Boston Properties (BXP) 10-K 28 Feb 19 2018 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2018	Feb. 22, 2019	Jun. 30, 2018
Document Information [Line Items]
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Entity Registrant Name	BOSTON PROPERTIES INC
Amendment Flag	false
Entity Central Index Key	1,037,540
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		154,509,216
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 19,330,126,978
Boston Properties Limited Partnership
Document Information [Line Items]
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Entity Registrant Name	BOSTON PROPERTIES LTD PARTNERSHIP
Amendment Flag	false
Entity Central Index Key	1,043,121
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		0
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
ASSETS
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $7,481,015 and $7,172,718 at December 31, 2018 and 2017, respectively )	$ 21,649,896	$ 21,096,642
Less: accumulated depreciation (amounts related to VIEs of $(965,500) and $(854,172) at December 31, 2018 and 2017, respectively	(4,897,777)	(4,589,634)
Total real estate	16,752,119	16,507,008
Cash and cash equivalents (amounts related to VIEs of $296,806 and $304,955 at December 31, 2018 and 2017, respectively)	543,359	434,767
Cash held in escrows	95,832	70,602
Investments in securities	28,198	29,161
Tenant and other receivables, net (amounts related to VIEs of $15,519 and $27,057 at December 31, 2018 and 2017, respectively)	86,629	92,186
Related party note receivable	80,000	0
Note receivable	19,468	0
Accrued rental income, net (amounts related to VIEs of $272,466 and $242,589 at December 31, 2018 and 2017, respectively)	934,896	861,575
Deferred charges, net (amounts related to VIEs of $263,402 and $281,678 at December 31, 2018 and 2017, respectively)	678,724	679,038
Prepaid expenses and other assets (amounts related to VIEs of $26,513 and $33,666 at December 31, 2018 and 2017, respectively)	80,943	77,971
Investments in unconsolidated joint ventures	956,309	619,925
Total assets	20,256,477	19,372,233
Liabilities:
Mortgage notes payable, net (amounts related to VIEs of $2,929,326 and $2,939,183 at December 31, 2018 and 2017, respectively)	2,964,572	2,979,281
Unsecured senior notes, net	7,544,697	7,247,330
Unsecured line of credit	0	45,000
Unsecured term loan, net	498,488	0
Accounts payable and accrued expenses (amounts related to VIEs of $75,786 and $106,683 at December 31, 2018 and 2017, respectively)	276,645	331,500
Dividends and distributions payable	165,114	139,040
Accrued interest payable	89,267	83,646
Other liabilities (amounts related to VIEs of $200,344 and $164,806 at December 31, 2018 and 2017, respectively)	503,726	443,980
Total liabilities	12,042,509	11,269,777
Commitments and contingencies	0	0
Equity / Capital:
Excess stock, $0.01 par value, 150,000,000 shares authorized, none issued or outstanding	0	0
Preferred stock, $0.01 par value, 50,000,000 shares authorized;
5.25% Series B cumulative redeemable preferred stock / units, liquidation preference $2,500 per share / unit, 80,000 shares / units issued and outstanding at December 31, 2018 and December 31, 2017, respectively	200,000	200,000
Common stock, $0.01 par value, 250,000,000 shares authorized, 154,537,378 and 154,404,186 issued and 154,458,478 and 154,325,286 outstanding at December 31, 2018 and December 31, 2017, respectively	1,545	1,543
Additional paid-in capital	6,407,623	6,377,908
Dividends in excess of earnings	(675,534)	(712,343)
Treasury common stock at cost, 78,900 shares at December 31, 2018 and December 31, 2017	(2,722)	(2,722)
Accumulated other comprehensive loss	(47,741)	(50,429)
Total stockholders' equity attributable to Boston Properties, Inc.	5,883,171	5,813,957
Noncontrolling interests:
Common units of the Operating Partnership	619,352	604,739
Property partnerships	1,711,445	1,683,760
Total equity / capital	8,213,968	8,102,456
Total liabilities and equity / capital	20,256,477	19,372,233
Boston Properties Limited Partnership
ASSETS
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $7,481,015 and $7,172,718 at December 31, 2018 and 2017, respectively )	21,251,540	20,685,164
Less: accumulated depreciation (amounts related to VIEs of $(965,500) and $(854,172) at December 31, 2018 and 2017, respectively	(4,800,475)	(4,496,959)
Total real estate	16,451,065	16,188,205
Cash and cash equivalents (amounts related to VIEs of $296,806 and $304,955 at December 31, 2018 and 2017, respectively)	543,359	434,767
Cash held in escrows	95,832	70,602
Investments in securities	28,198	29,161
Tenant and other receivables, net (amounts related to VIEs of $15,519 and $27,057 at December 31, 2018 and 2017, respectively)	86,629	92,186
Related party note receivable	80,000	0
Note receivable	19,468	0
Accrued rental income, net (amounts related to VIEs of $272,466 and $242,589 at December 31, 2018 and 2017, respectively)	934,896	861,575
Deferred charges, net (amounts related to VIEs of $263,402 and $281,678 at December 31, 2018 and 2017, respectively)	678,724	679,038
Prepaid expenses and other assets (amounts related to VIEs of $26,513 and $33,666 at December 31, 2018 and 2017, respectively)	80,943	77,971
Investments in unconsolidated joint ventures	956,309	619,925
Total assets	19,955,423	19,053,430
Liabilities:
Mortgage notes payable, net (amounts related to VIEs of $2,929,326 and $2,939,183 at December 31, 2018 and 2017, respectively)	2,964,572	2,979,281
Unsecured senior notes, net	7,544,697	7,247,330
Unsecured line of credit	0	45,000
Unsecured term loan, net	498,488	0
Accounts payable and accrued expenses (amounts related to VIEs of $75,786 and $106,683 at December 31, 2018 and 2017, respectively)	276,645	331,500
Dividends and distributions payable	165,114	139,040
Accrued interest payable	89,267	83,646
Other liabilities (amounts related to VIEs of $200,344 and $164,806 at December 31, 2018 and 2017, respectively)	503,726	443,980
Total liabilities	12,042,509	11,269,777
Commitments and contingencies	0	0
Noncontrolling interest:
Redeemable partnership units—16,783,558 and 16,810,378 common units and 991,577 and 818,343 long term incentive units outstanding at redemption value at December 31, 2018 and December 31, 2017, respectively	2,000,591	2,292,263
Preferred stock, $0.01 par value, 50,000,000 shares authorized;
5.25% Series B cumulative redeemable preferred stock / units, liquidation preference $2,500 per share / unit, 80,000 shares / units issued and outstanding at December 31, 2018 and December 31, 2017, respectively	193,623	193,623
Boston Properties Limited Partnership partners’ capital—1,722,336 and 1,719,540 general partner units and 152,736,142 and 152,605,746 limited partner units outstanding at December 31, 2018 and December 31, 2017, respectively	4,054,996	3,664,436
Accumulated other comprehensive loss	(47,741)	(50,429)
Total partners' capital	4,200,878	3,807,630
Noncontrolling interests:
