ratio not to exceed 60%, however, the leverage ratio may increase to no greater than 65% provided that it is reduced back to 60% within one year, (2) a secured debt leverage ratio not to exceed 55%, (3) a fixed charge coverage ratio of at least 1.40, (4) an unsecured debt leverage ratio not to exceed 60%, however, the unsecured debt leverage ratio may increase to no greater than 65% provided that it is reduced back to 60% within one year, (5) a minimum net worth requirement of $3.5 billion, (6) an unsecured debt interest coverage ratio of at least 1.75 and (7) limitations on permitted investments, development, partially owned entities, business outside of commercial real estate and commercial non-office properties. At December 31, 2011, the Company was in compliance with each of these financial and other covenant requirements.

Commitments And Contingencies	12 Months Ended
Commitments And Contingencies	Dec. 31, 2011
Commitments And Contingencies [Abstract]
Commitments And Contingencies	10. Commitments and Contingencies General In the normal course of business, the Company guarantees its performance of services or indemnifies third parties against its negligence. The Company has letter of credit and performance obligations of approximately $15.5 million related to lender and development requirements. Certain of the Company's joint venture agreements include provisions whereby, at certain specified times, each partner has the right to initiate a purchase or sale of its interest in the joint ventures. Under these provisions, the Company is not compelled to purchase the interest of its outside joint venture partners. In connection with the assumption of the General Motors Building's secured loan by the Company's unconsolidated joint venture, 767 Venture, LLC, the Company guaranteed the unconsolidated joint venture's obligation to fund various escrows, including tenant improvements, taxes and insurance in lieu of cash deposits. As of December 31, 2011, the maximum funding obligation under the guarantee was approximately $20.5 million. The Company earns a fee from the joint venture for providing the guarantee and has an agreement with the outside partners to reimburse the joint venture for their share of any payments made under the guarantee. In connection with the refinancing in March 2010 of the 125 West 55^thStreet property's secured loan by the Company's unconsolidated joint venture, 125 West 55^thStreet Venture LLC, the Company has guaranteed the unconsolidated joint venture's obligation to fund an escrow related to certain lease rollover costs in lieu of an initial cash deposit for the full amount. The maximum funding obligation under the guarantee was $21.3 million. At closing, the joint venture funded a $10.0 million cash deposit into the escrow account and the remaining $11.3 million will be further reduced with scheduled monthly deposits into the escrow account from operating cash flows. As of December 31, 2011, the remaining funding obligation under the guarantee was approximately $1.8 million. The Company earns a fee from the joint venture for providing the guarantee and has an agreement with the outside partners to reimburse the joint venture for their share of any payments made under the guarantee. In connection with the mortgage financing collateralized by the Company's One Freedom Square property located in Reston, Virginia, the Company has agreed to guarantee approximately $7.9 million related to its obligation to provide funds for certain tenant re-leasing costs. The mortgage financing matures on June 30, 2012. From time to time, the Company (or the applicable joint venture) has also agreed to guarantee portions of the principal, interest or other amounts in connection with other unconsolidated joint venture borrowings. In addition to the financial guarantees referenced above, the Company has agreed to customary environmental indemnifications and nonrecourse carve-outs (e.g., guarantees against fraud, misrepresentation and bankruptcy) on certain of its unconsolidated joint venture loans. Concentrations of Credit Risk Management of the Company performs ongoing credit evaluations of tenants and may require tenants to provide some form of credit support such as corporate guarantees and/or other financial guarantees. Although the Company's properties are geographically diverse and the tenants operate in a variety of industries, to the extent the Company has a significant concentration of rental revenue from any single tenant, the inability of that tenant to make its lease payments could have an adverse effect on the Company. Some potential losses are not covered by insurance. The Company carries insurance coverage on its properties of types and in amounts and with deductibles that it believes are in line with coverage customarily obtained by owners of similar properties. In response to the uncertainty in the insurance market following the terrorist attacks of September 11, 2001, the Federal Terrorism Risk Insurance Act (as amended, "TRIA") was enacted in November 2002 to require regulated insurers to make available coverage for "certified" acts of terrorism (as defined by the statute). The expiration date of TRIA was extended to December 31, 2014 by the Terrorism Risk Insurance Program Reauthorization Act of 2007 ("TRIPRA"). Currently, the Company's property insurance program per occurrence limits are $1.0 billion for its portfolio insurance program, including coverage for acts of terrorism certified under TRIA other than nuclear, biological, chemical or radiological terrorism ("Terrorism Coverage"). The Company also carries $250 million of Terrorism Coverage for 601 Lexington Avenue, New York, New York ("601 Lexington Avenue") in excess of the $1.0 billion of coverage in the Company's property insurance program which is provided by IXP, LLC ("IXP") as a direct insurer. The Company currently insures certain properties, including the General Motors Building located at 767 Fifth Avenue in New York, New York ("767 Fifth Avenue"), in separate stand alone insurance programs. The property insurance program per occurrence limits for 767 Fifth Avenue are $1.625 billion, including Terrorism Coverage, with $1.375 billion of Terrorism Coverage in excess of $250 million being provided by NYXP, LLC ("NYXP"), as a direct insurer. The Company also currently carries nuclear, biological, chemical and radiological terrorism insurance coverage for acts of terrorism certified under TRIA ("NBCR Coverage"), which is provided by IXP as a direct insurer, for the properties in our portfolio, including 767 Fifth Avenue, but excluding the properties owned by the Company's Value-Added Fund and certain other properties owned in joint ventures with third parties or which the Company manages. The per occurrence limit for NBCR Coverage is $1.0 billion. Under TRIA, after the payment of the required deductible and coinsurance, the additional Terrorism Coverage provided by IXP for 601 Lexington Avenue, the NBCR Coverage provided by IXP and the Terrorism Coverage provided by NYXP are backstopped by the Federal Government if the aggregate industry insured losses resulting from a certified act of terrorism exceed a "program trigger." The program trigger is $100 million and the coinsurance is 15%. Under TRIPRA, if the Federal Government pays out for a loss under TRIA, it is mandatory that the Federal Government recoup the full amount of the loss from insurers offering TRIA coverage after the payment of the loss pursuant to a formula in TRIPRA. The Company may elect to terminate the NBCR Coverage if the Federal Government seeks recoupment for losses paid under TRIA, if there is a change in its portfolio or for any other reason. The Company intends to continue to monitor the scope, nature and cost of available terrorism insurance and maintain terrorism insurance in amounts and on terms that are commercially reasonable. The Company also currently carries earthquake insurance on its properties located in areas known to be subject to earthquakes in an amount and subject to self-insurance that the Company believes are commercially reasonable. In addition, this insurance is subject to a deductible in the amount of 5% of the value of the affected property. Specifically, the Company currently carries earthquake insurance which covers its San Francisco region with a $120 million per occurrence limit and a $120 million annual aggregate limit, $20 million of which is provided by IXP, as a direct insurer. The amount of the Company's earthquake insurance coverage may not be sufficient to cover losses from earthquakes. In addition, the amount of earthquake coverage could impact the Company's ability to finance properties subject to earthquake risk. The Company may discontinue earthquake insurance on some or all of its properties in the future if the premiums exceed the Company's estimation of the value of the coverage. IXP, a captive insurance company which is a wholly-owned subsidiary of the Company, acts as a direct insurer with respect to a portion of the Company's earthquake insurance coverage for its Greater San Francisco properties, the additional Terrorism Coverage for 601 Lexington Avenue and the Company's NBCR Coverage. The additional Terrorism Coverage provided by IXP for 601 Lexington Avenue only applies to losses which exceed the program trigger under TRIA. NYXP, a captive insurance company which is a wholly-owned subsidiary of the Company, acts as a direct insurer with respect to a portion of the Company's Terrorism Coverage for 767 Fifth Avenue. Currently, NYXP only insures losses which exceed the program trigger under TRIA and NYXP reinsures with a third-party insurance company any coinsurance payable under TRIA. Insofar as the Company owns IXP and NYXP, it is responsible for their liquidity and capital resources, and the accounts of IXP and NYXP are part of the Company's consolidated financial statements. In particular, if a loss occurs which is covered by the Company's NBCR Coverage but is less than the applicable program trigger under TRIA, IXP would be responsible for the full amount of the loss without any backstop by the Federal Government. IXP and NYXP would also be responsible for any recoupment charges by the Federal Government in the event losses are paid out and their insurance policies are maintained after the payout by the Federal Government. If the Company experiences a loss and IXP or NYXP are required to pay under their insurance policies, the Company would ultimately record the loss to the extent of the required payment. Therefore, insurance coverage provided by IXP and NYXP should not be considered as the equivalent of third-party insurance, but rather as a modified form of self-insurance. The mortgages on the Company's properties typically contain requirements concerning the financial ratings of the insurers who provide policies covering the property. The Company provides the lenders on a regular basis with the identity of the insurance companies in the Company's insurance programs. The ratings of some of the Company's insurers are below the rating requirements in some of the Company's loan agreements and the lenders for these loans could attempt to claim an event of default has occurred under the loan. The Company believes it could obtain insurance with insurers which satisfy the rating requirements. Additionally, in the future, the Company's ability to obtain debt financing secured by individual properties, or the terms of such financing, may be adversely affected if lenders generally insist on ratings for insurers or amounts of insurance which are difficult to obtain or which result in a commercially unreasonable premium. There can be no assurance that a deficiency in the financial ratings of one or more of the Company's insurers will not have a material adverse effect on the Company. The Company continues to monitor the state of the insurance market in general, and the scope and costs of coverage for acts of terrorism and California earthquake risk in particular, but the Company cannot anticipate what coverage will be available on commercially reasonable terms in future policy years. There are other types of losses, such as from wars or the presence of mold at the Company's properties, for which the Company cannot obtain insurance at all or at a reasonable cost. With respect to such losses and losses from acts of terrorism, earthquakes or other catastrophic events, if the Company experiences a loss that is uninsured or that exceeds policy limits, the Company could lose the capital invested in the damaged properties, as well as the anticipated future revenues from those properties. Depending on the specific circumstances of each affected property, it is possible that the Company could be liable for mortgage indebtedness or other obligations related to the property. Any such loss could materially and adversely affect the Company's business and financial condition and results of operations. Legal Matters The Company is subject to various legal proceedings and claims that arise in the ordinary course of business. These matters are generally covered by insurance. Management believes that the final outcome of such matters will not have a material adverse effect on the financial position, results of operations or liquidity of the Company. State and Local Tax Matters Because the Company is organized and qualifies as a REIT, it is generally not subject to federal income taxes, but is subject to certain state and local taxes. In the normal course of business, certain entities through which the Company owns real estate either have undergone, or are currently undergoing, tax audits. Although the Company believes that it has substantial arguments in favor of its positions in the ongoing audits, in some instances there is no controlling precedent or interpretive guidance on the specific point at issue. Collectively, tax deficiency notices received to date from the jurisdictions conducting the ongoing audits have not been material. However, there can be no assurance that future audits will not occur with increased frequency or that the ultimate result of such audits will not have a material adverse effect on the Company's results of operations. Environmental Matters It is the Company's policy to retain independent environmental consultants to conduct or update Phase I environmental assessments (which generally do not involve invasive techniques such as soil or ground water sampling) and asbestos surveys in connection with the Company's acquisition of properties. These pre-purchase environmental assessments have not revealed environmental conditions that the Company believes will have a material adverse effect on its business, assets, financial condition, results of operations or liquidity, and the Company is not otherwise aware of environmental conditions with respect to its properties that the Company believes would have such a material adverse effect. However, from time to time environmental conditions at the Company's properties have required and may in the future require environmental testing and/or regulatory filings, as well as remedial action. In February 1999, the Company (through a joint venture) acquired from Exxon Corporation a property in Massachusetts that was formerly used as a petroleum bulk storage and distribution facility and was known by the state regulatory authority to contain soil and groundwater contamination. The Company developed an office park on the property. The Company engaged a specially licensed environmental consultant to oversee the management of contaminated soil and groundwater that was disturbed in the course of construction. Under the property acquisition agreement, Exxon agreed to (1) bear the liability arising from releases or discharges of oil and hazardous substances which occurred at the site prior to the Company's ownership, (2) continue monitoring and/or remediating such releases and discharges as necessary and appropriate to comply with applicable requirements, and (3) indemnify the Company for certain losses arising from preexisting site conditions. Any indemnity claim may be subject to various defenses, and there can be no assurance that the amounts paid under the indemnity, if any, would be sufficient to cover the liabilities arising from any such releases and discharges. Environmental investigations at some of the Company's properties and certain properties owned by affiliates of the Company have identified groundwater contamination migrating from off-site source properties. In each case the Company engaged a licensed environmental consultant to perform the necessary investigations and assessments and to prepare any required submittals to the regulatory authorities. In each case the environmental consultant concluded that the properties qualify under the regulatory program or the regulatory practice for a status which eliminates certain deadlines for conducting response actions at a site. The Company also believes that these properties qualify for liability relief under certain statutory provisions or regulatory practices regarding upgradient releases. Although the Company believes that the current or former owners of the upgradient source properties may bear responsibility for some or all of the costs of addressing the identified groundwater contamination, the Company will take such further response actions (if any) that it deems necessary or advisable. Other than periodic testing at some of these properties, no such additional response actions are anticipated at this time. Some of the Company's properties and certain properties owned by the Company's affiliates are located in urban, industrial and other previously developed areas where fill or current or historical uses of the areas have caused site contamination. Accordingly, it is sometimes necessary to institute special soil and/or groundwater handling procedures and/or include particular building design features in connection with development, construction and other property operations in order to achieve regulatory closure and/or ensure that contaminated materials are addressed in an appropriate manner. In these situations it is the Company's practice to investigate the nature and extent of detected contamination and estimate the costs of required response actions and special handling procedures. The Company then uses this information as part of its decision-making process with respect to the acquisition and/or development of the property. For example, the Company owns a parcel in Massachusetts which was formerly used as a quarry/asphalt batching facility. Pre-purchase testing indicated that the site contained relatively low levels of certain contaminants. The Company has developed an office park on this property. Prior to and during redevelopment activities, the Company engaged a specially licensed environmental consultant to monitor environmental conditions at the site and prepare necessary regulatory submittals based on the results of an environmental risk characterization. A submittal has been made to the regulatory authorities in order to achieve regulatory closure at this site. The submittal included an environmental deed restriction that mandates compliance with certain protective measures in a portion of the site where low levels of residual soil contamination have been left in place in accordance with applicable laws. The Company expects that resolution of the environmental matters relating to the above will not have a material impact on its business, assets, financial condition, results of operations or liquidity. However, the Company cannot assure you that it has identified all environmental liabilities at its properties, that all necessary remediation actions have been or will be undertaken at the Company's properties or that the Company will be indemnified, in full or at all, in the event that such environmental liabilities arise. Tax Protection Obligations In connection with the acquisition or contribution of six properties, the Company entered into agreements for the benefit of the selling or contributing parties which specifically state that until such time as the contributors do not hold at least a specified percentage of the OP Units owned by such person following the contribution of the properties, or until June 2017 for the General Motors Building, the Operating Partnership will not sell or otherwise transfer the properties in a taxable transaction. If the Company does sell or transfer the properties in a taxable transaction, it would be liable to the contributors for contractual damages.

- Definition

The entire disclosure for commitments and contingencies.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name FASB Interpretation (FIN)
-Number 14
-Paragraph 3
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 5
-Paragraph 9, 10, 11, 12
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.25)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6952336&loc=d3e14435-108349

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6398077&loc=d3e12565-110249

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 440
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6394976&loc=d3e25287-109308

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6449706&loc=d3e16207-108621

+ Details

Noncontrolling Interests

12 Months Ended

Dec. 31, 2011

Noncontrolling Interests [Abstract]

Noncontrolling Interests

11. Noncontrolling Interests

Noncontrolling interests relate to the interests in the Operating Partnership not owned by the Company and interests in property partnerships not wholly-owned by the Company. As of December 31, 2011, the noncontrolling interests consisted of 16,562,838 OP Units, 1,601,004 LTIP Units, 400,000 2011 OPP Units and 1,113,044 Series Two Preferred Units (or 1,460,688 OP Units on an as converted basis) held by parties other than the Company.

Noncontrolling Interest—Redeemable Preferred Units of the Operating Partnership

The Preferred Units at December 31, 2011 and 2010 consisted solely of 1,113,044 Series Two Preferred Units, which bear a preferred distribution equal to the greater of (1) the distribution which would have been paid in respect of the Series Two Preferred Unit had such Series Two Preferred Unit been converted into an OP Unit (including both regular and special distributions) or (2) 6.00% per annum on a liquidation preference of $50.00 per unit, and are convertible into OP Units at a rate of $38.10 per Preferred Unit (1.312336 OP Units for each Preferred Unit). The holders of Series Two Preferred Units have the right to require the Operating Partnership to redeem their units for cash at the redemption price of $50.00 per unit on May 14, 2012, May 14, 2013 and May 12, 2014. The maximum number of units that may be required to be redeemed from all holders on each of these dates is 1,007,662, which is one-sixth of the number of Series Two Preferred Units that were originally issued. The holders also had the right to have their Series Two Preferred Units redeemed for cash on May 12, 2009, May 12, 2010 and May 12, 2011, although no holder exercised such right. The Company also has the right, subject to certain conditions, to redeem Series Two Preferred Units for cash or to convert into OP Units any Series Two Preferred Units that are not redeemed when they are eligible for redemption.

On February 15, 2011, the Operating Partnership paid a distribution on its outstanding Series Two Preferred Units of $0.75616 per unit. On May 16, 2011, the Operating Partnership paid a distribution on its outstanding Series Two Preferred Units of $0.73151 per unit. On August 15, 2011, the Operating Partnership paid a distribution on its outstanding Series Two Preferred Units of $0.75616 per unit. On November 15, 2011, the Operating Partnership paid a distribution on its outstanding Series Two Preferred Units of $0.75616 per unit.

The following table reflects the activity for noncontrolling interests—redeemable preferred units for the years ended December 31, 2011, 2010 and 2009 (dollars in thousands):


Balance at December 31, 2008	$	55,652
Net income		3,594
Distributions		(3,594	)

Balance at December 31, 2009		55,652
Net income		3,343
Distributions		(3,343	)

Balance at December 31, 2010		55,652
Net income		3,339
Distributions		(3,339	)

Balance at December 31, 2011	$	55,652

Noncontrolling Interest—Common Units of the Operating Partnership

During the years ended December 31, 2011 and 2010, 2,919,323 and 591,900 OP Units, respectively, were presented by the holders for redemption (including 60,414 OP Units and 99,139 OP Units, respectively, issued upon conversion of LTIP Units) and were redeemed by the Company in exchange for an equal number of shares of Common Stock.

At December 31, 2010, the Company had outstanding 1,080,938 2008 OPP Units. Prior to the measurement date on February 5, 2011, 2008 OPP Units were entitled to receive per unit distributions equal to one-tenth (10%) of the regular quarterly distributions payable on an OP Unit, but were not entitled to receive any special distributions. After the measurement date, the number of 2008 OPP Units, both vested and unvested, which 2008 OPP award recipients had earned, if any, based on the establishment of an outperformance pool, would have been entitled to receive distributions in an amount per unit equal to distributions, both regular and special, payable on an OP Unit. On February 5, 2011, the measurement period for the Company's 2008 OPP Awards expired and the Company's TRS performance was not sufficient for employees to earn and therefore become eligible to vest in any of the 2008 OPP Awards. Accordingly, all 2008 OPP Awards were automatically forfeited and the Operating Partnership repaid employees an amount equal to $0.25 (which is equal to what they paid upon acceptance of the award) multiplied by the number of 2008 OPP Awards previously received.

At December 31, 2011, the Company had outstanding 400,000 2011 OPP Units (See Note 17). Prior to the measurement date on January 31, 2014, 2011 OPP Units will be entitled to receive per unit distributions equal to one-tenth (10%) of the regular quarterly distributions payable on an OP Unit, but will not be entitled to receive any special distributions. After the measurement date, the number of 2011 OPP Units, both vested and unvested, that 2011 OPP award recipients have earned, if any, based on the establishment of an outperformance pool, will be entitled to receive distributions in an amount per unit equal to distributions, both regular and special, payable on an OP Unit.

On January 28, 2011, the Operating Partnership paid a distribution on the OP Units and LTIP Units in the amount of $0.50 per unit, and a distribution on the 2008 OPP Units in the amount of $0.05 per unit, to holders of record as of the close of business on December 31, 2010. On April 29, 2011, the Operating Partnership paid a distribution on the OP Units and LTIP Units in the amount of $0.50 per unit, and a distribution on the 2011 OPP Units in the amount of $0.05 per unit, to holders of record as of the close of business on March 31, 2011. On July 29, 2011, the Operating Partnership paid a distribution on the OP Units and LTIP Units in the amount of $0.50 per unit, and a distribution on the 2011 OPP Units in the amount of $0.05 per unit, to holders of record as of the close of business on June 30, 2011. On October 31, 2011, the Operating Partnership paid a distribution on the OP Units and LTIP Units in the amount of $0.50 per unit and a distribution on the 2011 OPP Units in the amount of $0.05 per unit to holders of record as of the close of business on September 30, 2011. On December 14, 2011, Boston Properties, Inc., as general partner of the Operating Partnership, declared a distribution on the OP Units and LTIP Units in the amount of $0.55 per unit and a distribution on the 2011 OPP Units in the amount of $0.055 per unit, in each case payable on January 27, 2012 to holders of record as of the close of business on December 31, 2011.

The Series Two Preferred Units may be converted into OP Units at the election of the holder thereof at any time. A holder of an OP Unit may present such OP Unit to the Operating Partnership for redemption at any time (subject to restrictions agreed upon at the time of issuance of OP Units to particular holders that may restrict such redemption right for a period of time, generally one year from issuance). Upon presentation of an OP Unit for redemption, the Operating Partnership must redeem such OP Unit for cash equal to the then value of a share of common stock of the Company. The Company may, in its sole discretion, elect to assume and satisfy the redemption obligation by paying either cash or issuing one share of Common Stock. The value of the OP Units (not owned by the Company and including LTIP Units assuming that all conditions have been met for the conversion thereof) and Series Two Preferred Units (on an as converted basis) had all of such units been redeemed at December 31, 2011 was approximately $1.81 billion and $145.5 million, respectively, based on the closing price of the Company's common stock of $99.60 per share on December 31, 2011.

Noncontrolling Interest—Property Partnerships

The noncontrolling interests in property partnerships consist of the outside equity interests in joint ventures that are consolidated with the financial results of the Company because the Company exercises control over the entities that own the properties. The equity interests in these ventures that are not owned by the Company, totaling approximately $(1.1) million and $(0.6) million at December 31, 2011 and December 31, 2010, respectively.

- Definition

The entire disclosure for noncontrolling interest in consolidated subsidiaries, which could include the name of the subsidiary, the ownership percentage held by the parent, the ownership percentage held by the noncontrolling owners, the amount of the noncontrolling interest, the location of this amount on the balance sheet (when not reported separately), an explanation of the increase or decrease in the amount of the noncontrolling interest, the noncontrolling interest share of the net Income or Loss of the subsidiary, the location of this amount on the income statement (when not reported separately), the nature of the noncontrolling interest such as background information and terms, the amount of the noncontrolling interest represented by preferred stock, a description of the preferred stock, and the dividend requirements of the preferred stock.

+ References + Details

Stockholders' Equity	12 Months Ended
Stockholders' Equity	Dec. 31, 2011
Stockholders' Equity [Abstract]
Stockholders' Equity	12. Stockholders' Equity As of December 31, 2011, the Company had 148,107,611 shares of Common Stock outstanding. On January 28, 2011, the Company paid a dividend in the amount of $0.50 per share of Common Stock to shareholders of record as of the close of business on December 31, 2010. On April 29, 2011, the Company paid a dividend in the amount of $0.50 per share of Common Stock to shareholders of record as of the close of business on March 31, 2011. On July 29, 2011, the Company paid a dividend in the amount of $0.50 per share of Common Stock to shareholders of record as of the close of business on June 30, 2011. On October 31, 2011, the Company paid a dividend in the amount of $0.50 per share of Common Stock to shareholders of record as of the close of business on September 30, 2011. On December 14, 2011, the Company's Board of Directors declared a dividend in the amount of $0.55 per share of Common Stock payable on January 27, 2012 to shareholders of record as of the close of business on December 31, 2011. On April 21, 2010, the Company announced that it had established an "at the market" (ATM) stock offering program through which it may sell from time to time up to an aggregate of $400.0 million of its common stock through sales agents for a three-year period. During the year ended December 31, 2011, the Company utilized the initial ATM stock offering program to issue an aggregate of 4,228,993 shares of Common Stock for gross proceeds of approximately $400.0 million and net proceeds of approximately $394.7 million. No amount remains available for issuance under this ATM program. On June 2, 2011, the Company established a new ATM stock offering program through which it may sell from time to time up to an aggregate of $600.0 million of its common stock through sales agents over a three-year period. During the year ended December 31, 2011, the Company issued an aggregate of 431,223 shares of Common Stock under the ATM stock offering program for gross proceeds of approximately $44.9 million and net proceeds of approximately $44.3 million. As of December 31, 2011, approximately $555.1 million remained available for issuance under this ATM program. During the years ended December 31, 2011 and 2010, the Company issued 2,919,323 and 591,900 shares of its Common Stock, respectively, in connection with the redemption of an equal number of OP Units. During the years ended December 31, 2011 and 2010, the Company issued 316,159 and 638,957 shares of its Common Stock, respectively, upon the exercise of options to purchase Common Stock by certain employees.

- Definition

The entire disclosure for shareholders' equity, comprised of portions attributable to the parent entity and noncontrolling interest, if any, including other comprehensive income (as applicable). Including, but not limited to: (1) balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings; (2) accumulated balance for each classification of other comprehensive income and total amount of comprehensive income; (3) amount and nature of changes in separate accounts, including the number of shares authorized and outstanding, number of shares issued upon exercise and conversion, and for other comprehensive income, the adjustments for reclassifications to net income; (4) rights and privileges of each class of stock authorized; (5) basis of treasury stock, if other than cost, and amounts paid and accounting treatment for treasury stock purchased significantly in excess of market; (6) dividends paid or payable per share and in the aggregate for each class of stock for each period presented; (7) dividend restrictions and accumulated preferred dividends in arrears (in aggregate and per share amount); (8) retained earnings appropriations or restrictions, such as dividend restrictions; (9) impact of change in accounting principle, initial adoption of new accounting principle and correction of an error in previously issued financial statements; (10) shares held in trust for Employee Stock Ownership Plan (ESOP); (11) deferred compensation related to issuance of capital stock; (12) note received for issuance of stock; (13) unamortized discount on shares; (14) description, terms, and number of warrants or rights outstanding; (15) shares under subscription and subscription receivables, effective date of new retained earnings after quasi-reorganization and deficit eliminated by quasi-reorganization and, for a period of at least ten years after the effective date, the point in time from which the new retained dates; and (16) retroactive effective of subsequent change in capital structure.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Principles Board Opinion (APB)
-Number 12
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Article 3

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 4
-Section 08
-Paragraph d

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
-Number 43
-Chapter 1
-Section B
-Paragraph 7, 11A
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 129
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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
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-Number 210
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-Article 4

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Reference 8: http://www.xbrl.org/2003/role/presentationRef
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Reference 9: http://www.xbrl.org/2003/role/presentationRef
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Reference 10: http://www.xbrl.org/2003/role/presentationRef
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-Name Staff Accounting Bulletin (SAB)
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Reference 21: http://www.xbrl.org/2003/role/presentationRef
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-URI http://asc.fasb.org/extlink&oid=6521494

Reference 22: http://www.xbrl.org/2003/role/presentationRef
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+ Details

Future Minimum Rents

12 Months Ended

Dec. 31, 2011

Future Minimum Rents [Abstract]

Future Minimum Rents

13. Future Minimum Rents

The properties are leased to tenants under net operating leases with initial term expiration dates ranging from 2012 to 2048. The future contractual minimum lease payments to be received (excluding operating expense reimbursements) by the Company as of December 31, 2011, under non-cancelable operating leases which expire on various dates through 2048, are as follows:


Years Ending December 31,	(in thousands)
2012	$	1,305,070
2013		1,314,408
2014		1,275,588
2015		1,173,068
2016		1,044,669
Thereafter		5,052,985

No single tenant represented more than 10.0% of the Company's total rental revenue for the years ended December 31, 2011, 2010 and 2009.

- Definition

The entire disclosure for operating leases of a lessor. This may inlcude a general description of lessor's leasing arrangements for operating leases, including the basis on which contingent rental payments are determined, the existence and terms of renewal or purchase options and escalation clauses, restrictions imposed by lease arrangements, such as those concerning dividends, additional debt, and further leasing, rent holidays, rent concessions, or leasehold improvement incentives and unusual provisions or conditions.

+ References + Details

Segment Reporting

12 Months Ended

Dec. 31, 2011

Segment Reporting [Abstract]

Segment Reporting

14. Segment Reporting

The Company's segments are based on the Company's method of internal reporting which classifies its operations by both geographic area and property type. The Company's segments by geographic area are Boston, New York, Princeton, San Francisco and Washington, DC. Segments by property type include: Class A Office, Office/Technical, Residential and Hotel.

Asset information by segment is not reported because the Company does not use this measure to assess performance. Therefore, depreciation and amortization expense is not allocated among segments. Interest and other income, development and management services, general and administrative expenses, acquisition costs, interest expense, depreciation and amortization expense, suspension of development, gains (losses) from investments in securities, losses from early extinguishments of debt, income from unconsolidated joint ventures, gain on sale of real estate and noncontrolling interests are not included in Net Operating Income as internal reporting addresses these items on a corporate level.

Net Operating Income is not a measure of operating results or cash flows from operating activities as measured by accounting principles generally accepted in the United States of America, and it is not indicative of cash available to fund cash needs and should not be considered an alternative to cash flows as a measure of liquidity. All companies may not calculate Net Operating Income in the same manner. The Company considers Net Operating Income to be an appropriate supplemental measure to net income because it helps both investors and management to understand the core operations of the Company's properties.

