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Document And Entity Information - shares	9 Months Ended
Document And Entity Information - shares	Sep. 30, 2011	Nov. 01, 2011
Document And Entity Information [Abstract]
Document Type	10-Q
Document Period End Date	Sep. 30, 2011
Document Fiscal Year Focus	2011
Document Fiscal Period Focus	Q3
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		147,629,307

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2011	Dec. 31, 2010
ASSETS
Real estate, at cost	$ 12,031,660	$ 10,933,977
Construction in process	899,302	1,073,402
Land held for future development	266,834	757,556
Less: accumulated depreciation	(2,558,620)	(2,323,818)
Total real estate	10,639,176	10,441,117
Cash and cash equivalents	1,063,024	478,948
Cash held in escrows	36,759	308,031
Investments in securities	9,312	8,732
Tenant and other receivables (net of allowance for doubtful accounts of $1,650 and $2,081, respectively)	47,554	60,813
Related party notes receivable	276,375	270,000
Interest receivable from related party note receivable	84,782	69,005
Accrued rental income (net of allowance of $2,356 and $3,116, respectively)	508,838	442,683
Deferred charges, net	441,700	436,019
Prepaid expenses and other assets	102,812	65,663
Investments in unconsolidated joint ventures	770,466	767,252
Total assets	13,980,798	13,348,263
Liabilities:
Mortgage notes payable	3,179,034	3,047,586
Unsecured senior notes (net of discount of $8,014 and $8,402, respectively)	3,016,986	3,016,598
Unsecured exchangeable senior notes (net of discount of $4,699 and $8,249, respectively)	1,754,343	1,721,817
Unsecured line of credit
Accounts payable and accrued expenses	172,928	186,059
Dividends and distributions payable	83,584	81,031
Accrued interest payable	89,555	62,327
Other liabilities	244,555	213,000
Total liabilities	8,540,985	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, 147,706,147 and 140,278,005 issued and 147,627,247 and 140,199,105 outstanding at September 30, 2011 and December 31, 2010, respectively	1,476	1,402
Additional paid-in capital	4,916,440	4,417,162
Dividends in excess of earnings	(72,941)	(24,763)
Treasury common stock at cost, 78,900 shares at September 30, 2011 and December 31, 2010	(2,722)	(2,722)
Accumulated other comprehensive loss	(16,717)	(18,436)
Total stockholders' equity attributable to Boston Properties, Inc.	4,825,536	4,372,643
Noncontrolling interests:
Common units of the Operating Partnership	559,621	592,164
Property partnerships	(996)	(614)
Total equity	5,384,161	4,964,193
Total liabilities and equity	$ 13,980,798	$ 13,348,263

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2011	Dec. 31, 2010
Consolidated Balance Sheets [Abstract]
Tenant and other receivables, allowance for doubtful accounts	$ 1,650	$ 2,081
Accrued rental income, allowance	2,356	3,116
Unsecured senior notes, discount	8,014	8,402
Unsecured exchangeable senior notes, discount	$ 4,669	$ 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	147,706,147	140,278,005
Common stock, shares outstanding	147,627,247	140,199,105
Treasury common stock at cost, shares	78,900	78,900

Consolidated Statements Of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Revenue
Base rent	$ 360,595	$ 310,459	$ 1,048,604	$ 918,665
Recoveries from tenants	53,899	45,646	148,669	135,530
Parking and other	21,694	15,850	61,863	47,570
Total rental revenue	436,188	371,955	1,259,136	1,101,765
Hotel revenue	8,045	8,016	22,897	22,290
Development and management services	8,180	6,439	24,706	34,267
Total revenue	452,413	386,410	1,306,739	1,158,322
Expenses
Rental	154,985	128,041	439,831	376,310
Hotel	6,032	6,194	18,052	17,551
General and administrative	17,340	18,067	62,052	62,537
Acquisition costs	51	1,893	136	1,893
Suspension of development				(7,200)
Depreciation and amortization	109,495	81,133	330,003	245,608
Total expenses	287,903	235,328	850,074	696,699
Operating income	164,510	151,082	456,665	461,623
Income from unconsolidated joint ventures	11,326	11,565	28,184	26,940
Interest and other income	1,252	1,814	4,179	5,641
Gains (losses) from investments in securities	(860)	731	(481)	253
Interest expense	(95,777)	(97,103)	(290,164)	(285,887)
Losses from early extinguishments of debt				(8,221)
Income from continuing operations	80,451	68,089	198,383	200,349
Gain on sale of real estate				2,734
Net income	80,451	68,089	198,383	203,083
Net income attributable to noncontrolling interests
Noncontrolling interests in property partnerships	(86)	(889)	(1,118)	(2,557)
Noncontrolling interest-redeemable preferred units of the Operating Partnership	(832)	(820)	(2,497)	(2,548)
Noncontrolling interest-common units of the Operating Partnership	(8,991)	(8,712)	(23,409)	(25,841)
Noncontrolling interest in gain on sale of real estate-common units of the Operating Partnership				(351)
Net income attributable to Boston Properties, Inc.	$ 70,542	$ 57,668	$ 171,359	$ 171,786
Basic earnings per common share attributable to Boston Properties, Inc.:
Net income	$ 0.48	$ 0.41	$ 1.18	$ 1.23
Weighted average number of common shares outstanding	147,006	139,595	145,006	139,215
Diluted earnings per common share attributable to Boston Properties, Inc.:
Net income	$ 0.48	$ 0.41	$ 1.18	$ 1.23
Weighted average number of common and common equivalent shares outstanding	147,622	140,193	145,625	139,874

Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Consolidated Statements Of Comprehensive Income [Abstract]
Net income	$ 80,451	$ 68,089	$ 198,383	$ 203,083
Other comprehensive income:
Effective portion of interest rate contracts				421
Amortization of interest rate contracts	649	716	1,946	2,157
Other comprehensive income	649	716	1,946	2,578
Comprehensive income	81,100	68,805	200,329	205,661
Net income attributable to noncontrolling interests	(9,909)	(10,421)	(27,024)	(31,297)
Other comprehensive income attributable to noncontrolling interests	(72)	(91)	(227)	(331)
Comprehensive income attributable to Boston Properties, Inc.	$ 71,119	$ 58,293	$ 173,078	$ 174,033

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, 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
Statement of Stockholders' Equity [Line Items]
Conversion of operating partnership units to Common Stock, shares	473,000
Conversion of operating partnership units to Common Stock, value	$ 5	13,743				(13,748)
Reallocation of noncontrolling interest		12,944				(12,944)
Allocated net income for the year			171,786			28,749	200,535
Dividends/distributions declared			(209,168)			(32,069)	(241,237)
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	696,000
Net activity from stock option and incentive plan, value	$ 7	23,715				24,306	48,028
Distributions to noncontrolling interests in property partnerships						(1,500)	(1,500)
Amortization of interest rate contracts					2,247	331	2,578
Equity, value at Sep. 30, 2010	$ 1,401	4,424,711	58,051	(2,722)	(19,530)	616,182	5,078,093
Equity, shares at Sep. 30, 2010	140,058,000
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
Statement of Stockholders' Equity [Line Items]
Conversion of operating partnership units to Common Stock, shares	2,443,000
Conversion of operating partnership units to Common Stock, value	$ 24	71,157				(71,181)
Reallocation of noncontrolling interest		(26,755)				26,755
Allocated net income for the year			171,359			24,527	$ 195,886
Dividends/distributions declared			(219,537)			(29,120)	(248,657)
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	7,000
Shares issued pursuant to stock purchase plan, value		620					620
Net activity from stock option and incentive plan, shares	318,000
Net activity from stock option and incentive plan, value	$ 3	15,266				17,367	32,636
Distributions to noncontrolling interests in property partnerships						(1,500)	(1,500)
Amortization of interest rate contracts					1,719	227	1,946
Equity, value at Sep. 30, 2011	$ 1,476	$ 4,916,440	$ (72,941)	$ (2,722)	$ (16,717)	$ 558,625	$ 5,384,161
Equity, shares at Sep. 30, 2011	147,627,000						147,627,247

Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Cash flows from operating activities:
Net income	$ 198,383	$ 203,083
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	330,003	245,608
Non-cash compensation expense	23,702	26,725
Income from unconsolidated joint ventures	(28,184)	(26,940)
Distributions of net cash flow from operations of unconsolidated joint ventures	27,222	9,189
Losses (gains) from investments in securities	481	(253)
Non-cash portion of interest expense	41,016	42,199
Settlement of accreted debt discount on repurchases of unsecured exchangeable senior notes		(13,230)
Losses from early extinguishments of debt		8,221
Suspension of development		(7,200)
Gain on sale of real estate		(2,734)
Change in assets and liabilities:
Cash held in escrows	(6,228)	(1,404)
Tenant and other receivables, net	13,097	2,922
Accrued rental income, net	(66,155)	(57,887)
Prepaid expenses and other assets	(66,597)	(24,107)
Accounts payable and accrued expenses	5,341	(30,720)
Accrued interest payable	27,228	8,631
Other liabilities	(15,664)	(19,998)
Tenant leasing costs	(40,786)	(29,251)
Total adjustments	244,476	129,771
Net cash provided by operating activities	442,859	332,854
Cash flows from investing activities:
Acquisitions of real estate	(41,100)	(103,785)
Construction in progress	(205,580)	(233,814)
Building and other capital improvements	(29,406)	(14,377)
Tenant improvements	(50,400)	(91,742)
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)
Acquisitions of note receivable		(22,500)
Issuance of note receivable	(6,375)
Capital contributions to unconsolidated joint ventures	(17,867)	(61,426)
Capital distributions from unconsolidated joint ventures		27,150
Investments in securities, net	(1,061)	2,288
Net cash used in investing activities	(30,402)	(775,706)
Cash flows from financing activities:
Proceeds from mortgage notes payable	1,178,306	268,964
Repayments of mortgage notes payable	(1,196,074)	(301,531)
Proceeds from unsecured senior notes		699,237
Repurchases of unsecured exchangeable senior notes		(172,294)
Deposit on mortgage loan financing
Deferred financing costs	(9,103)	(7,563)
Net proceeds from ATM stock issuances	439,037
Net proceeds from equity transactions	9,554	21,933
Dividends and distributions	(248,601)	(243,253)
Distributions to noncontrolling interest in property partnership	(1,500)	(1,500)
Net cash provided by financing activities	171,619	263,993
Net increase in cash and cash equivalents	584,076	(178,859)
Cash and cash equivalents, beginning of period	478,948	1,448,933
Cash and cash equivalents, end of period	1,063,024	1,270,074
Supplemental disclosures:
Cash paid for interest	258,121	274,699
Interest capitalized	36,201	26,412
Non-cash investing and financing activities:
Additions to real estate included in accounts payable	15,161	6,927
Mortgage note payable assumed in connection with the acquisition of real estate	143,900	202,604
Note receivable converted to real estate		22,500
Dividends and distributions declared but not paid	83,584	81,068
Conversions of noncontrolling interests to stockholders' equity	71,181	13,748
Issuance of restricted securities to employees and directors	$ 25,087	$ 19,222

Organization

9 Months Ended

Sep. 30, 2011

Organization [Abstract]

Organization

1. 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 September 30, 2011 owned an approximate 88.0% (86.2% at September 30, 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 Notes 8 and 11).