Noncontrolling interests in property partnerships	1,711,445	1,683,760
Total equity / capital	5,912,323	5,491,390
Total liabilities and equity / capital	$ 19,955,423	$ 19,053,430

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
General Partners' Capital Account, Units Outstanding (in units)	1,722,336
Limited Partners' Capital Account, Units Outstanding (in units)	152,736,142
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
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares issued	154,537,378	154,404,186
Common stock, shares outstanding	154,458,478	154,325,286
Treasury common stock at cost, shares	78,900	78,900
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $7,481,015 and $7,172,718 at December 31, 2018 and 2017, respectively )	$ 21,649,896	$ 21,096,642
Less: accumulated depreciation (amounts related to VIEs of $(965,500) and $(854,172) at December 31, 2018 and 2017, respectively	(4,897,777)	(4,589,634)
Cash and cash equivalents (amounts related to VIEs of $296,806 and $304,955 at December 31, 2018 and 2017, respectively)	543,359	434,767
Cash held in escrows	95,832	70,602
Tenant and other receivables, net (amounts related to VIEs of $15,519 and $27,057 at December 31, 2018 and 2017, respectively)	86,629	92,186
Accrued rental income, net (amounts related to VIEs of $272,466 and $242,589 at December 31, 2018 and 2017, respectively)	934,896	861,575
Deferred charges, net (amounts related to VIEs of $263,402 and $281,678 at December 31, 2018 and 2017, respectively)	678,724	679,038
Prepaid expenses and other assets (amounts related to VIEs of $26,513 and $33,666 at December 31, 2018 and 2017, respectively)	80,943	77,971
Mortgage notes payable, net (amounts related to VIEs of $2,929,326 and $2,939,183 at December 31, 2018 and 2017, respectively)	2,964,572	2,979,281
Accounts payable and accrued expenses (amounts related to VIEs of $75,786 and $106,683 at December 31, 2018 and 2017, respectively)	276,645	331,500
Other liabilities (amounts related to VIEs of $200,344 and $164,806 at December 31, 2018 and 2017, respectively)	$ 503,726	$ 443,980
Series B Cumulative Redeemable Preferred Stock / Unit [Member]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	92,000	92,000
Series B Dividend Rate Percentage	5.25%	5.25%
Preferred stock / units, shares / units issued (in shares / units)	80,000	80,000
Series B Liquidation Preference Per Share/ Unit	$ 2,500	$ 2,500
Preferred stock / units, shares / units outstanding (in shares / units)	80,000	80,000
Boston Properties Limited Partnership
Redeemable Partnership Units Common Units Shares Outstanding (in units)	16,783,558	16,810,378
Redeemable Partnership Units Common Units Long Term Incentive Units At Redemption Value Units Outstanding (in units)	991,577	818,343
General Partners' Capital Account, Units Outstanding (in units)	1,722,336	1,719,540
Limited Partners' Capital Account, Units Outstanding (in units)	152,736,142	152,605,746
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $7,481,015 and $7,172,718 at December 31, 2018 and 2017, respectively )	$ 21,251,540	$ 20,685,164
Less: accumulated depreciation (amounts related to VIEs of $(965,500) and $(854,172) at December 31, 2018 and 2017, respectively	(4,800,475)	(4,496,959)
Cash and cash equivalents (amounts related to VIEs of $296,806 and $304,955 at December 31, 2018 and 2017, respectively)	543,359	434,767
Cash held in escrows	95,832	70,602
Tenant and other receivables, net (amounts related to VIEs of $15,519 and $27,057 at December 31, 2018 and 2017, respectively)	86,629	92,186
Accrued rental income, net (amounts related to VIEs of $272,466 and $242,589 at December 31, 2018 and 2017, respectively)	934,896	861,575
Deferred charges, net (amounts related to VIEs of $263,402 and $281,678 at December 31, 2018 and 2017, respectively)	678,724	679,038
Prepaid expenses and other assets (amounts related to VIEs of $26,513 and $33,666 at December 31, 2018 and 2017, respectively)	80,943	77,971
Mortgage notes payable, net (amounts related to VIEs of $2,929,326 and $2,939,183 at December 31, 2018 and 2017, respectively)	2,964,572	2,979,281
Accounts payable and accrued expenses (amounts related to VIEs of $75,786 and $106,683 at December 31, 2018 and 2017, respectively)	276,645	331,500
Other liabilities (amounts related to VIEs of $200,344 and $164,806 at December 31, 2018 and 2017, respectively)	$ 503,726	$ 443,980
Boston Properties Limited Partnership | Series B Cumulative Redeemable Preferred Stock / Unit [Member]
Series B Dividend Rate Percentage	5.25%	5.25%
Preferred stock / units, shares / units issued (in shares / units)	80,000	80,000
Series B Liquidation Preference Per Share/ Unit	$ 2,500	$ 2,500
Preferred stock / units, shares / units outstanding (in shares / units)	80,000	80,000
Variable Interest Entity, Primary Beneficiary [Member]
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $7,481,015 and $7,172,718 at December 31, 2018 and 2017, respectively )	$ 7,481,015	$ 7,172,718
Less: accumulated depreciation (amounts related to VIEs of $(965,500) and $(854,172) at December 31, 2018 and 2017, respectively	(965,500)	(854,172)
Cash and cash equivalents (amounts related to VIEs of $296,806 and $304,955 at December 31, 2018 and 2017, respectively)	296,806	304,955
Tenant and other receivables, net (amounts related to VIEs of $15,519 and $27,057 at December 31, 2018 and 2017, respectively)	15,519	27,057
Accrued rental income, net (amounts related to VIEs of $272,466 and $242,589 at December 31, 2018 and 2017, respectively)	272,466	242,589
Deferred charges, net (amounts related to VIEs of $263,402 and $281,678 at December 31, 2018 and 2017, respectively)	263,402	281,678
Prepaid expenses and other assets (amounts related to VIEs of $26,513 and $33,666 at December 31, 2018 and 2017, respectively)	26,513	33,666
Mortgage notes payable, net (amounts related to VIEs of $2,929,326 and $2,939,183 at December 31, 2018 and 2017, respectively)	2,929,326	2,939,183
Accounts payable and accrued expenses (amounts related to VIEs of $75,786 and $106,683 at December 31, 2018 and 2017, respectively)	75,786	106,683
Other liabilities (amounts related to VIEs of $200,344 and $164,806 at December 31, 2018 and 2017, respectively)	200,344	164,806
Variable Interest Entity, Primary Beneficiary [Member] | Boston Properties Limited Partnership
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $7,481,015 and $7,172,718 at December 31, 2018 and 2017, respectively )	7,481,015	7,172,718
Less: accumulated depreciation (amounts related to VIEs of $(965,500) and $(854,172) at December 31, 2018 and 2017, respectively	(965,500)	(854,172)
Cash and cash equivalents (amounts related to VIEs of $296,806 and $304,955 at December 31, 2018 and 2017, respectively)	296,806	304,955
Tenant and other receivables, net (amounts related to VIEs of $15,519 and $27,057 at December 31, 2018 and 2017, respectively)	15,519	27,057