Information by geographic area and property type (dollars in thousands):

For the year ended December 31, 2011:


	Boston			New York			Princeton			San Francisco			Washington, DC			Total
Rental Revenue:
Class A Office	$	543,494		$	458,791		$	62,648		$	213,257		$	359,544		$	1,637,734
Office/Technical		30,975			—			—			—			16,236			47,211
Residential		985			—			—			—			5,632			6,617
Hotel		34,529			—			—			—			—			34,529

Total		609,983			458,791			62,648			213,257			381,412			1,726,091
% of Grand Totals		35.34	%		26.58	%		3.63	%		12.35	%		22.10	%		100.0	%
Rental Expenses:
Class A Office		209,176			152,649			30,150			80,729			101,559			574,263
Office/Technical		9,955			—			—			—			4,280			14,235
Residential		521			—			—			—			4,958			5,479
Hotel		26,128			—			—			—			—			26,128

Total		245,780			152,649			30,150			80,729			110,797			620,105
% of Grand Totals		39.63	%		24.62	%		4.86	%		13.02	%		17.87	%		100.0	%

Net operating income	$	364,203		$	306,142		$	32,498		$	132,528		$	270,615		$	1,105,986

% of Grand Totals		32.93	%		27.68	%		2.94	%		11.98	%		24.47	%		100.0	%

For the year ended December 31, 2010:


	Boston			New York			Princeton			San Francisco			Washington, DC			Total
Rental Revenue:
Class A Office	$	368,841		$	445,296		$	65,475		$	215,468		$	335,508		$	1,430,588
Office/Technical		30,336			—			—			—			15,849			46,185
Residential		—			—			—			—			—			—
Hotel		32,800			—			—			—			—			32,800

Total		431,977			445,296			65,475			215,468			351,357			1,509,573
% of Grand Totals		28.62	%		29.50	%		4.34	%		14.27	%		23.27	%		100.0	%
Rental Expenses:
Class A Office		138,722			146,381			31,486			78,978			92,892			488,459
Office/Technical		9,067			—			—			—			4,168			13,235
Residential		—			—			—			—			—			—
Hotel		25,153			—			—			—			—			25,153

Total		172,942			146,381			31,486			78,978			97,060			526,847
% of Grand Totals		32.83	%		27.78	%		5.98	%		14.99	%		18.42	%		100.0	%

Net operating income	$	259,035		$	298,915		$	33,989		$	136,490		$	254,297		$	982,726

% of Grand Totals		26.36	%		30.42	%		3.45	%		13.89	%		25.88	%		100.0	%

For the year ended December 31, 2009:


	Boston			New York			Princeton			San Francisco			Washington, DC			Total
Rental Revenue:
Class A Office	$	364,064		$	441,571		$	63,189		$	218,432		$	318,786		$	1,406,042
Office/Technical		30,655			—			—			—			16,230			46,885
Residential		—			—			—			—			—			—
Hotel		30,385			—			—			—			—			30,385

Total		425,104			441,571			63,189			218,432			335,016			1,483,312
% of Grand Totals		28.66	%		29.77	%		4.26	%		14.73	%		22.58	%		100.0	%
Rental Expenses:
Class A Office		137,785			146,398			29,751			80,269			93,799			488,002
Office/Technical		9,475			—			—			—			4,322			13,797
Residential		—			—			—			—			—			—
Hotel		23,966			—			—			—			—			23,966

Total		171,226			146,398			29,751			80,269			98,121			525,765
% of Grand Totals		32.57	%		27.84	%		5.66	%		15.27	%		18.66	%		100.0	%

Net operating income	$	253,878		$	295,173		$	33,438		$	138,163		$	236,895		$	957,547

% of Grand Totals		26.51	%		30.83	%		3.49	%		14.43	%		24.74	%		100.0	%

The following is a reconciliation of Net Operating Income to net income attributable to Boston Properties, Inc. (in thousands):


	Years ended December 31,
	2011		2010			2009
Net operating income	$	1,105,986	$	982,726		$	957,547
Add:
Development and management services income		33,435		41,231			34,878
Income from unconsolidated joint ventures		85,896		36,774			12,058
Interest and other income		5,358		7,332			4,059
Gains on sales of real estate		—		2,734			11,760
Less:
General and administrative expense		81,442		79,658			75,447
Acquisition costs		155		2,614			—
Suspension of development		—		(7,200	)		27,766
Depreciation and amortization expense		439,184		338,371			321,681
Losses (gains) from investments in securities		443		(935	)		(2,434	)
Interest expense		394,131		378,079			322,833
Losses from early extinguishments of debt		1,494		89,883			510
Noncontrolling interests in property partnerships		1,558		3,464			2,778
Noncontrolling interest—redeemable preferred units of the Operating Partnership.		3,339		3,343			3,594
Noncontrolling interest—common units of the Operating Partnership		36,250		24,099			35,534
Noncontrolling interest in gains on sales of real estate—common units of the Operating Partnership		—		349			1,579

Net income attributable to Boston Properties, Inc.	$	272,679	$	159,072		$	231,014

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Paragraph 41
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e9038-108599

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 29
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8864-108599

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8971-108599

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 26
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8844-108599

Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8380-108599

Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8595-108599

Reference 15: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8933-108599

+ Details

Earnings Per Share

12 Months Ended

Dec. 31, 2011

Earnings Per Share [Abstract]

Earnings Per Share

15. Earnings Per Share

The following table provides a reconciliation of both the net income attributable to Boston Properties, Inc. and the number of common shares used in the computation of basic earnings per share ("EPS"), which is calculated by dividing net income attributable to Boston Properties, Inc. by the weighted-average number of common shares outstanding during the period. The terms of the Series Two Preferred Units enable the holders to obtain OP Units of the Operating Partnership, as well as Common Stock of the Company. As a result, the Series Two Preferred Units are considered participating securities and are included in the computation of basic and diluted earnings per share of the Company if the effect of applying the if-converted method is dilutive. Unvested share-based payment awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid) are participating securities and shall be included in the computation of EPS pursuant to the two-class method. As a result, unvested restricted common stock of the Company, LTIP Units, 2008 OPP Units and 2011 OPP Units are considered participating securities and are included in the computation of basic and diluted earnings per share of the Company if the effect of applying the if-converted method is dilutive. Because the 2008 OPP Units and 2011 OPP Units require the Company to outperform absolute and relative return thresholds, unless such thresholds have been met by the end of the applicable reporting period, the Company excludes such units from the diluted EPS calculation. For the year ended December 31, 2011, assuming the measurement period for the 2011 OPP Units ended on December 31, 2011, the Company's total return to stockholders compared to the absolute and relative return thresholds for the 2011 OPP Units would have resulted in participants earning and being eligible to vest in an aggregate of approximately 62,000 2011 OPP Units. As a result, these 2011 OPP Units have been included in the diluted EPS calculation. For the years ended December 31, 2011, 2010 and 2009, the absolute and relative return thresholds for the 2008 OPP Units were not met and as a result the 2008 OPP Units have been excluded from the diluted EPS calculation. Other potentially dilutive common shares, including stock options, restricted stock and other securities of the Operating Partnership that are exchangeable for the Company's Common Stock, and the related impact on earnings, are considered when calculating diluted EPS.


	For the year ended December 31, 2011
	Income (Numerator)		Shares (Denominator)		Per Share Amount
	(in thousands, except for per share amounts)
Basic Earnings:
Net income attributable to Boston Properties, Inc.	$	272,679		145,693	$	1.87
Effect of Dilutive Securities:
Stock Based Compensation and Exchangeable Senior Notes		—		525		(0.01	)
Diluted Earnings:

Net income	$	272,679		146,218	$	1.86


	For the year ended December 31, 2010
	Income (Numerator)		Shares (Denominator)		Per Share Amount
	(in thousands, except for per share amounts)
Basic Earnings:
Net income attributable to Boston Properties, Inc.	$	159,072		139,440	$	1.14
Effect of Dilutive Securities:
Stock Based Compensation		—		617		(0.00	)
Diluted Earnings:

Net income	$	159,072		140,057	$	1.14


	For the year ended December 31, 2009
	Income (Numerator)		Shares (Denominator)		Per Share Amount
	(in thousands, except for per share amounts)
Basic Earnings:
Net income attributable to Boston Properties, Inc.	$	231,014		131,050	$	1.76
Effect of Dilutive Securities:
Stock Based Compensation		—		462		(0.00	)
Diluted Earnings:

Net income	$	231,014		131,512	$	1.76

Employee Benefit Plans

12 Months Ended

Dec. 31, 2011

Employee Benefit Plans [Abstract]

Employee Benefit Plans

16.

Employee Benefit Plans

Effective January 1, 1985, the predecessor of the Company adopted a 401(k) Savings Plan (the "Plan") for its employees. Under the Plan, as amended, employees, as defined, are eligible to participate in the Plan after they have completed three months of service. Upon formation, the Company adopted the Plan and the terms of the Plan.

Effective January 1, 2000, the Company amended the Plan by increasing the Company's matching contribution to 200% of the first 3% from 200% of the first 2% of participant's eligible earnings contributed (utilizing earnings that are not in excess of an amount established by the IRS ($245,000, $245,000 and $245,000 in 2011, 2010 and 2009, respectively), indexed for inflation) and by eliminating the vesting requirement. The Company's aggregate matching contribution for the years ended December 31, 2011, 2010 and 2009 was $3.1 million, $2.9 million and $3.0 million, respectively.

Effective January 1, 2001, the Company amended the Plan to provide a supplemental retirement contribution to certain employees who have at least ten years of service on January 1, 2001, and who are 40 years of age or older as of January 1, 2001. The maximum supplemental retirement contribution will not exceed the annual limit on contributions established by the Internal Revenue Service. The Company will record an annual supplemental retirement credit for the benefit of each participant. The Company's supplemental retirement contribution and credit for the years ended December 31, 2011, 2010 and 2009 was $62,000, $48,000 and $122,000, respectively.

The Company also maintains a deferred compensation plan that is designed to allow officers of the Company to defer a portion of their current income on a pre-tax basis and receive a tax-deferred return on these deferrals. The Company's obligation under the plan is that of an unsecured promise to pay the deferred compensation to the plan participants in the future. At December 31, 2011 and 2010, the Company has funded approximately $9.5 million and $8.7 million, respectively, into a separate account, which is not restricted as to its use. The Company's liability under the plan is equal to the total amount of compensation deferred by the plan participants and earnings on the deferred compensation pursuant to investments elected by the plan participants. The Company's liability as of December 31, 2011 and 2010 was $9.5 million and $8.7 million, respectively, which are included in the accompanying Consolidated Balance Sheets.

Stock Option And Incentive Plan And Stock Purchase Plan

12 Months Ended

Dec. 31, 2011

Stock Option And Incentive Plan And Stock Purchase Plan [Abstract]

Stock Option And Incentive Plan And Stock Purchase Plan

17. Stock Option and Incentive Plan and Stock Purchase Plan

The Company has established a stock option and incentive plan for the purpose of attracting and retaining qualified employees and rewarding them for superior performance in achieving the Company's business goals and enhancing stockholder value.

Under the Company's 1997 Stock Option and Incentive Plan (the "1997 Plan"), the number of shares of Common Stock available for issuance was 4,019,174 shares. At December 31, 2011, the number of shares available for issuance under the plan was 1,895,963, of which a maximum of 1,589,342 shares may be granted as awards other than stock options. The 1997 Plan expires on May 15, 2017.

On January 20, 2011, the Compensation Committee of the Board of Directors of the Company approved outperformance awards under the Company's 1997 Plan to certain officers of the Company. These awards (the "2011 OPP Awards") are part of a broad-based, long-term incentive compensation program designed to provide the Company's management team with the potential to earn equity awards subject to the Company "outperforming" and creating shareholder value in a pay-for-performance structure. 2011 OPP Awards utilize total return to shareholders ("TRS") over a three-year measurement period as the performance metric and include two years of time-based vesting after the end of the performance measurement period (subject to acceleration in certain events) as a retention tool. Recipients of 2011 OPP Awards will share in an outperformance pool if the Company's TRS, including both share appreciation and dividends, exceeds absolute and relative hurdles over a three-year measurement period from February 1, 2011 to January 31, 2014, based on the average closing price of a share of the Company's common stock of $93.38 for the five trading days prior to and including February 1, 2011. The aggregate reward that recipients of all 2011 OPP Awards can earn, as measured by the outperformance pool, is subject to a maximum cap of $40.0 million.

The outperformance pool will consist of (i) two percent (2%) of the excess total return above a cumulative absolute TRS hurdle of 27% over the full three-year measurement period (equivalent to 9% per annum) (the "Absolute TRS Component") and (ii) two percent (2%) of the excess or deficient excess total return above or below a relative TRS hurdle equal to the total return of the SNL Equity REIT Index over the three-year measurement period (the "Relative TRS Component"). In the event that the Relative TRS Component is potentially positive because the Company's TRS is greater than the total return of the SNL Equity REIT Index, but the Company achieves a cumulative absolute TRS below 27% over the three-year measurement period (equivalent to 9% per annum), the actual contribution to the outperformance pool from the Relative TRS Component will be subject to a sliding scale factor as follows: (i) 100% of the potential Relative TRS Component will be earned if the Company's TRS is equal to or greater than a cumulative 27% over three years, (ii) 0% will be earned if the Company's TRS is 0% or less, and (iii) a percentage from 0% to 100% calculated by linear interpolation will be earned if the Company's cumulative TRS over three years is between 0% and 27%. For example, if the Company achieves a cumulative absolute TRS of 18% over the full three-year measurement period (equivalent to a 6% absolute annual TRS), the potential Relative TRS Component would be prorated by 66.67%. The potential Relative TRS Component before application of the sliding scale factor will be capped at $40.0 million. In the event that the Relative TRS Component is negative because the Company's TRS is less than the total return of the SNL Equity REIT Index, any outperformance reward potentially earned under the Absolute TRS Component will be reduced dollar for dollar, provided that the potential Absolute TRS Component before reduction for any negative Relative TRS Component will be capped at $40.0 million. The algebraic sum of the Absolute TRS Component and the Relative TRS Component determined as described above will never exceed $40.0 million.

Each employee's 2011 OPP Award was designated as a specified percentage of the aggregate outperformance pool. Assuming the applicable absolute and/or relative TRS thresholds are achieved at the end of the measurement period, the algebraic sum of the Absolute TRS Component and the Relative TRS Component will be calculated and then allocated among the 2011 OPP Award recipients in accordance with each individual's percentage. If there is a change of control prior to January 31, 2014, the measurement period will end on the change of control date and both the Absolute TRS Component (using a prorated absolute TRS hurdle) and the Relative TRS Component will be calculated and, assuming the applicable absolute and/or relative TRS thresholds are achieved over the shorter measurement period, allocated among the 2011 OPP Award recipients as of that date.

Rewards earned with respect to 2011 OPP Awards (if any) will vest 25% on February 1, 2014, 25% on February 1, 2015and 50% on February 1, 2016, based on continued employment. Vesting will be accelerated in the event of a change in control of the Company, termination of employment without cause, termination of employment by the award recipient for good reason, death, disability or retirement, although restrictions on transfer will continue to apply in certain of these situations. All determinations, interpretations and assumptions relating to the calculation of performance and vesting relating to 2011 OPP Awards will be made by the Compensation Committee. 2011 OPP Awards will be in the form of LTIP Units. LTIP Units will be issued prior to the determination of the outperformance pool, but will remain subject to forfeiture depending on the extent of rewards earned with respect to 2011 OPP Awards. The number of LTIP Units issued initially to recipients of the 2011 OPP Awards is an estimate of the maximum number of LTIP Units that they could earn, based on certain assumptions. The number of LTIP Units actually earned by each award recipient will be determined at the end of the performance measurement period by dividing his or her share of the outperformance pool by the average closing price of a REIT Share for the 15 trading days immediately preceding the measurement date. Total return for the Company and for the SNL Equity REIT Index over the three-year measurement period and other circumstances will determine how many LTIP Units are earned by each recipient; if they are fewer than the number issued initially, the balance will be forfeited as of the performance measurement date. Prior to the measurement date, LTIP units issued on account of 2011 OPP Awards will be entitled to receive per unit distributions equal to one-tenth (10%) of the regular quarterly distributions payable on an OP Unit, but will not be entitled to receive any special distributions. After the measurement date, the number of LTIP Units, both vested and unvested, which 2011 OPP Award recipients have earned based on the establishment of an outperformance pool, will be entitled to receive distributions in an amount per unit equal to distributions, both regular and special, payable on an OP Unit. LTIP Units are designed to qualify as "profits interests" in the Operating Partnership for federal income tax purposes. As a general matter, the profits interests characteristics of the LTIP Units mean that initially they will not be economically equivalent in value to an OP Unit. If and when events specified by applicable tax regulations occur, LTIP Units can over time increase in value up to the point where they are equivalent to OP Units on a one-for-one basis. After LTIP Units are fully vested, and to the extent the special tax rules applicable to profits interests have allowed them to become equivalent in value to OP Units, LTIP Units may be converted on a one-for-one basis into OP Units. OP Units in turn have a one-for-one relationship in value with Boston Properties, Inc. common stock, and are exchangeable on such one-for-one basis for cash or, at the election of the Company, Boston Properties, Inc. common stock.

The Company issued 19,030, 69,499 and 62,876 shares of restricted stock and 190,067, 252,597 and 515,007 LTIP Units to employees and directors under the 1997 Plan during the years ended December 31, 2011, 2010 and 2009, respectively. The Company issued 146,844 non-qualified stock options under the 1997 Plan during the year ended December 31, 2011. The Company issued 400,000 2011 OPP Units under the 1997 Plan during the year ended December 31, 2011. Employees paid $0.01 per share of restricted common stock and $0.25 per LTIP and 2011 OPP Unit. An LTIP Unit is generally the economic equivalent of a share of restricted stock in the Company. The aggregate value of the LTIP Units is included in Noncontrolling Interests in the Consolidated Balance Sheets. The restricted stock and LTIP Units granted to employees between January 1, 2004 and October 2006 vest over a five-year term. Grants of restricted stock and LTIP Units made on and after November 2006 vest in four equal annual installments. Restricted stock and LTIP Units are measured at fair value on the date of grant based on the number of shares or units granted, as adjusted for forfeitures, and the price of the Company's Common Stock on the date of grant as quoted on the New York Stock Exchange. Such value is recognized as an expense ratably over the corresponding employee service period. As the 2011 OPP Awards are subject to both a service condition and a market condition, the Company recognizes the compensation expense related to the 2011 OPP Awards under the graded vesting attribution method. Under the graded vesting attribution method, each portion of the award that vests at a different date is accounted for as a separate award and recognized over the period appropriate to that portion so that the compensation cost for each portion should be recognized in full by the time that portion vests. Dividends paid on both vested and unvested shares of restricted stock are charged directly to Earnings in Excess of Dividends in the Consolidated Balance Sheets. Stock-based compensation expense associated with restricted stock, LTIP Units and 2008 OPP Units and 2011 OPP Units was approximately $28.3 million, $31.9 million and $25.6 million for the years ended December 31, 2011, 2010 and 2009, respectively. Upon the conclusion of the three-year measurement period in February 2011, the 2008 OPP Awards were not earned, the program was terminated and the Company accelerated the then remaining unrecognized compensation expense totaling approximately $4.3 million during the year ended December 31, 2011. For the year ended December 31, 2010, stock-based compensation expense includes an aggregate of approximately $5.8 million of remaining previously unvested stock-based compensation granted between 2006 and 2009 to Edward H. Linde, the Company's late Chief Executive Officer, which expense was accelerated as a result of his passing on January 10, 2010. At December 31, 2011, there was $24.7 million of unrecognized compensation expense related to unvested restricted stock and LTIP Units and $5.5 million of unrecognized compensation expense related to unvested 2011 OPP Units that is expected to be recognized over a weighted-average period of approximately 2.5 years.

The shares of restricted stock were valued at approximately $1.8 million ($93.40 per share weighted-average), $4.5 million ($65.31 per share weighted-average) and $2.8 million ($43.89 per share weighted-average) for the years ended December 31, 2011, 2010 and 2009, respectively.

LTIP Units were valued using a Monte Carlo simulation method model in accordance with the provisions of ASC 718 "Compensation—Stock Compensation" ("ASC 718") (formerly SFAS No. 123R). LTIP Units issued during the years ended December 31, 2011, 2010 and 2009 were valued at approximately $16.5 million, $15.3 million and $21.1 million, respectively. The weighted-average per unit fair value of LTIP Unit grants in 2011, 2010 and 2009 was $86.74, $60.49 and $41.05, respectively. The per unit fair value of each LTIP Unit granted in 2011, 2010 and 2009 was estimated on the date of grant using the following assumptions; an expected life of 5.8 years, 5.7 years and 5.6 years, a risk-free interest rate of 2.22%, 2.60% and 1.87% and an expected price volatility of 30.0%, 36.0% and 40.0%, respectively.

The non-qualified stock options granted during the year ended December 31, 2011 had a fair value on the date of grant of $24.67 per option, which was computed using the Black-Scholes option-pricing model utilizing the following assumptions: an expected life of 6.0 years, a risk-free interest rate of 2.37%, an expected price volatility of 35.0% and an expected dividend yield of 3.0%. The exercise price of the options is $92.71, which was the closing price of the Company's common stock on the date of grant.

The 2011 OPP Units were valued at approximately $7.8 million utilizing a Monte Carlo simulation to estimate the probability of the performance vesting conditions being satisfied. The Monte Carlo simulation used a statistical formula underlying the Black-Scholes and binomial formulas and such simulation was run approximately 100,000 times. For each simulation, the payoff is calculated at the settlement date, which is then discounted to the award date at a risk-free interest rate. The average of the values over all simulations is the expected value of the unit on the award date. Assumptions used in the valuations included (1) factors associated with the underlying performance of the Company's stock price and total shareholder return over the term of the performance awards including total stock return volatility and risk-free interest and (2) factors associated with the relative performance of the Company's stock price and total shareholder return when compared to the SNL Equity REIT Index. The valuation was performed in a risk-neutral framework, so no assumption was made with respect to an equity risk premium. The fair value of the 2011 OPP Units is based on the sum of: (1) the present value of the expected payoff to the OPP Award on the measurement date, if the TRS over the applicable measurement period exceeds performance hurdles of the Absolute and the Relative Components; and (2) the present value of the distributions payable on the 2011 OPP Units. The ultimate reward realized on account of the OPP Award by the holders of the 2011 OPP Units is contingent on the TRS achieved on the measurement date, both in absolute terms and relative to the TRS of the SNL Equity REIT Index. The per unit fair value of each 2011 OPP Unit was estimated on the date of grant using the following assumptions in the Monte-Carlo valuation: expected price volatility for the Company and the SNL Equity REIT index of 41% and 37%, respectively; a risk free rate of 0.98%; and estimated total dividend payments over the measurement period of $6.10 per share.

A summary of the status of the Company's stock options as of December 31, 2011, 2010 and 2009 and changes during the years then ended are presented below:


	Shares			Weighted Average Exercise Price
Outstanding at December 31, 2008		1,206,402		$	34.23
Granted		—			—
Exercised		(242,507	)	$	33.41
Canceled		—			—

Outstanding at December 31, 2009		963,895		$	34.44
Granted		—			—
Exercised		(638,957	)	$	35.35
Canceled		—			—

Outstanding at December 31, 2010		324,938		$	32.65
Granted		146,844		$	92.71
Exercised		(316,159	)	$	32.63
Canceled		—			—

Outstanding at December 31, 2011		155,623		$	89.35

The following table summarizes information about stock options outstanding at December 31, 2011:


Options Outstanding							Options Exercisable
Range of Exercise Prices	Number Outstanding at 12/31/11		Weighted-Average Remaining Contractual Life		Weighted-Average Exercise Price		Number Exercisable at 12/31/11		Weighted-Average Exercise Price
$32.62-$34.14		8,779		0.1 Years	$	33.10		8,779	$	33.10
$92.71		146,844		9.1 Years	$	92.71		4,854	$	92.71

The total intrinsic value of the outstanding and exercisable stock options as of December 31, 2011 was approximately $0.6 million. In addition, the Company had 324,938 and 963,895 options exercisable at a weighted-average exercise price of $32.65 and $34.44 at December 31, 2010 and 2009, respectively.

The Company adopted the 1999 Non-Qualified Employee Stock Purchase Plan (the "Stock Purchase Plan") to encourage the ownership of Common Stock by eligible employees. The Stock Purchase Plan became effective on January 1, 1999 with an aggregate maximum of 250,000 shares of Common Stock available for issuance. The Stock Purchase Plan provides for eligible employees to purchase on the business day immediately following the end of the biannual purchase periods (i.e., January 1-June 30 and July 1-December 31) shares of Common Stock at a purchase price equal to 85% of the average closing prices of the Common Stock during the last ten business days of the purchase period. The Company issued 6,356, 9,131 and 12,105 shares with the weighted average purchase price equal to $80.13 per share, $61.61 per share and $42.65 per share under the Stock Purchase Plan during the years ended December 31, 2011, 2010 and 2009, respectively.

- Definition

Tabular disclosure of components of a stock option or other award plan under which equity-based compensation is awarded to employees, typically comprised of the amount of unearned compensation (deferred compensation cost), compensation expense, and changes in the quantity and fair value of the shares (or other type of equity) granted, exercised, forfeited, and issued and outstanding pertaining to that plan. Disclosure may also include nature and general terms of such arrangements that existed during the period and potential effects of those arrangements on shareholders, effect of compensation cost arising from equity-based payment arrangements on the income statement, method of estimating the fair value of the goods or services received, or the fair value of the equity instruments granted, during the period, cash flow effects resulting from equity-based payment arrangements and, for registrants that accelerate vesting of out of the money share options, reasons for the decision to accelerate.

+ References + Details

Related Party Transactions

12 Months Ended

Dec. 31, 2011

Related Party Transactions

18.

Related Party Transactions

A firm controlled by Mr. Raymond A. Ritchey's brother was paid aggregate leasing commissions of approximately $671,000, $960,000 and $257,000 for the years ended December 31, 2011, 2010 and 2009, respectively, related to certain exclusive leasing arrangements for certain Northern Virginia properties. Mr. Ritchey is an Executive Vice President of Boston Properties, Inc.

On June 30, 1998, the Company acquired from entities controlled by Mr. Alan B. Landis, a former director, a portfolio of properties known as the Carnegie Center Portfolio and Tower Center One and related operations and development rights (collectively, the "Carnegie Center Portfolio"). In connection with the acquisition of the Carnegie Center Portfolio, the Operating Partnership entered into a development agreement (the "Development Agreement") with affiliates of Mr. Landis providing for up to approximately 2,000,000 square feet of development in or adjacent to the Carnegie Center office complex. An affiliate of Mr. Landis was entitled to a purchase price for each parcel developed under the Development Agreement calculated on the basis of $20 per rentable square foot of property developed. Another affiliate of Mr. Landis was eligible to earn a contingent payment for each developed property that achieves a stabilized return in excess of a target annual return ranging between 10.5% and 11%. The Development Agreement also provided that upon negotiated terms and conditions, the Company and Mr. Landis would form a development company to provide development services for these development projects and would share the expenses and profits, if any, of this new company. In addition, in connection with the acquisition of the Carnegie Center Portfolio, Mr. Landis became a director of the Company pursuant to an Agreement Regarding Directorship, dated as of June 30, 1998, with the Company (the "Directorship Agreement"). Under the Directorship Agreement, the Company agreed to nominate Mr. Landis for re-election as a director at each annual meeting of stockholders of the Company in a year in which his term expires, provided that specified conditions are met.

On October 21, 2004, the Company entered into an agreement (the "2004 Agreement") to modify several provisions of the Development Agreement. Under the terms of the 2004 Agreement, the Operating Partnership and affiliates of Mr. Landis amended the Development Agreement to limit the rights of Mr. Landis and his affiliates to participate in the development of properties under the Development Agreement. Among other things, Mr. Landis agreed that (1) Mr. Landis and his affiliates will have no right to participate in any entity formed to acquire land parcels or the development company formed by the Operating Partnership to provide development services under the Development Agreement, (2) Mr. Landis will have no right or obligation to play a role in development activities engaged in by the development company formed by the Operating Partnership under the Development Agreement or receive compensation from the development company and (3) the affiliate of Mr. Landis will have no right to receive a contingent payment for developed properties based on stabilized returns. In exchange, the Company (together with the Operating Partnership) agreed to:

•

effective as of June 30, 1998, pay Mr. Landis $125,000 on January 1 of each year until the earlier of (A) January 1, 2018, (B) the termination of the Development Agreement or (C) the date on which all development properties under the Development Agreement have been conveyed pursuant to the Development Agreement, with $750,000, representing payments of this annual amount from 1998 to 2004, being paid upon execution of the 2004 Agreement; and

•

pay an affiliate of Mr. Landis, in connection with the development of land parcels acquired under the Development Agreement, an aggregate fixed amount of $10.50 per rentable square foot of property developed (with a portion of this amount (i.e., $5.50) being subject to adjustment, in specified circumstances, based on future increases in the Consumer Price Index) in lieu of a contingent payment based on stabilized returns, which payment could have been greater or less than $10.50 per rentable square foot of property developed.

The Operating Partnership also continues to be obligated to pay an affiliate of Mr. Landis the purchase price of $20 per rentable square foot of property developed for each land parcel acquired as provided in the original Development Agreement. During the 20-year term of the Development Agreement, until such time, if any, as the Operating Partnership elects to acquire a land parcel, an affiliate of Mr. Landis will remain responsible for all carrying costs associated with such land parcel. On July 24, 2007, the Company acquired from Mr. Landis 701 Carnegie Center, a land parcel located in Princeton, New Jersey for a purchase price of approximately $3.1 million.

In addition, in connection with entering into the 2004 Agreement, Mr. Landis resigned as a director of the Company effective as of May 11, 2005 and agreed that the Company had no future obligation to nominate Mr. Landis as a director of the Company under the Directorship Agreement or otherwise. Mr. Landis did not resign because of a disagreement with the Company on any matter relating to its operations, policies or practices. Mitchell S. Landis, the Senior Vice President and Regional Manager of the Company's Princeton, New Jersey region, is the brother of Alan B. Landis.

In accordance with the Company's 1997 Plan, and as approved by the Board of Directors, five non-employee directors made an election to receive deferred stock units in lieu of cash fees for 2011. The deferred stock units will be settled in shares of common stock upon the cessation of such director's service on the Board of Directors. As a result of these elections, the aggregate cash fees otherwise payable to a non-employee director during a fiscal quarter are converted into a number of deferred stock units equal to the aggregate cash fees divided by the last reported sales price of a share of the Company's common stock on the last trading of the applicable fiscal quarter. The deferred stock units are also credited with dividend equivalents as dividends are paid by the Company. At December 31, 2011 and 2010, the Company had outstanding 79,856 and 73,218 deferred stock units, respectively.

- Definition

The entire disclosure for related party transactions, including the nature of the relationship(s), a description of the transactions, the amount of the transactions, the effects of any change in the method of establishing the terms of the transaction from the previous period, stated interest rate, expiration date, terms and manner of settlement per the agreement with the related party, and amounts due to or from related parties. If the entity and one or more other entities are under common ownership or management control and this control affects the operating results or financial position, disclosure includes the nature of the control relationship even if there are no transactions between the entities. Disclosure may also include the aggregate amount of current and deferred tax expense for each statement of earnings presented where the entity is a member of a group that files a consolidated tax return, the amount of any tax related balances due to or from affiliates as of the date of each statement of financial position presented, the principal provisions of the method by which the consolidated amount of current and deferred tax expense is allocated to the members of the group and the nature and effect of any changes in that method. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 4
-Section 08
-Paragraph k

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 3A
-Section 04
-Paragraph b

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 57
-Paragraph 1-4
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39622-107864

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39603-107864

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(k))
-URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39691-107864

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39678-107864

+ Details

Selected Interim Financial Information

12 Months Ended

Dec. 31, 2011

Selected Interim Financial Information [Abstract]

Selected Interim Financial Information

19.