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 is obligated to 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 11).

At September 30, 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 or redeemed for cash at the election of the holder thereof or the Operating Partnership in accordance with the terms and conditions set forth in the applicable amendment to the partnership agreement (See Note 8).

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

Properties

At September 30, 2011, the Company owned or had interests in a portfolio of 153 commercial real estate properties (the "Properties") aggregating approximately 42.3 million net rentable square feet, including seven properties under construction totaling approximately 2.9 million net rentable square feet. In addition, the Company has structured parking for approximately 43,899 vehicles containing approximately 14.8 million square feet. At September 30, 2011, the Properties consist of:

•

147office properties, including 128 Class A office properties (including seven properties under construction) and 19 Office/Technical properties;

•

onehotel;

•

threeretail properties; and

•

tworesidential properties.

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 September 30, 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, 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.

- 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
-Name FASB Interpretation (FIN)
-Publisher FASB
-Number 46R
-Paragraph 4, 14, 15
-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
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+ Details

Basis Of Presentation And Summary Of Significant Accounting Policies

9 Months Ended

Sep. 30, 2011

Basis Of Presentation And Summary Of Significant Accounting Policies [Abstract]

Basis Of Presentation And Summary Of Significant Accounting Policies

2. Basis of Presentation and Summary of Significant Accounting Policies

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.

The accompanying interim financial statements are unaudited; however, the financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America for interim financial information and in conjunction with the rules and regulations of the Securities and Exchange Commission. Accordingly, they do not include all of the disclosures required by accounting principles generally accepted in the United States of America for complete financial statements. In the opinion of management, all adjustments (consisting solely of normal recurring matters) necessary for a fair statement of the financial statements for these interim periods have been included. The results of operations for the interim periods are not necessarily indicative of the results to be obtained for other interim periods or for the full fiscal year. The year-end consolidated balance sheet data was derived from audited financial statements, but does not include all disclosure required by accounting principles generally accepted in the United States of America. These financial statements should be read in conjunction with the Company's financial statements and notes thereto contained in the Company's Annual Report in the Company's Form 10-K for its fiscal year ended December 31, 2010. Certain prior year amounts have been reclassified to conform to the current year presentation.

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 September 30, 2011 and December 31, 2010 (in thousands):


	September 30, 2011					December 31, 2010
	Carrying Amount			Estimated Fair Value		Carrying Amount			Estimated Fair Value
Mortgage notes payable	$	3,179,034		$	3,337,861	$	3,047,586		$	3,121,193
Unsecured senior notes		3,016,986			3,073,469		3,016,598			3,241,542
Unsecured exchangeable senior notes		1,754,343	(1)		1,909,227		1,721,817	(1)		1,929,291

Total	$	7,950,363		$	8,320,557	$	7,786,001		$	8,292,026

(1)	Includes the net impact of Accounting Standards Codification ("ASC") ASC 470-20 (formerly known as FSP No. APB 14-1) totaling approximately $64.7 million and $93.6 million at September 30, 2011 and December 31, 2010, respectively.

Real Estate Activity During The Nine Months Ended September 30, 2011

9 Months Ended

Sep. 30, 2011

Real Estate Activity During The Nine Months Ended September 30, 2011 [Abstract]

Real Estate Activity During The Nine Months Ended September 30, 2011

3. Real Estate Activity During the Nine Months Ended September 30, 2011

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 966,000 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

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 for the remainder of 2011 and each of the four succeeding years (in thousands).


	Acquired In-Place Lease Intangibles		Acquired Net Above- Market Lease Intangibles
Period from October 1, 2011 through December 31, 2011	$	1,574	$	158
2012		5,192		520
2013		3,423		349
2014		2,543		221
2015		1,867		300

The accompanying pro forma information for the nine months ended September 30, 2011 and 2010 is presented as if the acquisition of Bay Colony Corporate Center on February 1, 2011 had occurred on January 1, 2010. This 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 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	Nine Months Ended September 30,
(in thousands, except per share data)	2011		2010
Total revenue	$	1,309,084	$	1,172,640
Income from continuing operations	$	198,209	$	193,864
Net income attributable to Boston Properties, Inc.	$	171,205	$	166,133
Basic earnings per share:
Net income per share attributable to Boston Properties, Inc.	$	1.18	$	1.19
Diluted earnings per share:
Net income per share attributable to Boston Properties, Inc.	$	1.18	$	1.19

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 790,000 net rentable square feet.

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 457,000 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 10,000 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.

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, to 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 September 30, 2011, the Company has received approximately $48.0 million and anticipates receiving another $8.9 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

Investments In Unconsolidated Joint Ventures

9 Months Ended

Sep. 30, 2011

Investments In Unconsolidated Joint Ventures [Abstract]

Investments In Unconsolidated Joint Ventures

4. Investments in Unconsolidated Joint Ventures

The investments in unconsolidated joint ventures consist of the following at September 30, 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 Venture LLC	Eighth Avenue and 46th Street		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	%
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 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.

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 balance sheets of the unconsolidated joint ventures are as follows:


	September 30, 2011			December 31, 2010
	(in thousands)
ASSETS
Real estate and development in process, net	$	4,991,083		$	5,028,851
Other assets		680,091			749,308

Total assets	$	5,671,174		$	5,778,159

LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Mortgage and notes payable	$	3,139,362		$	3,151,220
Other liabilities		907,144			969,082
Members'/Partners' equity		1,624,668			1,657,857

Total liabilities and members'/partners' equity	$	5,671,174		$	5,778,159

Company's share of equity	$	898,910		$	924,235
Basis differentials(1)		(128,444	)		(156,983	)

Carrying value of the Company's investments in unconsolidated joint ventures	$	770,466		$	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.

The combined summarized statements of operations of the unconsolidated joint ventures are as follows:


	For the three months ended September 30,						For the nine months ended September 30,
	2011			2010			2011			2010
	(in thousands)						(in thousands)
Total revenue(1)	$	150,101		$	155,126		$	440,733		$	457,217
Expenses
Operating		44,584			45,546			129,698			130,083
Depreciation and amortization		46,773			50,548			145,653			164,763

Total expenses		91,357			96,094			275,351			294,846
Operating income		58,744			59,032			165,382			162,371
Other expenses
Interest expense		57,699			59,120			172,467			176,705
Loss on guarantee obligation		—			3,581			—			3,581
Impairment loss		39,384			—			39,384			—

Net loss	$	(38,339	)	$	(3,669	)	$	(46,469	)	$	(17,915	)

Company's share of net loss	$	(23,231	)	$	(487	)	$	(28,570	)	$	(7,207	)
Basis differential		25,024			3,125			28,539			7,918
Elimination of inter-entity interest on partner loan		9,533			8,927			28,215			26,229

Income from unconsolidated joint ventures	$	11,326		$	11,565		$	28,184		$	26,940

(1)

Includes straight-line rent adjustments of $6.7 million and $5.9 million for the three months ended September 30, 2011 and 2010, respectively, and $14.8 million and $19.8 million for the nine months ended September 30, 2011 and 2010, respectively. Includes net "above-" and "below-market" rent adjustments of $28.3 million and $30.5 million for the three months ended September 30, 2011 and 2010, respectively, and $87.0 million and $97.6 million for the nine months ended September 30, 2011 and 2010, 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 bears 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 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 (See Note 13).

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 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 $6.4 million has been advanced. The loan from the Operating Partnership bears interest at a fixed rate of 10.0% per annum and matures on May 31, 2014.

On August 12, 2011, an unconsolidated joint venture in which the Company has a 60% interest entered into an agreement to sell 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 (See Note 13). 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 $425.7 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 of approximately $39.4 million, which is equal to the difference between the sale price less cost to sell and the carrying value of the net assets of the property. Because the Company had previously recognized an impairment loss on its investment in the unconsolidated joint venture 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")), no additional impairment loss has been recognized by the Company.

- 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	9 Months Ended
Mortgage Notes Payable	Sep. 30, 2011
Mortgage Notes Payable [Abstract]
Mortgage Notes Payable	5. Mortgage Notes Payable On January 12, 2011, the Company notified the master servicer of the 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. 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 601 Lexington Avenue. 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.

Unsecured Line Of Credit	9 Months Ended
Unsecured Line Of Credit	Sep. 30, 2011
Unsecured Line Of Credit [Abstract]
Unsecured Line Of Credit	6. 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 5). At September 30, 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 September 30, 2011, the Company was in compliance with each of these financial and other covenant requirements.

Commitments And Contingencies	9 Months Ended
Commitments And Contingencies	Sep. 30, 2011
Commitments And Contingencies [Abstract]
Commitments And Contingencies	7. 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 $16.1 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 September 30, 2011, the maximum funding obligation under the guarantee was approximately $10.6 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 September 30, 2011, the remaining funding obligation under the guarantee was approximately $3.2 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. *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 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.

- Definition

The entire disclosure for commitments and contingencies.

+ References

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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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+ Details

Noncontrolling Interests

9 Months Ended

Sep. 30, 2011

Noncontrolling Interests [Abstract]

Noncontrolling Interests

8. 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 September 30, 2011, the noncontrolling interests consisted of 17,037,553 OP Units, 1,603,205 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 September 30, 2011 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. On May 14, 2013 and May 12, 2014, 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.