Accrued rental income, net (amounts related to VIEs of $272,466 and $242,589 at December 31, 2018 and 2017, respectively)	272,466	242,589
Deferred charges, net (amounts related to VIEs of $263,402 and $281,678 at December 31, 2018 and 2017, respectively)	263,402	281,678
Prepaid expenses and other assets (amounts related to VIEs of $26,513 and $33,666 at December 31, 2018 and 2017, respectively)	26,513	33,666
Mortgage notes payable, net (amounts related to VIEs of $2,929,326 and $2,939,183 at December 31, 2018 and 2017, respectively)	2,929,326	2,939,183
Accounts payable and accrued expenses (amounts related to VIEs of $75,786 and $106,683 at December 31, 2018 and 2017, respectively)	75,786	106,683
Other liabilities (amounts related to VIEs of $200,344 and $164,806 at December 31, 2018 and 2017, respectively)	$ 200,344	$ 164,806

Consolidated Statements Of Oper

Consolidated Statements Of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue
Base rent	$ 2,103,723	$ 2,049,368	$ 2,017,767
Recoveries from tenants	402,066	367,500	358,975
Parking and other	107,421	105,000	100,910
Total rental revenue	2,613,210	2,521,868	2,477,652
Hotel revenue	49,118	45,603	44,884
Development and management services	45,158	34,605	28,284
Direct reimbursements of payroll and related costs from management services contracts	9,590	0	0
Total revenue	2,717,076	2,602,076	2,550,820
Expenses
Rental	979,151	929,977	889,768
Hotel	33,863	32,059	31,466
General and administrative	121,722	113,715	105,229
Payroll and related costs from management services contracts	9,590	0	0
Transaction costs	1,604	668	2,387
Depreciation and amortization	645,649	617,547	694,403
Total expenses	1,791,579	1,693,966	1,723,253
Other income (expense)
Income from unconsolidated joint ventures	2,222	11,232	8,074
Gain on sale of investment in unconsolidated joint venture	0	0	59,370
Gains on sales of real estate	182,356	7,663	80,606
Interest and other income	10,823	5,783	7,230
Gains (losses) from investments in securities	(1,865)	3,678	2,273
Impairment losses	(11,812)	0	(1,783)
Interest expense	(378,168)	(374,481)	(412,849)
Gains (losses) from early extinguishments of debt	(16,490)	496	(371)
Losses from interest rate contracts	0	0	(140)
Net income	712,563	562,481	569,977
Net income attributable to noncontrolling interests
Noncontrolling interests in property partnerships	(62,909)	(47,832)	2,068
Noncontrolling interest - common units of the Operating Partnership	(66,807)	(52,210)	(59,260)
Net income attributable to the Company	582,847	462,439	512,785
Preferred dividends / distributions	(10,500)	(10,500)	(10,500)
Net income attributable to the Company's common shareholders / unitholders	$ 572,347	$ 451,939	$ 502,285
Basic earnings per common share / unit attributable to the Company
Net income (in dollars per share / unit)	$ 3.71	$ 2.93	$ 3.27
Weighted average number of common shares / units outstanding (in shares / units)	154,427	154,190	153,715
Diluted earnings per common share / unit attributable to the Company
Diluted Earnings: Net income, Per Share / Unit Amount (in dollars per share / unit)	$ 3.70	$ 2.93	$ 3.26
Weighted average number of common and common equivalent shares / units outstanding (in shares / units)	154,682	154,390	153,977
Boston Properties Limited Partnership
Revenue
Base rent	$ 2,103,723	$ 2,049,368	$ 2,017,767
Recoveries from tenants	402,066	367,500	358,975
Parking and other	107,421	105,000	100,910
Total rental revenue	2,613,210	2,521,868	2,477,652
Hotel revenue	49,118	45,603	44,884
Development and management services	45,158	34,605	28,284
Direct reimbursements of payroll and related costs from management services contracts	9,590	0	0
Total revenue	2,717,076	2,602,076	2,550,820
Expenses
Rental	979,151	929,977	889,768
Hotel	33,863	32,059	31,466
General and administrative	121,722	113,715	105,229
Payroll and related costs from management services contracts	9,590	0	0
Transaction costs	1,604	668	2,387
Depreciation and amortization	637,891	609,407
Total expenses	1,783,821	1,685,826	1,711,626
Other income (expense)
Income from unconsolidated joint ventures	2,222	11,232	8,074
Gain on sale of investment in unconsolidated joint venture	0	0	59,370
Gains on sales of real estate	190,716	8,240	82,775
Interest and other income	10,823	5,783	7,230
Gains (losses) from investments in securities	(1,865)	3,678	2,273
Impairment losses	(10,181)	0	(1,783)
Interest expense	(378,168)	(374,481)	(412,849)
Gains (losses) from early extinguishments of debt	(16,490)	496	(371)
Losses from interest rate contracts	0	0	(140)
Net income	730,312	571,198	583,773
Net income attributable to noncontrolling interests
Noncontrolling interests in property partnerships	(62,909)	(47,832)	2,068
Net income attributable to the Company	667,403	523,366	585,841
Preferred dividends / distributions	(10,500)	(10,500)	(10,500)
Net income attributable to the Company's common shareholders / unitholders	$ 656,903	$ 512,866	$ 575,341
Basic earnings per common share / unit attributable to the Company
Net income (in dollars per share / unit)	$ 3.82	$ 2.99	$ 3.36
Weighted average number of common shares / units outstanding (in shares / units)	171,912	171,661	171,361
Diluted earnings per common share / unit attributable to the Company
Diluted Earnings: Net income, Per Share / Unit Amount (in dollars per share / unit)	$ 3.81	$ 2.98	$ 3.35
Weighted average number of common and common equivalent shares / units outstanding (in shares / units)	172,167	171,861	171,623

Consolidated Statements Of Comp

Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net income		$ 712,563	$ 562,481	$ 569,977
Other comprehensive income (loss):
Effective portion of interest rate contracts		(3,096)	(6,133)	(47,144)
Amortization of interest rate contracts	[1]	6,664	6,033	3,751
Other comprehensive income (loss)		3,568	(100)	(43,393)
Comprehensive Income		716,131	562,381	526,584
Comprehensive income attributable to noncontrolling interests		(129,716)	(100,042)	(57,192)
Other comprehensive income (loss) attributable to noncontrolling interests		(880)	1,922	5,256
Comprehensive income attributable to the Company		585,535	464,261	474,648
Boston Properties Limited Partnership
Net income		730,312	571,198	583,773
Other comprehensive income (loss):
Effective portion of interest rate contracts		(3,096)	(6,133)	(47,144)
Amortization of interest rate contracts	[2]	6,664	6,033	3,751
Other comprehensive income (loss)		3,568	(100)	(43,393)
Comprehensive Income		733,880	571,098	540,380
Comprehensive income attributable to noncontrolling interests		(63,485)	(45,704)	2,945
Comprehensive income attributable to the Company		$ 670,395	$ 525,394	$ 543,325
[1]	Amounts reclassified from comprehensive income primarily to interest expense within Boston Properties, Inc.’s Consolidated Statements of Operations
[2]	Amounts reclassified from comprehensive income primarily to interest expense within Boston Properties Limited Partnership's Consolidated Statements of Operations.