Selected Interim Financial Information (unaudited)

The tables below reflect the Company's selected quarterly information for the years ended December 31, 2011 and 2010. Certain prior period amounts have been reclassified to conform to the current year presentation. The quarter ended December 31, 2011 includes the gain on sale of Two Grand Central Tower totaling approximately $46.2 million, which is included within income from unconsolidated joint ventures on the Company's consolidated statements of operations (See Note 5). The quarter ended December 31, 2010 includes losses from early extinguishments of debt aggregating approximately $81.7 million primarily associated with the redemption of $700.0 million in aggregate principal amount of 6.25% senior notes due 2013.


	2011 Quarter Ended
	March 31,		June 30,		September 30,		December 31,
	(in thousands, except for per share amounts)
Total revenue	$	417,875	$	436,451	$	452,413	$	452,787
Income from continuing operations	$	48,194	$	69,738	$	80,451	$	115,443
Net income attributable to Boston Properties, Inc.	$	40,813	$	60,214	$	70,542	$	101,644
Income attributable to Boston Properties, Inc. per share—basic	$	0.29	$	0.41	$	0.48	$	0.69
Income attributable to Boston Properties, Inc. per share—diluted	$	0.29	$	0.41	$	0.48	$	0.69


	2010 Quarter Ended
	March 31,		June 30,		September 30,		December 31,
	(in thousands, except for per share amounts)
Total revenue	$	378,071	$	393,841	$	386,410	$	392,482
Income (loss) from continuing operations	$	60,742	$	71,518	$	68,089	$	(12,756	)
Net income (loss) attributable to Boston Properties, Inc.	$	52,714	$	61,412	$	57,668	$	(12,903	)
Income (loss) attributable to Boston Properties, Inc. per share—basic	$	0.38	$	0.44	$	0.41	$	(0.09	)
Income (loss) attributable to Boston Properties, Inc. per share—diluted	$	0.38	$	0.44	$	0.41	$	(0.09	)

- Definition

The entire disclosure for the quarterly financial data in the annual financial statements. The disclosure may include a tabular presentation of financial information for each fiscal quarter for the current and previous year, including revenues, gross profit, income or loss before extraordinary items and earnings per share data. It also includes an indication if the information in the note is unaudited, comments on the aggregate effect of year-end adjustments, and an explanation of matters or transactions that affect comparability or are pertinent to an understanding of the information furnished.

+ References + Details

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2011
Subsequent Events [Abstract]
Subsequent Events	20. Subsequent Events On January 3, 2012, the Company commenced the redevelopment of 12300 Sunrise Valley Drive, a Class A office project with approximately 256,000 net rentable square feet located in Reston, Virginia. The Company will capitalize incremental costs during the redevelopment. On January 10, 2012, the Company announced that holders of the 2.875% Exchangeable Senior Notes due 2037 (the "Notes") of its Operating Partnership have the right to surrender their Notes for purchase by the Operating Partnership (the "Put Right") on February 15, 2012. In connection with the Put Right, on January 10, 2012, the Operating Partnership distributed a Put Right Notice to the holders of the Notes and filed a Schedule TO with the Securities and Exchange Commission. The opportunity to exercise the Put Right expired at 5:00 p.m., New York City time, on February 8, 2012. On January 10, 2012, the Company also announced that the Operating Partnership issued a notice of redemption to the holders of the Notes to redeem, on February 20, 2012 (the "Redemption Date"), all of the Notes outstanding on the Redemption Date. In connection with the redemption, holders of the Notes had the right to exchange their Notes prior to 5:00 p.m., New York City time, on February 16, 2012. Notes with respect to which the Put Right was not exercised (or with respect to which the Put Right is exercised and subsequently withdrawn prior to the withdrawal deadline) and that were not surrendered for exchange prior to 5:00 p.m., New York City time, on February 16, 2012, were redeemed by the Operating Partnership on the Redemption Date at a redemption price equal to 100% of the principal amount of the Notes plus accrued and unpaid interest thereon to, but excluding, the Redemption Date. Holders of an aggregate of $242,735,000 of the Notes exercised the Put Right and the Company repurchased such Notes on February 15, 2012. On February 20, 2012, the Company redeemed the remaining $333,459,000 of outstanding Notes at a redemption price equal to 100% of the principal amount of the Notes plus accrued and unpaid interest thereon. On January 25, 2012, the Company's Compensation Committee approved outperformance awards under the Company's 1997 Plan to officers and employees of the Company. These awards (the "2012 OPP Awards") are part of a broad-based, long-term incentive compensation program designed to provide the Company's management team with the potential to earn equity awards subject to the Company "outperforming" and creating shareholder value in a pay-for-performance structure. Recipients of 2012 OPP Awards will share in a maximum outperformance pool of $40.0 million if the total return to shareholders, including both share appreciation and dividends, exceeds absolute and relative hurdles over a three-year measurement period from February 7, 2012 to February 6, 2015. Earned awards are generally subject to two-years of time-based vesting after the performance measurement date. The Company expects that under the Financial Accounting Standards Board's Accounting Standards Codification ("ASC") 718 "Compensation—Stock Compensation" the 2012 OPP Awards will have an aggregate value of approximately $7.7 million, which amount will be amortized into earnings over the five-year plan period under the graded vesting method. As previously disclosed, the Company notified the master servicer of the non-recourse mortgage loan collateralized by the Company's Montvale Center property located in Gaithersburg, Maryland that the cash flows generated from the property were insufficient to fund debt service payments and capital improvements necessary to lease and operate the property and that the Company was not prepared to fund any cash shortfalls. The Company is not current on making debt service payments and is currently accruing interest at the default interest rate of 9.93% per annum. The loan was originally scheduled to mature on June 6, 2012. However, a receiver has been appointed for the property and the Company expects the property to be transferred to the lender during the first quarter of 2012. On February 3, 2012, the Company issued 19,521 shares of restricted common stock, 156,652 LTIP units and 165,538 non-qualified stock options under the 1997 Plan to certain employees of the Company. On February 10, 2012, the Company entered into an agreement to acquire 453 Ravendale Avenue in Mountain View, California for an aggregate purchase price of approximately $6.7 million in cash. 453 Ravendale Avenue is an approximately 30,000 net rentable square foot office/technical property located in Mountain View, California. The closing is subject to customary closing conditions and termination rights for transactions of this type. There can be no assurance that the acquisition will be completed on the terms currently contemplated or at all. On February 13, 2012, E. Mitchell Norville announced that he will resign as Executive Vice President, Chief Operating Officer of the Company effective on February 29, 2012. In connection with his resignation, Mr. Norville entered into a separation agreement (the "Separation Agreement") with the Company. Under the Separation Agreement, the Company agreed to pay Mr. Norville cash payments totaling approximately $1,533,333 (less applicable deductions) in addition to his cash bonus for 2011, which was $950,000. In addition, Mr. Norville has agreed to provide consulting services to the Company for at least two months following the effective date of his resignation for which he will receive $20,000 per month. Under the Separation Agreement, Mr. Norville will be entitled to accelerated vesting with respect to 23,502 LTIP units in Boston Properties Limited Partnership and stock options to purchase 4,464 shares of common stock at an exercise price of $92.71 and 5,117 shares of common stock at an exercise price of $104.47. Mr. Norville will also retain approximately 36% of his 2011 outperformance award, which will remain subject to the performance-based vesting criteria originally established for the 2011 outperformance awards. Mr. Norville agreed to one-year non-competition, non-solicitation and non-interference provisions, and provided the Company with a general release of claims. On February 16, 2012, the Company entered into an agreement to acquire 100 Federal Street in Boston, Massachusetts for an aggregate investment of $615.0 million in cash. 100 Federal Street is an approximately 1,300,000 net rentable square foot, 37-story Class A office tower located in Boston, Massachusetts. The Company posted a cash deposit of $25.0 million to secure its obligations under the agreement, which amount will be credited to the Company at closing. The closing is subject to customary closing conditions and termination rights for transactions of this type. There can be no assurance that the acquisition will be completed on the terms currently contemplated, or at all.

Real Estate And Accumulated Depreciation

12 Months Ended

Dec. 31, 2011

Real Estate And Accumulated Depreciation [Abstract]

Real Estate And Accumulated Depreciation

Boston Properties, Inc.

Schedule 3—Real Estate and Accumulated Depreciation

December 31, 2011

(dollars in thousands)


Property Name	Type	Location	Encumbrances			Original				Costs Capitalized Subsequent to Acquisition					Building and Improvements		Land Held for Development		Development and Construction in Progress		Total		Accumulated Depreciation		Year(s) Built/ Renovated		Depreciable Lives (Years)
						Original							Land and
						Land		Building					Improvements
Embarcadero Center	Office	San Francisco, CA	$	370,091		$	179,697	$	847,410	$	278,722		$	195,984	$	1,109,845	$	—	$	—	$	1,305,829	$	397,177		1970/1989	(1)
Prudential Center	Office	Boston, MA		—			92,077		734,594		323,490			107,428		1,026,936		15,797		—		1,150,161		349,127		1965/1993/2002	(1)
399 Park Avenue	Office	New York, NY		—			339,200		700,358		89,720			354,107		775,171		—		—		1,129,278		177,001		1961	(1)
601 Lexington Avenue	Office	New York, NY		725,000			241,600		494,782		212,551			289,639		659,294		—		—		948,933		163,031		1977/1997	(1)
The John Hancock Tower and Garage	Office	Boston, MA		660,033			219,543		667,884		38,678			219,616		706,489		—		—		926,105		25,299		1976	(1)
Times Square Tower	Office	New York, NY		—			165,413		380,438		83,353			169,193		460,011		—		—		629,204		110,416		2004	(1)
Carnegie Center	Office	Princeton, NJ		—			105,107		377,259		59,401			103,062		436,766		1,939		—		541,767		147,906		1983-1999	(1)
Atlantic Wharf	Office	Boston, MA		—			63,988		454,537		—			63,988		454,537		—		—		518,525		10,101		2011	(1)
599 Lexington Avenue	Office	New York, NY		750,000			81,040		100,507		120,055			87,852		213,750		—		—		301,602		131,768		1986	(1)
Gateway Center	Office	San Francisco, CA		—			28,255		139,245		48,457			30,627		185,330		—		—		215,957		65,219		1984/1986/2002	(1)
South of Market	Office	Reston, VA		—			13,603		164,144		9,110			13,687		173,170		—		—		186,857		24,610		2008	(1)
2200 Pennsylvania Avenue	Office	Washington, DC		—			—		183,541		—			—		183,541		—		—		183,541		4,154		2011	(1)
Bay Colony Corporate Center	Office	Waltham, MA		145,673			18,789		148,451		4,670			18,789		153,121		—		—		171,910		6,248		1985-1989	(1)
Reservoir Place	Office	Waltham, MA		—			18,605		92,619		25,696			20,118		116,802		—		—		136,920		43,467		1955/1987	(1)
3200 Zanker Road	Office	San Jose, CA		—			36,705		82,863		13,542			36,997		93,454		2,659		—		133,110		18,206		1988	(1)
505 9th Street	Office	Washington, DC		125,844			38,885		83,719		5,661			42,082		86,183		—		—		128,265		13,800		2007	(1)
1333 New Hampshire Avenue	Office	Washington, DC		—			34,032		85,660		7,688			35,382		91,998		—		—		127,380		25,512		1996	(1)
Kingstowne Towne Center	Office	Alexandria, VA		54,790			18,021		109,038		(428	)		18,062		108,569		—		—		126,631		19,283		2003-2006	(1)
1330 Connecticut Avenue	Office	Washington, DC		—			25,982		82,311		16,182			27,135		97,340		—		—		124,475		23,054		1984	(1)
Capital Gallery	Office	Washington, DC		—			4,725		29,565		90,125			8,662		115,753		—		—		124,415		46,636		1981/2006	(1)
635 Massachusetts Avenue	Office	Washington, DC		—			95,281		22,221		2,510			95,293		22,257		2,462		—		120,012		12,876		1968/1992	(1)
Weston Corporate Center	Office	Weston, MA		—			25,753		92,312		(149	)		25,852		92,064		—		—		117,916		4,820		2010	(1)
One Freedom Square	Office	Reston, VA		66,092			9,929		84,504		15,290			11,293		98,430		—		—		109,723		36,740		2000	(1)
Two Freedom Square	Office	Reston, VA		—			13,930		77,739		12,649			15,420		88,898		—		—		104,318		30,804		2001	(1)
Seven Cambridge Center	Office	Cambridge, MA		—			3,457		97,136		2,880			4,125		99,348		—		—		103,473		35,558		2006	(1)
One and Two Reston Overlook	Office	Reston, VA		—			16,456		66,192		13,195			17,561		78,282		—		—		95,843		23,776		1999	(1)
Discovery Square	Office	Reston, VA		—			11,198		71,782		9,017			12,533		79,464		—		—		91,997		24,400		2001	(1)
140 Kendrick Street	Office	Needham, MA		50,291			18,095		66,905		4,246			19,092		70,154		—		—		89,246		13,686		2000	(1)
Waltham Weston Corporate Center	Office	Waltham, MA		—			10,385		60,694		9,625			11,097		69,607		—		—		80,704		24,588		2003	(1)
Five Cambridge Center	Office	Cambridge, MA		—			18,863		53,346		7,901			18,938		61,172		—		—		80,110		14,816		1981/1996	(1)
77 CityPoint	Office	Waltham, MA		—			13,847		60,383		3,115			13,873		63,472		—		—		77,345		7,532		2008	(1)
12300 Sunrise Valley Drive	Office	Reston, VA		—			9,062		58,884		8,489			11,009		65,426		—		—		76,435		41,344		1987/1988	(1)
Four Cambridge Center	Office	Cambridge, MA		—			19,104		52,078		3,888			19,148		55,922		—		—		75,070		8,553		1983/1998	(1)
Democracy Tower	Office	Reston, VA		—			—		73,335		431			—		73,766		—		—		73,766		6,284		2009	(1)
230 CityPoint	Office	Waltham, MA		—			13,189		49,823		10,489			13,593		59,908		—		—		73,501		13,395		1992	(1)
North First Business Park	Office	San Jose, CA		—			58,402		13,069		1,961			23,377		14,345		35,710		—		73,432		6,432		1981	(1)
2440 West El Camino Real	Office	Mountain View, CA		—			16,741		51,285		—			16,741		51,285		—		—		68,026		166		1987/2003	(1)
Wisconsin Place	Office	Chevy Chase, MD		—			—		53,349		12,952			—		66,301		—		—		66,301		6,123		2009	(1)
Reston Corporate Center	Office	Reston, VA		—			9,135		50,857		5,334			10,148		55,178		—		—		65,326		18,021		1984	(1)
New Dominion Technology Park, Bldg. Two	Office	Herndon, VA		63,000			5,584		51,868		3,694			6,510		54,636		—		—		61,146		12,970		2004	(1)
One Preserve Parkway	Office	Rockville, MD		—			5,357		42,186		7,156			5,357		49,342		—		—		54,699		4,618		2009	(1)
New Dominion Technology Park, Bldg. One	Office	Herndon, VA		47,406			3,880		43,227		3,882			4,583		46,406		—		—		50,989		16,382		2001	(1)
Sumner Square	Office	Washington, DC		23,827			624		28,745		21,294			1,478		49,185		—		—		50,663		19,627		1985	(1)
303 Almaden Boulevard	Office	San Jose, CA		—			10,836		35,606		3,983			10,947		39,478		—		—		50,425		7,502		1995	(1)
1301 New York Avenue	Office	Washington, DC		—			9,250		18,750		20,746			9,867		38,879		—		—		48,746		14,740		1983/1998	(1)
200 West Street	Office	Waltham, MA		—			16,148		24,983		7,455			16,813		31,773		—		—		48,586		12,209		1999	(1)
191 Spring Street	Office	Lexington, MA		—			2,850		27,166		17,481			3,151		44,346		—		—		47,497		26,795		1971/1995	(1)
Bedford Business Park	Office	Bedford, MA		—			534		3,403		40,988			2,218		42,707		—		—		44,925		24,518		1980	(1)
University Place	Office	Cambridge, MA		16,220			—		37,091		6,785			390		43,486		—		—		43,876		17,757		1985	(1)
2600 Tower Oaks Boulevard	Office	Rockville, MD		—			4,243		31,125		7,580			4,785		38,163		—		—		42,948		14,095		2001	(1)
Quorum Office Park	Office	Chelmsford, MA		—			3,750		32,454		5,196			5,187		36,213		—		—		41,400		11,042		2001	(1)
One Cambridge Center	Office	Cambridge, MA		—			134		25,110		13,264			548		37,960		—		—		38,508		22,813		1987	(1)
12290 Sunrise Valley Drive	Office	Reston, VA		—			3,594		32,977		1,374			4,009		33,936		—		—		37,945		10,329		2006	(1)
500 E Street	Office	Washington, DC		—			109		22,420		11,915			2,379		32,065		—		—		34,444		18,501		1987	(1)
Eight Cambridge Center	Office	Cambridge, MA		—			850		25,042		5,745			1,323		30,314		—		—		31,637		8,177		1999	(1)
10 and 20 Burlington Mall Road	Office	Burlington, MA		—			930		6,928		13,118			802		20,174		—		—		20,976		12,567		1984-1989/95-96	(1)
Ten Cambridge Center	Office	Cambridge, MA		—			1,299		12,943		6,109			2,395		17,956		—		—		20,351		10,120		1990	(1)
Three Cambridge Center	Office	Cambridge, MA		—			174		12,200		6,021			367		18,028		—		—		18,395		8,712		1987	(1)
201 Spring Street	Office	Lexington, MA		—			2,849		15,303		(154	)		3,124		14,874		—		—		17,998		5,082		1997	(1)
Montvale Center	Office	Gaithersburg, MD		25,000			1,574		9,786		6,558			2,555		15,363		—		—		17,918		9,665		1987	(1)
40 Shattuck Road	Office	Andover, MA		—			709		14,740		1,906			893		16,462		—		—		17,355		4,340		2001	(1)
Lexington Office Park	Office	Lexington, MA		—			998		1,426		12,975			1,264		14,135		—		—		15,399		8,959		1982	(1)
6601 & 6605 Springfield Center Drive	Office	Springfield, VA		—			14,041		2,375		(1,836	)		3,777		714		10,089		—		14,580		702		1990	(1)
92-100 Hayden Avenue	Office	Lexington, MA		—			594		6,748		6,976			802		13,516		—		—		14,318		8,127		1985	(1)
181 Spring Street	Office	Lexington, MA		—			1,066		9,520		2,407			1,160		11,833		—		—		12,993		3,783		1999	(1)
195 West Street	Office	Waltham, MA		—			1,611		6,652		4,175			1,858		10,580		—		—		12,438		5,310		1990	(1)
91 Hartwell Avenue	Office	Lexington, MA		—			784		6,464		4,458			941		10,765		—		—		11,706		6,874		1985	(1)
Waltham Office Center	Office	Waltham, MA		—			422		2,719		8,402			384		8,445		2,714		—		11,543		7,543		1968-1970/87-88	(1)
Eleven Cambridge Center	Office	Cambridge, MA		—			121		5,535		5,263			324		10,595		—		—		10,919		7,028		1984	(1)
7501 Boston Boulevard, Building Seven	Office	Springfield, VA		—			665		9,273		544			791		9,691		—		—		10,482		3,410		1997	(1)
33 Hayden Avenue	Office	Lexington, MA		—			266		3,234		6,042			425		9,117		—		—		9,542		6,740		1979	(1)
7435 Boston Boulevard, Building One	Office	Springfield, VA		—			392		3,822		3,734			659		7,289		—		—		7,948		4,793		1982	(1)
7450 Boston Boulevard, Building Three	Office	Springfield, VA		—			1,165		4,681		1,915			1,430		6,331		—		—		7,761		2,568		1987	(1)
8000 Grainger Court, Building Five	Office	Springfield, VA		—			366		4,282		2,745			601		6,792		—		—		7,393		4,531		1984	(1)
7500 Boston Boulevard, Building Six	Office	Springfield, VA		—			138		3,749		2,302			406		5,783		—		—		6,189		3,711		1985	(1)
7601 Boston Boulevard, Building Eight	Office	Springfield, VA		—			200		878		4,875			551		5,402		—		—		5,953		3,251		1986	(1)
Fourteen Cambridge Center	Office	Cambridge, MA		—			110		4,483		1,223			273		5,543		—		—		5,816		3,529		1983	(1)
7300 Boston Boulevard, Building Thirteen	Office	Springfield, VA		—			608		4,773		230			661		4,950		—		—		5,611		3,231		2002	(1)
8000 Corporate Court, Building Eleven	Office	Springfield, VA		—			136		3,071		1,483			775		3,915		—		—		4,690		2,089		1989	(1)
7375 Boston Boulevard, Building Ten	Office	Springfield, VA		—			23		2,685		1,007			93		3,622		—		—		3,715		2,049		1988	(1)
7374 Boston Boulevard, Building Four	Office	Springfield, VA		—			241		1,605		1,714			398		3,162		—		—		3,560		2,103		1984	(1)
7451 Boston Boulevard, Building Two	Office	Springfield, VA		—			249		1,542		1,313			613		2,491		—		—		3,104		2,017		1982	(1)
164 Lexington Road	Office	Billerica, MA		—			592		1,370		349			643		1,668		—		—		2,311		650		1982	(1)
32 Hartwell Avenue	Office	Lexington, MA		—			168		1,943		150			314		1,947		—		—		2,261		1,359		1968-1979/1987	(1)
17 Hartwell Avenue	Office	Lexington, MA		—			26		150		778			65		889		—		—		954		416		1968	(1)
Residences on The Avenue, 2221 I St., NW	Residential	Washington, DC		—			—		119,874		—			—		119,874		—		—		119,874		1,764		2011	(1)
The Lofts at Atlantic Wharf	Residential	Boston, MA		—			3,529		54,891		—			3,529		54,891		—		—		58,420		673		2011	(1)
Cambridge Center Marriott	Hotel	Cambridge, MA		—			478		37,918		33,215			1,201		70,410		—		—		71,611		40,030		1986	(1)
Cambridge Center East Garage	Garage	Cambridge, MA		—			—		35,035		1,487			103		36,419		—		—		36,522		4,758		1984	(1)
Cambridge Center West Garage	Garage	Cambridge, MA		—			1,256		15,697		1,158			1,434		16,677		—		—		18,111		2,538		2006	(1)
Cambridge Center North Garage	Garage	Cambridge, MA		—			1,163		11,633		2,750			1,579		13,967		—		—		15,546		7,334		1990	(1)
250 West 55th Street	Development	New York, NY		—			—		—		527,964			—		—		—		527,964		527,964		—		N/A	N/A
510 Madison Avenue	Development	New York, NY		—			—		—		345,910			45,320		109,867		—		190,723		345,910		1,112		N/A	N/A
12310 Sunrise Valley Drive	Development	Reston, VA		—			9,367		67,431		63,419			11,343		74,052		—		54,822		140,217		48,852		1987/1988	(1)
Reston Town Center Residential	Development	Reston, VA		—			—		—		24,969			—		—		—		24,969		24,969		—		N/A	N/A
17 Cambridge Center	Development	Cambridge, MA		—			—		—		20,207			—		—		—		20,207		20,207		—		N/A	N/A
Plaza at Almaden	Land	San Jose, CA		—			—		—		37,306			—		—		37,306		—		37,306		—		N/A	N/A
Springfield Metro Center	Land	Springfield, VA		—			—		—		31,845			—		—		31,845		—		31,845		—		N/A	N/A
Tower Oaks Master Plan	Land	Rockville, MD		—			—		—		28,619			—		—		28,619		—		28,619		—		N/A	N/A
Prospect Hill	Land	Waltham, MA		—			—		—		23,819			—		667		23,152		—		23,819		—		N/A	N/A
Washingtonian North	Land	Gaithersburg, MD		—			—		—		17,704			—		—		17,704		—		17,704		—		N/A	N/A
103 4th Avenue	Land	Waltham, MA		—			11,911		—		—			—		—		11,911		—		11,911		—		N/A	N/A
Cambridge Master Plan	Land	Cambridge, MA		—			—		—		10,693			—		—		10,693		—		10,693		—		N/A	N/A
Reston Gateway	Land	Reston, VA		—			—		—		9,458			—		—		9,458		—		9,458		—		N/A	N/A
Reston Eastgate	Land	Reston, VA		—			—		—		8,772			—		—		8,772		—		8,772		—		N/A	N/A
Crane Meadow	Land	Marlborough, MA		—			—		—		8,723			—		—		8,723		—		8,723		—		N/A	N/A
Broad Run Business Park	Land	Loudon County, VA		—			—		—		7,729			1,621		—		6,108		—		7,729		—		N/A	N/A
30 Shattuck Road	Land	Andover, MA		—			—		—		1,161			—		—		1,161		—		1,161		—		N/A	N/A

			$	3,123,267	(2)	$	2,216,058	$	8,104,331	$	3,042,724		$	2,356,522	$	9,921,084	$	266,822	$	818,685	$	13,363,113	$	2,626,324

Note: Total Real Estate does not include Furniture, Fixtures and Equipment totaling approximately $26,359. Accumulated Depreciation does not include approximately $16,662 of accumulated depreciation related to Furniture, Fixtures and Equipment.

The aggregate cost and accumulated depreciation for tax purposes was approximately $12.2 billion and $2.2 billion, respectively.

(1)	Depreciation of the buildings and improvements are calculated over lives ranging from the life of the lease to 40 years.

(2)	Includes the unamortized balance of the historical fair value adjustment totaling approximately $23.8 million.

Boston Properties, Inc.

Real Estate and Accumulated Depreciation

December 31, 2011

(dollars in thousands)

A summary of activity for real estate and accumulated depreciation is as follows:


	2011			2010			2009
Real Estate:
Balance at the beginning of the year	$	12,740,892		$	11,075,879		$	10,602,278
Additions to/improvements of real estate		668,084			1,669,926			481,237
Assets sold/written-off		(45,863	)		(4,913	)		(7,636	)

Balance at the end of the year	$	13,363,113		$	12,740,892		$	11,075,879

Accumulated Depreciation:
Balance at the beginning of the year	$	2,308,665		$	2,020,056		$	1,755,600
Depreciation expense		362,636			292,561			269,394
Assets sold/written-off		(44,977	)		(3,952	)		(4,938	)

Balance at the end of the year	$	2,626,324		$	2,308,665		$	2,020,056

Note: Real Estate and Accumulated Depreciation amounts do not include Furniture, Fixtures and Equipment.

- Definition

The entire disclosure for real estate and accumulated depreciation. This may include a schedule that describes the property and lists the initial cost of land, buildings and improvements, improvements and carrying costs capitalized after acquisition, and the total carrying cost for land, buildings and improvements for each property and in aggregate. The schedule also lists the accumulated depreciation for each property and in aggregate, the date each property was constructed and acquired, the useful life used to calculate depreciation and any encumbrances on the properties. The entity provides a reconciliation of the carrying amount of real estate from the beginning of the period to the end of the period. Any real estate investments that have been written down or reserved against are described, including the basis of the write-down. A material amount of intercompany profit in the total carrying amount of real estate is disclosed. The aggregate cost of all real estate investments for federal income tax purposes is also disclosed.

+ References + Details

Summary Of Significant Accounting Policies (Policy)

12 Months Ended

Dec. 31, 2011

Summary Of Significant Accounting Policies [Abstract]

Real Estate

Real Estate

Depreciation is computed on a straight-line basis over the estimated useful lives of the assets as follows:


Land improvements		25 to 40 years
Buildings and improvements		10 to 40 years
Tenant improvements		Shorter of useful life or terms of related lease
Furniture, fixtures, and equipment		3 to 7 years

Cash And Cash Equivalents

Cash and Cash Equivalents

Cash Held In Escrows

Cash Held in Escrows

Escrows include amounts established pursuant to various agreements for security deposits, property taxes, insurance and other costs.

Investment In Securities

Investments in Securities

Tenant And Other Receivables

Tenant and other receivables

Tenant and other accounts receivable, other than accrued rents receivable, are expected to be collected within one year.

Deferred Charges

Deferred Charges

Investments In Unconsolidated Joint Ventures

Investments in Unconsolidated Joint Ventures

Equity Offering Costs

Equity Offering Costs

Underwriting commissions and offering costs have been reflected as a reduction of additional paid-in capital.

Treasury Stock

Treasury Stock

The Company's share repurchases are reflected as treasury stock utilizing the cost method of accounting and are presented as a reduction to consolidated stockholders' equity.

Dividends

Dividends

The tax treatment of common dividends per share for federal income tax purposes is as follows:


	For the year ended December 31,
	2011					2010					2009
	Per Share		%			Per Share		%			Per Share		%
Ordinary income	$	2.06		97.39	%	$	1.17		58.39	%	$	2.15		90.93	%
Capital gain income		0.05		2.61	%		—		—			—		—
Return of capital		—		—			0.83		41.61	%		0.21		9.07	%

Total	$	2.11		100.00	%	$	2.00		100.00	%	$	2.36		100.00	%

Revenue Recognition

Revenue Recognition

Ground Leases

Ground Leases


Years Ending December 31,	(in thousands)
2012	$	12,693
2013		12,908
2014		13,272
2015		13,595
2016		13,820
Thereafter		927,394

Earnings Per Share

Earnings Per Share

Fair Value Of Financial Instruments

Fair Value of Financial Instruments


	December 31, 2011					December 31, 2010
	Carrying Amount			Estimated Fair Value		Carrying Amount			Estimated Fair Value
Mortgage notes payable	$	3,123,267		$	3,297,903	$	3,047,586		$	3,121,193
Unsecured senior notes		3,865,186			4,148,461		3,016,598			3,241,542
Unsecured exchangeable senior notes		1,715,685	(1)		1,904,115		1,721,817	(1)		1,929,291

Total	$	8,704,138		$	9,350,479	$	7,786,001		$	8,292,026

(1)	Includes the net impact of unamortized portion of imputed discounts under ASC 470-20 (formerly known as FSP No. APB 14-1) totaling approximately $54.5 million and $93.6 million at December 31, 2011 and 2010, respectively (See Note 8).