The following table reflects the activity of the noncontrolling interests—redeemable preferred units of the Operating Partnership for the nine months ended September 30, 2011 and 2010 (in thousands):


Balance at January 1, 2011	$	55,652
Net income		2,497
Distributions		(2,497	)

Balance at September 30, 2011	$	55,652


Balance at January 1, 2010	$	55,652
Net income		2,548
Distributions		(2,548	)

Balance at September 30, 2010	$	55,652

Noncontrolling Interest—Common Units of the Operating Partnership

During the nine months ended September 30, 2011, 2,442,407 OP Units were presented by the holders for redemption (including 58,213 OP Units issued upon conversion of LTIP Units) and were redeemed by the Company in exchange for an equal number of shares of Common Stock.

At September 30, 2011, the Company had outstanding 400,000 2011 OPP Units (See Note 10). 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 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.

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 September 16, 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 $0.50 per unit and a distribution on the 2011 OPP Units in the amount of $0.05 per unit, in each case payable on October 31, 2011 to holders of record as of the close of business on September 30, 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 September 30, 2011 was approximately $1.66 billion and $130.1 million, respectively, based on the closing price of the Company's common stock of $89.10 per share on September 30, 2011.

Noncontrolling Interest—Property Partnerships

The noncontrolling interests in property partnerships consist of the outside equity interest in 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 $(1.0) million at September 30, 2011 and approximately $(0.6) million at December 31, 2010, are included in Noncontrolling Interests—Property Partnerships on the accompanying Consolidated Balance Sheets.

- 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	9 Months Ended
Stockholders' Equity	Sep. 30, 2011
Stockholders' Equity [Abstract]
Stockholders' Equity	9. Stockholders' Equity As of September 30, 2011, the Company had 147,627,247 shares of Common Stock outstanding. During the nine months ended September 30, 2011, the Company utilized its initial "at the market" (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. This ATM stock offering program provided the Company with the ability to sell from time to time up to an aggregate of $400.0 million of its common stock through sales agents over a three-year period. 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 three months ended September 30, 2011, the Company issued an aggregate of 431,223 shares of stock under the ATM stock offering program for gross proceeds of approximately $44.9 million and net proceeds of approximately $44.4 million. As of September 30, 2011, approximately $555.1 million remained available for issuance under this ATM program. During the nine months ended September 30, 2011, the Company issued 312,711 shares of Common Stock upon the exercise of options to purchase Common Stock by certain employees. During the nine months ended September 30, 2011, the Company issued 2,442,407 shares of Common Stock in connection with the redemption of an equal number of OP Units. 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 September 16, 2011, the Company's Board of Directors declared a dividend in the amount of $0.50 per share of Common Stock payable on October 31, 2011 to shareholders of record as of the close of business on September 30, 2011.

- 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

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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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Reference 6: http://www.xbrl.org/2003/role/presentationRef
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+ Details

Earnings Per Share

9 Months Ended

Sep. 30, 2011

Earnings Per Share [Abstract]

Earnings Per Share

10. 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 three and nine months ended September 30, 2011, assuming the measurement period for the 2011 OPP Units ended on September 30, 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 325,000 2011 OPP Units. As a result, these 2011 OPP Units have been included in the diluted EPS calculation. For the three and nine months ended September 30, 2010, 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 three months ended September 30, 2011
	Income (Numerator)		Shares (Denominator)		Per Share Amount
	(in thousands, except for per share amounts)
Basic Earnings:
Net income attributable to Boston Properties, Inc.	$	70,542		147,006	$	0.48
Effect of Dilutive Securities:
Stock Based Compensation and Exchangeable Senior Notes		—		616		(0.00	)

Diluted Earnings:
Net income	$	70,542		147,622	$	0.48


	For the three months ended September 30, 2010
	Income (Numerator)		Shares (Denominator)		Per Share Amount
	(in thousands, except for per share amounts)
Basic Earnings:
Net income attributable to Boston Properties, Inc.	$	57,668		139,595	$	0.41
Effect of Dilutive Securities:
Stock Based Compensation and Exchangeable Senior Notes		—		598		(0.00	)

Diluted Earnings:
Net income	$	57,668		140,193	$	0.41


	For the nine months ended September 30, 2011
	Income (Numerator)		Shares (Denominator)		Per Share Amount
	(in thousands, except for per share amounts)
Basic Earnings:
Net income attributable to Boston Properties, Inc.	$	171,359		145,006	$	1.18
Effect of Dilutive Securities:
Stock Based Compensation		—		619		(0.00	)

Diluted Earnings:
Net income	$	171,359		145,625	$	1.18


	For the nine months ended September 30, 2010
	Income (Numerator)		Shares (Denominator)		Per Share Amount
	(in thousands, except for per share amounts)
Basic Earnings:
Net income attributable to Boston Properties, Inc.	$	171,786		139,215	$	1.23
Effect of Dilutive Securities:
Stock Based Compensation		—		659		(0.00	)

Diluted Earnings:
Net income	$	171,786		139,874	$	1.23

Stock Option and Incentive Plan	9 Months Ended
Stock Option and Incentive Plan	Sep. 30, 2011
Stock Option and Incentive Plan [Abstract]
Stock Option and Incentive Plan	11. Stock Option and Incentive Plan On January 20, 2011, the Compensation Committee of the Board of Directors of the Company approved outperformance awards under the Company's 1997 Stock Option and Incentive Plan (the "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, 2015 and 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 2011 OPP Units were valued at an aggregate of 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 total dividend payments over the measurement period of $6.10 per share. During the nine months ended September 30, 2011, the Company issued 19,030 shares of restricted common stock, 146,844 non-qualified stock options, 190,067 LTIP Units and 400,000 2011 OPP Units to employees and non-employee directors under the 1997 Plan. Employees and directors paid $0.01 per share of restricted common stock and $0.25 per LTIP Unit 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. Grants of restricted stock and LTIP Units 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 closing 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. The shares of restricted stock granted during the nine months ended September 30, 2011 were valued at approximately $1.8 million ($93.40 per share weighted-average). The non-qualified stock options granted during the nine months ended September 30, 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 LTIP Units granted during the nine months ended September 30, 2011 were valued at approximately $16.5 million ($86.74 per unit fair value weighted-average) using a Monte Carlo simulation method model. The per unit fair value of each LTIP Unit granted was estimated on the date of grant using the following assumptions: an expected life of 5.8 years, a risk-free interest rate of 2.22% and an expected price volatility of 30.0%. 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. Aggregate stock-based compensation expense associated with restricted stock, non-qualified stock options, LTIP Units, 2008 OPP Units and 2011 OPP Units was approximately $5.6 million and $6.1 million for the three months ended September 30, 2011 and 2010, respectively, and approximately $22.7 million and $26.0 million for the nine months ended September 30, 2011 and 2010, 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 nine months ended September 30, 2011. For the nine months ended September 30, 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 September 30, 2011, there was $29.5 million of unrecognized compensation expense related to unvested restricted stock and LTIP Units and $6.1 million of unrecognized compensation expense related to unvested 2011 OPP Units that is expected to be recognized over a weighted-average period of approximately 2.6 years.

- 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

Segment Information

9 Months Ended

Sep. 30, 2011

Segment Information [Abstract]

Segment Information

12. Segment Information

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 Greater Boston, Greater Washington, DC, Midtown Manhattan, Greater San Francisco and New Jersey. Segments by property type include: Class A Office, Office/Technical, Residential and Hotels.

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:

Three months ended September 30, 2011 (dollars in thousands):


	Greater Boston			Greater Washington, DC			Midtown Manhattan			Greater San Francisco			New Jersey			Total
Rental Revenue:
Class A	$	141,680		$	95,192		$	115,284		$	53,978		$	15,495		$	421,629
Office/Technical		7,871			4,235			—			—			—			12,106
Residential		284			2,169			—			—			—			2,453
Hotel		8,045			—			—			—			—			8,045

Total		157,880			101,596			115,284			53,978			15,495			444,233

% of Total		35.54	%		22.87	%		25.95	%		12.15	%		3.49	%		100.00	%
Real Estate Operating Expenses:
Class A		55,614			26,036			39,331			20,788			7,189			148,958
Office/Technical		2,501			1,108			—			—			—			3,609
Residential		270			2,148			—			—			—			2,418
Hotel		6,032			—			—			—			—			6,032

Total		64,417			29,292			39,331			20,788			7,189			161,017

% of Total		40.01	%		18.19	%		24.43	%		12.91	%		4.46	%		100.00	%

Net Operating Income	$	93,463		$	72,304		$	75,953		$	33,190		$	8,306		$	283,216

% of Total		33.00	%		25.53	%		26.82	%		11.72	%		2.93	%		100.00	%

Three months ended September 30, 2010 (dollars in thousands):


	Greater Boston			Greater Washington, DC			Midtown Manhattan			Greater San Francisco			New Jersey			Total
Rental Revenue:
Class A	$	94,016		$	84,708		$	111,383		$	54,268		$	16,041		$	360,416
Office/Technical		7,627			3,912			—			—			—			11,539
Residential		—			—			—			—			—			—
Hotel		8,016			—			—			—			—			8,016

Total		109,659			88,620			111,383			54,268			16,041			379,971

% of Total		28.86	%		23.32	%		29.32	%		14.28	%		4.22	%		100.00	%
Real Estate Operating Expenses:
Class A		36,082			24,243			35,908			20,317			8,081			124,631
Office/Technical		2,417			993			—			—			—			3,410
Residential		—			—			—			—			—			—
Hotel		6,194			—			—			—			—			6,194

Total		44,693			25,236			35,908			20,317			8,081			134,235

% of Total		33.29	%		18.80	%		26.75	%		15.14	%		6.02	%		100.00	%

Net Operating Income	$	64,966		$	63,384		$	75,475		$	33,951		$	7,960		$	245,736

% of Total		26.44	%		25.79	%		30.71	%		13.82	%		3.24	%		100.00	%

Nine months ended September 30, 2011 (dollars in thousands):


	Greater Boston			Greater Washington, DC			Midtown Manhattan			Greater San Francisco			New Jersey			Total
Rental Revenue:
Class A	$	405,234		$	265,286		$	341,698		$	161,039		$	47,585		$	1,220,842
Office/Technical		23,088			12,177			—			—			—			35,265
Residential		284			2,745			—			—			—			3,029
Hotel		22,897			—			—			—			—			22,897

Total		451,503			280,208			341,698			161,039			47,585			1,282,033

% of Total		35.22	%		21.86	%		26.65	%		12.56	%		3.71	%		100.00	%
Real Estate Operating Expenses:
Class A		154,580			74,221			114,423			60,241			22,591			426,056
Office/Technical		7,392			3,242			—			—			—			10,634
Residential		270			2,871			—			—			—			3,141
Hotel		18,052			—			—			—			—			18,052