Consolidated Statements Of Stoc

Consolidated Statements Of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Preferred Stock [Member]	Additional Paid-In Capital [Member]	Dividends In Excess Of Earnings [Member]	Treasury Stock, At Cost [Member]	Accumulated Other Comprehensive Loss [Member]	Noncontrolling Interests [Member]
Equity, value at Dec. 31, 2015	$ 7,886,927	$ 1,536	$ 200,000	$ 6,305,687	$ (780,952)	$ (2,722)	$ (14,114)	$ 2,177,492
Equity, shares at Dec. 31, 2015		153,580,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Redemption of operating partnership units to common stock		191,000
Redemption of operating partnership units to common stock	0	$ 2		6,459				(6,461)
Allocated net income for the year	569,977				512,785			57,192
Dividends/distributions declared	(474,614)				(425,527)			(49,087)
Shares issued pursuant to stock purchase plan, shares		6,000
Shares issued pursuant to stock purchase plan, value	730			730
Net activity from stock option and incentive plan, shares		13,000
Net activity from stock option and incentive plan, value	31,910			3,979				27,931
Sale of interests in property partnerships	0			1,195				(1,195)
Contributions from noncontrolling interests in property partnerships	11,951							11,951
Distributions to noncontrolling interests in property partnerships	(51,564)							(51,564)
Effective portion of interest rate contracts	(47,144)						(41,502)	(5,642)
Amortization of interest rate contracts	3,751						3,365	386
Reallocation of noncontrolling interest	0			15,374				(15,374)
Equity, value at Dec. 31, 2016	7,931,924	$ 1,538	200,000	6,333,424	(693,694)	(2,722)	(52,251)	2,145,629
Equity, shares at Dec. 31, 2016		153,790,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of a change in accounting principle	(2,035)				(272)			(1,763)
Redemption of operating partnership units to common stock		495,000
Redemption of operating partnership units to common stock	0	$ 5		16,911				(16,916)
Allocated net income for the year	562,481				462,439			100,042
Dividends/distributions declared	(535,310)				(480,816)			(54,494)
Shares issued pursuant to stock purchase plan, shares		6,000
Shares issued pursuant to stock purchase plan, value	795			795
Net activity from stock option and incentive plan, shares		34,000
Net activity from stock option and incentive plan, value	37,292			3,899				33,393
Contributions from noncontrolling interests in property partnerships	161,585							161,585
Distributions to noncontrolling interests in property partnerships	(54,176)							(54,176)
Effective portion of interest rate contracts	(6,133)						(3,305)	(2,828)
Amortization of interest rate contracts	6,033						5,127	906
Reallocation of noncontrolling interest	0			22,879				(22,879)
Equity, value at Dec. 31, 2017	$ 8,102,456	$ 1,543	200,000	6,377,908	(712,343)	(2,722)	(50,429)	2,288,499
Equity, shares at Dec. 31, 2017	154,325,286	154,325,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of a change in accounting principle	$ 5,496				4,933			563
Redemption of operating partnership units to common stock		83,000
Redemption of operating partnership units to common stock	0	$ 2		2,878				(2,880)
Allocated net income for the year	712,563				582,847			129,716
Dividends/distributions declared	(613,702)				(550,971)			(62,731)
Shares issued pursuant to stock purchase plan, shares		6,000
Shares issued pursuant to stock purchase plan, value	797			797
Net activity from stock option and incentive plan, shares		44,000
Net activity from stock option and incentive plan, value	38,590			1,729				36,861
Contributions from noncontrolling interests in property partnerships	46,701							46,701
Distributions to noncontrolling interests in property partnerships	(82,501)							(82,501)
Effective portion of interest rate contracts	(3,096)						(2,781)	(315)
Amortization of interest rate contracts	6,664						5,469	1,195
Reallocation of noncontrolling interest	0			24,311				(24,311)
Equity, value at Dec. 31, 2018	$ 8,213,968	$ 1,545	$ 200,000	$ 6,407,623	$ (675,534)	$ (2,722)	$ (47,741)	$ 2,330,797
Equity, shares at Dec. 31, 2018	154,458,478	154,458,000

Consolidated Statement of Partn

Consolidated Statement of Partners' Capital Statement - USD ($) $ in Thousands	Total	Boston Properties Limited Partnership
Beginning balance at Dec. 31, 2015		$ 3,684,522
Increase (Decrease) in Partners' Capital [Roll Forward]
Contributions		3,144
Net income allocable to general and limited partner units		526,581
Distributions		(425,527)
Other comprehensive Income (loss)		(38,137)
Unearned compensation		2,760
Conversion of redeemable partnership units		6,461
Adjustment to reflect redeemable partnership units at redemption value		51,913
Ending Balance at Dec. 31, 2016		3,811,717
Increase (Decrease) in Partners' Capital [Roll Forward]
Cumulative effect of a change in accounting principle	$ (2,035)	(272)
Contributions		4,937
Net income allocable to general and limited partner units		471,156
Distributions		(480,816)
Accumulated Other Comprehensive Loss Allocable To General And Limited Partner Units		1,822
Unearned compensation		(243)
Conversion of redeemable partnership units		16,916
Adjustment to reflect redeemable partnership units at redemption value		(17,587)
Ending Balance at Dec. 31, 2017		3,807,630
Increase (Decrease) in Partners' Capital [Roll Forward]
Cumulative effect of a change in accounting principle	$ 5,496	4,933
Contributions		1,642
Net income allocable to general and limited partner units		600,596
Distributions		(550,971)
Accumulated Other Comprehensive Loss Allocable To General And Limited Partner Units		2,688
Unearned compensation		884
Conversion of redeemable partnership units		2,880
Adjustment to reflect redeemable partnership units at redemption value		330,596
Ending Balance at Dec. 31, 2018		$ 4,200,878

Consolidated Statements Of Cash

Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net income	$ 712,563	$ 562,481	$ 569,977
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	645,649	617,547	694,403
Impairment loss	11,812	0	1,783
Non-cash compensation expense	40,117	35,361	32,911
Income from unconsolidated joint ventures	(2,222)	(11,232)	(8,074)
Gain on sale of investment in unconsolidated joint venture	0	0	(59,370)
Distributions of net cash flow from operations of unconsolidated joint ventures	6,703	26,858	24,955
(Gains) losses on investments in securities	1,865	(3,678)	(2,273)
Non-cash portion of interest expense	21,303	(1,284)	(35,052)
Settlement of accreted debt discount on redemption of unsecured senior notes	(483)	(1,980)	0
Losses (gains) from early extinguishments of debt	16,490	(496)	371
Gains on sales of real estate	(182,356)	(7,663)	(80,606)
Change in assets and liabilities:
Tenant and other receivables, net	29,204	2,433	3,688
Note receivable	(13)	0	0
Accrued rental income, net	(43,662)	(58,355)	(28,127)
Prepaid expenses and other assets	12,472	51,425	52,923
Accounts payable and accrued expenses	1,353	10,482	15,666
Accrued interest payable	5,237	(160,521)	53,547
Other liabilities	4,955	(44,970)	(106,071)
Tenant leasing costs	(130,742)	(104,429)	(96,103)
Total adjustments	437,682	349,498	464,571
Net cash provided by operating activities	1,150,245	911,979	1,034,548
Cash flows from investing activities:
Acquisitions of real estate	0	(15,953)	(78,000)
Construction in progress	(694,791)	(608,404)	(500,350)
Building and other capital improvements	(189,771)	(222,482)	(150,640)
Tenant improvements	(210,034)	(205,331)	(230,298)
Proceeds from sales of real estate	455,409	29,810	122,750
Capital contributions to unconsolidated joint ventures	(345,717)	(109,015)	(575,795)
Capital distributions from unconsolidated joint ventures	0	251,000	20,440
Proceeds from sale of investment in unconsolidated joint venture	0	0	55,707
Deposit on capital lease	(13,615)	0	0
Issuance of related party note receivable	(80,000)	0	0
Issuance of note receivable	(19,455)	0	0
Investments in securities, net	(902)	(1,669)	(1,161)
Net cash used in investing activities	(1,098,876)	(882,044)	(1,337,347)
Cash flows from financing activities:
Proceeds from mortgage notes payable	0	2,300,000	0
Repayments of mortgage notes payable	(18,634)	(1,317,653)	(1,326,865)