Derivative Instruments And Hedging Activities

Derivative Instruments and Hedging Activities

Income Taxes

Income Taxes

The following reconciles GAAP net income attributable to Boston Properties, Inc. to taxable income:


	For the year ended December 31,
	2011			2010			2009
	(in thousands)
Net income attributable to Boston Properties, Inc.	$	272,679		$	159,072		$	231,014
Straight-line rent adjustments		(77,422	)		(75,943	)		(38,287	)
Book/Tax differences from depreciation and amortization		117,675			67,362			61,366
Book/Tax differences on gains/losses from capital transactions		(38,443	)		(2,373	)		(10,111	)
Book/Tax differences from stock-based compensation		827			(1,957	)		15,966
Book/Tax differences on losses from early extinguishments of debt		40			6,448			—
Impairment loss on investments in unconsolidated joint ventures		—			—			6,374
Other book/tax differences, net		29,349			3,921			492

Taxable income	$	304,705		$	156,530		$	266,814

Stock-Based Employee Compensation Plans

Use Of Estimates In The Preparation Of Financial Statements

Use of Estimates in the Preparation of Financial Statements

Summary Of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2011

Summary Of Significant Accounting Policies [Abstract]

Schedule Of Estimated Useful Lives


Land improvements		25 to 40 years
Buildings and improvements		10 to 40 years
Tenant improvements		Shorter of useful life or terms of related lease
Furniture, fixtures, and equipment		3 to 7 years

Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes


	For the year ended December 31,
	2011					2010					2009
	Per Share		%			Per Share		%			Per Share		%
Ordinary income	$	2.06		97.39	%	$	1.17		58.39	%	$	2.15		90.93	%
Capital gain income		0.05		2.61	%		—		—			—		—
Return of capital		—		—			0.83		41.61	%		0.21		9.07	%

Total	$	2.11		100.00	%	$	2.00		100.00	%	$	2.36		100.00	%

Schedule Of Future Contractual Minimum Lease Payments Under Non-Cancelable Ground Leases


Years Ending December 31,	(in thousands)
2012	$	12,693
2013		12,908
2014		13,272
2015		13,595
2016		13,820
Thereafter		927,394

Carrying Value Of Indebtedness And Corresponding Estimate Of Fair Value


	December 31, 2011					December 31, 2010
	Carrying Amount			Estimated Fair Value		Carrying Amount			Estimated Fair Value
Mortgage notes payable	$	3,123,267		$	3,297,903	$	3,047,586		$	3,121,193
Unsecured senior notes		3,865,186			4,148,461		3,016,598			3,241,542
Unsecured exchangeable senior notes		1,715,685	(1)		1,904,115		1,721,817	(1)		1,929,291

Total	$	8,704,138		$	9,350,479	$	7,786,001		$	8,292,026

(1)	Includes the net impact of unamortized portion of imputed discounts under ASC 470-20 (formerly known as FSP No. APB 14-1) totaling approximately $54.5 million and $93.6 million at December 31, 2011 and 2010, respectively (See Note 8).

GAAP Reconciliation Of Net Income To Taxable Income


	For the year ended December 31,
	2011			2010			2009
	(in thousands)
Net income attributable to Boston Properties, Inc.	$	272,679		$	159,072		$	231,014
Straight-line rent adjustments		(77,422	)		(75,943	)		(38,287	)
Book/Tax differences from depreciation and amortization		117,675			67,362			61,366
Book/Tax differences on gains/losses from capital transactions		(38,443	)		(2,373	)		(10,111	)
Book/Tax differences from stock-based compensation		827			(1,957	)		15,966
Book/Tax differences on losses from early extinguishments of debt		40			6,448			—
Impairment loss on investments in unconsolidated joint ventures		—			—			6,374
Other book/tax differences, net		29,349			3,921			492

Taxable income	$	304,705		$	156,530		$	266,814

- Definition

Tabular disclosure of the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments, assets, and liabilities. Such certain disclosures about the financial instruments, assets, and liabilities include: (1) the fair value of the required items together with their carrying amounts (as appropriate) and (2) the methodology and assumptions used in developing such estimates of fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 10
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 14
-Subparagraph a
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 15
-Subparagraph b-d
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 157
-Paragraph 32
-Subparagraph a, c(1), c(2), c(3), d
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 159
-Paragraph 18
-Subparagraph c(2), d, e, f
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 159
-Paragraph 19
-Subparagraph a, b, c(1), d(1)
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6947722&loc=d3e13433-108611

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=6947722&loc=d3e13467-108611

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=6947722&loc=d3e13476-108611

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14172-108612

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6447952&loc=d3e13220-108610

+ Details

Real Estate (Tables)

12 Months Ended

Dec. 31, 2011

Real Estate Properties [Line Items]

Schedule Of Real Estate Properties


	2011			2010
Land	$	2,356,522		$	2,216,768
Land held for future development		266,822			757,556
Buildings and improvements		8,658,468			7,602,704
Tenant improvements		1,262,616			1,090,462
Furniture, fixtures and equipment		26,359			24,043
Construction in progress		818,685			1,073,402

Total		13,389,472			12,764,935
Less: Accumulated depreciation		(2,642,986	)		(2,323,818	)

	$	10,746,486		$	10,441,117

Estimated Amortization Of The Acquired Above Market Leases (Net Of Acquired Below Market Leases) And The Acquired In-Place Lease Intangibles


	Acquired In-Place Lease Intangibles		Acquired Net Above-/(Below-) Market Lease Intangibles
2012	$	6,397	$	124
2013		4,647		(54	)
2014		3,576		(183	)
2015		2,539		(72	)
2016		1,171		41

Pro Forma In Connection With Acquisition


Pro Forma (Unaudited)	Year Ended December 31,
(in thousands, except per share data)	2011		2010
Total revenue	$	1,768,805	$	1,577,441
Income from continuing operations	$	315,457	$	180,957
Net income attributable to Boston Properties, Inc.	$	274,123	$	153,282
Basic earnings per share:
Net income per share attributable to Boston Properties, Inc.	$	1.88	$	1.10
Diluted earnings per share:
Net income per share attributable to Boston Properties, Inc.	$	1.87	$	1.09

Bay Colony Corporate Center [Member]

Real Estate Properties [Line Items]

Schedule Of Allocation Of The Aggregate Purchase Price Of Acquisition


Land	$	18,769
Building and improvements		136,081
Tenant improvements		12,370
In-place lease intangibles		20,626
Above market rents		5,802
Below market rents		(3,332	)
Above market assumed debt adjustment		(5,316	)

Total aggregate purchase price	$	185,000
Less: Indebtedness assumed		(143,900	)

Net assets acquired	$	41,100

2440 West El Camino Real [Member]

Real Estate Properties [Line Items]

Schedule Of Allocation Of The Aggregate Purchase Price Of Acquisition


Land	$	16,741
Building and improvements		47,199
Tenant improvements		4,086
In-place lease intangibles		5,284
Above market rents		30
Below market rents		(2,260	)

Net assets acquired	$	71,080

- Definition

Tabular disclosure of pro forma results of operations for a material business acquisition or series of individually immaterial business acquisitions that are material in the aggregate.

+ References + Details

- Definition

Tabular disclosure of a material business combination completed during the period, including background, timing, and recognized assets and liabilities. This table does not include leveraged buyouts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141
-Paragraph 51
-Subparagraph a
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141
-Paragraph 52
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141R
-Paragraph 68
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141R
-Appendix F
-Paragraph F4
-Subparagraph e

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6972119&loc=d3e1392-128463

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6972119&loc=d3e1486-128463

+ Details

Deferred Charges (Tables)

12 Months Ended

Dec. 31, 2011

Deferred Charges [Abstract]

Schedule Of Deferred Charges


	2011			2010
Leasing costs (and lease related intangibles)	$	598,352		$	558,620
Financing costs		85,554			89,680

		683,906			648,300
Less: Accumulated amortization		(238,503	)		(212,281	)

	$	445,403		$	436,019

Investments In Unconsolidated Joint Ventures (Tables)

12 Months Ended

Dec. 31, 2011

Investments In Unconsolidated Joint Ventures [Abstract]

Investments In Unconsolidated Joint Ventures


Entity	Properties	Nominal % Ownership
Square 407 Limited Partnership	Market Square North	50.0	%
The Metropolitan Square Associates LLC	Metropolitan Square	51.0	%
BP/CRF 901 New York Avenue LLC	901 New York Avenue	25.0	%(1)
WP Project Developer LLC	Wisconsin Place Land and Infrastructure	33.3	%(2)
RBP Joint VentureLLC	Eighth Avenue and 46thStreet	50.0	%(3)
Boston Properties Office Value-Added Fund, L.P.	300 Billerica Road and Mountain View Research and Technology Parks	37.6	%(1)(4)
Annapolis Junction NFM, LLC	Annapolis Junction	50.0	%(5)
767 Venture, LLC	The General Motors Building	60.0	%
2 GCT Venture LLC	Two Grand Central Tower	60.0	%(6)
540 Madison Venture LLC	540 Madison Avenue	60.0	%
125 West 55^thStreet Venture LLC	125 West 55^thStreet	60.0	%
500 North Capitol LLC	500 North Capitol Street, NW	30.0	%

(1)	The Company's economic ownership can increase based on the achievement of certain return thresholds.

(2)	The Company's wholly-owned entity that owns the office component of the project owns a 33.3% interest in the entity owning the land and infrastructure of the project.

(3)	This property is not in operation and consists of assembled land.

(4)	Represents the Company's effective ownership interest. The Company has a 25.0% interest in the 300 Billerica Road property and a 39.5% interest in the Mountain View Research and Technology Park properties.

(5)	Comprised of one building, one building under construction and two undeveloped land parcels.

(6)	The property was sold on October 25, 2011. As of December 31, 2011, the investment is comprised of working capital and a portion of the sale proceeds.

Balance Sheets Of The Unconsolidated Joint Ventures


	December 31,
Balance Sheets	2011			2010
Real estate and development in process, net	$	4,542,594		$	5,028,851
Other assets		668,113			749,308

Total assets	$	5,210,707		$	5,778,159

Mortgage and Notes payable	$	2,988,894		$	3,151,220
Other liabilities		854,257			969,082
Members'/Partners' equity		1,367,556			1,657,857

Total liabilities and members'/partners' equity	$	5,210,707		$	5,778,159

Company's share of equity	$	799,479		$	924,235
Basis differential(1)		(129,757	)		(156,983	)

Carrying value of the Company's investments in unconsolidated joint ventures	$	669,722		$	767,252

(1)

Statements Of Operations Of The Joint Ventures


Statements of Operations	Year Ended December 31,
	2011			2010			2009
	(in thousands)
Total revenue(1)	$	589,294		$	607,915		$	595,533
Expenses
Operating		170,404			175,309			163,209
Depreciation and amortization		190,437			215,533			232,047

Total expenses		360,841			390,842			395,256

Operating income		228,453			217,073			200,277
Other income (expense)
Interest expense		(228,494	)		(235,723	)		(232,978	)
Gains from early extinguishments of debt		—			17,920			—
Loss on guarantee obligation		—			(3,800	)		—
Impairment losses		(40,468	)		—			(24,568	)

Net loss	$	(40,509	)	$	(4,530	)	$	(57,269	)

Company's share of net loss	$	(25,374	)	$	(5,691	)	$	(22,197	)
Impairment losses on investments		—			—			(9,385	)
Gain on sale of real estate		46,166			572			—
Basis differential		27,226			6,565			11,299
Elimination of inter-entity interest on partner loan		37,878			35,328			32,341

Income from unconsolidated joint ventures	$	85,896		$	36,774		$	12,058

(1)

Mortgage Notes Payable (Tables)

12 Months Ended

Dec. 31, 2011

Mortgage Notes Payable [Abstract]

Schedule Of Aggregate Principal Payments On Mortgage Notes


	Principal Payments
	(in thousands)
2012	$	248,986
2013		103,209
2014		87,757
2015		26,182
2016		397,629
Thereafter		2,235,710

Total aggregate principal payments		3,099,473
Unamortized balance of historical fair value adjustments		23,794

Total carrying value of mortgage notes payable	$	3,123,267

Unsecured Senior Notes (Tables)

12 Months Ended

Dec. 31, 2011

Unsecured Senior Notes [Abstract]

Schedule of Unsecured Senior Notes


	Coupon/ Stated Rate			Effective Rate(1)			Principal Amount			Maturity Date(2)
10 Year Unsecured Senior Notes		6.250	%		6.381	%	$	182,432		January 15, 2013
10 Year Unsecured Senior Notes		6.250	%		6.291	%		42,568		January 15, 2013
12 Year Unsecured Senior Notes		5.625	%		5.693	%		300,000		April 15, 2015
12 Year Unsecured Senior Notes		5.000	%		5.194	%		250,000		June 1, 2015
10 Year Unsecured Senior Notes		5.875	%		5.967	%		700,000		October 15, 2019
10 Year Unsecured Senior Notes		5.625	%		5.708	%		700,000		November 15, 2020
10 Year Unsecured Senior Notes		4.125	%		4.289	%		850,000		May 15, 2021
7 Year Unsecured Senior Notes		3.700	%		3.853	%		850,000		November 15, 2018

Total principal								3,875,000
Net unamortized discount								(9,814	)

Total							$	3,865,186

(1)	Yield on issuance date including the effects of discounts on the notes.

(2)	No principal amounts are due prior to maturity.

Unsecured Exchangeable Senior Notes (Tables)

12 Months Ended

Dec. 31, 2011

Unsecured Exchangeable Senior Notes [Abstract]

Schedule of Unsecured Exchangeable Senior Notes


	Coupon/ Stated Rate			Effective Rate(1)			Exchange Rate			Principal Amount			First Optional Redemption Date by Company	Maturity Date
3.625% Exchangeable Senior Notes		3.625	%		4.037	%		8.5051	(2)	$	747,500		N/A	February 15, 2014
2.875% Exchangeable Senior Notes		2.875	%		3.462	%		7.0430	(3)		576,194		February 20, 2012(4)	February 15, 2037
3.750% Exchangeable Senior Notes		3.750	%		3.787	%		10.0066	(5)		450,000		May 18, 2013(6)	May 15, 2036

Total principal											1,773,694
Net unamortized discount											(3,462	)
Adjustment for the equity component allocation, net of accumulated amortization											(54,547	)

Total										$	1,715,685

(1)	Yield on issuance date including the effects of discounts on the notes but excluding the effects of the adjustment for the equity component allocation.

(2)

(3)

(4)

(5)

(6)

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 22
-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28541-108399

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21506-112644

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21538-112644

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21521-112644

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e),(f))
-URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690

+ Details

Noncontrolling Interests (Tables)

12 Months Ended

Dec. 31, 2011

Noncontrolling Interests [Abstract]

Noncontrolling Interests - Redeemable Preferred Units


Balance at December 31, 2008	$	55,652
Net income		3,594
Distributions		(3,594	)

Balance at December 31, 2009		55,652
Net income		3,343
Distributions		(3,343	)

Balance at December 31, 2010		55,652
Net income		3,339
Distributions		(3,339	)

Balance at December 31, 2011	$	55,652

Future Minimum Rents (Tables)

12 Months Ended

Dec. 31, 2011

Future Minimum Rents [Abstract]

Schedule Of Future Contractual Minimum Lease Payments Receivable


Years Ending December 31,	(in thousands)
2012	$	1,305,070
2013		1,314,408
2014		1,275,588
2015		1,173,068
2016		1,044,669
Thereafter		5,052,985

Segment Reporting (Tables)

12 Months Ended

Dec. 31, 2011

Segment Reporting [Abstract]

Schedule Of Segment Information By Geographic Area And Property Type

For the year ended December 31, 2011:


	Boston			New York			Princeton			San Francisco			Washington, DC			Total
Rental Revenue:
Class A Office	$	543,494		$	458,791		$	62,648		$	213,257		$	359,544		$	1,637,734
Office/Technical		30,975			—			—			—			16,236			47,211
Residential		985			—			—			—			5,632			6,617
Hotel		34,529			—			—			—			—			34,529

Total		609,983			458,791			62,648			213,257			381,412			1,726,091
% of Grand Totals		35.34	%		26.58	%		3.63	%		12.35	%		22.10	%		100.0	%
Rental Expenses:
Class A Office		209,176			152,649			30,150			80,729			101,559			574,263
Office/Technical		9,955			—			—			—			4,280			14,235
Residential		521			—			—			—			4,958			5,479
Hotel		26,128			—			—			—			—			26,128

Total		245,780			152,649			30,150			80,729			110,797			620,105
% of Grand Totals		39.63	%		24.62	%		4.86	%		13.02	%		17.87	%		100.0	%

Net operating income	$	364,203		$	306,142		$	32,498		$	132,528		$	270,615		$	1,105,986

% of Grand Totals		32.93	%		27.68	%		2.94	%		11.98	%		24.47	%		100.0	%

For the year ended December 31, 2010:


	Boston			New York			Princeton			San Francisco			Washington, DC			Total
Rental Revenue:
Class A Office	$	368,841		$	445,296		$	65,475		$	215,468		$	335,508		$	1,430,588
Office/Technical		30,336			—			—			—			15,849			46,185
Residential		—			—			—			—			—			—
Hotel		32,800			—			—			—			—			32,800

Total		431,977			445,296			65,475			215,468			351,357			1,509,573
% of Grand Totals		28.62	%		29.50	%		4.34	%		14.27	%		23.27	%		100.0	%
Rental Expenses:
Class A Office		138,722			146,381			31,486			78,978			92,892			488,459
Office/Technical		9,067			—			—			—			4,168			13,235
Residential		—			—			—			—			—			—
Hotel		25,153			—			—			—			—			25,153

Total		172,942			146,381			31,486			78,978			97,060			526,847
% of Grand Totals		32.83	%		27.78	%		5.98	%		14.99	%		18.42	%		100.0	%

Net operating income	$	259,035		$	298,915		$	33,989		$	136,490		$	254,297		$	982,726

% of Grand Totals		26.36	%		30.42	%		3.45	%		13.89	%		25.88	%		100.0	%

For the year ended December 31, 2009:


	Boston			New York			Princeton			San Francisco			Washington, DC			Total
Rental Revenue:
Class A Office	$	364,064		$	441,571		$	63,189		$	218,432		$	318,786		$	1,406,042
Office/Technical		30,655			—			—			—			16,230			46,885
Residential		—			—			—			—			—			—
Hotel		30,385			—			—			—			—			30,385

Total		425,104			441,571			63,189			218,432			335,016			1,483,312
% of Grand Totals		28.66	%		29.77	%		4.26	%		14.73	%		22.58	%		100.0	%
Rental Expenses:
Class A Office		137,785			146,398			29,751			80,269			93,799			488,002
Office/Technical		9,475			—			—			—			4,322			13,797
Residential		—			—			—			—			—			—
Hotel		23,966			—			—			—			—			23,966

Total		171,226			146,398			29,751			80,269			98,121			525,765
% of Grand Totals		32.57	%		27.84	%		5.66	%		15.27	%		18.66	%		100.0	%

Net operating income	$	253,878		$	295,173		$	33,438		$	138,163		$	236,895		$	957,547

% of Grand Totals		26.51	%		30.83	%		3.49	%		14.43	%		24.74	%		100.0	%

Schedule Of Reconciliation Of Net Operating Income To Net Income


	Years ended December 31,
	2011		2010			2009
Net operating income	$	1,105,986	$	982,726		$	957,547
Add:
Development and management services income		33,435		41,231			34,878
Income from unconsolidated joint ventures		85,896		36,774			12,058
Interest and other income		5,358		7,332			4,059
Gains on sales of real estate		—		2,734			11,760
Less:
General and administrative expense		81,442		79,658			75,447
Acquisition costs		155		2,614			—
Suspension of development		—		(7,200	)		27,766
Depreciation and amortization expense		439,184		338,371			321,681
Losses (gains) from investments in securities		443		(935	)		(2,434	)
Interest expense		394,131		378,079			322,833
Losses from early extinguishments of debt		1,494		89,883			510
Noncontrolling interests in property partnerships		1,558		3,464			2,778
Noncontrolling interest—redeemable preferred units of the Operating Partnership.		3,339		3,343			3,594
Noncontrolling interest—common units of the Operating Partnership		36,250		24,099			35,534
Noncontrolling interest in gains on sales of real estate—common units of the Operating Partnership		—		349			1,579

Net income attributable to Boston Properties, Inc.	$	272,679	$	159,072		$	231,014

- Definition

Tabular disclosure of the profit or loss and total assets for each reportable segment. An entity discloses certain information on each reportable segment if the amounts (a) are included in the measure of segment profit or loss reviewed by the chief operating decision maker or (b) are otherwise regularly provided to the chief operating decision maker, even if not included in that measure of segment profit or loss.

+ References + Details

Earnings Per Share (Tables)

12 Months Ended

Dec. 31, 2011

Earnings Per Share [Abstract]

Computation Of Basic And Diluted Earnings Per Share


	For the year ended December 31, 2011
	Income (Numerator)		Shares (Denominator)		Per Share Amount
	(in thousands, except for per share amounts)
Basic Earnings:
Net income attributable to Boston Properties, Inc.	$	272,679		145,693	$	1.87
Effect of Dilutive Securities:
Stock Based Compensation and Exchangeable Senior Notes		—		525		(0.01	)
Diluted Earnings:

Net income	$	272,679		146,218	$	1.86


	For the year ended December 31, 2010
	Income (Numerator)		Shares (Denominator)		Per Share Amount
	(in thousands, except for per share amounts)
Basic Earnings:
Net income attributable to Boston Properties, Inc.	$	159,072		139,440	$	1.14
Effect of Dilutive Securities:
Stock Based Compensation		—		617		(0.00	)
Diluted Earnings:

Net income	$	159,072		140,057	$	1.14


	For the year ended December 31, 2009
	Income (Numerator)		Shares (Denominator)		Per Share Amount
	(in thousands, except for per share amounts)
Basic Earnings:
Net income attributable to Boston Properties, Inc.	$	231,014		131,050	$	1.76
Effect of Dilutive Securities:
Stock Based Compensation		—		462		(0.00	)
Diluted Earnings:

Net income	$	231,014		131,512	$	1.76

Stock Option And Incentive Plan And Stock Purchase Plan (Tables)

12 Months Ended

Dec. 31, 2011

Stock Option And Incentive Plan And Stock Purchase Plan [Abstract]

Schedule Of Stock Options Status


	Shares			Weighted Average Exercise Price
Outstanding at December 31, 2008		1,206,402		$	34.23
Granted		—			—
Exercised		(242,507	)	$	33.41
Canceled		—			—

Outstanding at December 31, 2009		963,895		$	34.44
Granted		—			—
Exercised		(638,957	)	$	35.35
Canceled		—			—

Outstanding at December 31, 2010		324,938		$	32.65
Granted		146,844		$	92.71
Exercised		(316,159	)	$	32.63
Canceled		—			—

Outstanding at December 31, 2011		155,623		$	89.35

Schedule Of Stock Options Outstanding


Options Outstanding							Options Exercisable
Range of Exercise Prices	Number Outstanding at 12/31/11		Weighted-Average Remaining Contractual Life		Weighted-Average Exercise Price		Number Exercisable at 12/31/11		Weighted-Average Exercise Price
$32.62-$34.14		8,779		0.1 Years	$	33.10		8,779	$	33.10
$92.71		146,844		9.1 Years	$	92.71		4,854	$	92.71

Selected Interim Financial Information (unaudited) (Tables)

12 Months Ended

Dec. 31, 2011

Selected Interim Financial Information [Abstract]

Selected Quarterly Information


	2011 Quarter Ended
	March 31,		June 30,		September 30,		December 31,
	(in thousands, except for per share amounts)
Total revenue	$	417,875	$	436,451	$	452,413	$	452,787
Income from continuing operations	$	48,194	$	69,738	$	80,451	$	115,443
Net income attributable to Boston Properties, Inc.	$	40,813	$	60,214	$	70,542	$	101,644
Income attributable to Boston Properties, Inc. per share—basic	$	0.29	$	0.41	$	0.48	$	0.69
Income attributable to Boston Properties, Inc. per share—diluted	$	0.29	$	0.41	$	0.48	$	0.69


	2010 Quarter Ended
	March 31,		June 30,		September 30,		December 31,
	(in thousands, except for per share amounts)
Total revenue	$	378,071	$	393,841	$	386,410	$	392,482
Income (loss) from continuing operations	$	60,742	$	71,518	$	68,089	$	(12,756	)
Net income (loss) attributable to Boston Properties, Inc.	$	52,714	$	61,412	$	57,668	$	(12,903	)
Income (loss) attributable to Boston Properties, Inc. per share—basic	$	0.38	$	0.44	$	0.41	$	(0.09	)
Income (loss) attributable to Boston Properties, Inc. per share—diluted	$	0.38	$	0.44	$	0.41	$	(0.09	)

Organization And Basis Of Presentation (Details) sqft in Millions	12 Months Ended
	Dec. 31, 2011 sqft A years shares	Dec. 31, 2010
Real Estate Properties [Line Items]
General and limited partnership interest in the operating partnership	88.30%	86.20%
Restriction on redemption of OP units from date of issuance (years) \| years	1
One OP unit is equivalent to one share of Common Stock	1
Number of series of preferred units outstanding	1
OP unit conversion rate	1
Number of vehicles in structured parking	44,528
Area of parking in square feet \| sqft	15.1
Area of undeveloped land parcels owned in acres \| A	510.5
Value-added fund institutional investors	2
Commercial Real Estate Properties [Member]
Real Estate Properties [Line Items]
Square footage of real estate property	42,200,000
Number of real estate properties	153
Total Office Properties [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	146
Total Properties Under Construction [ Member]
Real Estate Properties [Line Items]
Square footage of real estate property	2,600,000
Number of real estate properties	7
Office Properties Under Construction [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	6
Class A Office Properties [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	128
Office/Technical Properties [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	18
Hotel Property [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	1
Retail Properties [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	3
Residential Properties [Member]
Real Estate Properties [Line Items]
Number of real estate properties	3
Residential Properties Under Construction [Member]
Real Estate Properties [Line Items]
Number of real estate properties	1
Investments Through Value-Added Fund [Member]
Real Estate Properties [Line Items]
Number of real estate properties	24

Summary Of Significant Accounting Policies (Narrative) (Details)	12 Months Ended
	Dec. 31, 2011 USD ($) years	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Probable sale term of property after classified as held for sale in years	1
Maximum period after construction the Company considers a construction project as substantially completed (years) \| years	1
Interest costs capitalized	$ 48,178,000	$ 40,981,000	$ 48,816,000
Salaries and related costs capitalized	6,500,000	6,200,000	7,900,000
FDIC Insurance Limit	250,000
Gains (losses) from investments in securities	(443,000)	935,000	2,434,000
Gain (loss) on investments excluded investment in unregistered money market fund			2,200,000
Separate unrestricted cash for deferred compensation plan	9,500,000	8,700,000
Internal leasing salaries and related costs capitalized	4,400,000	5,400,000	3,300,000
Net difference between tax basis and Company's assets and liabilities	900,000,000	1,200,000,000
Company Amount [Member]
Summary Of Significant Accounting Policies [Line Items]
Straight-line rent adjustments	77,000,000	85,100,000	42,200,000
Above And Below Market Rent Adjustments	$ 10,800,000	$ 2,400,000	$ 4,200,000
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
REIT annual taxable income distribution requirement percentage	90.00%
Company annual taxable income distribution	100.00%
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Operating ground lease obligations expiration date	2068

Summary Of Significant Accounting Policies (Schedule Of Estimated Useful Lives) (Details)	12 Months Ended
	Dec. 31, 2011 years
Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life, minimum (years)	25
Estimated useful life, maximum (years)	40
Buildings And Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life, minimum (years)	10
Estimated useful life, maximum (years)	40
Tenant Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life, Description	Shorter of useful life or terms of related lease
Furniture, Fixtures, And Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life, minimum (years)	3
Estimated useful life, maximum (years)	7

Summary Of Significant Accounting Policies (Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Summary Of Significant Accounting Policies [Line Items]
Dividends, treatment for federal tax purposes	$ 2.11	$ 2.00	$ 2.36
Dividends, treatment for federal tax purposes (percent)	100.00%	100.00%	100.00%
Ordinary Income [Member]
Summary Of Significant Accounting Policies [Line Items]
Dividends, treatment for federal tax purposes	$ 2.06	$ 1.17	$ 2.15
Dividends, treatment for federal tax purposes (percent)	97.39%	58.39%	90.93%
Capital Gain Income [Member]
Summary Of Significant Accounting Policies [Line Items]
Dividends, treatment for federal tax purposes	$ 0.05
Dividends, treatment for federal tax purposes (percent)	2.61%
Return Of Capital [Member]
Summary Of Significant Accounting Policies [Line Items]
Dividends, treatment for federal tax purposes		$ 0.83	$ 0.21
Dividends, treatment for federal tax purposes (percent)		41.61%	9.07%

Summary Of Significant Accounting Policies (Schedule Of Future Contractual Minimum Lease Payments Under Non-Cancelable Ground Leases) (Details) $ in Thousands	Dec. 31, 2011 USD ($)
Summary Of Significant Accounting Policies [Abstract]
2012	$ 12,693
2013	12,908
2014	13,272
2015	13,595
2016	13,820
Thereafter	$ 927,394

Summary Of Significant Accounting Policies (Carrying Value Of Indebtedness And Corresponding Estimate Of Fair Value) (Details) - USD ($)
$ in Thousands

Dec. 31, 2011

Dec. 31, 2010

Summary Of Significant Accounting Policies [Line Items]

Mortgage notes payable, net

$ 3,123,267

$ 3,047,586

Unsecured senior notes

3,865,186

3,016,598

Unsecured exchangeable senior notes

1,715,685

1,721,817

Total

3,099,473

Net of the adjustment for the equity component allocation

54,547

ASC 470-20 Adjustment [Member]

Summary Of Significant Accounting Policies [Line Items]

Net of the adjustment for the equity component allocation

54,500

93,600

Carrying Amount [Member]

Summary Of Significant Accounting Policies [Line Items]

Mortgage notes payable, net

3,123,267

3,047,586

Unsecured senior notes

3,865,186

3,016,598

Unsecured exchangeable senior notes

^[1]

1,715,685

1,721,817

Total

8,704,138

7,786,001

Estimated Fair Value [Member]

Summary Of Significant Accounting Policies [Line Items]

Mortgage notes payable, net

3,297,903

3,121,193

Unsecured senior notes

4,148,461

3,241,542

Unsecured exchangeable senior notes

1,904,115

1,929,291

Total

$ 9,350,479

$ 8,292,026

[1]	Includes the net impact of unamortized portion of imputed discounts under ASC 470-20 (formerly known as FSP No. APB 14-1) totaling approximately $54.5 million and $93.6 million at December 31, 2011 and 2010, respectively (See Note 8).