Total		180,294			80,334			114,423			60,241			22,591			457,883

% of Total		39.38	%		17.54	%		24.99	%		13.16	%		4.93	%		100.00	%

Net Operating Income	$	271,209		$	199,874		$	227,275		$	100,798		$	24,994		$	824,150

% of Total		32.91	%		24.25	%		27.58	%		12.23	%		3.03	%		100.00	%

Nine months ended September 30, 2010 (dollars in thousands):


	Greater Boston			Greater Washington, DC			Midtown Manhattan			Greater San Francisco			New Jersey			Total
Rental Revenue:
Class A	$	273,702		$	251,126		$	332,301		$	160,899		$	49,046		$	1,067,074
Office/Technical		22,808			11,883			—			—			—			34,691
Residential		—			—			—			—			—			—
Hotel		22,290			—			—			—			—			22,290

Total		318,800			263,009			332,301			160,899			49,046			1,124,055

% of Total		28.36	%		23.40	%		29.56	%		14.32	%		4.36	%		100.00	%
Real Estate Operating Expenses:
Class A		103,481			69,968			110,177			59,047			23,710			366,383
Office/Technical		6,790			3,137			—			—			—			9,927
Residential		—			—			—			—			—			—
Hotel		17,551			—			—			—			—			17,551

Total		127,822			73,105			110,177			59,047			23,710			393,861

% of Total		32.46	%		18.56	%		27.97	%		14.99	%		6.02	%		100.00	%

Net Operating Income	$	190,978		$	189,904		$	222,124		$	101,852		$	25,336		$	730,194

% of Total		26.15	%		26.01	%		30.42	%		13.95	%		3.47	%		100.00	%

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


	Three months ended September 30,					Nine months ended September 30,
	2011		2010			2011		2010
Net Operating Income	$	283,216	$	245,736		$	824,150	$	730,194
Add:
Development and management services income		8,180		6,439			24,706		34,267
Income from unconsolidated joint ventures		11,326		11,565			28,184		26,940
Interest and other income		1,252		1,814			4,179		5,641
Gains on sales of real estate		—		—			—		2,734
Less:
General and administrative expense		17,340		18,067			62,052		62,537
Acquisition costs		51		1,893			136		1,893
Suspension of development		—		—			—		(7,200	)
Depreciation and amortization expense		109,495		81,133			330,003		245,608
Losses (gains) from investments in securities		860		(731	)		481		(253	)
Interest expense		95,777		97,103			290,164		285,887
Losses from early extinguishments of debt		—		—			—		8,221
Noncontrolling interest in property partnerships		86		889			1,118		2,557
Noncontrolling interest—redeemable preferred units of the Operating Partnership		832		820			2,497		2,548
Noncontrolling interest—common units of the Operating Partnership		8,991		8,712			23,409		25,841
Noncontrolling interest in gains on sales of real estate—common units of the Operating Partnership		—		—			—		351

Net income attributable to Boston Properties, Inc.	$	70,542	$	57,668		$	171,359	$	171,786

- 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)
-Number 131
-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 Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8981-108599

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8984-108599

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e9054-108599

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 40
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e9031-108599

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 31
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8924-108599

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8538-108599

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Section 50
-Paragraph 30
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8906-108599

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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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
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-Name Accounting Standards Codification
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-Paragraph 29
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Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Paragraph 33
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Reference 12: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 280
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-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
-Topic 280
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-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
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-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

Subsequent Events	9 Months Ended
Subsequent Events	Sep. 30, 2011
Subsequent Events [Abstract]
Subsequent Events	13. Subsequent Events On October 14, 2011, an unconsolidated joint venture in which the Company has a 30% interest obtained construction financing totaling $107.0 million collateralized by its 500 North Capitol Street, NW redevelopment project located in Washington, DC. 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 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 $209.8 million, of which the Company's share was approximately $125.9 million, after the payment of transaction costs of approximately $14.6 million. Two Grand Central Tower is an approximately 650,000 net rentable square foot Class A office tower. On November 3, 2011, the Company's Operating Partnership agreed to sell $850.0 million of 3.700% senior unsecured notes due 2018 in an underwritten public offering. 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 offering is expected to close on November 10, 2011. The estimated net proceeds from the offering are expected to be approximately $841.2 million after deducting underwriting discounts and estimated transaction expenses. On November 4, 2011, the Company's Operating Partnership agreed to repurchase approximately $50.0 million aggregate principal amount of its 2.875% exchangeable senior notes due 2037 for approximately $50.2 million. The repurchase is expected to settle on November 9, 2011.

Basis Of Presentation And Summary Of Significant Accounting Policies (Policy)	9 Months Ended
	Sep. 30, 2011
Basis Of Presentation And Summary Of Significant Accounting Policies [Abstract]
Accounting Policies	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. The accompanying interim financial statements are unaudited; however, the financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America for interim financial information and in conjunction with the rules and regulations of the Securities and Exchange Commission. Accordingly, they do not include all of the disclosures required by accounting principles generally accepted in the United States of America for complete financial statements. In the opinion of management, all adjustments (consisting solely of normal recurring matters) necessary for a fair statement of the financial statements for these interim periods have been included. The results of operations for the interim periods are not necessarily indicative of the results to be obtained for other interim periods or for the full fiscal year. The year-end consolidated balance sheet data was derived from audited financial statements, but does not include all disclosure required by accounting principles generally accepted in the United States of America. These financial statements should be read in conjunction with the Company's financial statements and notes thereto contained in the Company's Annual Report in the Company's Form 10-K for its fiscal year ended December 31, 2010. Certain prior year amounts have been reclassified to conform to the current year presentation. 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.

Basis Of Presentation And Summary Of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2011

Basis Of Presentation And Summary Of Significant Accounting Policies [Abstract]

Carrying Value Of Indebtedness And Corresponding Estimate Of Fair Value


	September 30, 2011					December 31, 2010
	Carrying Amount			Estimated Fair Value		Carrying Amount			Estimated Fair Value
Mortgage notes payable	$	3,179,034		$	3,337,861	$	3,047,586		$	3,121,193
Unsecured senior notes		3,016,986			3,073,469		3,016,598			3,241,542
Unsecured exchangeable senior notes		1,754,343	(1)		1,909,227		1,721,817	(1)		1,929,291

Total	$	7,950,363		$	8,320,557	$	7,786,001		$	8,292,026

(1)	Includes the net impact of Accounting Standards Codification ("ASC") ASC 470-20 (formerly known as FSP No. APB 14-1) totaling approximately $64.7 million and $93.6 million at September 30, 2011 and December 31, 2010, respectively.

- 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 Activity During The Nine Months Ended September 30, 2011 (Tables)

9 Months Ended

Sep. 30, 2011

Real Estate Activity During The Nine Months Ended September 30, 2011 [Abstract]

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

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- Market Lease Intangibles
Period from October 1, 2011 through December 31, 2011	$	1,574	$	158
2012		5,192		520
2013		3,423		349
2014		2,543		221
2015		1,867		300

Pro Forma In Connection With Acquisition


Pro Forma	Nine Months Ended September 30,
(in thousands, except per share data)	2011		2010
Total revenue	$	1,309,084	$	1,172,640
Income from continuing operations	$	198,209	$	193,864
Net income attributable to Boston Properties, Inc.	$	171,205	$	166,133
Basic earnings per share:
Net income per share attributable to Boston Properties, Inc.	$	1.18	$	1.19
Diluted earnings per share:
Net income per share attributable to Boston Properties, Inc.	$	1.18	$	1.19

- 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

Investments In Unconsolidated Joint Ventures (Tables)

9 Months Ended

Sep. 30, 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 Venture LLC	Eighth Avenue and 46th Street		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	%
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 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.

Balance Sheets Of The Unconsolidated Joint Ventures


	September 30, 2011			December 31, 2010
	(in thousands)
ASSETS
Real estate and development in process, net	$	4,991,083		$	5,028,851
Other assets		680,091			749,308

Total assets	$	5,671,174		$	5,778,159

LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Mortgage and notes payable	$	3,139,362		$	3,151,220
Other liabilities		907,144			969,082
Members'/Partners' equity		1,624,668			1,657,857

Total liabilities and members'/partners' equity	$	5,671,174		$	5,778,159

Company's share of equity	$	898,910		$	924,235
Basis differentials(1)		(128,444	)		(156,983	)

Carrying value of the Company's investments in unconsolidated joint ventures	$	770,466		$	767,252

(1)

Statements Of Operations Of The Joint Ventures


	For the three months ended September 30,						For the nine months ended September 30,
	2011			2010			2011			2010
	(in thousands)						(in thousands)
Total revenue(1)	$	150,101		$	155,126		$	440,733		$	457,217
Expenses
Operating		44,584			45,546			129,698			130,083
Depreciation and amortization		46,773			50,548			145,653			164,763

Total expenses		91,357			96,094			275,351			294,846
Operating income		58,744			59,032			165,382			162,371
Other expenses
Interest expense		57,699			59,120			172,467			176,705
Loss on guarantee obligation		—			3,581			—			3,581
Impairment loss		39,384			—			39,384			—

Net loss	$	(38,339	)	$	(3,669	)	$	(46,469	)	$	(17,915	)

Company's share of net loss	$	(23,231	)	$	(487	)	$	(28,570	)	$	(7,207	)
Basis differential		25,024			3,125			28,539			7,918
Elimination of inter-entity interest on partner loan		9,533			8,927			28,215			26,229

Income from unconsolidated joint ventures	$	11,326		$	11,565		$	28,184		$	26,940

(1)

Noncontrolling Interests (Tables)

9 Months Ended

Sep. 30, 2011

Noncontrolling Interests [Abstract]

Noncontrolling Interests - Redeemable Preferred Units


Balance at January 1, 2011	$	55,652
Net income		2,497
Distributions		(2,497	)

Balance at September 30, 2011	$	55,652


Balance at January 1, 2010	$	55,652
Net income		2,548
Distributions		(2,548	)

Balance at September 30, 2010	$	55,652

Earnings Per Share (Tables)

9 Months Ended

Sep. 30, 2011

Earnings Per Share [Abstract]

Computation Of Basic And Diluted Earnings Per Share

	For the three months ended September 30, 2011
	Income (Numerator)		Shares (Denominator)		Per Share Amount
	(in thousands, except for per share amounts)
Basic Earnings:
Net income attributable to Boston Properties, Inc.	$	70,542		147,006	$	0.48
Effect of Dilutive Securities:
Stock Based Compensation and Exchangeable Senior Notes		—		616		(0.00	)