Proceeds from unsecured senior notes	996,410	847,935	1,989,790
Redemption of unsecured senior notes	(699,517)	(848,020)	0
Borrowings on unsecured line of credit	745,000	580,000	25,000
Repayments of unsecured line of credit	(790,000)	(535,000)	(25,000)
Proceeds from unsecured term loan	500,000	0	0
Repayments of mezzanine notes payable	0	(306,000)	0
Repayments of outside members’ notes payable	0	(70,424)	0
Payments on capital lease obligations	(1,353)	(493)	(745)
Payments on real estate financing transactions	(960)	(2,840)	(5,260)
Deposit on mortgage note payable interest rate lock	0	(23,200)	0
Return of deposit on mortgage note payable interest rate lock	0	23,200	0
Deferred financing costs	(8,362)	(50,705)	(16,121)
Debt prepayment and extinguishment costs	(15,973)	(12,784)	0
Net proceeds from equity transactions	(730)	241	(271)
Dividends and distributions	(587,628)	(526,578)	(671,626)
Contributions from noncontrolling interests in property partnerships	46,701	52,009	11,951
Distributions to noncontrolling interests in property partnerships	(82,501)	(54,342)	(55,474)
Net cash provided by (used in) financing activities	82,453	55,346	(74,621)
Net increase (decrease) in cash and cash equivalents	133,822	85,281	(377,420)
Cash and cash equivalents and cash held in escrows, beginning of year	505,369	420,088	797,508
Cash and cash equivalents and cash held in escrows, end of year	639,191	505,369	420,088
Reconciliation of cash and cash equivalents and cash held in escrow
Cash and cash equivalents, beginning of year	434,767	356,914	723,718
Cash held in escrows, beginning of period	70,602	63,174	73,790
Cash and cash equivalents, end of year	543,359	434,767	356,914
Cash held in escrows,end of period	95,832	70,602	63,174
Supplemental disclosures:
Cash paid for interest	416,019	598,486	433,591
Interest capitalized	65,766	61,070	39,200
Non-cash investing and financing activities:
Write-off of fully depreciated real estate	(135,431)	(124,891)	(206,721)
Change in real estate included in accounts payable and accrued expenses	(44,866)	27,978	(1,481)
Real estate acquired through capital lease	12,397	28,962	21,000
Outside members’ notes payable contributed to noncontrolling interests in property partnerships	0	109,576	0
Dividends and distributions declared but not paid	165,114	139,040	130,308
Conversions of noncontrolling interests to stockholders’ equity	2,880	16,916	6,461
Issuance of restricted securities to employees and directors	37,052	35,989	33,615
Boston Properties Limited Partnership
Net income	730,312	571,198	583,773
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	637,891	609,407	682,776
Impairment loss	10,181	0	1,783
Non-cash compensation expense	40,117	35,361	32,911
Income from unconsolidated joint ventures	(2,222)	(11,232)	(8,074)
Gain on sale of investment in unconsolidated joint venture	0	0	(59,370)
Distributions of net cash flow from operations of unconsolidated joint ventures	6,703	26,858	24,955
(Gains) losses on investments in securities	1,865	(3,678)	(2,273)
Non-cash portion of interest expense	21,303	(1,284)	(35,052)
Settlement of accreted debt discount on redemption of unsecured senior notes	(483)	(1,980)	0
Losses (gains) from early extinguishments of debt	16,490	(496)	371
Gains on sales of real estate	(190,716)	(8,240)	(82,775)
Change in assets and liabilities:
Tenant and other receivables, net	29,204	2,433	3,688
Note receivable	(13)	0	0
Accrued rental income, net	(43,662)	(58,355)	(28,127)
Prepaid expenses and other assets	12,472	51,425	52,923
Accounts payable and accrued expenses	1,353	10,482	15,666
Accrued interest payable	5,237	(160,521)	53,547
Other liabilities	4,955	(44,970)	(106,071)
Tenant leasing costs	(130,742)	(104,429)	(96,103)
Total adjustments	419,933	340,781	450,775
Net cash provided by operating activities	1,150,245	911,979	1,034,548
Cash flows from investing activities:
Acquisitions of real estate	0	(15,953)	(78,000)
Construction in progress	(694,791)	(608,404)	(500,350)
Building and other capital improvements	(189,771)	(222,482)	(150,640)
Tenant improvements	(210,034)	(205,331)	(230,298)
Proceeds from sales of real estate	455,409	29,810	122,750
Capital contributions to unconsolidated joint ventures	(345,717)	(109,015)	(575,795)
Capital distributions from unconsolidated joint ventures	0	251,000	20,440
Proceeds from sale of investment in unconsolidated joint venture	0	0	55,707
Deposit on capital lease	(13,615)	0	0
Issuance of related party note receivable	(80,000)	0	0
Issuance of note receivable	(19,455)	0	0
Investments in securities, net	(902)	(1,669)	(1,161)
Net cash used in investing activities	(1,098,876)	(882,044)	(1,337,347)
Cash flows from financing activities:
Proceeds from mortgage notes payable	0	2,300,000	0
Repayments of mortgage notes payable	(18,634)	(1,317,653)	(1,326,865)
Proceeds from unsecured senior notes	996,410	847,935	1,989,790
Redemption of unsecured senior notes	(699,517)	(848,020)	0
Borrowings on unsecured line of credit	745,000	580,000	25,000
Repayments of unsecured line of credit	(790,000)	(535,000)	(25,000)
Proceeds from unsecured term loan	500,000	0	0
Repayments of mezzanine notes payable	0	(306,000)	0
Repayments of outside members’ notes payable	0	(70,424)	0
Payments on capital lease obligations	(1,353)	(493)	(745)
Payments on real estate financing transactions	(960)	(2,840)	(5,260)
Deposit on mortgage note payable interest rate lock	0	(23,200)	0
Return of deposit on mortgage note payable interest rate lock	0	23,200	0
Deferred financing costs	(8,362)	(50,705)	(16,121)
Debt prepayment and extinguishment costs	(15,973)	(12,784)	0
Net proceeds from equity transactions	(730)	241	(271)
Dividends and distributions	(587,628)	(526,578)	(671,626)
Contributions from noncontrolling interests in property partnerships	46,701	52,009	11,951
Distributions to noncontrolling interests in property partnerships	(82,501)	(54,342)	(55,474)
Net cash provided by (used in) financing activities	82,453	55,346	(74,621)
Net increase (decrease) in cash and cash equivalents	133,822	85,281	(377,420)
Cash and cash equivalents and cash held in escrows, beginning of year	505,369	420,088	797,508
Cash and cash equivalents and cash held in escrows, end of year	639,191	505,369	420,088
Reconciliation of cash and cash equivalents and cash held in escrow
Cash and cash equivalents, beginning of year	434,767	356,914	723,718
Cash held in escrows, beginning of period	70,602	63,174	73,790
Cash and cash equivalents, end of year	543,359	434,767	356,914
Cash held in escrows,end of period	95,832	70,602	63,174
Supplemental disclosures:
Cash paid for interest	416,019	598,486	433,591
Interest capitalized	65,766	61,070	39,237
Non-cash investing and financing activities:
Write-off of fully depreciated real estate	(135,431)	(123,714)	(202,388)
Change in real estate included in accounts payable and accrued expenses	(44,866)	27,978	(1,481)
Real estate acquired through capital lease	12,397	28,962	21,000
Outside members’ notes payable contributed to noncontrolling interests in property partnerships	0	109,576	0
Dividends and distributions declared but not paid	165,114	139,040	130,308
Conversions of noncontrolling interests to stockholders’ equity	2,880	16,916	6,461
Issuance Of Restricted Units To Employees And Directors	$ 37,052	$ 35,989	$ 33,615

Organization