Summary Of Significant Accounting Policies (GAAP Reconciliation Of Net Income To Taxable Income) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Summary Of Significant Accounting Policies [Line Items]
Net income attributable to Boston Properties, Inc.	$ 101,644	$ 70,542	$ 60,214	$ 40,813	$ (12,903)	$ 57,668	$ 61,412	$ 52,714	$ 272,679	$ 159,072	$ 231,014
GAAP Reconciliation Of Net Income To Taxable Income [Member]
Summary Of Significant Accounting Policies [Line Items]
Net income attributable to Boston Properties, Inc.									272,679	159,072	231,014
Straight-line rent adjustments									(77,422)	(75,943)	(38,287)
Book/Tax differences from depreciation and amortization									117,675	67,362	61,366
Book/Tax differences on gains/losses from capital transactions									(38,443)	(2,373)	(10,111)
Book/Tax differences from stock-based compensation									827	(1,957)	15,966
Book/Tax differences on losses from early extinguishments of debt									40	6,448
Impairment loss on investments in unconsolidated joint ventures											6,374
Other book/tax differences, net									29,349	3,921	492
Taxable income									$ 304,705	$ 156,530	$ 266,814

Real Estate (Narrative) (Details)																		1 Months Ended	3 Months Ended								11 Months Ended	12 Months Ended
Real Estate (Narrative) (Details)	Jan. 03, 2012	Nov. 22, 2011 USD ($)	Nov. 15, 2011	Aug. 17, 2011	Jul. 14, 2011 years	Jul. 13, 2011	Jul. 05, 2011	Jun. 06, 2011 USD ($) A	May 24, 2011	May 24, 2011	May 23, 2011 USD ($) years	May 11, 2011	May 01, 2011	Mar. 01, 2011	Mar. 01, 2011	Feb. 01, 2011 USD ($) A	Jan. 14, 2011	Dec. 31, 2011 USD ($)	Dec. 31, 2011 USD ($)	Sep. 30, 2011 USD ($)	Jun. 30, 2011 USD ($)	Mar. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Sep. 30, 2010 USD ($)	Jun. 30, 2010 USD ($)	Mar. 31, 2010 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 19, 2011
Real Estate Properties [Line Items]
Total revenue																			$ 452,787,000	$ 452,413,000	$ 436,451,000	$ 417,875,000	$ 392,482,000	$ 386,410,000	$ 393,841,000	$ 378,071,000		$ 1,759,526,000	$ 1,550,804,000	$ 1,518,190,000
Operating income																												618,640,000	$ 610,514,000	$ 567,531,000
Atlantic Wharf Development [Member]
Real Estate Properties [Line Items]
Square footage of real estate property																	798,000
Percentage of office component of the development project placed in-service			100.00%
Office component placed in-service (percentage)																	57.00%
Atlantic Wharf Development Residential [Member]
Real Estate Properties [Line Items]
Square footage of real estate property																				9,000
Number of units in real estate property																				86
Placed in-service (percentage)																				100.00%
Pennsylvania Avenue Development [Member]
Real Estate Properties [Line Items]
Square footage of real estate property														459,000
Percentage of office component of the development project placed in-service				100.00%
Office component placed in-service (percentage)															13.00%
510 Madison Avenue [Member]
Real Estate Properties [Line Items]
Square footage of real estate property													347,000
Placed in-service (percentage)													16.00%
2221 I Street [Member]
Real Estate Properties [Line Items]
Square footage of real estate property												50,000
Percentage of residential component of the development project placed in-service						100.00%
Number of units in real estate property												335
12310 Sunrise Valley Drive [Member]
Real Estate Properties [Line Items]
Square footage of real estate property							268,000
12300 Sunrise Valley Drive [Member]
Real Estate Properties [Line Items]
Square footage of real estate property	256,000
250 West 55th Street [Member]
Real Estate Properties [Line Items]
Square footage of real estate property										989,000
Square footage of signed lease									184,000
Carnegie Center [Member]
Real Estate Properties [Line Items]
Square footage of real estate property								2,000,000
Number of units in real estate property								16
Acres of land \| A								560
Disposition price								$ 468,000,000
75 Ames Street [Member]
Real Estate Properties [Line Items]
Square footage of real estate property											250,000
Gross proceeds from transaction											$ 56,800,000
Gross proceeds from transaction received																												48,900,000
Development revenue											$ 11,400,000
Approximate proceeds per year from ground lease																												459,000
Term of lease (years) \| years											99
Cambridge Center Member
Real Estate Properties [Line Items]
Square footage of real estate property					190,000
Term of lease (years) \| years					15
Percentage of development leased					100.00%
Reston Town Center Residential [Member]
Real Estate Properties [Line Items]
Number of units in real estate property																															359
Anticipated Through Q3 Two Thousand Fourteen Member \| 75 Ames Street [Member]
Real Estate Properties [Line Items]
Development revenue																												$ 7,900,000
Bay Colony Corporate Center [Member]
Real Estate Properties [Line Items]
Acquisition aggregate purchase price																$ 185,000,000
Cash portion of purchase price																41,100,000
Portion of acquisition included in debt																$ 143,900,000
Interest at a fixed rate																6.53%
Maturity date																Jun. 11, 2012
Square footage of real estate property																985,000
Total revenue																											$ 19,100,000
Operating income																											$ (11,800,000)
Number of real estate properties																4
Acres of land \| A																58
2440 West El Camino Real [Member]
Real Estate Properties [Line Items]
Acquisition aggregate purchase price		$ 71,100,000
Square footage of real estate property		140,000
Total revenue																		$ 800,000
Operating income																		$ 200,000

Real Estate (Schedule Of Real Estate Properties) (Details) - USD ($) $ in Thousands	Dec. 31, 2011	Dec. 31, 2010
Real Estate [Abstract]
Land	$ 2,356,522	$ 2,216,768
Land held for future development	266,822	757,556
Buildings and improvements	8,658,468	7,602,704
Tenant improvements	1,262,616	1,090,462
Furniture, fixtures and equipment	26,359	24,043
Construction in progress	818,685	1,073,402
Total	13,389,472	12,764,935
Less: Accumulated depreciation	(2,642,986)	(2,323,818)
Total real estate	$ 10,746,486	$ 10,441,117

Real Estate (Schedule Of Allocation Of The Aggregate Purchase Price Of Acquisition) (Details) - USD ($) $ in Thousands	Feb. 01, 2011	Nov. 22, 2011
Bay Colony Corporate Center [Member]
Restructuring Cost and Reserve [Line Items]
Land	$ 18,769
Building and improvements	136,081
Tenant improvements	12,370
In-place lease intangibles	20,626
Above market rents	5,802
Below market rents	(3,332)
Above market assumed debt adjustment	(5,316)
Total aggregate purchase price	185,000
Less: Indebtedness assumed	(143,900)
Net assets acquired	$ 41,100
2440 West El Camino Real [Member]
Restructuring Cost and Reserve [Line Items]
Land		$ 16,741
Building and improvements		47,199
Tenant improvements		4,086
In-place lease intangibles		5,284
Above market rents		30
Below market rents		(2,260)
Total aggregate purchase price		71,100
Net assets acquired		$ 71,080

Real Estate (Summary Of Estimated Amortization Of The Acquired Above Market Leases (Net Of Acquired Below Market Leases) And The Acquired In-Place Lease Intangibles) (Details) - Bay Colony Corporate Center [Member] $ in Thousands	12 Months Ended
	Dec. 31, 2011 USD ($)
Acquired In-Place Lease Intangibles [Member]
Restructuring Cost and Reserve [Line Items]
2012	$ 6,397
2013	4,647
2014	3,576
2015	2,539
2016	1,171
Acquired Net Above-Market Lease Intangibles [Member]
Restructuring Cost and Reserve [Line Items]
2012	124
2013	(54)
2014	(183)
2015	(72)
2016	$ 41

Real Estate (Pro Forma In Connection With Acquisition) (Details) - Bay Colony Corporate Center [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Restructuring Cost and Reserve [Line Items]
Total revenue	$ 1,768,805	$ 1,577,441
Income from continuing operations	315,457	180,957
Net income attributable to Boston Properties, Inc.	$ 274,123	$ 153,282
Basic earnings per share: Net income per share attributable to Boston Properties, Inc.	$ 1.88	$ 1.10
Diluted earnings per share: Net income per share attributable to Boston Properties, Inc.	$ 1.87	$ 1.09

- Definition

The pro forma basic net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

+ References + Details

- Definition

The pro forma diluted net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

+ References + Details

Deferred Charges (Schedule Of Deferred Charges) (Details) - USD ($) $ in Thousands	Dec. 31, 2011	Dec. 31, 2010
Deferred Charges [Abstract]
Leasing costs (and lease related intangibles)	$ 598,352	$ 558,620
Financing costs	85,554	89,680
Deferred costs, gross	683,906	648,300
Less: Accumulated amortization	(238,503)	(212,281)
Deferred charges, total	$ 445,403	$ 436,019

- Definition

For an unclassified balance sheet, this element represents costs incurred by the lessor that are (a) costs to originate a lease incurred in transactions with independent third parties that (i) result directly from and are essential to acquire that lease and (ii) would not have been incurred had that leasing transaction not occurred and (b) certain costs directly related to specified activities performed by the lessor for that lease. Those activities are: evaluating the prospective lessee's financial condition; evaluating and recording guarantees, collateral, and other security arrangements; negotiating lease terms; preparing and processing lease documents; and closing the transaction. This amount is before considering accumulated amortization representing the periodic charge to earnings to recognize the deferred costs over the term of the related lease.

+ References + Details

Investments In Unconsolidated Joint Ventures (Narrative) (Details) $ in Thousands												3 Months Ended	12 Months Ended
	Nov. 22, 2011 USD ($)	Nov. 17, 2011 USD ($) years	Oct. 25, 2011 USD ($)	Oct. 14, 2011 USD ($) years	Oct. 14, 2011 USD ($)	Jun. 29, 2011	Jun. 28, 2011 USD ($)	Jun. 28, 2011 USD ($)	Jun. 03, 2011	Mar. 16, 2011 USD ($)	Jan. 18, 2011	Mar. 31, 2011 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2008 USD ($)	Mar. 26, 2011
Schedule of Equity Method Investments [Line Items]
Mortgage notes payable													$ 3,123,267	$ 3,047,586
Repayments of mortgage notes payable													1,251,841	730,191	$ 125,238
Mountain View Technology Park [Member]
Schedule of Equity Method Investments [Line Items]
Repayments of mortgage notes payable	$ 4,600
Mountain View Technology Park [Member] \| Previous Mortgage Loan [Member]
Schedule of Equity Method Investments [Line Items]
Initial mortgage loan extension of maturity date (months)										2
Description of variable rate basis										LIBOR plus 1.50% per annum
Basis spread on variable rate basis										1.50%
Mortgage notes payable	$ 24,600									$ 24,700
Mountain View Technology Park [Member] \| New Mortgage Loan [Member]
Schedule of Equity Method Investments [Line Items]
Description of variable rate basis	LIBOR plus 2.50% per annum
Basis spread on variable rate basis	2.50%
Maturity date	Nov. 22, 2014
Mortgage notes payable	$ 20,000
Mountain View Technology Park [Member] \| Previous Maturity Date [Member]
Schedule of Equity Method Investments [Line Items]
Maturity date										May 31, 2011
Mountain View Technology Park [Member] \| Original Maturity Date [Member]
Schedule of Equity Method Investments [Line Items]
Maturity date										Mar. 31, 2011
Mountain View Technology Park [Member] \| Extended Maturity Date [Member]
Schedule of Equity Method Investments [Line Items]
Maturity date						Nov. 15, 2011
Mountain View Research Park [Member]
Schedule of Equity Method Investments [Line Items]
Repayments of mortgage notes payable								$ 20,300
Mountain View Research Park [Member] \| Previous Mortgage Loan [Member]
Schedule of Equity Method Investments [Line Items]
Description of variable rate basis								LIBOR plus 1.75% per annum
Basis spread on variable rate basis							1.75%	1.75%
Maturity date							May 31, 2011
Mortgage notes payable							$ 112,300	$ 112,300
Mountain View Research Park [Member] \| New Mortgage Loan [Member]
Schedule of Equity Method Investments [Line Items]
Description of variable rate basis								LIBOR plus 2.50% per annum
Basis spread on variable rate basis							2.50%	2.50%
Maturity date							May 31, 2014
Mortgage notes payable							$ 92,000	$ 92,000
500 North Capitol Street, NW [Member]
Schedule of Equity Method Investments [Line Items]
Description of variable rate basis					LIBOR plus 1.65% per annum
Basis spread on variable rate basis				1.65%	1.65%
Maturity date				Oct. 14, 2014
Square footage of signed lease											171,000
Ownership percentage																	30.00%
Construction loans payable				$ 33,300	$ 33,300
Construction loan facility borrowing capacity				107,000	107,000
Repayments of mortgage notes payable				$ 22,000
Number of extension options				2
Mortgage loan extension options (years) \| years				1
Development costs funded with construction loan				$ 11,300	$ 11,300
Annapolis Junction [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage												50.00%
Annapolis Junction [Member] \| Previous Mortgage Loan [Member]
Schedule of Equity Method Investments [Line Items]
Description of variable rate basis												LIBOR plus 1.00% per annum
Basis spread on variable rate basis												1.00%
Maturity date												Sep. 12, 2011
Mortgage notes payable												$ 42,700
Annapolis Junction [Member] \| New Mortgage Loan [Member]
Schedule of Equity Method Investments [Line Items]
Mortgage loan extension of maturity date (months)												36
Description of variable rate basis												LIBOR plus 1.75% per annum
Basis spread on variable rate basis												1.75%
Maturity date												Mar. 31, 2018
Mortgage notes payable												$ 42,300
Number of extension options												1
Mortgage loan extension options (years)												3
Two Grand Central Tower [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage			60.00%
Carrying value of debt assumed in sale			$ 176,600
Square footage of real estate property			650,000
Contractual sale price			$ 401,000
Carrying value of net assets of property sold			427,100
Cash proceeds from sale of real estate property			210,000
Transaction costs on sale of real estate			14,400
Gains on sales of real estate			46,200
Annapolis Junction New Development Project [Member]
Schedule of Equity Method Investments [Line Items]
Description of variable rate basis		LIBOR plus 1.65% per annum
Basis spread on variable rate basis		1.65%
Maturity date		Nov. 17, 2013
Ownership percentage									50.00%
Construction loan facility borrowing capacity		$ 19,000
Square footage of real estate property									120,000
Number of extension options		2
Mortgage loan extension options (years) \| years		1
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Impairment loss on investment in unconsolidated joint venture																$ 74,300
Operating Partnership [Member] \| Mountain View Technology Park [Member]
Schedule of Equity Method Investments [Line Items]
Interest at a fixed rate	10.00%
Maturity date	Nov. 22, 2014
Loan to Value-Added Fund	$ 6,000
Operating Partnership [Member] \| Mountain View Technology Park [Member] \| Advanced To Date [Member]
Schedule of Equity Method Investments [Line Items]
Loan to Value-Added Fund													3,700
Operating Partnership [Member] \| Mountain View Research Park [Member]
Schedule of Equity Method Investments [Line Items]
Interest at a fixed rate							10.00%	10.00%
Maturity date								May 31, 2014
Loan to Value-Added Fund							$ 12,000	$ 12,000
Operating Partnership [Member] \| Mountain View Research Park [Member] \| Advanced To Date [Member]
Schedule of Equity Method Investments [Line Items]
Loan to Value-Added Fund													6,700
Company Share [Member] \| Two Grand Central Tower [Member]
Schedule of Equity Method Investments [Line Items]
Cash proceeds from sale of real estate property			$ 126,000
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Mortgage notes payable													2,988,894	3,151,220
Impairment of Real Estate													40,468		24,568
Impairment loss on investment in unconsolidated joint venture															$ 9,385
Gains on sales of real estate													$ 46,166	$ 572

Investments In Unconsolidated Joint Ventures (Investments In Unconsolidated Joint Ventures) (Details)

12 Months Ended

Dec. 31, 2011

Square 407 Limited Partnership [Member]

Schedule of Equity Method Investments [Line Items]

Nominal % Ownership

50.00%

Properties

Market Square North

The Metropolitan Square Associates LLC [Member]

Schedule of Equity Method Investments [Line Items]

Nominal % Ownership

51.00%

Properties

Metropolitan Square

BP/CRF 901 New York Avenue LLC [Member]

Schedule of Equity Method Investments [Line Items]

Nominal % Ownership

25.00%

^[1]

Properties

901 New York Avenue

^[1]

WP Project Developer LLC [Member]

Schedule of Equity Method Investments [Line Items]

Nominal % Ownership

33.30%

^[2]

Properties

Wisconsin Place Land and Infrastructure

^[2]

RBP Joint Venture LLC [Member]

Schedule of Equity Method Investments [Line Items]

Nominal % Ownership

50.00%

^[3]

Properties

Eighth Avenue and 46th Street

^[3]

Boston Properties Office Value-Added Fund, L.P. [Member]

Schedule of Equity Method Investments [Line Items]

Nominal % Ownership

37.60%

^[1],[4]

Properties

300 Billerica Road and Mountain View Research and Technology Parks

^[1],[4]

Annapolis Junction NFM, LLC [Member]

Schedule of Equity Method Investments [Line Items]

Nominal % Ownership

50.00%

^[5]

Properties

Annapolis Junction

^[5]

Number of real estate properties

Parcels of undeveloped land

Annapolis Junction NFM, LLC [Member] | Under Construction [Member]

Schedule of Equity Method Investments [Line Items]

Number of real estate properties

767 Venture, LLC [Member]

Schedule of Equity Method Investments [Line Items]

Nominal % Ownership

60.00%

Properties

The General Motors Building

2 GCT Venture LLC [Member]

Schedule of Equity Method Investments [Line Items]

Nominal % Ownership

60.00%

^[6]

Properties

Two Grand Central Tower

540 Madison Venture LLC [Member]

Schedule of Equity Method Investments [Line Items]

Nominal % Ownership

60.00%

Properties

540 Madison Avenue

125 West 55th Street Venture LLC [Member]

Schedule of Equity Method Investments [Line Items]

Nominal % Ownership

60.00%

Properties

125 West 55th Street

500 North Capitol LLC [Member]

Schedule of Equity Method Investments [Line Items]

Nominal % Ownership

30.00%

Properties

500 North Capitol Street, NW

Entity Owning Land And Infrastructure Of Project [Member]

Schedule of Equity Method Investments [Line Items]

Nominal % Ownership

33.30%

300 Billerica Road [Member]

Schedule of Equity Method Investments [Line Items]

Nominal % Ownership

25.00%

Mountain View Research And Technology Park [Member]

Schedule of Equity Method Investments [Line Items]

Nominal % Ownership

39.50%

[1]	The Company's economic ownership can increase based on the achievement of certain return thresholds.
[2]	The Company's wholly-owned entity that owns the office component of the project owns a 33.3% interest in the entity owning the land and infrastructure of the project.
[3]	This property is not in operation and consists of assembled land.
[4]	Represents the Company's effective ownership interest. The Company has a 25.0% interest in the 300 Billerica Road property and a 39.5% interest in the Mountain View Research and Technology Park properties.
[5]	Comprised of one building, one building under construction and two undeveloped land parcels.
[6]	The property was sold on October 25, 2011. As of December 31, 2011, the investment is comprised of working capital and a portion of the sale proceeds.

Investments In Unconsolidated Joint Ventures (Balance Sheets Of The Unconsolidated Joint Ventures) (Details) - USD ($)
$ in Thousands

Dec. 31, 2011

Dec. 31, 2010

Schedule of Equity Method Investments [Line Items]

Real estate and development in process, net

$ 10,746,486

$ 10,441,117

Mortgage and Notes payable

3,123,267

3,047,586

Other liabilities

293,515

237,467

Total liabilities and members'/partners' equity

14,782,966

13,348,263

Carrying value of the Company's investments in unconsolidated joint ventures

669,722

767,252

Unconsolidated Joint Ventures [Member]

Schedule of Equity Method Investments [Line Items]

Real estate and development in process, net

4,542,594

5,028,851

Other assets

668,113

749,308

Total assets

5,210,707

5,778,159

Mortgage and Notes payable

2,988,894

3,151,220

Other liabilities

854,257

969,082

Members'/Partners' equity

1,367,556

1,657,857

Total liabilities and members'/partners' equity

5,210,707

5,778,159

Company's share of equity

799,479

924,235

Basis differential

^[1]

(129,757)

(156,983)

Carrying value of the Company's investments in unconsolidated joint ventures

$ 669,722

$ 767,252

[1]

Investments In Unconsolidated Joint Ventures (Statements Of Operations Of The Joint Ventures) (Details) - USD ($)
$ in Thousands

3 Months Ended

12 Months Ended

Dec. 31, 2011

Sep. 30, 2011

Jun. 30, 2011

Mar. 31, 2011

Dec. 31, 2010

Sep. 30, 2010

Jun. 30, 2010

Mar. 31, 2010

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2009

Dec. 31, 2008

Schedule of Equity Method Investments [Line Items]

Total revenue

$ 452,787

$ 452,413

$ 436,451

$ 417,875

$ 392,482

$ 386,410

$ 393,841

$ 378,071

$ 1,759,526

$ 1,550,804

$ 1,518,190

Depreciation and amortization

439,184

338,371

321,681

Total expenses

1,140,886

940,290

950,659

Operating income

618,640

610,514

567,531

Interest expense

394,131

378,079

322,833

Gains (losses) from early extinguishments of debt

(1,494)

(89,883)

(510)

Net loss

(313,826)

(190,327)

(274,499)

Income from unconsolidated joint ventures

85,896

36,774

12,058

Unconsolidated Joint Ventures [Member]

Schedule of Equity Method Investments [Line Items]

Total revenue

^[1]

589,294

607,915

595,533

Operating

170,404

175,309

163,209

Depreciation and amortization

190,437

215,533

232,047

Total expenses

360,841

390,842

395,256

Operating income

228,453

217,073

200,277

Interest expense

(228,494)

(235,723)

(232,978)

Gains (losses) from early extinguishments of debt

17,920

Loss on guarantee obligation

(3,800)

Impairment losses

(40,468)

(24,568)

Net loss

(40,509)

(4,530)

(57,269)

Company's share of net loss

(25,374)

(5,691)

(22,197)

Impairment losses on investment

(9,385)

Gain on sale of real estate

46,166

572

Basis differential

27,226

6,565

11,299

Elimination of inter-entity interest on partner loan

37,878

35,328

32,341

Income from unconsolidated joint ventures

85,896

36,774

12,058

Unconsolidated Joint Ventures [Member]

Schedule of Equity Method Investments [Line Items]

Impairment losses on investment

$ (74,300)

Straight-line rent adjustments

21,900

24,500

28,000

"Above" and "below" market rent adjustments, net

$ 120,300

$ 132,100

$ 157,500

[1]

Mortgage Notes Payable (Narrative) (Details)							12 Months Ended
Mortgage Notes Payable (Narrative) (Details)	Nov. 16, 2011 USD ($) years	Nov. 09, 2011 USD ($)	Aug. 19, 2011 USD ($)	May 11, 2011 USD ($)	Feb. 01, 2011 USD ($)	Jan. 12, 2011 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)
Mortgage Notes Payable [Line Items]
Mortgage notes payable, net							$ 3,123,267,000	$ 3,047,586,000
Final maturity date of mortgage notes							April 10, 2022
Amount of mortgage loan that was repaid							$ 1,251,841,000	730,191,000	$ 125,238,000
Outstanding balance of mortgage loan accounted for at fair value							$ 953,100,000	$ 883,400,000
Number of mortgage loans accounted for fair value							6	6
Interest expense decrease due to recording mortgage loans at fair value							$ 9,200,000	$ 3,800,000	4,100,000
Cumulative liability related to fair value adjustments included in mortgage notes payable							23,794,000	27,700,000
Repayment of line of credit								700,000,000
Repayments of line of credit							453,300,000
Loss on extinguishment of debt							(1,494,000)	$ (89,883,000)	$ (510,000)
Basis point increase in variable rate of debt outstanding								1.00%
Increase in interest expense if variable rate increases on debt outstanding								$ 3,200,000
Total real estate							10,746,486,000	10,441,117,000
Fixed Rate Mortgages [Member]
Mortgage Notes Payable [Line Items]
Mortgage notes payable, net							$ 3,100,000,000	$ 2,700,000,000
Contractual interest rate, range minimum							4.75%	5.55%
Contractual interest rate, range maximum							9.93%	7.75%
Contractual interest rate, weighted-average							5.75%	6.18%
Variable Rate Mortgages [Member]
Mortgage Notes Payable [Line Items]
Mortgage notes payable, net								$ 317,500,000
London Interbank Offered Rate							0.30%	0.26%
Montvale Center [Member]
Mortgage Notes Payable [Line Items]
Debt default, accrued interest rate						9.93%
Maturity date						Jun. 06, 2012
Minimum [Member] \| Mortgages [Member]
Mortgage Notes Payable [Line Items]
Number of real estate assets used to collateralize each loan							1	1
Minimum [Member] \| Variable Rate Mortgages [Member]
Mortgage Notes Payable [Line Items]
Spread on variable rate basis								0.30%
Maximum [Member] \| Variable Rate Mortgages [Member]
Mortgage Notes Payable [Line Items]
Spread on variable rate basis								2.20%
Montvale Center [Member]
Mortgage Notes Payable [Line Items]
Mortgage notes payable, net						$ 25,000,000
Debt default, accrued interest rate						9.93%
Total real estate							$ 8,300,000
Bay Colony Corporate Center [Member]
Mortgage Notes Payable [Line Items]
Portion of acquisition included in debt					$ 143,900,000
Interest at a fixed rate					6.53%
Maturity date					Jun. 11, 2012
Outstanding balance of mortgage loan accounted for at fair value					$ 149,200,000
Interest rate used to account for mortgage loan at fair value upon assumption					3.75%
601 Lexington Avenue [Member]
Mortgage Notes Payable [Line Items]
Mortgage notes payable, net			$ 725,000,000
Amount of mortgage loan that was repaid				$ 453,300,000
Interest at a fixed rate			4.75%	7.19%
Maturity date			Apr. 10, 2022	May 11, 2011
Repayments of line of credit			$ 453,300,000
510 Madison Avenue [Member]
Mortgage Notes Payable [Line Items]
Amount of mortgage loan that was repaid			$ 267,500,000
Reservoir Place [Member]
Mortgage Notes Payable [Line Items]
Spread on variable rate basis		2.20%
Amount of mortgage loan that was repaid		$ 50,000,000
Maturity date		Jul. 30, 2014
Description of variable rate basis		Eurodollar plus <font class="_mt">2.20</font>% per annum
Penalty for early repayment of debt		$ 0
Loss on extinguishment of debt		$ 500,000
Atlantic Wharf Development [Member]
Mortgage Notes Payable [Line Items]
Spread on variable rate basis	3.00%
Maturity date	Apr. 21, 2012
Loss from early extinguishment of debt	$ 400,000
Cancellation of construction loan facility borrowing capacity	$ 192,500,000
Number of extension options	2
Mortgage loan extension options (years) \| years	1
Description of variable rate basis	LIBOR plus <font class="_mt">3.00</font>% per annum

Mortgage Notes Payable (Schedule Of Aggregate Principal Payments On Mortgage Notes) (Details) - USD ($) $ in Thousands	Dec. 31, 2011	Dec. 31, 2010
Mortgage Notes Payable [Abstract]
2012	$ 248,986
2013	103,209
2014	87,757
2015	26,182
2016	397,629
Thereafter	2,235,710
Total aggregate principal payments	(3,099,473)
Unamortized balance of historical fair value adjustments	23,794	$ 27,700
Total carrying value of mortgage notes payable	$ 3,123,267	$ 3,047,586

Unsecured Senior Notes (Narrative) (Details) - USD ($)		12 Months Ended
Unsecured Senior Notes (Narrative) (Details) - USD ($)	Nov. 10, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Unsecured Senior Notes [Line Items]
Proceeds from unsecured senior notes		$ 848,019,000	$ 1,542,947,000	$ 699,517,000
Maximum secured debt leverage ratio		55.00%
Senior Notes [Member]
Unsecured Senior Notes [Line Items]
Maximum leverage ratio		60.00%
Maximum secured debt leverage ratio		50.00%
Minimum interest coverage ratio		1.50
Minimum unencumbered asset value percentage of unsecured debt		150.00%
7 Year Unsecured Senior Notes, 3.853% [Member]
Unsecured Senior Notes [Line Items]
Public offering date	November 10, 2011
Aggregate principal amount	$ 850,000,000
Interest at a fixed rate	3.70%
Note price, percentage of principal amount	99.767%
Effective interest rate	3.853%
Proceeds from unsecured senior notes	$ 841,200,000
Maturity date	Nov. 15, 2018

Unsecured Senior Notes (Unsecured Senior Notes Outstanding Table) (Details) - USD ($)
$ in Thousands

12 Months Ended

Dec. 31, 2011

Dec. 31, 2010

Unsecured Senior Notes [Line Items]

Principal Amount

$ 1,773,694

Net discount

(9,814)

$ (8,402)

Unsecured senior notes

3,865,186

$ 3,016,598

Senior Notes [Member]

Unsecured Senior Notes [Line Items]

Principal Amount

3,875,000

Net discount

(9,814)

Unsecured senior notes

$ 3,865,186

10 Year Unsecured Senior Notes, 6.381% [Member]

Unsecured Senior Notes [Line Items]

Coupon/Stated Rate

6.25%

Effective Rate

^[1]

6.381%

Principal Amount

$ 182,432

Maturity Date

^[2]

Jan. 15, 2013

10 Year Unsecured Senior Notes, 6.291% [Member]

Unsecured Senior Notes [Line Items]

Coupon/Stated Rate

6.25%

Effective Rate

^[1]

6.291%

Principal Amount

$ 42,568

Maturity Date

^[2]

Jan. 15, 2013

12 Year Unsecured Senior Notes, 5.693% [Member]

Unsecured Senior Notes [Line Items]

Coupon/Stated Rate

5.625%

Effective Rate

^[1]

5.693%

Principal Amount

$ 300,000

Maturity Date

^[2]

Apr. 15, 2015

12 Year Unsecured Senior Notes, 5.194% [Member]

Unsecured Senior Notes [Line Items]

Coupon/Stated Rate

5.00%

Effective Rate

^[1]

5.194%

Principal Amount

$ 250,000

Maturity Date

^[2]

Jun. 01, 2015

10 Year Unsecured Senior Notes, 5.967% [Member]

Unsecured Senior Notes [Line Items]

Coupon/Stated Rate

5.875%

Effective Rate

^[1]

5.967%

Principal Amount

$ 700,000

Maturity Date

^[2]

Oct. 15, 2019

10 Year Unsecured Senior Notes, 5.708% [Member]

Unsecured Senior Notes [Line Items]

Coupon/Stated Rate

5.625%

Effective Rate

^[1]

5.708%

Principal Amount

$ 700,000

Maturity Date

^[2]

Nov. 15, 2020

10 Year Unsecured Senior Notes, 4.289% [Member]

Unsecured Senior Notes [Line Items]

Coupon/Stated Rate

4.125%

Effective Rate

^[1]

4.289%

Principal Amount

$ 850,000

Maturity Date

^[2]

May 15, 2021

7 Year Unsecured Senior Notes, 3.853% [Member]

Unsecured Senior Notes [Line Items]

Coupon/Stated Rate

3.70%

Effective Rate

^[1]

3.853%

Principal Amount

$ 850,000

Maturity Date

^[2]

Nov. 15, 2018

[1]	Yield on issuance date including the effects of discounts on the notes.
[2]	No principal amounts are due prior to maturity.