Diluted Earnings:
Net income	$	70,542		147,622	$	0.48


	For the three months ended September 30, 2010
	Income (Numerator)		Shares (Denominator)		Per Share Amount
	(in thousands, except for per share amounts)
Basic Earnings:
Net income attributable to Boston Properties, Inc.	$	57,668		139,595	$	0.41
Effect of Dilutive Securities:
Stock Based Compensation and Exchangeable Senior Notes		—		598		(0.00	)

Diluted Earnings:
Net income	$	57,668		140,193	$	0.41


	For the nine months ended September 30, 2011
	Income (Numerator)		Shares (Denominator)		Per Share Amount
	(in thousands, except for per share amounts)
Basic Earnings:
Net income attributable to Boston Properties, Inc.	$	171,359		145,006	$	1.18
Effect of Dilutive Securities:
Stock Based Compensation		—		619		(0.00	)

Diluted Earnings:
Net income	$	171,359		145,625	$	1.18


	For the nine months ended September 30, 2010
	Income (Numerator)		Shares (Denominator)		Per Share Amount
	(in thousands, except for per share amounts)
Basic Earnings:
Net income attributable to Boston Properties, Inc.	$	171,786		139,215	$	1.23
Effect of Dilutive Securities:
Stock Based Compensation		—		659		(0.00	)

Diluted Earnings:
Net income	$	171,786		139,874	$	1.23

Segment Information (Tables)

9 Months Ended

Sep. 30, 2011

Segment Information [Abstract]

Reconciliation Of Net Operating Income To Net Income


	Three months ended September 30,					Nine months ended September 30,
	2011		2010			2011		2010
Net Operating Income	$	283,216	$	245,736		$	824,150	$	730,194
Add:
Development and management services income		8,180		6,439			24,706		34,267
Income from unconsolidated joint ventures		11,326		11,565			28,184		26,940
Interest and other income		1,252		1,814			4,179		5,641
Gains on sales of real estate		—		—			—		2,734
Less:
General and administrative expense		17,340		18,067			62,052		62,537
Acquisition costs		51		1,893			136		1,893
Suspension of development		—		—			—		(7,200	)
Depreciation and amortization expense		109,495		81,133			330,003		245,608
Losses (gains) from investments in securities		860		(731	)		481		(253	)
Interest expense		95,777		97,103			290,164		285,887
Losses from early extinguishments of debt		—		—			—		8,221
Noncontrolling interest in property partnerships		86		889			1,118		2,557
Noncontrolling interest—redeemable preferred units of the Operating Partnership		832		820			2,497		2,548
Noncontrolling interest—common units of the Operating Partnership		8,991		8,712			23,409		25,841
Noncontrolling interest in gains on sales of real estate—common units of the Operating Partnership		—		—			—		351

Net income attributable to Boston Properties, Inc.	$	70,542	$	57,668		$	171,359	$	171,786

Organization (Narrative) (Details) sqft in Millions	9 Months Ended
Organization (Narrative) (Details) sqft in Millions	Sep. 30, 2011 sqft years shares	Sep. 30, 2010
Real Estate Properties [Line Items]
General and limited partnership interest in the operating partnership	88.00%	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	43,899
Area of parking in square feet \| sqft	14.8
Area of undeveloped land parcels owned in acres	510.5
Value-added fund institutional investors	2
Commercial Real Estate Properties [Member]
Real Estate Properties [Line Items]
Square footage of real estate property	42,300,000
Number of real estate properties	153
Total Office Properties [Member]
Real Estate Properties [Line Items]
Number of real estate properties	147
Total Properties Under Construction [Member]
Real Estate Properties [Line Items]
Square footage of real estate property	2,900,000
Number of real estate properties	7
Office Properties Under Construction [Member]
Real Estate Properties [Line Items]
Number of real estate properties	7
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	19
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	2
Investments Through The Value-Added Fund [Member]
Real Estate Properties [Line Items]
Number of real estate properties	24

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

Sep. 30, 2011

Dec. 31, 2010

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Mortgage and notes payable

$ 3,179,034

$ 3,047,586

Unsecured senior notes

3,016,986

3,016,598

Unsecured exchangeable senior notes

1,754,343

1,721,817

ASC 470-20 Adjustment [Member]

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Net of the adjustment for the equity component allocation

64,700

93,600

Carrying Amount [Member]

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Mortgage and notes payable

3,179,034

3,047,586

Unsecured senior notes

3,016,986

3,016,598

Unsecured exchangeable senior notes

^[1]

1,754,343

1,721,817

Total

7,950,363

7,786,001

Estimated Fair Value [Member]

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Mortgage and notes payable

3,337,861

3,121,193

Unsecured senior notes

3,073,469

3,241,542

Unsecured exchangeable senior notes

1,909,227

1,929,291

Total

$ 8,320,557

$ 8,292,026

[1]	Includes the net impact of Accounting Standards Codification ("ASC") ASC 470-20 (formerly known as FSP No. APB 14-1) totaling approximately $64.7 million and $93.6 million at September 30, 2011 and December 31, 2010, respectively.

Real Estate Activity During The Nine Months Ended September 30, 2011 (Narrative) (Details)													3 Months Ended	9 Months Ended
	Nov. 04, 2011	Nov. 03, 2011	Jul. 14, 2011 years	Jul. 05, 2011	Jun. 06, 2011 USD ($)	May 24, 2011	May 23, 2011 USD ($)	May 11, 2011	May 01, 2011	Mar. 01, 2011	Feb. 01, 2011 USD ($)	Jan. 14, 2011	Sep. 30, 2011 USD ($)	Sep. 30, 2011 USD ($)
Real Estate Properties [Line Items]
Interest at a fixed rate	2.875%	3.70%
Maturity date	Feb. 15, 2037	Nov. 15, 2018
Bay Colony Corporate Center [Member]
Real Estate Properties [Line Items]
Acquisition date											February 1, 2011
Acquisition aggregate purchase price											$ 185,000,000		$ 185,000,000	$ 185,000,000
Cash portion of purchase price											41,100,000
Portion of acquisition included in debt											$ 143,900,000			$ 143,900,000
Interest at a fixed rate											6.53%
Maturity date											Jun. 11, 2012
Square footage of real estate property											966,000
Number of real estate properties											4
Acres of land											58
Atlantic Wharf Development [Member]
Real Estate Properties [Line Items]
Square footage of real estate property												790,000	10,000
Number of units in real estate property													86	86
Office component placed in-service (percentage)												57.00%
Placed in-service (percentage)													100.00%
Pennsylvania Avenue Development [Member]
Real Estate Properties [Line Items]
Square footage of real estate property										457,000
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
Number of units in real estate property								335
One Two Three One Zero Sunrise Valley Drive [Member]
Real Estate Properties [Line Items]
Square footage of real estate property				268,000
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 real estate properties					16
Acres of land					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														$ 48,000,000
Development revenue							11,400,000
Approximate proceeds per year from ground lease							$ 459,000
Term of lease (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%
Anticipated Through Q3 2014 [Member] \| 75 Ames Street [Member]
Real Estate Properties [Line Items]
Development revenue							$ 8,900,000

Real Estate Activity During The Nine Months Ended September 30, 2011 (Schedule Of Allocation Of The Aggregate Purchase Price Of Acquisition) (Details) - Bay Colony Corporate Center [Member] - USD ($) $ in Thousands		9 Months Ended
	Feb. 01, 2011	Sep. 30, 2011
Real Estate Properties [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	185,000
Less: Indebtedness assumed	$ (143,900)	(143,900)
Net assets acquired		$ 41,100

Real Estate Activity During The Nine Months Ended September 30, 2011 (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	9 Months Ended
	Sep. 30, 2011 USD ($)
Acquired In-Place Lease Intangibles [Member]
Real Estate Properties [Line Items]
Period from October 1, 2011 through December 31, 2011	$ 1,574
2012	5,192
2013	3,423
2014	2,543
2015	1,867
Acquired Net Above Market Lease Intangibles [Member]
Real Estate Properties [Line Items]
Period from October 1, 2011 through December 31, 2011	158
2012	520
2013	349
2014	221
2015	$ 300

Real Estate Activity During The Nine Months Ended September 30, 2011 (Pro Forma In Connection With Acquisition) (Details) - Bay Colony Corporate Center [Member] - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Real Estate Properties [Line Items]
Total revenue	$ 1,309,084	$ 1,172,640
Income from continuing operations	198,209	193,864
Net income attributable to Boston Properties, Inc.	$ 171,205	$ 166,133
Basic earnings per share: Net income per share attributable to Boston Properties, Inc.	$ 1.18	$ 1.19
Diluted earnings per share: Net income per share attributable to Boston Properties, Inc.	$ 1.18	$ 1.19

- 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

Investments In Unconsolidated Joint Ventures (Narrative) (Details) $ in Millions								3 Months Ended
	Nov. 04, 2011	Nov. 03, 2011	Aug. 12, 2011 USD ($)	Jun. 28, 2011 USD ($)	Jun. 03, 2011	Mar. 16, 2011 USD ($)	Jan. 18, 2011	Mar. 31, 2011 USD ($)	Mar. 26, 2011
Schedule of Equity Method Investments [Line Items]
Interest at a fixed rate	2.875%	3.70%
Maturity date	Feb. 15, 2037	Nov. 15, 2018
Mountain View Technology Park [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%
Carrying amount of loan						$ 24.7
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]
Repayment of previous mortgage by investor				$ 20.3
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%
Maturity date				May 31, 2011
Carrying amount of loan				$ 112.3
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%
Maturity date				May 31, 2014
Carrying amount of loan				$ 92.0
Five Hundred North Capitol Street, NW [Member]
Schedule of Equity Method Investments [Line Items]
Square footage of signed lease							171,000
Ownership percentage									30.00%
Annapolis Junction [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage					50.00%			50.00%
Square footage of real estate property					120,000
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
Carrying amount of loan								$ 42.7
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
Carrying amount of loan								$ 42.3
Number of extension options								1
Mortgage loan extension option (years)								3
Two Grand Central Tower [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage			60.00%
Carrying amount of loan			$ 176.6
Square footage of real estate property			650,000
Contractual sale price			$ 401.0
Impairment of long-lived assets to be disposed of			39.4
Carrying value of net assets of property sold			$ 425.7
Operating Partnership [Member] \| Mountain View Research Park [Member]
Schedule of Equity Method Investments [Line Items]
Interest at a fixed rate				10.00%
Loan to value-added fund				$ 12.0
Operating Partnership [Member] \| Mountain View Research Park [Member] \| Advanced To Date [Member]
Schedule of Equity Method Investments [Line Items]
Loan to value-added fund				$ 6.4

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

9 Months Ended

Sep. 30, 2011

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%

Entity Owning Land And Infrastructure Of Project [Member]

Schedule of Equity Method Investments [Line Items]

Nominal % Ownership

33.30%

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%

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

[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 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.