Organization	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	1. Organization Boston Properties, Inc., a Delaware corporation, is a fully integrated, self-administered and self-managed real estate investment trust (“REIT”). Boston Properties, Inc. is the sole general partner of Boston Properties Limited Partnership, its operating partnership and at December 31, 2018 owned an approximate 89.7% ( 89.7% at December 31, 2017 ) general and limited partnership interest in Boston Properties Limited Partnership. Unless stated otherwise or the context requires, the “Company” refers to Boston Properties, Inc. and its subsidiaries, including Boston Properties Limited Partnership and its consolidated subsidiaries. Partnership interests in Boston Properties Limited Partnership include: • common units of partnership interest (also referred to as “OP Units”), • long term incentive units of partnership interest (also referred to as “LTIP Units”), and • preferred units of partnership interest (also referred to as “Preferred Units”). Unless specifically noted otherwise, all references to OP Units exclude units held by Boston Properties, Inc. A holder of an OP Unit may present such OP Unit to Boston Properties Limited 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, Boston Properties Limited Partnership is obligated to redeem the OP Unit for cash equal to the value of a share of common stock of Boston Properties, Inc. (“Common Stock”). In lieu of a cash redemption, Boston Properties, Inc. may elect to acquire the 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 Boston Properties, Inc. 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. The Company uses LTIP Units as a form of equity-based award for annual long-term incentive equity compensation. The Company has also issued LTIP Units to employees in the form of (1) 2012 outperformance plan awards (“2012 OPP Units”) and (2) 2013, 2014, 2015, 2016, 2017 and 2018 multi-year, long-term incentive program awards (also referred to as “MYLTIP Units”), each of which, upon the satisfaction of certain performance and vesting conditions, is convertible into one OP Unit. The three-year measurement periods for the 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units and 2015 MYLTIP Units expired on February 6, 2015, February 4, 2016, February 3, 2017 and February 4, 2018, respectively, and Boston Properties, Inc.’s total stockholder return (“TSR”) was sufficient for employees to earn and therefore become eligible to vest in a portion of the awards. Unless and until they are earned, the rights, preferences and privileges of the 2016, 2017 and 2018 MYLTIP Units differ from other LTIP Units granted to employees (including the 2012 OPP Units, the 2013 MYLTIP Units, the 2014 MYLTIP Units and the 2015 MYLTIP Units, which have been earned). Therefore, unless specifically noted otherwise, all references to LTIP Units exclude the 2016, 2017 and 2018 MYLTIP Units. LTIP Units (including the earned 2012 OPP Units, the 2013 MYLTIP Units, the 2014 MYLTIP Units and the 2015 MYLTIP 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 Notes 10 , 16 and 19 ). At December 31, 2018 , there was one series of Preferred Units outstanding (i.e., Series B Preferred Units). The Series B Preferred Units were issued to Boston Properties, Inc. on March 27, 2013 in connection with the issuance of 80,000 shares ( 8,000,000 depositary shares each representing 1/100th of a share) of 5.25% Series B Cumulative Redeemable Preferred Stock (the “Series B Preferred Stock”). Boston Properties, Inc. contributed the net proceeds from the offering to Boston Properties Limited Partnership in exchange for 80,000 Series B Preferred Units having terms and preferences generally mirroring those of the Series B Preferred Stock (See Note 11 ). Properties At December 31, 2018 , the Company owned or had interests in a portfolio of 197 commercial real estate properties (the “Properties”) aggregating approximately 51.6 million net rentable square feet of primarily Class A office properties, including 11 properties under construction/redevelopment totaling approximately 5.3 million net rentable square feet. At December 31, 2018 , the Properties consisted of: • 178 office properties (including nine properties under construction/redevelopment); • twelve retail properties; • six residential properties (including two properties under construction); and • one hotel. The Company considers Class A office properties to be well 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. Basis of Presentation The accompanying consolidated financial statements are presented using the accrual basis of accounting in conformity with accounting principles generally accepted in the United States of America. Boston Properties, Inc. does not have any other significant assets, liabilities or operations, other than its investment in Boston Properties Limited Partnership, nor does it have employees of its own. Boston Properties Limited Partnership, not Boston Properties, Inc., generally executes all significant business relationships other than transactions involving securities of Boston Properties, Inc. All majority-owned subsidiaries and joint ventures over which the Company has financial and operating control and variable interest entities (“VIEs”) 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. Variable Interest Entities (VIEs) On January 1, 2016, the Company adopted Accounting Standards Update (“ASU”) ASU 2015-02, “Consolidation (Topic 810): Amendments to the Consolidation Analysis” (“ASU 2015-02”). ASU 2015-02 affects reporting entities that are required to evaluate whether they should consolidate certain legal entities. ASU 2015-02 (1) modifies the evaluation of whether limited partnerships and similar legal entities are VIEs or voting interest entities, (2) eliminates the presumption that a general partner should consolidate a limited partnership and (3) affects the consolidation analysis of reporting entities that are involved with VIEs, particularly those that have fee arrangements and related party relationships. The Company reviewed all of its legal entities in accordance with ASU 2015-02 and concluded that certain of its legal entities, including Boston Properties Limited Partnership, which had been consolidated in accordance with the voting interest model, are now variable interest entities under the VIE model, as discussed below. The adoption of the guidance did not alter any of the Company’s consolidation conclusions, but resulted in additional disclosures. Consolidated VIEs are those where the Company is considered to be the primary beneficiary of a VIE. The primary beneficiary is the entity that has a controlling financial interest in the VIE, which is defined by the entity having both of the following characteristics: (1) the power to direct the activities that, when taken together, most significantly impact the VIE’s performance and (2) the obligation to absorb losses or the right to receive the returns from the VIE that could potentially be significant to the VIE. The Company has determined that it is the primary beneficiary for seven of the ten entities that are VIEs. Consolidated Variable Interest Entities As of December 31, 2018 , Boston Properties, Inc. has identified seven consolidated VIEs, including Boston Properties Limited Partnership. Excluding Boston Properties Limited Partnership, the VIEs are the following six in-service properties: 767 Fifth Avenue (the General Motors Building), Time Square Tower, 601 Lexington Avenue, Atlantic Wharf Office Building, 100 Federal Street and Salesforce Tower. The Company consolidates these VIEs because it is the primary beneficiary. The third parties’ interests in these consolidated entities (i.e., excluding Boston Properties Limited Partnership's interest), are reflected as noncontrolling interests in property partnerships in the accompanying Consolidated Financial Statements (See Note 10 ). In addition, Boston Properties, Inc.’s only significant asset is its investment in Boston Properties Limited Partnership and, consequently, substantially all of Boston Properties, Inc.’s assets and liabilities are the assets and liabilities of Boston Properties Limited Partnership. Variable Interest Entities Not Consolidated The Company has determined that its 7750 Wisconsin Avenue LLC and Office Tower Developer LLC joint ventures, which own 7750 Wisconsin Avenue and 100 Causeway Street (which is the office component of The Hub on Causeway mixed-use development project), respectively, are VIEs. The Company also determined that the landlord entity for its Platform 16 ground lease is a VIE. The Company does not consolidate these entities as the Company does not have the power to direct the activities that, when taken together, most significantly impact the VIE’s performance and, therefore, the Company is not considered to be the primary beneficiary.