Unsecured Exchangeable Senior Notes (Narrative) (Details) - USD ($)

12 Months Ended

Feb. 20, 2012

Feb. 15, 2012

Nov. 09, 2011

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2009

Jan. 10, 2012

Debt Instrument [Line Items]

Net of the adjustment for the equity component allocation

$ 54,547,000

Proceeds attributable to equity component of the notes

230,300,000

Deferred financing costs attributable to equity component

1,000,000

Aggregate contractual interest expense

66,300,000

$ 69,000,000

$ 74,400,000

Non-cash interest expense

38,800,000

38,300,000

38,600,000

Carrying amount of equity component

202,500,000

207,100,000

Losses from early extinguishments of debt

1,494,000

89,883,000

$ 510,000

Unsecured exchangeable senior notes

1,715,685,000

1,721,817,000

Notes outstanding

1,773,694,000

Amount paid for repurchase

700,000,000

ASC 470-20 Adjustment [Member]

Debt Instrument [Line Items]

Net of the adjustment for the equity component allocation

$ 93,600,000

3.625% Exchangeable Senior Notes [Member]

Debt Instrument [Line Items]

Initial face amount of senior long term debt

$ 747,500,000

Coupon/Stated Rate

3.625%

Effective interest rate

^[1]

4.037%

Notes outstanding

$ 747,500,000

3.625% Exchangeable Senior Notes [Member] | Debt Component [Member]

Debt Instrument [Line Items]

Effective interest rate

6.555%

2.875% Exchangeable Senior Notes [Member]

Debt Instrument [Line Items]

Initial face amount of senior long term debt

$ 862,500,000

Coupon/Stated Rate

2.875%

Effective interest rate

^[1]

3.462%

Losses from early extinguishments of debt

$ 600,000

Notes outstanding

$ 576,194,000

Value of repurchase of senior notes due in 2037

$ 50,000,000

Amount paid for repurchase

$ 333,459,000

$ 242,735,000

50,200,000

Carrying value of repurchased notes

$ 49,600,000

2.875% Exchangeable Senior Notes [Member] | Debt Component [Member]

Debt Instrument [Line Items]

Effective interest rate

5.63%

3.750% Exchangeable Senior Notes [Member]

Debt Instrument [Line Items]

Initial face amount of senior long term debt

$ 450,000,000

Coupon/Stated Rate

3.75%

Effective interest rate

^[1]

3.787%

Notes outstanding

$ 450,000,000

3.750% Exchangeable Senior Notes [Member] | Debt Component [Member]

Debt Instrument [Line Items]

Effective interest rate

5.958%

[1]	Yield on issuance date including the effects of discounts on the notes but excluding the effects of the adjustment for the equity component allocation.

Unsecured Exchangeable Senior Notes (Schedule of Unsecured Exchangeable Senior Notes) (Details)

12 Months Ended

Feb. 20, 2012

Jan. 10, 2012

Dec. 17, 2007

$ / shares

Dec. 31, 2011

USD ($)

$ / shares

Dec. 31, 2007

USD ($)

$ / shares

Dec. 31, 2010

USD ($)

Aug. 13, 2008

$ / shares

Debt Instrument [Line Items]

Principal Amount

$ 1,773,694,000

Net unamortized discount

(3,462,000)

$ (8,249,000)

Adjustment for the equity component allocation, net of accumulated amortization

(54,547,000)

Total Principal Amount

$ 1,715,685,000

$ 1,721,817,000

3.625% Exchangeable Senior Notes [Member]

Debt Instrument [Line Items]

Coupon/Stated Rate

3.625%

Effective Rate

^[1]

4.037%

Exchange Rate

^[2]

8.5051

Principal Amount

$ 747,500,000

Maturity Date

Feb. 15, 2014

Initial exchange on principal amount of note

$ 1,000

Initial exchange of shares | $ / shares

$ 117.58

Revised exchange price due to capped call transaction | $ / shares

137.17

Effective exchange price | $ / shares

135.25

Premium over closing price

40.00%

Closing price per share of common stock | $ / shares

$ 97.98

Net cost of capped call transaction

$ 44,400,000

Initial exchange rate

8.5051

2.875% Exchangeable Senior Notes [Member]

Debt Instrument [Line Items]

Coupon/Stated Rate

2.875%

Effective Rate

^[1]

3.462%

Exchange Rate

^[3]

7.0430

Principal Amount

$ 576,194,000

First optional redemption date

^[4]

<font style="font-family: Times New Roman;" class="_mt" size="2">February 20, 2012</font>

Maturity Date

Feb. 15, 2037

Initial exchange on principal amount of note

$ 1,000

Special distribution per share common stock | $ / shares

$ 5.98

Initial exchange rate

6.6090

Revised exchange rate

7.0430

Revised exchange price resulting from special distribution | $ / shares

$ 141.98

Repurchase price for the notes

100.00%

Debt Instrument Redemption Price Principal Percentage

100.00%

3.750% Exchangeable Senior Notes [Member]

Debt Instrument [Line Items]

Coupon/Stated Rate

3.75%

Effective Rate

^[1]

3.787%

Exchange Rate

^[5]

10.0066

Principal Amount

$ 450,000,000

First optional redemption date

^[6]

Maturity Date

May 15, 2036

Initial exchange on principal amount of note

$ 1,000

Special distribution per share common stock | $ / shares

$ 5.98

Initial exchange rate

9.3900

Revised exchange rate

10.0066

Revised exchange price resulting from special distribution | $ / shares

$ 99.93

Repurchase price for the notes

100.00%

[1]	Yield on issuance date including the effects of discounts on the notes but excluding the effects of the adjustment for the equity component allocation.
[2]	The initial exchange rate is 8.5051 shares per $1,000 principal amount of the notes (or an initial exchange price of approximately $117.58 per share of Boston Properties, Inc.'s common stock). In addition, the Company entered into capped call transactions with affiliates of certain of the initial purchasers, which are intended to reduce the potential dilution upon future exchange of the notes. The capped call transactions were intended to increase the effective exchange price to the Company of the notes from $117.58 to approximately $137.17 per share (subject to adjustment), representing an overall effective premium of approximately 40% over the closing price on August 13, 2008 of $97.98 per share of Boston Properties, Inc.'s common stock. The net cost of the capped call transactions was approximately $44.4 million. As of December 31, 2011, the effective exchange price was $135.25 per share.
[3]	In connection with the special distribution of $5.98 per share of Boston Properties, Inc.'s common stock declared on December 17, 2007, the exchange rate was adjusted from 6.6090 to 7.0430 shares per $1,000 principal amount of notes effective as of December 31, 2007, resulting in an exchange price of approximately $141.98 per share of Boston Properties, Inc.'s common stock (See Note 20).
[4]	Holders may require the Operating Partnership to repurchase the notes for cash on February 15, 2012, 2017, 2022, 2027 and 2032 and at any time prior to their maturity upon a fundamental change, in each case at a price equal to 100% of the principal amount of the notes being repurchased plus any accrued and unpaid interest up to, but excluding, the repurchase date. The Operating Partnership repurchased/redeemed the notes for cash in February 2012 at a price equal to 100% of the principal amount of the notes being repurchased/redeemed plus any accrued and unpaid interest up to, but excluding, the repurchase/redemption date (See Note 20).
[5]	In connection with the special distribution of $5.98 per share of Boston Properties, Inc.'s common stock declared on December 17, 2007, the exchange rate was adjusted from 9.3900 to 10.0066 shares per $1,000 principal amount of notes effective as of December 31, 2007, resulting in an exchange price of approximately $99.93 per share of Boston Properties, Inc.'s common stock.
[6]	Holders may require the Operating Partnership to repurchase the notes for cash on May 18, 2013 and May 15, 2016, 2021, 2026 and 2031 and at any time prior to their maturity upon a fundamental change, in each case at a price equal to 100% of the principal amount of the notes being repurchased plus any accrued and unpaid interest up to, but excluding, the repurchase date.

Unsecured Line Of Credit (Details)	12 Months Ended
Unsecured Line Of Credit (Details)	Dec. 31, 2011 USD ($) years
Line of Credit Facility [Line Items]
Line of credit facility, extension fee	0.20%
Provision for extension, years \| years	1
Line of credit facility, facility fee percentage	0.225%
Frequency of payment	quarterly
Line of credit facility terms	<div> <p style="margin-top: 0px; text-indent: 32px; margin-bottom: 0px;"><font style="font-family: Times New Roman;" class="_mt" size="2"> </font> </p> <p style="margin-top: 0px; text-indent: 32px; margin-bottom: 0px;"><font style="font-family: Times New Roman;" class="_mt" size="2">The terms of the Unsecured Line of Credit require that the Company maintain a number of customary financial and other covenants on an ongoing basis, including: (1) a leverage ratio not to exceed <font class="_mt">60</font>%, however, the leverage ratio may increase to no greater than <font class="_mt">65</font>% provided that it is reduced back to <font class="_mt">60</font>% within <font class="_mt">one</font> year, (2) a secured debt leverage ratio not to exceed <font class="_mt">55</font>%, (3) a fixed charge coverage ratio of at least <font class="_mt">1.40</font>, (4) an unsecured debt leverage ratio not to exceed <font class="_mt">60</font>%, however, the unsecured debt leverage ratio may increase to no greater than <font class="_mt">65</font>% provided that it is reduced back to <font class="_mt">60</font>% within <font class="_mt">one</font> year, (5) a minimum net worth requirement of $<font class="_mt">3.5</font> billion, (6) an unsecured debt interest coverage ratio of at least <font class="_mt">1.75</font> and (7) limitations on permitted investments, development, partially owned entities, business outside of commercial real estate and commercial non-office properties. At December 31, 2011, the Company was in compliance with each of these financial and other covenant requirements. </font></p></div>
Maximum leverage ratio	60.00%
Leverage ratio maximum increasing limit	65.00%
Leverage ratio reduction limit	60.00%
Leverage ratio reduction period (years) \| years	1
Maximum secured debt leverage ratio	55.00%
Fixed charge coverage ratio, minimum	1.40
Maximum unsecured debt leverage ratio	60.00%
Unsecured debt leverage ratio maximum increasing limit	65.00%
Unsecured debt leverage ratio reduction limit	60.00%
Unsecured debt leverage ratio reduction period (years) \| years	1
Unsecured debt interest coverage ratio, minimum	1.75
Line of credit facility, amount outstanding	$ 0
Repayments of unsecured line of credit	453,300,000
Minimum net worth requirement	3,500,000,000
Potential Borrowing Capacity Subject To Syndication [Member]
Line of Credit Facility [Line Items]
Current lenders' total commitment	1,000,000,000
Prior To Amendment [Member]
Line of Credit Facility [Line Items]
Current lenders' total commitment	$ 1,000,000,000
Line of credit facility, expiration date	August 3, 2011
Basis spread on variable rate basis	0.475%
Description of variable rate basis	Eurodollar plus <font class="_mt">0.475</font>% per annum
After The Amendment [Member]
Line of Credit Facility [Line Items]
Current lenders' total commitment	$ 750,000,000
Line of credit facility, expiration date	June 24, 2014
Basis spread on variable rate basis	1.225%
Description of variable rate basis	Eurodollar plus <font class="_mt">1.225</font>% per annum

Commitments And Contingencies (Details) $ in Millions	12 Months Ended
Commitments And Contingencies (Details) $ in Millions	Dec. 31, 2011 USD ($)	Mar. 31, 2010 USD ($)
Commitments And Contingencies [Line Items]
Letter of credit and performance obligations	$ 15.5
Property insurance program per occurrence limits	1,000.0
Per occurrence limit for NBCR Coverage	1,000.0
Value of program trigger	$ 100.0
Coinsurance of program trigger	15.00%
Deductible in insurance as a percentage of the value of the affected property, San Francisco	5.00%
Per occurrence limit of the earthquake insurance which covers San Francisco region	$ 120.0
Annual aggregate limit of the earthquake insurance which covers San Francisco region	120.0
Amount of earthquake insurance provided by IXP, LLC as direct insurer San Francisco	$ 20.0
Contractual tax agreements, number of properties	6
Tax protection agreement, expiration date for one property	Jun. 01, 2017
767 Venture, LLC [Member]
Commitments And Contingencies [Line Items]
Maximum funding obligation	$ 20.5
Coverage for acts of Terrorism certified under TRIA in excess of amount provided by NYIXP, LLC, as a direct insurer	1,375.0
Property insurance program per occurrence limits	1,625.0
Coverage for acts of terrorism certified under TRIA in excess	250.0
125 West 55th Street Venture LLC [Member]
Commitments And Contingencies [Line Items]
Maximum funding obligation	1.8	$ 21.3
Cash deposit into the escrow account		10.0
Escrow account remaining funding obligation		$ 11.3
601 Lexington Avenue [Member]
Commitments And Contingencies [Line Items]
Coverage for acts of Terrorism certified under TRIA in excess of amount provided by NYIXP, LLC, as a direct insurer	250.0
One Freedom Square [Member]
Commitments And Contingencies [Line Items]
Guarantee obligation related to tenant re-leasing costs	$ 7.9
Maturity date	Jun. 30, 2012

Noncontrolling Interests (Narrative) (Details) - Noncontrolling Interests [Member]	Dec. 31, 2011 shares
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Operating Partnership (OP) Units	16,562,838
Long-Term Incentive Plan (LTIP) Units	1,601,004
Outperformance awards in LTIP Units	400,000
Series Two Preferred Units	1,113,044
Convertible Operating Partnership (OP) Units	1,460,688

Noncontrolling Interests (Redeemable Preferred Units) (Narrative) (Details)	12 Months Ended
	Dec. 31, 2011 $ / shares shares	Nov. 15, 2011 $ / shares	Aug. 15, 2011 $ / shares	May 16, 2011 $ / shares	May 12, 2011	Feb. 15, 2011 $ / shares	May 12, 2010	May 12, 2009
Noncontrolling Interests [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Series Two Preferred Units \| shares	1,113,044
Series Two Preferred Units [Member] \| Noncontrolling Interests [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Series Two Preferred Units \| shares	1,113,044
Liquidation preference percentage	6.00%
Preferred Units liquidation preference \| $ / shares	$ 50.00
Operating Units liquidation preference \| $ / shares	$ 38.10
OP Units for each Preferred Unit \| shares	1.312336
Distributions to Series Two Preferred Units \| $ / shares		$ 0.75616	$ 0.75616	$ 0.73151		$ 0.75616
Number of holders exercising redemption rights					0		0	0
Redemption Year Two Thousand Twelve [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Maximum redeemable Preferred Units \| shares	1,007,662
Dates Series Two Preferred holders can require Operating Partnership to redeem their units for cash	May 14, 2012
Series Two Preferred Units redemption price per unit \| $ / shares	$ 50.00
Maximum portion that may be required for redemption of total	0.166666666667
Redemption Year Two Thousand Thirteen [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Maximum redeemable Preferred Units \| shares	1,007,662
Dates Series Two Preferred holders can require Operating Partnership to redeem their units for cash	May 14, 2013
Series Two Preferred Units redemption price per unit \| $ / shares	$ 50.00
Maximum portion that may be required for redemption of total	0.166666666667
Redemption Year Two Thousand Fourteen [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Maximum redeemable Preferred Units \| shares	1,007,662
Dates Series Two Preferred holders can require Operating Partnership to redeem their units for cash	May 12, 2014
Series Two Preferred Units redemption price per unit \| $ / shares	$ 50.00
Maximum portion that may be required for redemption of total	0.166666666667

Noncontrolling Interests (Redeemable Preferred Units) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Noncontrolling Interests [Abstract]
Beginning Balance	$ 55,652	$ 55,652	$ 55,652
Net income	3,339	3,343	3,594
Distributions	(3,339)	(3,343)	(3,594)
Ending Balance	$ 55,652	$ 55,652	$ 55,652

- Definition

The carrying value (book value) of an entity's issued and outstanding stock which is not included within permanent equity in Stockholders Equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with a put option held by an ESOP and stock redeemable by a holder only in the event of a change in control of the issuer.

+ References + Details

Noncontrolling Interests (Common Units) (Narrative) (Details)		3 Months Ended					12 Months Ended
	Feb. 05, 2011 USD ($)	Dec. 31, 2011 USD ($) $ / shares shares	Sep. 30, 2011 $ / shares	Jun. 30, 2011 $ / shares	Mar. 31, 2011 $ / shares	Dec. 31, 2010 $ / shares shares	Dec. 31, 2011 USD ($) $ / shares shares	Dec. 31, 2011 USD ($) years $ / shares shares	Dec. 31, 2011 USD ($) $ / shares shares	Dec. 31, 2010 shares
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Dividends declared date		Dec. 14, 2011
Dividend payable date		Jan. 27, 2012	Oct. 31, 2011	Jul. 29, 2011	Apr. 29, 2011	Jan. 28, 2011
Dividends payable, date declared		Dec. 14, 2011
OP Units [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
OP Units for redemption \| shares									2,919,323	591,900
Redemption of OP units issued on conversion of LTIP Units \| shares									60,414	99,139
Outperformance awards in LTIP Units \| shares		400,000				1,080,938	400,000	400,000	400,000	1,080,938
Outperformance Awards LTIP Units distribution as percentage of OP Unit distribution prior to measurement date							10.00%			10.00%
Repayment amount per forfeited OPP Award \| $	$ 0.25
Distributions made to OP and LTIP units per unit \| $ / shares			$ 0.50	$ 0.50	$ 0.50	$ 0.50
Distribution paid to outperformance awards, OPP Units \| $ / shares			$ 0.05	$ 0.05	$ 0.05	$ 0.05
Distribution declared to OP and LTIP units by Boston Properties, Inc. \| $ / shares		$ 0.55					$ 0.55	$ 0.55	$ 0.55
Distribution declared to outperformance awards OPP Units by Boston Properties, Inc. \| $ / shares		$ 0.055					$ 0.055	$ 0.055	$ 0.055
Dividends declared date		Dec. 14, 2011
Dividend payable date		Jan. 27, 2012	Oct. 31, 2011	Jul. 29, 2011		Jan. 28, 2011
Holders of record date		December 31, 2011	September 30, 2011	June 30, 2011	March 31, 2011	December 31, 2010
Dividends payable, date declared		Dec. 14, 2011
Restriction on redemption of OP Unit to Common Stock, years							1	1
Redemption of OP Unit equivalence to Common Stock \| shares									1
Common units of operating partnership if converted value \| $		$ 1,810,000,000					$ 1,810,000,000	$ 1,810,000,000	$ 1,810,000,000
Value of Series Two Preferred Units assuming conversion \| $		$ 145,500,000					$ 145,500,000	$ 145,500,000	$ 145,500,000
Noncontrolling Interests [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Outperformance awards in LTIP Units \| shares		400,000					400,000	400,000	400,000
Series Two Preferred Units [Member] \| Noncontrolling Interests [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Closing price of common stock \| $ / shares		$ 99.60					$ 99.60	$ 99.60	$ 99.60

Noncontrolling Interests (Property Partnerships) (Narrative) (Details) - USD ($) $ in Thousands	Dec. 31, 2011	Dec. 31, 2010
Noncontrolling Interests [Abstract]
Property partnerships	$ (1,063)	$ (614)

Stockholders' Equity (Details)	3 Months Ended					12 Months Ended
Stockholders' Equity (Details)	Dec. 31, 2011 $ / shares shares	Sep. 30, 2011 $ / shares	Jun. 30, 2011 $ / shares	Mar. 31, 2011 $ / shares	Dec. 31, 2010 $ / shares shares	Dec. 31, 2011 USD ($) $ / shares shares	Dec. 31, 2010 shares	Dec. 31, 2009 shares
Class of Stock [Line Items]
Common stock, shares outstanding \| shares	148,107,611				140,199,105	148,107,611	140,199,105
Dividend paid on common stock \| $ / shares		$ 0.50	$ 0.50	$ 0.50	$ 0.50
Dividend shareholder of record date	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010
Dividends payable, date declared	Dec. 14, 2011
Dividends payable, amount per share \| $ / shares	$ 0.55					$ 0.55
Dividend payable date	Jan. 27, 2012	Oct. 31, 2011	Jul. 29, 2011	Apr. 29, 2011	Jan. 28, 2011
At the market stock offering program, shares issued \| shares	148,186,511				140,278,005	148,186,511	140,278,005
At the market stock offering program, aggregate value of common stock						$ 400,000,000
At the market stock offering program, net proceeds						$ 439,037,000
Shares of its Common Stock in connection with the redemption of an equal number of OP Units \| shares						2,919,323	591,900
Shares of Common Stock upon the exercise of options to purchase Common Stock by certain employees \| shares						316,159	638,957	242,507
Initial Atm Program [Member]
Class of Stock [Line Items]
At the market stock offering program, shares issued \| shares	4,228,993					4,228,993
At market stock offering program remained available for issuance						$ 0
At the market stock offering program maximum length of sale (years)						3
At the market stock offering program, gross proceeds						$ 400,000,000
At the market stock offering program, net proceeds						$ 394,700,000
Second Atm Program [Member]
Class of Stock [Line Items]
At the market stock offering program, shares issued \| shares	431,223					431,223
At market stock offering program remained available for issuance						$ 555,100,000
At the market stock offering program, aggregate value of common stock						$ 600,000,000
At the market stock offering program maximum length of sale (years)						3
At the market stock offering program, gross proceeds						$ 44,900,000
At the market stock offering program, net proceeds						$ 44,300,000

Future Minimum Rents (Schedule Of Future Contractual Minimum Lease Payments Receivable) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2011 USD ($)	Dec. 31, 2010	Dec. 31, 2009
2012	$ 1,305,070
2013	1,314,408
2014	1,275,588
2015	1,173,068
2016	1,044,669
Thereafter	$ 5,052,985
Maximum percent of revenue generated from single tenant	10.00%	10.00%	10.00%
Number of tenants above concentration amount	0	0	0
Maximum [Member]
Lease Expiration Date	2048
Minimum [Member]
Lease Expiration Date	2012

Segment Reporting (Schedule Of Segment Reporting By Geographic Area And Property Type) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 1,637,734	$ 1,430,588	$ 1,406,042
Rental Revenue: Office/Technical	47,211	46,185	46,885
Rental Revenue: Residential	6,617
Rental Revenue: Hotel	34,529	32,800	30,385
Rental Revenue: Total	$ 1,726,091	$ 1,509,573	$ 1,483,312
Rental Revenue: % of Grand Totals	100.00%	100.00%	100.00%
Rental Expenses: Class A Office	$ 574,263	$ 488,459	$ 488,002
Rental Expenses: Office/Technical	14,235	13,235	13,797
Rental Expenses: Residential	5,479
Rental Expenses: Hotel	26,128	25,153	23,966
Rental Expenses: Total	$ 620,105	$ 526,847	$ 525,765
Rental Expenses: % Of Grand Totals	100.00%	100.00%	100.00%
Net Operating Income: % of Grand Totals	100.00%	100.00%	100.00%
Boston [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 543,494	$ 368,841	$ 364,064
Rental Revenue: Office/Technical	30,975	30,336	30,655
Rental Revenue: Residential	985
Rental Revenue: Hotel	34,529	32,800	30,385
Rental Revenue: Total	$ 609,983	$ 431,977	$ 425,104
Rental Revenue: % of Grand Totals	35.34%	28.62%	28.66%
Rental Expenses: Class A Office	$ 209,176	$ 138,722	$ 137,785
Rental Expenses: Office/Technical	9,955	9,067	9,475
Rental Expenses: Residential	521
Rental Expenses: Hotel	26,128	25,153	23,966
Rental Expenses: Total	$ 245,780	$ 172,942	$ 171,226
Rental Expenses: % Of Grand Totals	39.63%	32.83%	32.57%
Net Operating Income	$ 364,203	$ 259,035	$ 253,878
Net Operating Income: % of Grand Totals	32.93%	26.36%	26.51%
New York [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 458,791	$ 445,296	$ 441,571
Rental Revenue: Residential
Rental Revenue: Total	$ 458,791	$ 445,296	$ 441,571
Rental Revenue: % of Grand Totals	26.58%	29.50%	29.77%
Rental Expenses: Class A Office	$ 152,649	$ 146,381	$ 146,398
Rental Expenses: Residential
Rental Expenses: Total	$ 152,649	$ 146,381	$ 146,398
Rental Expenses: % Of Grand Totals	24.62%	27.78%	27.84%
Net Operating Income	$ 306,142	$ 298,915	$ 295,173
Net Operating Income: % of Grand Totals	27.68%	30.42%	30.83%
Princeton [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 62,648	$ 65,475	$ 63,189
Rental Revenue: Residential
Rental Revenue: Total	$ 62,648	$ 65,475	$ 63,189
Rental Revenue: % of Grand Totals	3.63%	4.34%	4.26%
Rental Expenses: Class A Office	$ 30,150	$ 31,486	$ 29,751
Rental Expenses: Residential
Rental Expenses: Total	$ 30,150	$ 31,486	$ 29,751
Rental Expenses: % Of Grand Totals	4.86%	5.98%	5.66%
Net Operating Income	$ 32,498	$ 33,989	$ 33,438
Net Operating Income: % of Grand Totals	2.94%	3.45%	3.49%
San Francisco [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 213,257	$ 215,468	$ 218,432
Rental Revenue: Residential
Rental Revenue: Total	$ 213,257	$ 215,468	$ 218,432
Rental Revenue: % of Grand Totals	12.35%	14.27%	14.73%
Rental Expenses: Class A Office	$ 80,729	$ 78,978	$ 80,269
Rental Expenses: Residential
Rental Expenses: Total	$ 80,729	$ 78,978	$ 80,269
Rental Expenses: % Of Grand Totals	13.02%	14.99%	15.27%
Net Operating Income	$ 132,528	$ 136,490	$ 138,163
Net Operating Income: % of Grand Totals	11.98%	13.89%	14.43%
Washington, DC [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 359,544	$ 335,508	$ 318,786
Rental Revenue: Office/Technical	16,236	15,849	16,230
Rental Revenue: Residential	5,632
Rental Revenue: Total	$ 381,412	$ 351,357	$ 335,016
Rental Revenue: % of Grand Totals	22.10%	23.27%	22.58%
Rental Expenses: Class A Office	$ 101,559	$ 92,892	$ 93,799
Rental Expenses: Office/Technical	4,280	4,168	4,322
Rental Expenses: Residential	4,958
Rental Expenses: Total	$ 110,797	$ 97,060	$ 98,121
Rental Expenses: % Of Grand Totals	17.87%	18.42%	18.66%
Net Operating Income	$ 270,615	$ 254,297	$ 236,895
Net Operating Income: % of Grand Totals	24.47%	25.88%	24.74%
Segment, Continuing Operations [Member]
Segment Reporting Information [Line Items]
Net Operating Income	$ 1,105,986	$ 982,726	$ 957,547

Segment Reporting (Schedule Of Reconciliation Of Net Operating Income To Net Income) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Segment Reporting Information [Line Items]
Net operating income									$ 618,640	$ 610,514	$ 567,531
Development and management services income									33,435	41,231	34,878
Income from unconsolidated joint ventures									85,896	36,774	12,058
Interest and other income									5,358	7,332	4,059
Gains on sales of real estate										2,734	11,760
General and administrative expense									81,442	79,658	75,447
Acquisition costs									155	2,614
Suspension of development										(7,200)	27,766
Depreciation and amortization expense									439,184	338,371	321,681
Gains (losses) from investments in securities									443	(935)	(2,434)
Interest expense									394,131	378,079	322,833
Losses from early extinguishments of debt									1,494	89,883	510
Noncontrolling interests in property partnerships									1,558	3,464	2,778
Noncontrolling interest-redeemable preferred units of the Operating Partnership									3,339	3,343	3,594
Noncontrolling interest-common units of the Operating Partnership									36,250	24,099	35,534
Noncontrolling interest in gains on sales of real estate-common units of the Operating Partnership										349	1,579
Net income attributable to Boston Properties, Inc.	$ 101,644	$ 70,542	$ 60,214	$ 40,813	$ (12,903)	$ 57,668	$ 61,412	$ 52,714	272,679	159,072	231,014
Business Intersegment, Eliminations [Member]
Segment Reporting Information [Line Items]
Net operating income									1,105,986	982,726	957,547
Development and management services income									33,435	41,231	34,878
Income from unconsolidated joint ventures									85,896	36,774	12,058
Interest and other income									5,358	7,332	4,059
Gains on sales of real estate										2,734	11,760
General and administrative expense									81,442	79,658	75,447
Acquisition costs									155	2,614
Suspension of development										(7,200)	27,766
Depreciation and amortization expense									439,184	338,371	321,681
Gains (losses) from investments in securities									443	(935)	(2,434)
Interest expense									394,131	378,079	322,833
Losses from early extinguishments of debt									1,494	89,883	510
Noncontrolling interests in property partnerships									1,558	3,464	2,778
Noncontrolling interest-redeemable preferred units of the Operating Partnership									3,339	3,343	3,594
Noncontrolling interest-common units of the Operating Partnership									36,250	24,099	35,534
Noncontrolling interest in gains on sales of real estate-common units of the Operating Partnership										349	1,579
Net income attributable to Boston Properties, Inc.									$ 272,679	$ 159,072	$ 231,014

Earnings Per Share (Details) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2011 USD ($) $ / shares	Sep. 30, 2011 USD ($) $ / shares	Jun. 30, 2011 USD ($) $ / shares	Mar. 31, 2011 USD ($) $ / shares	Dec. 31, 2010 USD ($) $ / shares	Sep. 30, 2010 USD ($) $ / shares	Jun. 30, 2010 USD ($) $ / shares	Mar. 31, 2010 USD ($) $ / shares	Dec. 31, 2011 USD ($) $ / shares shares	Dec. 31, 2010 USD ($) $ / shares shares	Dec. 31, 2009 USD ($) $ / shares shares
Earnings Per Share [Abstract]
Net income attributable to Boston Properties, Inc., Income (Numerator) \| $	$ 101,644	$ 70,542	$ 60,214	$ 40,813	$ (12,903)	$ 57,668	$ 61,412	$ 52,714	$ 272,679	$ 159,072	$ 231,014
Net income attributable to Boston Properties Inc., Shares (Denominator)									145,693,000	139,440,000	131,050,000
Net income attributable to Boston Properties Inc., Per Share Amount \| $ / shares	$ 0.69	$ 0.48	$ 0.41	$ 0.29	$ (0.09)	$ 0.41	$ 0.44	$ 0.38	$ 1.87	$ 1.14	$ 1.76
Stock Based Compensation and Exchangeable Senior Notes, Income (Numerator) \| $
Stock Based Compensation, Shares (Denominator)										617,000	462,000
Stock Based Compensation and Exchangeable Senior Notes, Shares (Denominator)									525,000
Stock Based Compensation and Exchangeable Senior Notes, Per Share Amount \| $ / shares									(0.01)	0.00	0.00
Diluted Earnings: Net income, Income (Numerator) \| $									$ 272,679	$ 159,072	$ 231,014
Diluted Earnings: Net income, Shares (Denominator)									146,218,000	140,057,000	131,512,000
Diluted Earnings: Net income, Per Share Amount \| $ / shares	$ 0.69	$ 0.48	$ 0.41	$ 0.29	$ (0.09)	$ 0.41	$ 0.44	$ 0.38	$ 1.86	$ 1.14	$ 1.76
Eligible 2011 OPP units included in earnings per share calculation									62,000