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

Sep. 30, 2011

Dec. 31, 2010

Schedule of Equity Method Investments [Line Items]

Real estate and development in process, net

$ 10,639,176

$ 10,441,117

Mortgage and notes payable

3,179,034

3,047,586

Other liabilities

244,555

213,000

Total liabilities and members'/partners' equity

13,980,798

13,348,263

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

770,466

767,252

Unconsolidated Joint Ventures [Member]

Schedule of Equity Method Investments [Line Items]

Real estate and development in process, net

4,991,083

5,028,851

Other assets

680,091

749,308

Total assets

5,671,174

5,778,159

Mortgage and notes payable

3,139,362

3,151,220

Other liabilities

907,144

969,082

Members'/Partners' equity

1,624,668

1,657,857

Total liabilities and members'/partners' equity

5,671,174

5,778,159

Company's share of equity

898,910

924,235

Basis differentials

^[1]

(128,444)

(156,983)

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

$ 770,466

$ 767,252

[1]

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

3 Months Ended

9 Months Ended

Sep. 30, 2011

Sep. 30, 2010

Sep. 30, 2011

Sep. 30, 2010

Schedule of Equity Method Investments [Line Items]

Total revenue

$ 452,413

$ 386,410

$ 1,306,739

$ 1,158,322

Depreciation and amortization

109,495

81,133

330,003

245,608

Total expenses

287,903

235,328

850,074

696,699

Operating income

164,510

151,082

456,665

461,623

Interest expense

95,777

97,103

290,164

285,887

Net loss

(80,451)

(68,089)

(198,383)

(203,083)

Income from unconsolidated joint ventures

11,326

11,565

28,184

26,940

Unconsolidated Joint Ventures [Member]

Schedule of Equity Method Investments [Line Items]

Total revenue

^[1]

150,101

155,126

440,733

457,217

Operating

44,584

45,546

129,698

130,083

Depreciation and amortization

46,773

50,548

145,653

164,763

Total expenses

91,357

96,094

275,351

294,846

Operating income

58,744

59,032

165,382

162,371

Interest expense

57,699

59,120

172,467

176,705

Loss on guarantee obligation

3,581

Net loss

(38,339)

(3,669)

(46,469)

(17,915)

Company's share of net loss

(23,231)

(487)

(28,570)

(7,207)

Basis differential

25,024

3,125

28,539

7,918

Elimination of inter-entity interest on partner loan

9,533

8,927

28,215

26,229

Income from unconsolidated joint ventures

$ 11,326

$ 11,565

$ 28,184

$ 26,940

[1]

Investments In Unconsolidated Joint Ventures (Statements Of Operations Of The Joint Ventures) (Parenthetical) (Details) - Unconsolidated Joint Ventures [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Schedule of Equity Method Investments [Line Items]
Straight-line rent adjustments	$ 6.7	$ 5.9	$ 14.8	$ 19.8
"Above" and "below" market rent adjustments, net	$ 28.3	$ 30.5	$ 87.0	$ 97.6

Mortgage Notes Payable (Details) - USD ($) $ in Thousands						9 Months Ended
Mortgage Notes Payable (Details) - USD ($) $ in Thousands	Nov. 04, 2011	Nov. 03, 2011	Aug. 19, 2011	May 11, 2011	Feb. 01, 2011	Sep. 30, 2011	Sep. 30, 2010	Jan. 12, 2011
Mortgage Loans on Real Estate [Line Items]
Interest at a fixed rate	2.875%	3.70%
Maturity date	Feb. 15, 2037	Nov. 15, 2018
Amount of mortgage loan that was repaid						$ 1,196,074	$ 301,531
Repayments of unsecured line of credit						453,300
Montvale Center [Member]
Mortgage Loans on Real Estate [Line Items]
Debt default, accrued interest rate								9.93%
Bay Colony Corporate Center [Member]
Mortgage Loans on Real Estate [Line Items]
Interest at a fixed rate					6.53%
Maturity date					Jun. 11, 2012
Portion of acquisition included in debt					$ 143,900	$ 143,900
Outstanding balance of mortgage loan accounted for at fair value					$ 149,200
Interest rate used to account for mortgage loan at fair value upon assumption					3.75%
601 Lexington Avenue [Member]
Mortgage Loans on Real Estate [Line Items]
Carrying amount of loan			$ 725,000
Interest at a fixed rate			4.75%	7.19%
Maturity date			Apr. 10, 2022	May 11, 2011
Amount of mortgage loan that was repaid				$ 453,300
Repayments of unsecured line of credit			$ 453,300
510 Madison Avenue [Member]
Mortgage Loans on Real Estate [Line Items]
Refinancing of secured debt			$ 267,500

Unsecured Line Of Credit (Details) $ in Millions	9 Months Ended
Unsecured Line Of Credit (Details) $ in Millions	Sep. 30, 2011 USD ($)
Line of Credit Facility [Line Items]
Line of credit facility, extension fee	0.20%
Provision for extension, years	1
Line of credit facility, facility fee percentage	0.225%
Frequency of payment	quarterly
Maximum leverage ratio	60.00%
Leverage ratio maximum increasing limit	65.00%
Leverage ratio reduction limit	60.00%
Leverage ratio reduction period (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)	1
Unsecured debt interest coverage ratio, minimum	1.75
Line of credit facility, amount outstanding	$ 0.0
Repayments of unsecured line of credit	453.3
Minimum net worth requirement	3,500.0
Potential Borrowing Capacity Subject To Syndication [Member]
Line of Credit Facility [Line Items]
Current lenders' total commitment	1,000.0
Prior To Amendment [Member]
Line of Credit Facility [Line Items]
Current lenders' total commitment	$ 1,000.0
Line of credit facility, expiration date	August 3, 2011
Basis spread on variable rate basis	0.475%
Description of variable rate basis	Eurodollar plus 0.475% per annum
After The Amendment [Member]
Line of Credit Facility [Line Items]
Current lenders' total commitment	$ 750.0
Line of credit facility, expiration date	June 24, 2014
Basis spread on variable rate basis	1.225%
Description of variable rate basis	Eurodollar plus 1.225% per annum

Commitments And Contingencies (Details) - USD ($) $ in Millions			9 Months Ended
	Nov. 04, 2011	Nov. 03, 2011	Sep. 30, 2011
Commitments And Contingencies [Line Items]
Letter of credit and performance obligations			$ 16.1
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
Maturity date	Feb. 15, 2037	Nov. 15, 2018
767 Venture, LLC [Member]
Commitments And Contingencies [Line Items]
Maximum funding obligation			10.6
Coverage for acts of Terrorism certified under TRIA in excess of amount provided by IXP, 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			21.3
Maximum exposure as of period end			3.2
Cash deposit into the escrow account			10.0
Escrow account remaining funding obligation			11.3
One Freedom Square [Member]
Commitments And Contingencies [Line Items]
Guarantee obligation related to tenant re-leasing costs			$ 7.9
Maturity date			Jun. 30, 2012
601 Lexington Avenue [Member]
Commitments And Contingencies [Line Items]
Coverage for acts of Terrorism certified under TRIA in excess of amount provided by IXP, LLC, as a direct insurer			$ 250.0

Noncontrolling Interests (Narrative) (Details) - Noncontrolling Interests [Member]	Sep. 30, 2011 shares
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Operating Partnership (OP) Units	17,037,553
Long-Term Incentive Plan (LTIP) Units	1,603,205
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)	9 Months Ended
	Sep. 30, 2011 USD ($) $ / shares shares	Aug. 15, 2011	May 16, 2011	May 12, 2011	Feb. 15, 2011	May 12, 2010	May 12, 2009
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	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 \| $	$ 50
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	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 \| $	$ 50
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	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 \| $	$ 50
Maximum portion that may be required for redemption of total	0.166666666667
Noncontrolling Interests [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Series Two Preferred Units	1,113,044
Noncontrolling Interests [Member] \| Series Two Preferred Units [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Series Two Preferred Units	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	1.312336
Distributions to Series Two Preferred Units		0.75616	0.73151		0.75616
Number of holders exercising redemption rights				0		0	0

Noncontrolling Interests (Redeemable Preferred Units) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Noncontrolling Interests [Abstract]
Beginning Balance			$ 55,652	$ 55,652
Net income	$ 832	$ 820	2,497	2,548
Distributions			(2,497)	(2,548)
Ending Balance	$ 55,652	$ 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) - USD ($)		3 Months Ended				6 Months Ended	9 Months Ended	12 Months Ended
	Feb. 05, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Jun. 30, 2011	Sep. 30, 2011	Dec. 31, 2010
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Dividend paid date			Jul. 29, 2011	Apr. 29, 2011				Jan. 28, 2011
Dividend payable date		Oct. 31, 2011
Dividends payable, date declared		Sep. 16, 2011
OP Units [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
OP Units for redemption							2,442,407
Redemption of OP units issued on conversion of LTIP Units							58,213
Outperformance awards in LTIP Units		400,000					400,000
Outperformance Awards LTIP Units distribution as percentage of OP Unit distribution prior to measurement date							10.00%
Repayment Amount per Forfeited OPP Award	$ 0.25
Distributions made to OP and LTIP units per unit				$ 0.50		$ 0.50		$ 0.50
Distribution paid to outperformance awards, OPP Units				$ 0.05		$ 0.05		$ 0.05
Distribution declared to OP and LTIP units by Boston Properties, Inc.		$ 0.50					$ 0.50
Distribution declared to outperformance awards OPP Units by Boston Properties, Inc.		$ 0.05					$ 0.05
Dividend paid date			Jul. 29, 2011	Apr. 29, 2011	Jan. 28, 2011
Dividend payable date		Oct. 31, 2011
Holders of record date		September 30, 2011	June 30, 2011	March 31, 2011	December 31, 2010
Dividends payable, date declared		Sep. 16, 2011
Restriction on redemption of OP Unit to Common Stock, years							1
Redemption of OP Unit equivalence to Common Stock							1
Common units of operating partnership if converted value		$ 1,660,000,000					$ 1,660,000,000
Value of Series Two Preferred Units assuming conversion		$ 130,100,000					$ 130,100,000
Noncontrolling Interests [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Outperformance awards in LTIP Units		400,000					400,000
Noncontrolling Interests [Member] \| Series Two Preferred Units [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Closing price of common stock		$ 89.10					$ 89.10