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Basis Of Presentation And Summary Of Significant Accounting Policies	2. Summary of Significant Accounting Policies Real Estate Upon acquisitions of real estate, which includes the consolidation of previously unconsolidated joint ventures, the Company assesses the fair value of acquired tangible and intangible assets (including land, buildings, tenant improvements, “above-” and “below-market” leases, leasing and assumed financing origination costs, acquired in-place leases, other identified intangible assets and assumed liabilities) and allocates the purchase price to the acquired assets and assumed liabilities, including land and buildings as if vacant. The Company assesses and considers fair value based on estimated cash flow projections that utilize discount and/or capitalization rates that it deems appropriate, as well as available market information. Estimates of future cash flows are based on a number of factors including the historical operating results, known and anticipated trends, and market and economic conditions. The fair value of the tangible assets of an acquired property considers the value of the property as if it were vacant. The Company also considers an allocation of purchase price of other acquired intangibles, including acquired in-place leases that may have a customer relationship intangible value, including (but not limited to) the nature and extent of the existing relationship with the tenants, the tenants’ credit quality and expectations of lease renewals. Based on its acquisitions to date, the Company’s allocation to customer relationship intangible assets has been immaterial. The Company records acquired “above-” and “below-market” leases at their fair values (using a discount rate which reflects the risks associated with the leases acquired) equal to the difference between (1) the contractual amounts to be paid pursuant to each in-place lease and (2) management’s estimate of fair market lease rates for each corresponding in-place lease, measured over a period equal to the remaining term of the lease for above-market leases and the initial term plus the term of any below-market fixed rate renewal options for below-market leases. Acquired “above-” and “below-market” lease values have been reflected within Prepaid Expenses and Other Assets and Other Liabilities, respectively, in the Company’s Consolidated Balance Sheets. Other intangible assets acquired include amounts for in-place lease values that are based on the Company’s evaluation of the specific characteristics of each tenant’s lease. Factors to be considered include estimates of carrying costs during hypothetical expected lease-up periods considering current market conditions, and costs to execute similar leases. In estimating carrying costs, the Company includes real estate taxes, insurance and other operating expenses and estimates of lost rentals at market rates during the expected lease-up periods, depending on local market conditions. In estimating costs to execute similar leases, the Company considers leasing commissions, legal and other related expenses. Management reviews its long-lived assets for impairment following the end of each quarter and when there is an event or change in circumstances that indicates an impairment in value. An impairment loss is recognized if the carrying amount of an asset is not recoverable and exceeds its fair value. The evaluation of anticipated cash flows is highly subjective and is based in part on assumptions regarding anticipated hold periods, future occupancy, rental rates and capital requirements that could differ materially from actual results in future periods. Because cash flows on properties considered to be “long-lived assets to be held and used” are considered on an undiscounted basis to determine whether an asset has been impaired, the Company’s established strategy of holding properties over the long term directly decreases the likelihood of recording an impairment loss. If the Company’s strategy changes or market conditions otherwise dictate an earlier sale date, an impairment loss may be recognized and such loss could be material. If the Company determines that an impairment has occurred, the affected assets must be reduced to their fair value. Guidance in Accounting Standards Codification (“ASC”) 360 “Property Plant and Equipment” (“ASC 360”) requires that qualifying assets and liabilities and the results of operations that have been sold, or otherwise qualify as “held for sale,” be presented as discontinued operations in all periods presented if the property operations are expected to be eliminated and the Company will not have significant continuing involvement following the sale. Discontinued operations presentation applies only to disposals representing a strategic shift that has (or will have) a major effect on an entity’s operations and financial results (e.g., a disposal of a major geographical area, a major line of business, a major equity method investment or other major parts of an entity). The components of the property’s net income that are reflected as discontinued operations include the net gain (or loss) upon the disposition of the property held for sale, operating results, depreciation and interest expense (if the property is subject to a secured loan). The Company generally considers assets to be “held for sale” when the transaction has been approved by Boston Properties, Inc.’s Board of Directors, or a committee thereof, and there are no known significant contingencies relating to the sale, such that a sale of the property within one year is considered probable. Following the classification of a property as “held for sale,” no further depreciation is recorded on the assets, and the asset is written down to the lower of carrying value or fair market value, less cost to sell. Real estate is stated at depreciated cost. A variety of costs are incurred in the acquisition, development and leasing of properties. The cost of buildings and improvements includes the purchase price of property, legal fees and other acquisition costs. The Company capitalizes acquisition costs that it incurs to effect an asset acquisition and expenses acquisition costs that it incurs to effect a business combination, including legal, due diligence and other closing related costs. Costs directly related to the development of properties are capitalized. Capitalized development costs include interest, internal wages, property taxes, insurance, and other project costs incurred during the period of development. After the determination is made to capitalize a cost, it is allocated to the specific component of the project that benefited from the investment. Determination of when a development project commences and capitalization begins, and when a development project is substantially complete and held available for occupancy and capitalization must cease, involves a degree of judgment. The Company’s capitalization policy on development properties follows the guidance in ASC 835-20 “Capitalization of Interest” and ASC 970 “Real Estate-General.” The costs of land and buildings under development include specifically identifiable costs. Capitalized costs include pre-construction costs necessary to the development of the property, development costs, construction costs, interest costs, real estate taxes, salaries and related costs and other costs incurred during the period of development. The Company begins the capitalization of costs during the pre-construction period, which it defines as activities that are necessary for the development of the property. The Company considers a construction project as substantially complete and held available for occupancy upon the completion of tenant improvements, but no later than one year from cessation of major construction activity. The Company ceases capitalization on the portion (1) substantially completed, (2) occupied or held available for occupancy, and capitalizes only those costs associated with the portion under construction or (3) if activities necessary for the development of the property have been suspended. Interest costs capitalized for the years ended December 31, 2018 , 2017 and 2016 were approximately $65.8 million , $61.1 million and $39.2 million , respectively. Salaries and related costs capitalized for the years ended December 31, 2018 , 2017 and 2016 were approximately $12.5 million , $13.2 million and $11.1 million , respectively. Expenditures for repairs and maintenance are charged to operations as incurred. Significant betterments are capitalized. When assets are sold or retired, their costs and related accumulated depreciation are removed from the accounts with the resulting gains or losses reflected in net income or loss for the period. The Company computes depreciation and amortization on properties using the straight-line method based on estimated useful asset lives. In accordance with ASC 805 “Business Combinations,” the Company allocates the acquisition cost of real estate to its components and depreciates or amortizes these assets (or liabilities) over their useful lives. The amortization of acquired “above-” and “below-market” leases and acquired in-place leases is recorded as an adjustment to revenue and depreciation and amortization, respectively, in the Consolidated Statements of Operations. Depreciation is computed on a straight-line basis over the estimated useful lives of the assets as follows: Land improvements 25 to 40 years Buildings and improvements 10 to 40 years Tenant improvements Shorter of useful life or terms of related lease Furniture, fixtures, and equipment 3 to 7 years Cash and Cash Equivalents Cash and cash equivalents consist of cash on hand and investments with maturities of three months or less from the date of purchase. The majority of the Company’s cash and cash equivalents are held at major commercial banks which may at times exceed the Federal Deposit Insurance Corporation limit of $250,000 . Cash Held in Escrows Escrows include amounts established pursuant to various agreements for security deposits, property taxes, insurance and other costs. Escrows also include cash held by qualified intermediaries for possible investments in like-kind exchanges in accordance with Section 1031 of the Internal Revenue Code in connection with sales of the Company’s properties. Investments in Securities The Company accounts for investments in trading securities at fair value, with gains or losses resulting from changes in fair value recognized currently in earnings. The designation of trading securities is generally determined at acquisition. The Company maintains a deferred compensation plan that is designed to allow officers of Boston Properties, Inc. to defer a portion of their current income on a pre-tax basis and receive a tax-deferred return on these deferrals. The Company’s obligation under the plan is that of an unsecured promise to pay the deferred compensation to the plan participants in the future. At December 31, 2018 and 2017 , the Company had maintained approximately $28.2 million and $29.2 million , respectively, in a separate account, which is not restricted as to its use. The Company recognized gains (losses) of approximately $(1.9) million , $3.7 million and $2.3 million on its investments in the account associated with the Company’s deferred compensation