Employee Benefit Plans (Details)	12 Months Ended			132 Months Ended	144 Months Ended	180 Months Ended
Employee Benefit Plans (Details)	Dec. 31, 2011 USD ($) months	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2011 USD ($) years	Dec. 31, 2011 USD ($)	Dec. 31, 1999
Employee Benefit Plans [Abstract]
Eligibility period for 401(k) savings plan (in months) \| months	3
Matching contribution percent, 401(k)					200.00%	200.00%
Participants maximum matching contribution, percent					3.00%	2.00%
Maximum eligible earnings as established by the IRS for matching contributions	$ 245,000	$ 245,000	$ 245,000
Annual aggregate matching contributions	3,100,000	2,900,000	3,000,000
Years of service for supplemental retirement contribution \| years				10
Age of employee for supplemental retirement contribution \| years				40
Annual supplemental retirement contribution and credit	62,000	48,000	$ 122,000
Separate unrestricted cash for deferred compensation plan	9,500,000	8,700,000		$ 9,500,000	$ 9,500,000
Actual liability for deferred compensation plan	$ 9,500,000	$ 8,700,000		$ 9,500,000	$ 9,500,000

Stock Option And Incentive Plan And Stock Purchase Plan (Narrative) (Details) $ / shares in Units, $ in Millions		12 Months Ended
	Feb. 01, 2011 $ / shares days	Dec. 31, 2011 USD ($) days years shares	May 15, 2007 shares
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Stock option and incentive plan 1997 end date		May 15, 2017
Number of common stock shares available for issuance \| shares			4,019,174
Number of shares available for issuance under stock option and incentive plan \| shares		1,895,963
Number of shares available for grant other than stock options \| shares		1,589,342
LTIP And Common Units Equivalency Ratio		one-for-one
TRS Component Sliding Scale One [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
TRS measurement, years		3
Cumulative absolute TRS hurdle		27.00%
Percentage of the potential relative TRS component earned if the Company's TRS is equal to or greater than a cumulative 27% over three years		100.00%
TRS Component Sliding Scale Two [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Cumulative absolute TRS hurdle, annum		0.00%
Percentage earned if the Company's TRS is 0% or less		0.00%
TRS Component Sliding Scale Three [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
TRS measurement, years		3
Percentage calculated by linear interpolation earned if the Company's cumulative TRS over three years is between 0% and 27%, minimum		0.00%
Percentage calculated by linear interpolation earned if the Company's cumulative TRS over three years is between 0% and 27%, maximum		100.00%
TRS Component Hypothetical Situation [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
TRS measurement, years		3
Cumulative absolute TRS hurdle		18.00%
Cumulative absolute TRS hurdle, annum		6.00%
Potential relative TRS component proration percentage		66.67%
OPP Units Two Thousand And Eight [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
TRS measurement, years		3
OPP Units Two Thousand And Eleven [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Award additional vesting period, years		2
Measurement Period For Outperformance Awards		February 1, 2011 to January 31, 2014
Start of the measurement period		Feb. 01, 2011
End of the measurement period		Jan. 31, 2014
Trading days prior to and including February 1, 2011 \| days	5
TRS measurement, years		3
Average closing price of common stock for five trading days prior and including February 1, 2011 \| $ / shares	$ 93.38
Aggregate rewards of OPP awards, maximum cap \| $		$ 40.0
Excess total return above a cumulative absolute TRS hurdle		2.00%
Cumulative absolute TRS hurdle		27.00%
Cumulative absolute TRS hurdle, annum		9.00%
Measurement period for cumulative absolute TRS hurdle (years)		3
Excess or deficient total return of relative TRS hurdle equal to total return of REIT Index		2.00%
Distributions percent before measurement date		10.00%
Performance measurement period, days \| days		15
Distributions Percent Before Measurement Date		10.00%
OPP Awards Vesting 2014 [Member] \| OPP Units Two Thousand And Eleven [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Vesting Percentage		25.00%
Vesting Date		Feb. 01, 2014
OPP Awards Vesting 2015 [Member] \| OPP Units Two Thousand And Eleven [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Vesting Percentage		25.00%
Vesting Date		Feb. 01, 2015
OPP Awards Vesting 2016 [Member] \| OPP Units Two Thousand And Eleven [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Vesting Percentage		50.00%
Vesting Date		Feb. 01, 2016
Minimum [Member] \| TRS Component Sliding Scale Three [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Cumulative absolute TRS hurdle		0.00%
Maximum [Member] \| TRS Component Sliding Scale Three [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Cumulative absolute TRS hurdle		27.00%

Stock Option And Incentive Plan And Stock Purchase Plan (Restricted Stock) (Narrative) (Details)	12 Months Ended			34 Months Ended	48 Months Ended	62 Months Ended
	Dec. 31, 2011 USD ($) years $ / shares days shares	Dec. 31, 2010 USD ($) years $ / shares shares	Dec. 31, 2009 USD ($) years $ / shares shares	Oct. 31, 2006	Dec. 31, 2009 USD ($) $ / shares shares	Dec. 31, 2011 USD ($) $ / shares shares	Feb. 03, 2012 shares	Jan. 01, 1999 shares
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Shares issued \| shares	148,186,511	140,278,005				148,186,511
LTIP units issued \| shares							156,652
Non-qualified stock options issued \| shares	146,844					146,844	165,538
2011 OPP units issued \| shares	400,000
Stock-based compensation associated with restricted stock, LTIP Units, 2008 OPP Units, and 2011 OPP Units	$ 28,300,000	$ 31,900,000	$ 25,600,000
Accelerated amount of unvested compensation expense					$ 5,800,000
Accelerated Compensation Expenses Related To 2008 Opp Units	$ 4,300,000
Weighted-average period (years) \| years	2.5
Value of shares of common stock	$ 1,481,000	$ 1,402,000				$ 1,481,000
Total intrinsic value of the outstanding and exercisable stock options	$ 600,000					$ 600,000
Options exercisable \| shares		324,938	963,895		963,895
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value \| $ / shares	$ 92.71
Weighted-average exercise price \| $ / shares		$ 32.65	$ 34.44		$ 34.44
Restricted Stock [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Shares issued \| shares	19,030	69,499	62,876		62,876	19,030	19,521
Employee and director payment per share \| $ / shares	0.01
Value of shares of common stock	$ 1,800,000	$ 4,500,000	$ 2,800,000		$ 2,800,000	$ 1,800,000
Employee's weighted average cost per share \| $ / shares	$ 93.40	$ 65.31	$ 43.89		$ 43.89	$ 93.40
LTIP Units [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
LTIP units issued \| shares	190,067	252,597	515,007		515,007	190,067
Value of LTIP units issued	$ 16,500,000	$ 15,300,000	$ 21,100,000
Per unit fair value weighted-average \| $ / shares	$ 86.74	$ 60.49	$ 41.05		$ 41.05	$ 86.74
Expected life assumed to calculate per unit fair value per LTIP unit (years) \| years	5.8	5.7	5.6
Risk-free rate	2.22%	2.60%	1.87%
Expected price volatility	30.00%	36.00%	40.00%
Method of valuation	LTIP Units were valued using a Monte Carlo simulation method model in accordance with the provisions of ASC 718 "Compensation-Stock Compensation" ("ASC 718") (formerly SFAS No. 123R).
LTIPs And Restricted Stock [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Time based vesting (years)				five
Vesting annual installments						4
Unrecognized compensation expenses	$ 24,700,000					$ 24,700,000
LTIPs and OPP Awards [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Employee and director payment per share \| $ / shares	0.25
OPP Units Two Thousand And Eleven [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Unrecognized compensation expenses	$ 5,500,000					5,500,000
Risk-free rate	0.98%
Expected price volatility	41.00%
Value of OPP units	$ 7,800,000					$ 7,800,000
Method of valuation	The Monte Carlo simulation used a statistical formula underlying the Black-Scholes and binomial formulas and such simulation was run approximately 100,000 times.
Estimated dividend payments, per share	$ 6.10
OPP Units Two Thousand And Eleven [Member] \| SNL Equity REIT [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Expected price volatility	37.00%
Non Qualified Stock Options [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Expected life assumed to calculate per unit fair value per LTIP unit (years) \| years	6.0
Risk-free rate	2.37%
Expected price volatility	35.00%
Expected dividend rate	3.00%
Method of valuation	The non-qualified stock options granted during the year ended December 31, 2011 had a fair value on the date of grant of $24.67 per option, which was computed using the Black-Scholes option-pricing model utilizing the following assumptions: an expected life of 6.0 years, a risk-free interest rate of 2.37%, an expected price volatility of 35.0% and an expected dividend yield of 3.0%.
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value \| $ / shares	$ 24.67
Weighted-average exercise price \| $ / shares	$ 92.71					$ 92.71
Non Qualified Employee Stock Purchase Plan [Member]
Stock Option And Incentive Plan And Stock Purchase Plan [Line Items]
Maximum common stock available for issuance \| shares								250,000
Employee common stock options, percent of average closing price	85.00%
Shares issued \| shares	6,356	9,131	12,105
Number of days used in calculation, average closing prices of common stock \| days	10
Shares issued, weighted-average purchase price per share \| $ / shares	$ 80.13	$ 61.61	$ 42.65		$ 42.65	$ 80.13

Stock Option And Incentive Plan And Stock Purchase Plan (Schedule Of Stock Options Status) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Stock Option And Incentive Plan And Stock Purchase Plan [Abstract]
Outstanding, Shares	324,938	963,895	1,206,402
Outstanding, Weighted Average Exercise Price	$ 32.65	$ 34.44	$ 34.23
Granted, Shares	146,844
Granted, Weighted Average Exercise Price	$ 92.71
Exercised, Shares	(316,159)	(638,957)	(242,507)
Exercised, Weighted Average Exercise Price	$ 32.63	$ 35.35	$ 33.41
Canceled, Shares
Canceled, Weighted Average Exercise Price
Outstanding, Shares	155,623	324,938	963,895
Outstanding, Weighted Average Exercise Price	$ 89.35	$ 32.65	$ 34.44

Stock Option And Incentive Plan And Stock Purchase Plan (Schedule Of Stock Options Outstanding) (Details)	12 Months Ended
	Dec. 31, 2011 years $ / shares shares	Dec. 31, 2010 $ / shares shares	Dec. 31, 2009 $ / shares shares	Dec. 31, 2008 $ / shares shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number Outstanding at 12/31/11 \| shares	155,623	324,938	963,895	1,206,402
Outstanding, Weighted-Average Exercise Price	$ 89.35	$ 32.65	$ 34.44	$ 34.23
Number Exercisable at 12/31/11 \| shares		324,938	963,895
Exercisable, Weighted-Average Exercise Price		$ 32.65	$ 34.44
Exercise Price Of $32.62 - $34.14 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, lower	32.62
Range of Exercise Prices, upper	$ 34.14
Number Outstanding at 12/31/11 \| shares	8,779
Weighted-Average Remaining Contractual Life (Years) \| years	0.1
Outstanding, Weighted-Average Exercise Price	$ 33.10
Number Exercisable at 12/31/11 \| shares	8,779
Exercisable, Weighted-Average Exercise Price	$ 33.10
Exercise Price Of $92.71 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price	$ 92.71
Number Outstanding at 12/31/11 \| shares	146,844
Weighted-Average Remaining Contractual Life (Years) \| years	9.1
Outstanding, Weighted-Average Exercise Price	$ 92.71
Number Exercisable at 12/31/11 \| shares	4,854
Exercisable, Weighted-Average Exercise Price	$ 92.71

Related Party Transactions (Details)	3 Months Ended	12 Months Ended
Related Party Transactions (Details)	Jun. 30, 1988	Dec. 31, 2011 USD ($) sqft	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2007 USD ($)	Dec. 31, 2004 USD ($)	Dec. 31, 1998 USD ($) years
Related Party Transaction [Line Items]
Deferred stock units outstanding		79,856	73,218
Number of non-employee directors electing to receive deferred stock units		5
Former Director [Member]
Related Party Transaction [Line Items]
Acquired properties date	Jun. 30, 1998
Annual development agreement payments		$ 125,000
Development agreement payments made annually from 1998 through 2004						$ 750,000
Purchase price of land parcel					$ 3,100,000
Acquisition date					July 24, 2007
Brother Of Executive Vice President [Member]
Related Party Transaction [Line Items]
Aggregate leasing commissions paid to related party		$ 671,000	$ 960,000	$ 257,000
Affiliate Of Former Director [Member]
Related Party Transaction [Line Items]
Square feet of development \| sqft		2,000,000
Purchase price per rentable square foot of property developed		$ 20					$ 20
Stabilized annual return percentage minimum							10.50%
Stabilized annual return percentage maximum							11.00%
Aggregate fixed price per rentable square foot of developed property						10.50
Amount subject to adjustment to aggregated fixed amount per square foot of developed property						$ 5.50
Year term of development agreement (years) \| years							20

Selected Interim Financial Information (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Selected Interim Financial Information [Line Items]
Total revenue	$ 452,787	$ 452,413	$ 436,451	$ 417,875	$ 392,482	$ 386,410	$ 393,841	$ 378,071	$ 1,759,526	$ 1,550,804	$ 1,518,190
Income from continuing operations	115,443	80,451	69,738	48,194	(12,756)	68,089	71,518	60,742	313,826	187,593	262,739
Net income attributable to Boston Properties, Inc.	$ 101,644	$ 70,542	$ 60,214	$ 40,813	$ (12,903)	$ 57,668	$ 61,412	$ 52,714	$ 272,679	$ 159,072	$ 231,014
Income attributable to Boston Properties, Inc. per share-basic	$ 0.69	$ 0.48	$ 0.41	$ 0.29	$ (0.09)	$ 0.41	$ 0.44	$ 0.38	$ 1.87	$ 1.14	$ 1.76
Income attributable to Boston Properties, Inc. per share-diluted	$ 0.69	$ 0.48	$ 0.41	$ 0.29	$ (0.09)	$ 0.41	$ 0.44	$ 0.38	$ 1.86	$ 1.14	$ 1.76
Loss on extinguishment of debt									$ (1,494)	$ (89,883)	$ (510)
Repayments of unsecured debt										$ 700,000
6.25% Senior Notes Due 2013 [Member]
Selected Interim Financial Information [Line Items]
Loss on extinguishment of debt					$ 81,700
Repayments of unsecured debt					$ 700,000
Coupon/Stated Rate					6.25%					6.25%
Two Grand Central Tower [Member]
Selected Interim Financial Information [Line Items]
Gains on sales of real estate	$ 46,200

Subsequent Events (Details)												12 Months Ended
Subsequent Events (Details)	Feb. 20, 2012 USD ($)	Feb. 16, 2012 USD ($)	Feb. 15, 2012 USD ($)	Feb. 13, 2012 USD ($) months $ / shares years shares	Feb. 10, 2012 USD ($)	Jan. 25, 2012 USD ($) years	Jan. 10, 2012	Jan. 03, 2012	Nov. 09, 2011 USD ($)	Jul. 05, 2011	Jan. 12, 2011	Dec. 31, 2011 USD ($) days years shares	Dec. 31, 2010 USD ($) shares	Feb. 03, 2012 shares	Dec. 31, 2009 shares
Subsequent Event [Line Items]
Principal Amount												$ 1,773,694,000
Repayments of unsecured debt													$ 700,000,000
Shares issued \| shares												148,186,511	140,278,005
LTIP units issued \| shares														156,652
Non-qualified stock options issued \| shares												146,844		165,538
OPP Units Two Thousand And Eleven [Member]
Subsequent Event [Line Items]
Aggregate rewards of OPP awards, maximum cap												$ 40,000,000
Performance measurement period, years \| days												15
Measurement period for 2012 OPP Awards												February 1, 2011 to January 31, 2014
Award additional vesting period, years \| years												2
OPP Units Two Thousand And Twelve [Member]
Subsequent Event [Line Items]
Aggregate rewards of OPP awards, maximum cap						$ 40,000,000
Performance measurement period, years \| years						3
Measurement period for 2012 OPP Awards						February 7, 2012 to February 6, 2015
Award additional vesting period, years \| years						2
Aggregate value of 2012 OPP Awards						$ 7,700,000
Amortization into earnings period, years \| years						5
Restricted Stock [Member]
Subsequent Event [Line Items]
Shares issued \| shares												19,030	69,499	19,521	62,876
2.875% Exchangeable Senior Notes [Member]
Subsequent Event [Line Items]
Stated interest rate							2.875%					2.875%
Debt instrument repurchase date by company							Feb. 15, 2012
Put Right expiration date							Feb. 08, 2012
Notes redemption date							Feb. 20, 2012
Debt instrument in connection with redemption last day to exchange notes							Feb. 16, 2012
Debt instrument redemption price percentage of principal	100.00%						100.00%
Principal Amount												$ 576,194,000
Repayments of unsecured debt	$ 333,459,000		$ 242,735,000						$ 50,200,000
Maturity date												Feb. 15, 2037
Montvale Center [Member]
Subsequent Event [Line Items]
Maturity date											Jun. 06, 2012
Debt Instrument, Debt Default, Accrued Interest Rate											9.93%
12310 Sunrise Valley Drive [Member]
Subsequent Event [Line Items]
Net rentable square footage										268,000
12300 Sunrise Valley Drive [Member]
Subsequent Event [Line Items]
Net rentable square footage								256,000
453 Ravendale Avenue [Member]
Subsequent Event [Line Items]
Net rentable square footage					30,000
Acquisition aggregate purchase price					$ 6,700,000
100 Federal Street [Member]
Subsequent Event [Line Items]
Net rentable square footage		1,300,000
Acquisition aggregate purchase price		$ 615,000,000
Number of floors in building		37
Earnest Money Deposits		$ 25,000,000
Executive Vice President [Member]
Subsequent Event [Line Items]
Cash payment related to resignation				$ 1,533,333
Consulting period, months \| months				2
Consulting fee, per month				$ 20,000
Accelerated share vesting with respect to LTIP units \| shares				23,502
Accelerated share vesting with respect to stock options \| shares				4,464
Accelerated share vesting with respect to common stock \| shares				5,117
Common stock exercise price per share for stock options \| $ / shares				$ 92.71
Common stock exercise price per share for common stock \| $ / shares				$ 104.47
Non-compete agreement, years \| years				1
2011 Outperformance Award [Member] \| Executive Vice President [Member]
Subsequent Event [Line Items]
Percentage of outperformance award retained by Mr. Norville				36.00%
For 2011 [Member] \| Executive Vice President [Member]
Subsequent Event [Line Items]
Cash bonus for 2011 as part of resignation agreement				$ 950,000

Real Estate And Accumulated Depreciation (Schedule Of Real Estate And Accumulated Depreciation) (Details)
$ in Thousands

12 Months Ended

Dec. 31, 2011

USD ($)

years

Dec. 31, 2010

USD ($)

Real Estate and Accumulated Depreciation [Line Items]

Encumbrances

^[1]

$ 3,123,267

Original Land

2,216,058

Original Building

8,104,331

Costs Capitalized Subsequent to Acquisition

3,042,724

Land and Improvements

2,356,522

Building and Improvements

9,921,084

Land Held for Development

266,822

Development and Construction in Progress

818,685

Total

13,363,113

Accumulated Depreciation

2,626,324

Furniture, fixtures and equipment

26,359

$ 24,043

Furniture, fixtures and equipment, accumulated depreciation

16,662

Real estate aggregate cost for tax purposes

12,200,000

Real estate aggregate accumulated depreciation for tax purposes

$ 2,200,000

Depreciation of building life (in years) | years

Unamortized balance of historical fair value adjustments

$ 23,794

$ 27,700

Embarcadero Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

Embarcadero Center

Office

San Francisco, CA

$ 370,091

179,697

847,410

Costs Capitalized Subsequent to Acquisition

278,722

Land and Improvements

195,984

Building and Improvements

1,109,845

Total

1,305,829

Accumulated Depreciation

$ 397,177

Year(s) Built/Renovated

1970/1989

Depreciable Lives (Years)

^[2]

(1)

Prudential Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

Prudential Center

Office

Boston, MA

$ 92,077

734,594

Costs Capitalized Subsequent to Acquisition

323,490

Land and Improvements

107,428

Building and Improvements

1,026,936

Land Held for Development

15,797

Total

1,150,161

Accumulated Depreciation

$ 349,127

Year(s) Built/Renovated

1965/1993/2002

Depreciable Lives (Years)

^[2]

(1)

399 Park Avenue [Member]

Real Estate and Accumulated Depreciation [Line Items]

399 Park Avenue

Office

New York, NY

$ 339,200

700,358

Costs Capitalized Subsequent to Acquisition

89,720

Land and Improvements

354,107

Building and Improvements

775,171

Total

1,129,278

Accumulated Depreciation

$ 177,001

Year(s) Built/Renovated

1961

Depreciable Lives (Years)

^[2]

(1)

601 Lexington Avenue [Member]

Real Estate and Accumulated Depreciation [Line Items]

601 Lexington Avenue

Office

New York, NY

$ 725,000

241,600

494,782

Costs Capitalized Subsequent to Acquisition

212,551

Land and Improvements

289,639

Building and Improvements

659,294

Total

948,933

Accumulated Depreciation

$ 163,031

Year(s) Built/Renovated

1977/1997

Depreciable Lives (Years)

^[2]

(1)

The John Hancock Tower And Garage [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

The John Hancock Tower and Garage

Office

Boston, MA

$ 660,033

219,543

667,884

Costs Capitalized Subsequent to Acquisition

38,678

Land and Improvements

219,616

Building and Improvements

706,489

Total

926,105

Accumulated Depreciation

$ 25,299

Year(s) Built/Renovated

1976

Depreciable Lives (Years)

^[2]

(1)

Times Square Tower [Member]

Real Estate and Accumulated Depreciation [Line Items]

Times Square Tower

Office

New York, NY

$ 165,413

380,438

Costs Capitalized Subsequent to Acquisition

83,353

Land and Improvements

169,193

Building and Improvements

460,011

Total

629,204

Accumulated Depreciation

$ 110,416

Year(s) Built/Renovated

2004

Depreciable Lives (Years)

^[2]

(1)

Carnegie Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

Carnegie Center

Office

Princeton, NJ

$ 105,107

377,259

Costs Capitalized Subsequent to Acquisition

59,401

Land and Improvements

103,062

Building and Improvements

436,766

Land Held for Development

1,939

Total

541,767

Accumulated Depreciation

$ 147,906

Year(s) Built/Renovated

1983-1999

Depreciable Lives (Years)

^[2]

(1)

Atlantic Wharf [Member]

Real Estate and Accumulated Depreciation [Line Items]

Atlantic Wharf

Office

Boston, MA

$ 63,988

454,537

Land and Improvements

63,988

Building and Improvements

454,537

Total

518,525

Accumulated Depreciation

$ 10,101

Year(s) Built/Renovated

2011

Depreciable Lives (Years)

^[2]

(1)

599 Lexington Avenue [Member]

Real Estate and Accumulated Depreciation [Line Items]

599 Lexington Avenue

Office

New York, NY

$ 750,000

81,040

100,507

Costs Capitalized Subsequent to Acquisition

120,055

Land and Improvements

87,852

Building and Improvements

213,750

Total

301,602

Accumulated Depreciation

$ 131,768

Year(s) Built/Renovated

1986

Depreciable Lives (Years)

^[2]

(1)

Gateway Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

Gateway Center

Office

San Francisco, CA

$ 28,255

139,245

Costs Capitalized Subsequent to Acquisition

48,457

Land and Improvements

30,627

Building and Improvements

185,330

Total

215,957

Accumulated Depreciation

$ 65,219

Year(s) Built/Renovated

1984/1986/2002

Depreciable Lives (Years)

^[2]

(1)

South of Market [Member]

Real Estate and Accumulated Depreciation [Line Items]

South of Market

Office

Reston, VA

$ 13,603

164,144

Costs Capitalized Subsequent to Acquisition

9,110

Land and Improvements

13,687

Building and Improvements

173,170

Total

186,857

Accumulated Depreciation

$ 24,610

Year(s) Built/Renovated

2008

Depreciable Lives (Years)

^[2]

(1)

2200 Pennsylvania Avenue [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

2200 Pennsylvania Avenue

Type

Office

Location

Washington, DC

Original Building

$ 183,541

Building and Improvements

183,541

Total

183,541

Accumulated Depreciation

$ 4,154

Year(s) Built/Renovated

2011

Depreciable Lives (Years)

^[2]

(1)

Bay Colony Corporate Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Bay Colony Corporate Center

Office

Waltham, MA

$ 145,673

18,789

148,451

Costs Capitalized Subsequent to Acquisition

4,670

Land and Improvements

18,789

Building and Improvements

153,121

Total

171,910

Accumulated Depreciation

$ 6,248

Year(s) Built/Renovated

1985-1989

Depreciable Lives (Years)

^[2]

(1)

Reservoir Place [Member]

Real Estate and Accumulated Depreciation [Line Items]

Reservoir Place

Office

Waltham, MA

$ 18,605

92,619

Costs Capitalized Subsequent to Acquisition

25,696

Land and Improvements

20,118

Building and Improvements

116,802

Total

136,920

Accumulated Depreciation

$ 43,467

Year(s) Built/Renovated

1955/1987

Depreciable Lives (Years)

^[2]

(1)

3200 Zanker Road [Member]

Real Estate and Accumulated Depreciation [Line Items]

3200 Zanker Road

Office

San Jose, CA

$ 36,705

82,863

Costs Capitalized Subsequent to Acquisition

13,542

Land and Improvements

36,997

Building and Improvements

93,454

Land Held for Development

2,659

Total

133,110

Accumulated Depreciation

$ 18,206

Year(s) Built/Renovated

1988

Depreciable Lives (Years)

^[2]

(1)

505 9th Street [Member]

Real Estate and Accumulated Depreciation [Line Items]

505 9th Street

Office

Washington, DC

$ 125,844

38,885

83,719

Costs Capitalized Subsequent to Acquisition

5,661

Land and Improvements

42,082

Building and Improvements

86,183

Total

128,265

Accumulated Depreciation

$ 13,800

Year(s) Built/Renovated

2007

Depreciable Lives (Years)

^[2]

(1)

1333 New Hampshire Avenue [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

1333 New Hampshire Avenue

Office

Washington, DC

$ 34,032

85,660

Costs Capitalized Subsequent to Acquisition

7,688

Land and Improvements

35,382

Building and Improvements

91,998

Total

127,380

Accumulated Depreciation

$ 25,512

Year(s) Built/Renovated

1996

Depreciable Lives (Years)

^[2]

(1)

Kingstowne Towne Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Kingstowne Towne Center

Office

Alexandria, VA

$ 54,790

18,021

109,038

Costs Capitalized Subsequent to Acquisition

(428)

Land and Improvements

18,062

Building and Improvements

108,569

Total

126,631

Accumulated Depreciation

$ 19,283

Year(s) Built/Renovated

2003-2006

Depreciable Lives (Years)

^[2]

(1)

1330 Connecticut Avenue [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

1330 Connecticut Avenue

Office

Washington, DC

$ 25,982

82,311

Costs Capitalized Subsequent to Acquisition

16,182

Land and Improvements

27,135

Building and Improvements

97,340

Total

124,475

Accumulated Depreciation

$ 23,054

Year(s) Built/Renovated

1984

Depreciable Lives (Years)

^[2]

(1)

Capital Gallery [Member]

Real Estate and Accumulated Depreciation [Line Items]

Capital Gallery

Office

Washington, DC

$ 4,725

29,565

Costs Capitalized Subsequent to Acquisition

90,125

Land and Improvements

8,662

Building and Improvements

115,753

Total

124,415

Accumulated Depreciation

$ 46,636

Year(s) Built/Renovated

1981/2006

Depreciable Lives (Years)

^[2]

(1)

635 Massachusetts Avenue [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

635 Massachusetts Avenue

Office

Washington, DC

$ 95,281

22,221

Costs Capitalized Subsequent to Acquisition

2,510

Land and Improvements

95,293

Building and Improvements

22,257

Land Held for Development

2,462

Total

120,012

Accumulated Depreciation

$ 12,876

Year(s) Built/Renovated

1968/1992

Depreciable Lives (Years)

^[2]

(1)

Weston Corporate Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Weston Corporate Center

Office

Weston, MA

$ 25,753

92,312

Costs Capitalized Subsequent to Acquisition

(149)

Land and Improvements

25,852

Building and Improvements

92,064

Total

117,916

Accumulated Depreciation

$ 4,820

Year(s) Built/Renovated

2010

Depreciable Lives (Years)

^[2]

(1)

One Freedom Square [Member]

Real Estate and Accumulated Depreciation [Line Items]

One Freedom Square

Office

Reston, VA

$ 66,092

9,929

84,504

Costs Capitalized Subsequent to Acquisition

15,290

Land and Improvements

11,293

Building and Improvements

98,430

Total

109,723

Accumulated Depreciation

$ 36,740

Year(s) Built/Renovated

2000

Depreciable Lives (Years)

^[2]

(1)

Two Freedom Square [Member]

Real Estate and Accumulated Depreciation [Line Items]

Two Freedom Square

Office

Reston, VA

$ 13,930

77,739

Costs Capitalized Subsequent to Acquisition

12,649

Land and Improvements

15,420

Building and Improvements

88,898

Total

104,318

Accumulated Depreciation

$ 30,804

Year(s) Built/Renovated

2001

Depreciable Lives (Years)

^[2]

(1)

Seven Cambridge Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Seven Cambridge Center

Office

Cambridge, MA

$ 3,457

97,136

Costs Capitalized Subsequent to Acquisition

2,880

Land and Improvements

4,125

Building and Improvements

99,348

Total

103,473

Accumulated Depreciation

$ 35,558

Year(s) Built/Renovated

2006

Depreciable Lives (Years)

^[2]

(1)

One And Two Reston Overlook [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

One and Two Reston Overlook

Office

Reston, VA

$ 16,456

66,192

Costs Capitalized Subsequent to Acquisition

13,195

Land and Improvements

17,561

Building and Improvements

78,282

Total

95,843

Accumulated Depreciation

$ 23,776

Year(s) Built/Renovated

1999

Depreciable Lives (Years)

^[2]

(1)

Discovery Square [Member]

Real Estate and Accumulated Depreciation [Line Items]

Discovery Square

Office

Reston, VA

$ 11,198

71,782

Costs Capitalized Subsequent to Acquisition

9,017

Land and Improvements

12,533

Building and Improvements

79,464

Total

91,997

Accumulated Depreciation

$ 24,400

Year(s) Built/Renovated

2001

Depreciable Lives (Years)

^[2]

(1)

140 Kendrick Street [Member]

Real Estate and Accumulated Depreciation [Line Items]

140 Kendrick Street

Office

Needham, MA

$ 50,291

18,095

66,905

Costs Capitalized Subsequent to Acquisition

4,246

Land and Improvements

19,092

Building and Improvements

70,154

Total

89,246

Accumulated Depreciation

$ 13,686

Year(s) Built/Renovated

2000

Depreciable Lives (Years)

^[2]

(1)

Waltham Weston Corporate Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Waltham Weston Corporate Center

Office

Waltham, MA

$ 10,385

60,694

Costs Capitalized Subsequent to Acquisition

9,625

Land and Improvements

11,097

Building and Improvements

69,607

Total

80,704

Accumulated Depreciation

$ 24,588

Year(s) Built/Renovated

2003

Depreciable Lives (Years)

^[2]

(1)

Five Cambridge Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Five Cambridge Center

Office

Cambridge, MA

$ 18,863

53,346

Costs Capitalized Subsequent to Acquisition

7,901

Land and Improvements

18,938

Building and Improvements

61,172

Total

80,110

Accumulated Depreciation

$ 14,816

Year(s) Built/Renovated

1981/1996

Depreciable Lives (Years)