Noncontrolling Interests (Property Partnerships) (Narrative) (Details) - USD ($) $ in Thousands	Sep. 30, 2011	Dec. 31, 2010
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Property partnerships	$ 996	$ 614
Noncontrolling Interests [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Property partnerships	$ (1,000)	$ (600)

Stockholders' Equity (Details)	3 Months Ended			9 Months Ended	12 Months Ended
Stockholders' Equity (Details)	Sep. 30, 2011 USD ($) $ / shares shares	Jun. 30, 2011 $ / shares	Mar. 31, 2011 $ / shares	Sep. 30, 2011 USD ($) $ / shares shares	Dec. 31, 2010 $ / shares shares
Class of Stock [Line Items]
Common stock, shares outstanding \| shares	147,627,247			147,627,247	140,199,105
At the market stock offering program, net proceeds				$ 439,037,000
Shares of Common Stock upon the exercise of options to purchase Common Stock by certain employees \| shares				312,711
Shares of its Common Stock in connection with the redemption of an equal number of OP Units \| shares				2,442,407
Dividend paid on common stock \| $ / shares		$ 0.50	$ 0.50		$ 0.50
Dividends payable, amount per share \| $ / shares	$ 0.50			$ 0.50
Dividend paid date		Jul. 29, 2011	Apr. 29, 2011		Jan. 28, 2011
Dividend shareholder of record date	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011		Dec. 31, 2010
Dividends payable, date declared	Sep. 16, 2011
Dividend payable date	Oct. 31, 2011
Initial ATM Program [Member]
Class of Stock [Line Items]
At the market stock offering program, shares issued \| shares				4,228,993
At the market stock offering program, gross proceeds				$ 400,000,000
At the market stock offering program, net proceeds				394,700,000
At the market stock offering program, remained available for issuance				0
At the market stock offering program, aggregate value of common stock				$ 400,000,000
At the market stock offering program maximum length of sale (years)				3
Second ATM Program [Member]
Class of Stock [Line Items]
At the market stock offering program, shares issued \| shares	431,223
At the market stock offering program, gross proceeds	$ 44,900,000
At the market stock offering program, net proceeds	44,400,000
At the 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

Earnings Per Share (Computation Of Basic And Diluted Earnings Per Share) (Details) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011 USD ($) $ / shares shares	Sep. 30, 2010 USD ($) $ / shares shares	Sep. 30, 2011 USD ($) $ / shares shares	Sep. 30, 2010 USD ($) $ / shares shares
Earnings Per Share [Abstract]
Net income attributable to Boston Properties, Inc., Income (Numerator) \| $	$ 70,542	$ 57,668	$ 171,359	$ 171,786
Net income attributable to Boston Properties Inc., Shares (Denominator) \| shares	147,006	139,595	145,006	139,215
Net income attributable to Boston Properties Inc., Per Share Amount \| $ / shares	$ 0.48	$ 0.41	$ 1.18	$ 1.23
Stock Based Compensation and Exchangeable Senior Notes, Income (Numerator) \| $
Stock Based Compensation and Exchangeable Senior Notes, Shares (Denominator) \| shares	616	598	619	659
Stock Based Compensation and Exchangeable Senior Notes, Per Share Amount \| $ / shares	0.00	0.00	0.00	0.00
Diluted Earnings: Net income, Income (Numerator) \| $	$ 70,542	$ 57,668	$ 171,359	$ 171,786
Diluted Earnings: Net income, Shares (Denominator) \| shares	147,622	140,193	145,625	139,874
Diluted Earnings: Net income, Per Share Amount \| $ / shares	$ 0.48	$ 0.41	$ 1.18	$ 1.23

Stock Option and Incentive Plan (Outperformance Awards) (Narrative) (Details)	9 Months Ended				12 Months Ended
	Sep. 30, 2011	Sep. 30, 2011 years	Sep. 30, 2011	Sep. 30, 2011 USD ($)	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Feb. 01, 2016	Feb. 01, 2015	Feb. 01, 2014
Stock Option And Incentive Plan And Stock Repurchase Plan [Line Items]
LTIP and common units equivalency ratio	one-for-one
TRS Component Sliding Scale One [Member]
Stock Option And Incentive Plan And Stock Repurchase 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 Repurchase 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 Repurchase 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 Repurchase 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 Eleven [Member]
Stock Option And Incentive Plan And Stock Repurchase Plan [Line Items]
TRS measurement, years		3	3
Award additional vesting period, years \| years		2
Measurement period for 2011 OPP Awards	February 1, 2011 to January 31, 2014
Average closing price of common stock for five trading days prior and including February 1, 2011				$ 93.38
Trading days prior to and including February 1, 2011			5
Aggregate rewards of OPP awards, maximum cap				$ 40,000,000
Excess total return above a cumulative absolute TRS hurdle			2.00%
Cumulative absolute TRS hurdle			27.00%
Cumulative absolute TRS hurdle, annum			9.00%
Vesting percentage for 2011 OPP Awards								50.00%	25.00%	25.00%
Vesting date					Feb. 01, 2016	Feb. 01, 2015	Feb. 01, 2014
Performance measurement period, days			15
Distributions percent before measurement date			10.00%
Maximum [Member] \| TRS Component Sliding Scale Three [Member]
Stock Option And Incentive Plan And Stock Repurchase Plan [Line Items]
Cumulative absolute TRS hurdle			27.00%
Minimum [Member] \| TRS Component Sliding Scale Three [Member]
Stock Option And Incentive Plan And Stock Repurchase Plan [Line Items]
Cumulative absolute TRS hurdle			0.00%

Stock Option and Incentive Plan (Restricted Stock and LTIP Units) (Narrative) (Details)	3 Months Ended		9 Months Ended							48 Months Ended
	Sep. 30, 2011 USD ($) $ / shares shares	Sep. 30, 2010 USD ($)	Sep. 30, 2011 USD ($) $ / shares shares	Sep. 30, 2011 USD ($) $ / shares years shares	Sep. 30, 2011 USD ($) $ / shares shares	Sep. 30, 2011 USD ($) $ / shares shares	Sep. 30, 2011 USD ($) $ / shares shares	Sep. 30, 2011 USD ($) $ / shares shares	Sep. 30, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2010 USD ($) shares
Stock Option And Incentive Plan And Stock Repurchase Plan [Line Items]
Shares issued \| shares	147,706,147		147,706,147	147,706,147	147,706,147	147,706,147	147,706,147	147,706,147			140,278,005
Non-qualified stock options issued \| shares						146,844
LTIP units issued \| shares	190,067		190,067	190,067	190,067	190,067	190,067	190,067
2011 OPP units issued \| shares						400,000
Value of shares of common stock	$ 1,476,000		$ 1,476,000	$ 1,476,000	$ 1,476,000	$ 1,476,000	$ 1,476,000	$ 1,476,000			$ 1,402,000
Stock-based compensation associated with restricted stock, LTIP Units, and 2011 OPP Units	$ 5,600,000	$ 6,100,000						22,700,000	$ 26,000,000
Accelerated amount of unvested compensation expense										$ 5,800,000
Accelerated compensation expenses related to 2008 OPP units								$ 4,300,000
Restricted Stock [Member]
Stock Option And Incentive Plan And Stock Repurchase Plan [Line Items]
Shares issued \| shares	19,030		19,030	19,030	19,030	19,030	19,030	19,030
Employee and director payment per share \| $ / shares					0.01
Value of shares of common stock	$ 1,800,000		$ 1,800,000	$ 1,800,000	$ 1,800,000	$ 1,800,000	$ 1,800,000	$ 1,800,000
Employee's cost per share \| $ / shares	$ 93.40		$ 93.40	$ 93.40	$ 93.40	$ 93.40	$ 93.40	$ 93.40
LTIP Units [Member]
Stock Option And Incentive Plan And Stock Repurchase Plan [Line Items]
Expected price volatility							30.00%
Risk-free rate							2.22%
Expected life assumed to calculate per unit fair value per LTIP unit (years)							5.8
Value of LTIP units issued								$ 16,500,000
Per unit fair value weighted-average \| $ / shares	$ 86.74		$ 86.74	$ 86.74	$ 86.74	$ 86.74	$ 86.74	$ 86.74
LTIPs And Restricted Stock [Member]
Stock Option And Incentive Plan And Stock Repurchase Plan [Line Items]
Vesting annual installments							4
Unrecognized compensation expenses	$ 29,500,000		$ 29,500,000	$ 29,500,000	$ 29,500,000	$ 29,500,000	$ 29,500,000	$ 29,500,000
OPP Units Two Thousand And Eleven [Member]
Stock Option And Incentive Plan And Stock Repurchase Plan [Line Items]
Aggregate value of 2011 OPP Awards								7,800,000
Expected price volatility							41.00%
Risk-free rate							0.98%
Estimated dividend payments								6.10
Unrecognized compensation expenses	$ 6,100,000		$ 6,100,000	$ 6,100,000	$ 6,100,000	$ 6,100,000	$ 6,100,000	$ 6,100,000
Weighted-average period (years)							2.6
TRS measurement, years				3			3
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.
OPP Units Two Thousand And Eleven [Member] \| SNL Equity REIT Index [Member]
Stock Option And Incentive Plan And Stock Repurchase Plan [Line Items]
Expected price volatility							37.00%
OPP Units Two Thousand And Eight [Member]
Stock Option And Incentive Plan And Stock Repurchase Plan [Line Items]
TRS measurement, years							3
Non-Qualified Stock Options [Member]
Stock Option And Incentive Plan And Stock Repurchase Plan [Line Items]
Expected price volatility							35.00%
Risk-free rate							2.37%
Fair value per option on grant date \| $ / shares					$ 24.67
Expected life assumed to calculate per unit fair value per LTIP unit (years)							6.0
Dividend yield							3.00%
Exercise price on option grant date \| $ / shares	$ 92.71		$ 92.71	$ 92.71	$ 92.71	$ 92.71	$ 92.71	$ 92.71
LTIP And OPP Awards [Member]
Stock Option And Incentive Plan And Stock Repurchase Plan [Line Items]
Employee and director payment per share \| $ / shares					0.25

Segment Information (Segment Reporting by Geographic Area and Property Type) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Segment Reporting Information [Line Items]
Rental Revenue: Class A	$ 421,629	$ 360,416	$ 1,220,842	$ 1,067,074
Rental Revenue: Office/Technical	12,106	11,539	35,265	34,691
Rental Revenue: Residential	2,453		3,029
Rental Revenue: Hotel	8,045	8,016	22,897	22,290
Rental Revenue: Total	$ 444,233	$ 379,971	$ 1,282,033	$ 1,124,055
Rental Revenue: % of Total	100.00%	100.00%	100.00%	100.00%
Real Estate Operating Expenses: Class A	$ 148,958	$ 124,631	$ 426,056	$ 366,383
Real Estate Operating Expenses: Office/Technical	3,609	3,410	10,634	9,927
Real Estate Operating Expenses: Residential	2,418		3,141
Real Estate Operating Expenses: Hotel	6,032	6,194	18,052	17,551
Real Estate Operating Expenses: Total	$ 161,017	$ 134,235	$ 457,883	$ 393,861
Real Estate Operating Expenses: % of Total	100.00%	100.00%	100.00%	100.00%
Net Operating Income	$ 164,510	$ 151,082	$ 456,665	$ 461,623
Net Operating Income: % of Total	100.00%	100.00%	100.00%	100.00%
Greater Boston [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A	$ 141,680	$ 94,016	$ 405,234	$ 273,702
Rental Revenue: Office/Technical	7,871	7,627	23,088	22,808
Rental Revenue: Residential	284		284
Rental Revenue: Hotel	8,045	8,016	22,897	22,290
Rental Revenue: Total	$ 157,880	$ 109,659	$ 451,503	$ 318,800
Rental Revenue: % of Total	35.54%	28.86%	35.22%	28.36%
Real Estate Operating Expenses: Class A	$ 55,614	$ 36,082	$ 154,580	$ 103,481
Real Estate Operating Expenses: Office/Technical	2,501	2,417	7,392	6,790
Real Estate Operating Expenses: Residential	270		270
Real Estate Operating Expenses: Hotel	6,032	6,194	18,052	17,551
Real Estate Operating Expenses: Total	$ 64,417	$ 44,693	$ 180,294	$ 127,822
Real Estate Operating Expenses: % of Total	40.01%	33.29%	39.38%	32.46%
Net Operating Income	$ 93,463	$ 64,966	$ 271,209	$ 190,978
Net Operating Income: % of Total	33.00%	26.44%	32.91%	26.15%
Greater Washington, DC [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A	$ 95,192	$ 84,708	$ 265,286	$ 251,126
Rental Revenue: Office/Technical	4,235	3,912	12,177	11,883
Rental Revenue: Residential	2,169		2,745
Rental Revenue: Total	$ 101,596	$ 88,620	$ 280,208	$ 263,009
Rental Revenue: % of Total	22.87%	23.32%	21.86%	23.40%
Real Estate Operating Expenses: Class A	$ 26,036	$ 24,243	$ 74,221	$ 69,968
Real Estate Operating Expenses: Office/Technical	1,108	993	3,242	3,137
Real Estate Operating Expenses: Residential	2,148		2,871
Real Estate Operating Expenses: Total	$ 29,292	$ 25,236	$ 80,334	$ 73,105
Real Estate Operating Expenses: % of Total	18.19%	18.80%	17.54%	18.56%
Net Operating Income	$ 72,304	$ 63,384	$ 199,874	$ 189,904
Net Operating Income: % of Total	25.53%	25.79%	24.25%	26.01%
Midtown Manhattan [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A	$ 115,284	$ 111,383	$ 341,698	$ 332,301
Rental Revenue: Total	$ 115,284	$ 111,383	$ 341,698	$ 332,301
Rental Revenue: % of Total	25.95%	29.32%	26.65%	29.56%
Real Estate Operating Expenses: Class A	$ 39,331	$ 35,908	$ 114,423	$ 110,177
Real Estate Operating Expenses: Total	$ 39,331	$ 35,908	$ 114,423	$ 110,177
Real Estate Operating Expenses: % of Total	24.43%	26.75%	24.99%	27.97%
Net Operating Income	$ 75,953	$ 75,475	$ 227,275	$ 222,124
Net Operating Income: % of Total	26.82%	30.71%	27.58%	30.42%
Greater San Francisco [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A	$ 53,978	$ 54,268	$ 161,039	$ 160,899
Rental Revenue: Total	$ 53,978	$ 54,268	$ 161,039	$ 160,899
Rental Revenue: % of Total	12.15%	14.28%	12.56%	14.32%
Real Estate Operating Expenses: Class A	$ 20,788	$ 20,317	$ 60,241	$ 59,047
Real Estate Operating Expenses: Total	$ 20,788	$ 20,317	$ 60,241	$ 59,047
Real Estate Operating Expenses: % of Total	12.91%	15.14%	13.16%	14.99%
Net Operating Income	$ 33,190	$ 33,951	$ 100,798	$ 101,852
Net Operating Income: % of Total	11.72%	13.82%	12.23%	13.95%
New Jersey [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A	$ 15,495	$ 16,041	$ 47,585	$ 49,046
Rental Revenue: Total	$ 15,495	$ 16,041	$ 47,585	$ 49,046
Rental Revenue: % of Total	3.49%	4.22%	3.71%	4.36%
Real Estate Operating Expenses: Class A	$ 7,189	$ 8,081	$ 22,591	$ 23,710
Real Estate Operating Expenses: Total	$ 7,189	$ 8,081	$ 22,591	$ 23,710
Real Estate Operating Expenses: % of Total	4.46%	6.02%	4.93%	6.02%
Net Operating Income	$ 8,306	$ 7,960	$ 24,994	$ 25,336
Net Operating Income: % of Total	2.93%	3.24%	3.03%	3.47%
Segment, Continuing Operations [Member]
Segment Reporting Information [Line Items]
Net Operating Income	$ 283,216	$ 245,736	$ 824,150	$ 730,194

Segment Information (Reconciliation of Net Operating Income to Net Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Segment Reporting Information [Line Items]
Net Operating Income	$ 164,510	$ 151,082	$ 456,665	$ 461,623
Development and management services income	8,180	6,439	24,706	34,267
Income from unconsolidated joint ventures	11,326	11,565	28,184	26,940
Interest and other income	1,252	1,814	4,179	5,641
Gain on sales of real estate				2,734
General and administrative expense	17,340	18,067	62,052	62,537
Acquisition costs	51	1,893	136	1,893
Suspension of development				(7,200)
Depreciation and amortization expense	109,495	81,133	330,003	245,608
Losses (gains) from investments in securities	(860)	731	(481)	253
Interest expense	95,777	97,103	290,164	285,887
Losses from early extinguishments of debt				8,221
Noncontrolling interest in property partnerships	86	889	1,118	2,557
Noncontrolling interest-redeemable preferred units of the Operating Partnership	832	820	2,497	2,548
Noncontrolling interest-common units of the Operating Partnership	8,991	8,712	23,409	25,841
Noncontrolling interest-common units of the Operating Partnership				351
Net income attributable to Boston Properties, Inc.	70,542	57,668	171,359	171,786
Business Intersegment, Eliminations [Member]
Segment Reporting Information [Line Items]
Net Operating Income	283,216	245,736	824,150	730,194
Development and management services income	8,180	6,439	24,706	34,267
Income from unconsolidated joint ventures	11,326	11,565	28,184	26,940
Interest and other income	1,252	1,814	4,179	5,641
Gain on sales of real estate				2,734
General and administrative expense	17,340	18,067	62,052	62,537
Acquisition costs	51	1,893	136	1,893
Suspension of development				(7,200)
Depreciation and amortization expense	109,495	81,133	330,003	245,608
Losses (gains) from investments in securities	860	(731)	481	(253)
Interest expense	95,777	97,103	290,164	285,887
Losses from early extinguishments of debt				8,221
Noncontrolling interest in property partnerships	86	889	1,118	2,557
Noncontrolling interest-redeemable preferred units of the Operating Partnership	832	820	2,497	2,548
Noncontrolling interest-common units of the Operating Partnership	8,991	8,712	23,409	25,841
Noncontrolling interest-common units of the Operating Partnership				351
Net income attributable to Boston Properties, Inc.	$ 70,542	$ 57,668	$ 171,359	$ 171,786

Subsequent Events (Details) $ in Thousands					9 Months Ended
Subsequent Events (Details) $ in Thousands	Nov. 04, 2011 USD ($)	Nov. 03, 2011 USD ($)	Oct. 25, 2011 USD ($)	Oct. 14, 2011 USD ($)	Sep. 30, 2010 USD ($)
Subsequent Event [Line Items]
Maturity date	Feb. 15, 2037	Nov. 15, 2018
Proceeds from issuance of senior long-term debt		$ 850,000
Long-term debt, percentage bearing fixed interest rate	2.875%	3.70%
Senior notes pricing		99.767%
Effective rate		3.853%
Offering close date		November 10, 2011
Proceeds from unsecured senior notes		$ 841,200			$ 699,237
Exchangeable senior notes repurchase prinicipal amount due 2037	$ 50,000
Repurchase settlement date	Nov. 09, 2011
Payments for repurchase of exchangeable senior debt	$ 50,200
500 North Capitol Street [Member]
Subsequent Event [Line Items]
Ownership percentage				30.00%
Construction loan commitment				$ 107,000
Construction loan				$ 33,300
Basis spread on variable rate basis				1.65%
Description of variable rate basis				LIBOR plus 1.65% per annum
Maturity date				Oct. 14, 2014
Number of extension options				2
Extension option years				1
Carrying amount of loan				$ 22,000
Development costs				$ 11,300
Two Grand Central Tower [Member]
Subsequent Event [Line Items]
Ownership percentage			60.00%
Square footage of real estate property			650,000
Carrying amount of loan			$ 176,600
Contractual sale price			401,000
Equity method investment, net sales proceeds			209,800
Transaction costs			14,600
Company's Share [Member] \| Two Grand Central Tower [Member]
Subsequent Event [Line Items]
Equity method investment, net sales proceeds			$ 125,900