^[2]

(1)

77 CityPoint [Member]

Real Estate and Accumulated Depreciation [Line Items]

77 CityPoint

Office

Waltham, MA

$ 13,847

60,383

Costs Capitalized Subsequent to Acquisition

3,115

Land and Improvements

13,873

Building and Improvements

63,472

Total

77,345

Accumulated Depreciation

$ 7,532

Year(s) Built/Renovated

2008

Depreciable Lives (Years)

^[2]

(1)

12300 Sunrise Valley Drive [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

12300 Sunrise Valley Drive

Office

Reston, VA

$ 9,062

58,884

Costs Capitalized Subsequent to Acquisition

8,489

Land and Improvements

11,009

Building and Improvements

65,426

Total

76,435

Accumulated Depreciation

$ 41,344

Year(s) Built/Renovated

1987/1988

Depreciable Lives (Years)

^[2]

(1)

Four Cambridge Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Four Cambridge Center

Office

Cambridge, MA

$ 19,104

52,078

Costs Capitalized Subsequent to Acquisition

3,888

Land and Improvements

19,148

Building and Improvements

55,922

Total

75,070

Accumulated Depreciation

$ 8,553

Year(s) Built/Renovated

1983/1998

Depreciable Lives (Years)

^[2]

(1)

Democracy Tower [Member]

Real Estate and Accumulated Depreciation [Line Items]

Democracy Tower

Office

Reston, VA

$ 73,335

Costs Capitalized Subsequent to Acquisition

431

Building and Improvements

73,766

Total

73,766

Accumulated Depreciation

$ 6,284

Year(s) Built/Renovated

2009

Depreciable Lives (Years)

^[2]

(1)

230 CityPoint [Member]

Real Estate and Accumulated Depreciation [Line Items]

230 CityPoint

Office

Waltham, MA

$ 13,189

49,823

Costs Capitalized Subsequent to Acquisition

10,489

Land and Improvements

13,593

Building and Improvements

59,908

Total

73,501

Accumulated Depreciation

$ 13,395

Year(s) Built/Renovated

1992

Depreciable Lives (Years)

^[2]

(1)

North First Business Park [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

North First Business Park

Office

San Jose, CA

$ 58,402

13,069

Costs Capitalized Subsequent to Acquisition

1,961

Land and Improvements

23,377

Building and Improvements

14,345

Land Held for Development

35,710

Total

73,432

Accumulated Depreciation

$ 6,432

Year(s) Built/Renovated

1981

Depreciable Lives (Years)

^[2]

(1)

2440 West El Camino Real [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

2440 West El Camino Real

Office

Mountain View, CA

$ 16,741

51,285

Land and Improvements

16,741

Building and Improvements

51,285

Total

68,026

Accumulated Depreciation

$ 166

Year(s) Built/Renovated

1987/2003

Depreciable Lives (Years)

^[2]

(1)

Wisconsin Place [Member]

Real Estate and Accumulated Depreciation [Line Items]

Wisconsin Place

Office

Chevy Chase, MD

$ 53,349

Costs Capitalized Subsequent to Acquisition

12,952

Building and Improvements

66,301

Total

66,301

Accumulated Depreciation

$ 6,123

Year(s) Built/Renovated

2009

Depreciable Lives (Years)

^[2]

(1)

Reston Corporate Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Reston Corporate Center

Office

Reston, VA

$ 9,135

50,857

Costs Capitalized Subsequent to Acquisition

5,334

Land and Improvements

10,148

Building and Improvements

55,178

Total

65,326

Accumulated Depreciation

$ 18,021

Year(s) Built/Renovated

1984

Depreciable Lives (Years)

^[2]

(1)

New Dominion Technology Park, Bldg. Two [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

New Dominion Technology Park, Bldg. Two

Office

Herndon, VA

$ 63,000

5,584

51,868

Costs Capitalized Subsequent to Acquisition

3,694

Land and Improvements

6,510

Building and Improvements

54,636

Total

61,146

Accumulated Depreciation

$ 12,970

Year(s) Built/Renovated

2004

Depreciable Lives (Years)

^[2]

(1)

One Preserve Parkway [Member]

Real Estate and Accumulated Depreciation [Line Items]

One Preserve Parkway

Office

Rockville, MD

$ 5,357

42,186

Costs Capitalized Subsequent to Acquisition

7,156

Land and Improvements

5,357

Building and Improvements

49,342

Total

54,699

Accumulated Depreciation

$ 4,618

Year(s) Built/Renovated

2009

Depreciable Lives (Years)

^[2]

(1)

New Dominion Technology Park, Bldg. One [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

New Dominion Technology Park, Bldg. One

Office

Herndon, VA

$ 47,406

3,880

43,227

Costs Capitalized Subsequent to Acquisition

3,882

Land and Improvements

4,583

Building and Improvements

46,406

Total

50,989

Accumulated Depreciation

$ 16,382

Year(s) Built/Renovated

2001

Depreciable Lives (Years)

^[2]

(1)

Sumner Square [Member]

Real Estate and Accumulated Depreciation [Line Items]

Sumner Square

Office

Washington, DC

$ 23,827

624

28,745

Costs Capitalized Subsequent to Acquisition

21,294

Land and Improvements

1,478

Building and Improvements

49,185

Total

50,663

Accumulated Depreciation

$ 19,627

Year(s) Built/Renovated

1985

Depreciable Lives (Years)

^[2]

(1)

303 Almaden Boulevard [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

303 Almaden Boulevard

Office

San Jose, CA

$ 10,836

35,606

Costs Capitalized Subsequent to Acquisition

3,983

Land and Improvements

10,947

Building and Improvements

39,478

Total

50,425

Accumulated Depreciation

$ 7,502

Year(s) Built/Renovated

1995

Depreciable Lives (Years)

^[2]

(1)

1301 New York Avenue [Member]

Real Estate and Accumulated Depreciation [Line Items]

1301 New York Avenue

Office

Washington, DC

$ 9,250

18,750

Costs Capitalized Subsequent to Acquisition

20,746

Land and Improvements

9,867

Building and Improvements

38,879

Total

48,746

Accumulated Depreciation

$ 14,740

Year(s) Built/Renovated

1983/1998

Depreciable Lives (Years)

^[2]

(1)

200 West Street [Member]

Real Estate and Accumulated Depreciation [Line Items]

200 West Street

Office

Waltham, MA

$ 16,148

24,983

Costs Capitalized Subsequent to Acquisition

7,455

Land and Improvements

16,813

Building and Improvements

31,773

Total

48,586

Accumulated Depreciation

$ 12,209

Year(s) Built/Renovated

1999

Depreciable Lives (Years)

^[2]

(1)

191 Spring Street [Member]

Real Estate and Accumulated Depreciation [Line Items]

191 Spring Street

Office

Lexington, MA

$ 2,850

27,166

Costs Capitalized Subsequent to Acquisition

17,481

Land and Improvements

3,151

Building and Improvements

44,346

Total

47,497

Accumulated Depreciation

$ 26,795

Year(s) Built/Renovated

1971/1995

Depreciable Lives (Years)

^[2]

(1)

Bedford Business Park [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Bedford Business Park

Office

Bedford, MA

$ 534

3,403

Costs Capitalized Subsequent to Acquisition

40,988

Land and Improvements

2,218

Building and Improvements

42,707

Total

44,925

Accumulated Depreciation

$ 24,518

Year(s) Built/Renovated

1980

Depreciable Lives (Years)

^[2]

(1)

University Place [Member]

Real Estate and Accumulated Depreciation [Line Items]

University Place

Office

Cambridge, MA

$ 16,220

37,091

Costs Capitalized Subsequent to Acquisition

6,785

Land and Improvements

390

Building and Improvements

43,486

Total

43,876

Accumulated Depreciation

$ 17,757

Year(s) Built/Renovated

1985

Depreciable Lives (Years)

^[2]

(1)

2600 Tower Oaks Boulevard [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

2600 Tower Oaks Boulevard

Office

Rockville, MD

$ 4,243

31,125

Costs Capitalized Subsequent to Acquisition

7,580

Land and Improvements

4,785

Building and Improvements

38,163

Total

42,948

Accumulated Depreciation

$ 14,095

Year(s) Built/Renovated

2001

Depreciable Lives (Years)

^[2]

(1)

Quorum Office Park [Member]

Real Estate and Accumulated Depreciation [Line Items]

Quorum Office Park

Office

Chelmsford, MA

$ 3,750

32,454

Costs Capitalized Subsequent to Acquisition

5,196

Land and Improvements

5,187

Building and Improvements

36,213

Total

41,400

Accumulated Depreciation

$ 11,042

Year(s) Built/Renovated

2001

Depreciable Lives (Years)

^[2]

(1)

One Cambridge Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

One Cambridge Center

Office

Cambridge, MA

$ 134

25,110

Costs Capitalized Subsequent to Acquisition

13,264

Land and Improvements

548

Building and Improvements

37,960

Total

38,508

Accumulated Depreciation

$ 22,813

Year(s) Built/Renovated

1987

Depreciable Lives (Years)

^[2]

(1)

12290 Sunrise Valley Drive [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

12290 Sunrise Valley Drive

Office

Reston, VA

$ 3,594

32,977

Costs Capitalized Subsequent to Acquisition

1,374

Land and Improvements

4,009

Building and Improvements

33,936

Total

37,945

Accumulated Depreciation

$ 10,329

Year(s) Built/Renovated

2006

Depreciable Lives (Years)

^[2]

(1)

500 E Street [Member]

Real Estate and Accumulated Depreciation [Line Items]

500 E Street

Office

Washington, DC

$ 109

22,420

Costs Capitalized Subsequent to Acquisition

11,915

Land and Improvements

2,379

Building and Improvements

32,065

Total

34,444

Accumulated Depreciation

$ 18,501

Year(s) Built/Renovated

1987

Depreciable Lives (Years)

^[2]

(1)

Eight Cambridge Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Eight Cambridge Center

Office

Cambridge, MA

$ 850

25,042

Costs Capitalized Subsequent to Acquisition

5,745

Land and Improvements

1,323

Building and Improvements

30,314

Total

31,637

Accumulated Depreciation

$ 8,177

Year(s) Built/Renovated

1999

Depreciable Lives (Years)

^[2]

(1)

10 and 20 Burlington Mall Road [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

10 and 20 Burlington Mall Road

Office

Burlington, MA

$ 930

6,928

Costs Capitalized Subsequent to Acquisition

13,118

Land and Improvements

802

Building and Improvements

20,174

Total

20,976

Accumulated Depreciation

$ 12,567

Year(s) Built/Renovated

1984-1989/95-96

Depreciable Lives (Years)

^[2]

(1)

Ten Cambridge Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

Ten Cambridge Center

Office

Cambridge, MA

$ 1,299

12,943

Costs Capitalized Subsequent to Acquisition

6,109

Land and Improvements

2,395

Building and Improvements

17,956

Total

20,351

Accumulated Depreciation

$ 10,120

Year(s) Built/Renovated

1990

Depreciable Lives (Years)

^[2]

(1)

Three Cambridge Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Three Cambridge Center

Office

Cambridge, MA

$ 174

12,200

Costs Capitalized Subsequent to Acquisition

6,021

Land and Improvements

367

Building and Improvements

18,028

Total

18,395

Accumulated Depreciation

$ 8,712

Year(s) Built/Renovated

1987

Depreciable Lives (Years)

^[2]

(1)

201 Spring Street [Member]

Real Estate and Accumulated Depreciation [Line Items]

201 Spring Street

Office

Lexington, MA

$ 2,849

15,303

Costs Capitalized Subsequent to Acquisition

(154)

Land and Improvements

3,124

Building and Improvements

14,874

Total

17,998

Accumulated Depreciation

$ 5,082

Year(s) Built/Renovated

1997

Depreciable Lives (Years)

^[2]

(1)

Montvale Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

Montvale Center

Office

Gaithersburg, MD

$ 25,000

1,574

9,786

Costs Capitalized Subsequent to Acquisition

6,558

Land and Improvements

2,555

Building and Improvements

15,363

Total

17,918

Accumulated Depreciation

$ 9,665

Year(s) Built/Renovated

1987

Depreciable Lives (Years)

^[2]

(1)

40 Shattuck Road [Member]

Real Estate and Accumulated Depreciation [Line Items]

40 Shattuck Road

Office

Andover, MA

$ 709

14,740

Costs Capitalized Subsequent to Acquisition

1,906

Land and Improvements

893

Building and Improvements

16,462

Total

17,355

Accumulated Depreciation

$ 4,340

Year(s) Built/Renovated

2001

Depreciable Lives (Years)

^[2]

(1)

Lexington Office Park [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Lexington Office Park

Office

Lexington, MA

$ 998

1,426

Costs Capitalized Subsequent to Acquisition

12,975

Land and Improvements

1,264

Building and Improvements

14,135

Total

15,399

Accumulated Depreciation

$ 8,959

Year(s) Built/Renovated

1982

Depreciable Lives (Years)

^[2]

(1)

6601 & 6605 Springfield Center Drive [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

6601 & 6605 Springfield Center Drive

Office

Springfield, VA

$ 14,041

2,375

Costs Capitalized Subsequent to Acquisition

(1,836)

Land and Improvements

3,777

Building and Improvements

714

Land Held for Development

10,089

Total

14,580

Accumulated Depreciation

$ 702

Year(s) Built/Renovated

1990

Depreciable Lives (Years)

^[2]

(1)

92-100 Hayden Avenue [Member]

Real Estate and Accumulated Depreciation [Line Items]

92-100 Hayden Avenue

Office

Lexington, MA

$ 594

6,748

Costs Capitalized Subsequent to Acquisition

6,976

Land and Improvements

802

Building and Improvements

13,516

Total

14,318

Accumulated Depreciation

$ 8,127

Year(s) Built/Renovated

1985

Depreciable Lives (Years)

^[2]

(1)

181 Spring Street [Member]

Real Estate and Accumulated Depreciation [Line Items]

181 Spring Street

Office

Lexington, MA

$ 1,066

9,520

Costs Capitalized Subsequent to Acquisition

2,407

Land and Improvements

1,160

Building and Improvements

11,833

Total

12,993

Accumulated Depreciation

$ 3,783

Year(s) Built/Renovated

1999

Depreciable Lives (Years)

^[2]

(1)

195 West Street [Member]

Real Estate and Accumulated Depreciation [Line Items]

195 West Street

Office

Waltham, MA

$ 1,611

6,652

Costs Capitalized Subsequent to Acquisition

4,175

Land and Improvements

1,858

Building and Improvements

10,580

Total

12,438

Accumulated Depreciation

$ 5,310

Year(s) Built/Renovated

1990

Depreciable Lives (Years)

^[2]

(1)

91 Hartwell Avenue [Member]

Real Estate and Accumulated Depreciation [Line Items]

91 Hartwell Avenue

Office

Lexington, MA

$ 784

6,464

Costs Capitalized Subsequent to Acquisition

4,458

Land and Improvements

941

Building and Improvements

10,765

Total

11,706

Accumulated Depreciation

$ 6,874

Year(s) Built/Renovated

1985

Depreciable Lives (Years)

^[2]

(1)

Waltham Office Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Waltham Office Center

Office

Waltham, MA

$ 422

2,719

Costs Capitalized Subsequent to Acquisition

8,402

Land and Improvements

384

Building and Improvements

8,445

Land Held for Development

2,714

Total

11,543

Accumulated Depreciation

$ 7,543

Year(s) Built/Renovated

1968-1970/87-88

Depreciable Lives (Years)

^[2]

(1)

Eleven Cambridge Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Eleven Cambridge Center

Office

Cambridge, MA

$ 121

5,535

Costs Capitalized Subsequent to Acquisition

5,263

Land and Improvements

324

Building and Improvements

10,595

Total

10,919

Accumulated Depreciation

$ 7,028

Year(s) Built/Renovated

1984

Depreciable Lives (Years)

^[2]

(1)

7501 Boston Boulevard, Building Seven [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

7501 Boston Boulevard, Building Seven

Office

Springfield, VA

$ 665

9,273

Costs Capitalized Subsequent to Acquisition

544

Land and Improvements

791

Building and Improvements

9,691

Total

10,482

Accumulated Depreciation

$ 3,410

Year(s) Built/Renovated

1997

Depreciable Lives (Years)

^[2]

(1)

33 Hayden Avenue [Member]

Real Estate and Accumulated Depreciation [Line Items]

33 Hayden Avenue

Office

Lexington, MA

$ 266

3,234

Costs Capitalized Subsequent to Acquisition

6,042

Land and Improvements

425

Building and Improvements

9,117

Total

9,542

Accumulated Depreciation

$ 6,740

Year(s) Built/Renovated

1979

Depreciable Lives (Years)

^[2]

(1)

7435 Boston Boulevard, Building One [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

7435 Boston Boulevard, Building One

Office

Springfield, VA

$ 392

3,822

Costs Capitalized Subsequent to Acquisition

3,734

Land and Improvements

659

Building and Improvements

7,289

Total

7,948

Accumulated Depreciation

$ 4,793

Year(s) Built/Renovated

1982

Depreciable Lives (Years)

^[2]

(1)

7450 Boston Boulevard, Building Three [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

7450 Boston Boulevard, Building Three

Office

Springfield, VA

$ 1,165

4,681

Costs Capitalized Subsequent to Acquisition

1,915

Land and Improvements

1,430

Building and Improvements

6,331

Total

7,761

Accumulated Depreciation

$ 2,568

Year(s) Built/Renovated

1987

Depreciable Lives (Years)

^[2]

(1)

8000 Grainger Court, Building Five [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

8000 Grainger Court, Building Five

Office

Springfield, VA

$ 366

4,282

Costs Capitalized Subsequent to Acquisition

2,745

Land and Improvements

601

Building and Improvements

6,792

Total

7,393

Accumulated Depreciation

$ 4,531

Year(s) Built/Renovated

1984

Depreciable Lives (Years)

^[2]

(1)

7500 Boston Boulevard, Building Six [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

7500 Boston Boulevard, Building Six

Office

Springfield, VA

$ 138

3,749

Costs Capitalized Subsequent to Acquisition

2,302

Land and Improvements

406

Building and Improvements

5,783

Total

6,189

Accumulated Depreciation

$ 3,711

Year(s) Built/Renovated

1985

Depreciable Lives (Years)

^[2]

(1)

7601 Boston Boulevard, Building Eight [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

7601 Boston Boulevard, Building Eight

Office

Springfield, VA

$ 200

878

Costs Capitalized Subsequent to Acquisition

4,875

Land and Improvements

551

Building and Improvements

5,402

Total

5,953

Accumulated Depreciation

$ 3,251

Year(s) Built/Renovated

1986

Depreciable Lives (Years)

^[2]

(1)

Fourteen Cambridge Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Fourteen Cambridge Center

Office

Cambridge, MA

$ 110

4,483

Costs Capitalized Subsequent to Acquisition

1,223

Land and Improvements

273

Building and Improvements

5,543

Total

5,816

Accumulated Depreciation

$ 3,529

Year(s) Built/Renovated

1983

Depreciable Lives (Years)

^[2]

(1)

7300 Boston Boulevard, Building Thirteen [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

7300 Boston Boulevard, Building Thirteen

Office

Springfield, VA

$ 608

4,773

Costs Capitalized Subsequent to Acquisition

230

Land and Improvements

661

Building and Improvements

4,950

Total

5,611

Accumulated Depreciation

$ 3,231

Year(s) Built/Renovated

2002

Depreciable Lives (Years)

^[2]

(1)

8000 Corporate Court, Building Eleven [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

8000 Corporate Court, Building Eleven

Office

Springfield, VA

$ 136

3,071

Costs Capitalized Subsequent to Acquisition

1,483

Land and Improvements

775

Building and Improvements

3,915

Total

4,690

Accumulated Depreciation

$ 2,089

Year(s) Built/Renovated

1989

Depreciable Lives (Years)

^[2]

(1)

7375 Boston Boulevard, Building Ten [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

7375 Boston Boulevard, Building Ten

Office

Springfield, VA

$ 23

2,685

Costs Capitalized Subsequent to Acquisition

1,007

Land and Improvements

Building and Improvements

3,622

Total

3,715

Accumulated Depreciation

$ 2,049

Year(s) Built/Renovated

1988

Depreciable Lives (Years)

^[2]

(1)

7374 Boston Boulevard, Building Four [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

7374 Boston Boulevard, Building Four

Office

Springfield, VA

$ 241

1,605

Costs Capitalized Subsequent to Acquisition

1,714

Land and Improvements

398

Building and Improvements

3,162

Total

3,560

Accumulated Depreciation

$ 2,103

Year(s) Built/Renovated

1984

Depreciable Lives (Years)

^[2]

(1)

7451 Boston Boulevard, Building Two [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

7451 Boston Boulevard, Building Two

Office

Springfield, VA

$ 249

1,542

Costs Capitalized Subsequent to Acquisition

1,313

Land and Improvements

613

Building and Improvements

2,491

Total

3,104

Accumulated Depreciation

$ 2,017

Year(s) Built/Renovated

1982

Depreciable Lives (Years)

^[2]

(1)

164 Lexington Road [Member]

Real Estate and Accumulated Depreciation [Line Items]

164 Lexington Road

Office

Billerica, MA

$ 592

1,370

Costs Capitalized Subsequent to Acquisition

349

Land and Improvements

643

Building and Improvements

1,668

Total

2,311

Accumulated Depreciation

$ 650

Year(s) Built/Renovated

1982

Depreciable Lives (Years)

^[2]

(1)

32 Hartwell Avenue [Member]

Real Estate and Accumulated Depreciation [Line Items]

32 Hartwell Avenue

Office

Lexington, MA

$ 168

1,943

Costs Capitalized Subsequent to Acquisition

150

Land and Improvements

314

Building and Improvements

1,947

Total

2,261

Accumulated Depreciation

$ 1,359

Year(s) Built/Renovated

1968-1979/1987

Depreciable Lives (Years)

^[2]

(1)

17 Hartwell Avenue [Member]

Real Estate and Accumulated Depreciation [Line Items]

17 Hartwell Avenue

Office

Lexington, MA

$ 26

150

Costs Capitalized Subsequent to Acquisition

778

Land and Improvements

Building and Improvements

889

Total

954

Accumulated Depreciation

$ 416

Year(s) Built/Renovated

1968

Depreciable Lives (Years)

^[2]

(1)

Residences on The Avenue, 2221 I St., NW [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Residences on The Avenue, 2221 I St., NW

Type

Residential

Location

Washington, DC

Original Building

$ 119,874

Building and Improvements

119,874

Total

119,874

Accumulated Depreciation

$ 1,764

Year(s) Built/Renovated

2011

Depreciable Lives (Years)

^[2]

(1)

The Lofts At Atlantic Wharf [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

The Lofts at Atlantic Wharf

Residential

Boston, MA

$ 3,529

54,891

Land and Improvements

3,529

Building and Improvements

54,891

Total

58,420

Accumulated Depreciation

$ 673

Year(s) Built/Renovated

2011

Depreciable Lives (Years)

^[2]

(1)

Cambridge Center Marriott [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Cambridge Center Marriott

Hotel

Cambridge, MA

$ 478

37,918

Costs Capitalized Subsequent to Acquisition

33,215

Land and Improvements

1,201

Building and Improvements

70,410

Total

71,611

Accumulated Depreciation

$ 40,030

Year(s) Built/Renovated

1986

Depreciable Lives (Years)

^[2]

(1)

Cambridge Center East Garage [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Cambridge Center East Garage

Type

Garage

Location

Cambridge, MA

Original Building

$ 35,035

Costs Capitalized Subsequent to Acquisition

1,487

Land and Improvements

103

Building and Improvements

36,419

Total

36,522

Accumulated Depreciation

$ 4,758

Year(s) Built/Renovated

1984

Depreciable Lives (Years)

^[2]

(1)

Cambridge Center West Garage [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Cambridge Center West Garage

Garage

Cambridge, MA

$ 1,256

15,697

Costs Capitalized Subsequent to Acquisition

1,158

Land and Improvements

1,434

Building and Improvements

16,677

Total

18,111

Accumulated Depreciation

$ 2,538

Year(s) Built/Renovated

2006

Depreciable Lives (Years)

^[2]

(1)

Cambridge Center North Garage [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Cambridge Center North Garage

Garage

Cambridge, MA

$ 1,163

11,633

Costs Capitalized Subsequent to Acquisition

2,750

Land and Improvements

1,579

Building and Improvements

13,967

Total

15,546

Accumulated Depreciation

$ 7,334

Year(s) Built/Renovated

1990

Depreciable Lives (Years)

^[2]

(1)

250 West 55th Street [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

250 West 55th Street

Type

Development

Location

New York, NY

Costs Capitalized Subsequent to Acquisition

$ 527,964

Development and Construction in Progress

527,964

Total

$ 527,964

Year(s) Built/Renovated

N/A

Depreciable Lives (Years)

N/A

510 Madison Avenue [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

510 Madison Avenue

Type

Development

Location

New York, NY

Costs Capitalized Subsequent to Acquisition

$ 345,910

Land and Improvements

45,320

Building and Improvements

109,867

Development and Construction in Progress

190,723

Total

345,910

Accumulated Depreciation

$ 1,112

Year(s) Built/Renovated

N/A

Depreciable Lives (Years)

N/A

12310 Sunrise Valley Drive [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

12310 Sunrise Valley Drive

Development

Reston, VA

$ 9,367

67,431

Costs Capitalized Subsequent to Acquisition

63,419

Land and Improvements

11,343

Building and Improvements

74,052

Development and Construction in Progress

54,822

Total

140,217

Accumulated Depreciation

$ 48,852

Year(s) Built/Renovated

1987/1988

Depreciable Lives (Years)

^[2]

(1)

Reston Town Center Residential [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Reston Town Center Residential

Type

Development

Location

Reston, VA

Costs Capitalized Subsequent to Acquisition

$ 24,969

Development and Construction in Progress

24,969

Total

$ 24,969

Year(s) Built/Renovated

N/A

Depreciable Lives (Years)

N/A

17 Cambridge Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

17 Cambridge Center

Type

Development

Location

Cambridge, MA

Costs Capitalized Subsequent to Acquisition

$ 20,207

Development and Construction in Progress

20,207

Total

$ 20,207

Year(s) Built/Renovated

N/A

Depreciable Lives (Years)

N/A

Plaza at Almaden [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Plaza at Almaden

Type

Land

Location

San Jose, CA

Costs Capitalized Subsequent to Acquisition

$ 37,306

Land Held for Development

37,306

Total

$ 37,306

Year(s) Built/Renovated

N/A

Depreciable Lives (Years)

N/A

Springfield Metro Center [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Springfield Metro Center

Type

Land

Location

Springfield, VA

Costs Capitalized Subsequent to Acquisition

$ 31,845

Land Held for Development

31,845

Total

$ 31,845

Year(s) Built/Renovated

N/A

Depreciable Lives (Years)

N/A

Tower Oaks Master Plan [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Tower Oaks Master Plan

Type

Land

Location

Rockville, MD

Costs Capitalized Subsequent to Acquisition

$ 28,619

Land Held for Development

28,619

Total

$ 28,619

Year(s) Built/Renovated

N/A

Depreciable Lives (Years)

N/A

Prospect Hill [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Prospect Hill

Type

Land

Location

Waltham, MA

Costs Capitalized Subsequent to Acquisition

$ 23,819

Building and Improvements

667

Land Held for Development

23,152

Total

$ 23,819

Year(s) Built/Renovated

N/A

Depreciable Lives (Years)

N/A

Washingtonian North [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Washingtonian North

Type

Land

Location

Gaithersburg, MD

Costs Capitalized Subsequent to Acquisition

$ 17,704

Land Held for Development

17,704

Total

$ 17,704

Year(s) Built/Renovated

N/A

Depreciable Lives (Years)

N/A

103 4th Avenue [Member]

Real Estate and Accumulated Depreciation [Line Items]

103 4th Avenue

Land

Waltham, MA

$ 11,911

Land Held for Development

11,911

Total

$ 11,911

Year(s) Built/Renovated

N/A

Depreciable Lives (Years)

N/A

Cambridge Master Plan [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Cambridge Master Plan

Type

Land

Location

Cambridge, MA

Costs Capitalized Subsequent to Acquisition

$ 10,693

Land Held for Development

10,693

Total

$ 10,693

Year(s) Built/Renovated

N/A

Depreciable Lives (Years)

N/A

Reston Gateway [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Reston Gateway

Type

Land

Location

Reston, VA

Costs Capitalized Subsequent to Acquisition

$ 9,458

Land Held for Development

9,458

Total

$ 9,458

Year(s) Built/Renovated

N/A

Depreciable Lives (Years)

N/A

Reston Eastgate [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Reston Eastgate

Type

Land

Location

Reston, VA

Costs Capitalized Subsequent to Acquisition

$ 8,772

Land Held for Development

8,772

Total

$ 8,772

Year(s) Built/Renovated

N/A

Depreciable Lives (Years)

N/A

Crane Meadow [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Crane Meadow

Type

Land

Location

Marlborough, MA

Costs Capitalized Subsequent to Acquisition

$ 8,723

Land Held for Development

8,723

Total

$ 8,723

Year(s) Built/Renovated

N/A

Depreciable Lives (Years)

N/A

Broad Run Business Park [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

Broad Run Business Park

Type

Land

Location

Loudon County, VA

Costs Capitalized Subsequent to Acquisition

$ 7,729

Land and Improvements

1,621

Land Held for Development

6,108

Total

$ 7,729

Year(s) Built/Renovated

N/A

Depreciable Lives (Years)

N/A

30 Shattuck Road [Member]

Real Estate and Accumulated Depreciation [Line Items]

Property Name

30 Shattuck Road

Type

Land

Location

Andover, MA

Costs Capitalized Subsequent to Acquisition

$ 1,161

Land Held for Development

1,161

Total

$ 1,161

Year(s) Built/Renovated

N/A

Depreciable Lives (Years)

N/A

[1]	Includes the unamortized balance of the historical fair value adjustment totaling approximately $23.8 million.
[2]	Depreciation of the buildings and improvements are calculated over lives ranging from the life of the lease to 40 years.

Real Estate And Accumulated Depreciation (Activity Of Real Estate And Accumulated Depreciation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Real Estate And Accumulated Depreciation [Abstract]
Real Estate, Balance at the beginning of the year	$ 12,740,892	$ 11,075,879	$ 10,602,278
Real Estate, Additions to/improvements of real estate	668,084	1,669,926	481,237
Real Estate, Assets sold/written-off	(45,863)	(4,913)	(7,636)
Real Estate, Balance at the end of the year	13,363,113	12,740,892	11,075,879
Accumulated Depreciation, Balance at the beginning of the year	2,308,665	2,020,056	1,755,600
Accumulated Depreciation, Depreciation expense	362,636	292,561	269,394
Accumulated Depreciation, Assets sold/written-off	(44,977)	(3,952)	(4,938)
Accumulated Depreciation, Balance at the end of the year	$ 2,626,324	$ 2,308,665	$ 2,020,056