plan during the years ended December 31, 2018 , 2017 and 2016 , respectively. Tenant and Other Receivables Tenant and other accounts receivable, other than accrued rents receivable, are expected to be collected within one year. Notes Receivable The Company accounts for notes receivable at their unamortized cost, net of any unamortized deferred fees or costs, premiums or discounts and an allowance for loan losses. Loan fees and direct costs associated with loans originated by the Company are deferred and amortized over the term of the note as interest income. Deferred Charges Deferred charges include leasing costs and certain financing fees. Leasing costs include acquired intangible in-place lease values and direct and incremental fees and costs incurred in the successful negotiation of leases, including brokerage, legal, internal leasing employee salaries and other costs which have been deferred and are being amortized on a straight-line basis over the terms of the respective leases. Unamortized leasing costs are charged to expense upon the early termination of the lease. Fully amortized deferred leasing costs are removed from the books upon the expiration of the lease. Internal leasing salaries and related costs capitalized for the years ended December 31, 2018 , 2017 and 2016 were approximately $5.4 million , $5.0 million and $7.2 million , respectively (see New Accounting Pronouncements Issued but not yet Adopted “ Leases ”). Financing fees included in deferred charges consist of external fees and costs incurred to obtain the Company's revolving facility and if applicable, the delayed draw facility and construction financing arrangements where there are not sufficient amounts outstanding. Such financing costs have been deferred and are being amortized over the terms of the respective financing and included within interest expense. Unamortized financing costs are charged to expense upon the early repayment or significant modification of the financing. Fully amortized deferred financing costs are removed from the books upon the maturity of the debt. External fees and costs incurred to obtain mortgage financings and unsecured senior notes have been deferred and are presented as direct deductions from the carrying amounts of the corresponding debt liability. Such financing costs are being amortized over the terms of the respective financing and included within interest expense. Unamortized financing costs are charged to expense upon the early repayment or significant modification of the financing. Investments in Unconsolidated Joint Ventures The Company consolidates VIEs in which it is considered to be the primary beneficiary. VIEs are entities in which the equity investors do not have sufficient equity at risk to finance their endeavors without additional financial support or that the holders of the equity investment at risk do not have substantive participating rights. The primary beneficiary is defined by the entity having both of the following characteristics: (1) the power to direct the activities that, when taken together, most significantly impact the variable interest entity’s performance, and (2) the obligation to absorb losses and the right to receive the returns from the variable interest entity that could potentially be significant to the VIE. For ventures that are not VIEs, the Company consolidates entities for which it has significant decision making control over the ventures’ operations. The Company’s judgment with respect to its level of influence or control of an entity involves the consideration of various factors including the form of the Company’s ownership interest, its representation in the entity’s governance, the size of its investment (including loans), estimates of future cash flows, its ability to participate in policy making decisions and the rights of the other investors to participate in the decision making process and to replace the Company as manager and/or liquidate the venture, if applicable. The Company’s assessment of its influence or control over an entity affects the presentation of these investments in the Company’s consolidated financial statements. In addition to evaluating control rights, the Company consolidates entities in which the outside partner has no substantive kick-out rights to remove the Company as the managing member. Accounts of the consolidated entity are included in the accounts of the Company and the noncontrolling interest is reflected on the Consolidated Balance Sheets as a component of equity or in temporary equity between liabilities and equity. Investments in unconsolidated joint ventures are recorded initially at cost, and subsequently adjusted for equity in earnings and cash contributions and distributions. Any difference between the carrying amount of these investments on the balance sheet and the underlying equity in net assets is amortized as an adjustment to equity in earnings of unconsolidated joint ventures over the life of the related asset. Under the equity method of accounting, the net equity investment of the Company is reflected within the Consolidated Balance Sheets, and the Company’s share of net income or loss from the joint ventures is included within the Consolidated Statements of Operations. The joint venture agreements may designate different percentage allocations among investors for profits and losses; however, the Company’s recognition of joint venture income or loss generally follows the joint venture’s distribution priorities, which may change upon the achievement of certain investment return thresholds. The Company may account for cash distributions in excess of its investment in an unconsolidated joint venture as income when the Company is not the general partner in a limited partnership and when the Company has neither the requirement nor the intent to provide financial support to the joint venture. The Company’s investments in unconsolidated joint ventures are reviewed for impairment periodically and the Company records impairment charges when events or circumstances change indicating that a decline in the fair values below the carrying values has occurred and such decline is other-than-temporary. The ultimate realization of the investment in unconsolidated joint ventures is dependent on a number of factors, including the performance of each investment and market conditions. The Company will record an impairment charge if it determines that a decline in the value below the carrying value of an investment in an unconsolidated joint venture is other-than-temporary. To the extent that the Company contributed assets to a joint venture, the Company’s investment in the joint venture was recorded at the Company’s cost basis in the assets that were contributed to the joint venture. To the extent that the Company’s cost basis is different than the basis reflected at the joint venture level, the basis difference is amortized over the life of the related asset and included in the Company’s share of equity in net income of the joint venture. In accordance with the provisions of ASC 610-20 “Gains and Losses from the Derecognition of Nonfinancial Assets” (“ASC 610-20”), the Company will recognize a full gain on both the retained and sold portions of real estate contributed or sold to a joint venture by recognizing its new equity method investment interest at fair value. The combined summarized financial information of the unconsolidated joint ventures is disclosed in Note 5 . Revenue Recognition In general, the Company commences rental revenue recognition when the tenant takes possession of the leased space and the leased space is substantially ready for its intended use. Contractual rental revenue is reported on a straight-line basis over the terms of the respective leases. The impact of the straight-line rent adjustment increased revenue by approximately $51.9 million , $54.8 million and $31.7 million for the years ended December 31, 2018 , 2017 and 2016 , respectively, as the revenue recorded exceeded amounts billed. Accrued rental income, as reported on the Consolidated Balance Sheets, represents cumulative rental income earned in excess of rent payments received pursuant to the terms of the individual lease agreements. The Company maintains an allowance against accrued rental income for future potential tenant credit losses. The credit assessment is based on the estimated accrued rental income that is recoverable over the term of the lease. The Company also maintains an allowance for doubtful accounts for estimated losses resulting from the inability of tenants to make required rent payments. The computation of this allowance is based on the tenants’ payment history and current credit status, as well as certain industry or geographic specific credit considerations. If the Company’s estimates of collectability differ from the cash received, then the timing and amount of the Company’s reported revenue could be impacted. The credit risk is mitigated by the high quality of the Company’s existing tenant base, reviews of prospective tenants’ risk profiles prior to lease execution and consistent monitoring of the Company’s portfolio to identify potential problem tenants. In accordance with ASC 805, the Company recognizes acquired in-place “above-” and “below-market” leases at their fair values as rental revenue over the original term of the respective leases. The impact of the acquired in-place “above-” and “below-market” leases increased revenue by approximately $23.8 million , $23.5 million and $30.2 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. The following table summarizes the scheduled amortization of the Company’s acquired “above-” and “below-market” lease intangibles for each of the five succeeding years (in thousands). Acquired Above-Market Lease Intangibles Acquired Below-Market Lease Intangibles 2019 $ 7,099 $ 27,327 2020 5,394 10,462 2021 2,988 6,348 2022 314 5,669 2023 168 5,558 Recoveries from tenants, consisting of amounts due from tenants for common area maintenance, real estate taxes and other recoverable costs, are recognized as revenue in the period during which the expenses are incurred. The Company recognizes these reimbursements on a gross basis, as the Company obtains control of the goods and services before they are transferred to the tenant. The Company also receives reimbursements of payroll and payroll related costs from third parties that the Company reflects on a gross basis. The Company’s parking revenue is derived primarily from monthly and transient daily parking. In addition, the Company has certain lease arrangements for parking accounted for under the guidance in ASC 840 “Leases” (“ASC 840”). The monthly and transient daily parking revenue falls within the scope of ASC 606 “Revenue from Contracts with Customers” (“ASC 606”) and is accounted for at the point in time when control of the goods or services transfers to the customer and the Company’s performance obligation is satisfied (see New Accounting Pronouncements Adopted “ Revenue from Contracts with Customers ”). The Company’s hotel revenue is derived from room rentals and other sources such as charges to guests for telephone service, movie and vending commissions, meeting and banquet room revenue and laundry services. Hotel revenue is recognized as the hotel rooms are occupied and the services are rendered to the hotel customers (see New Accounting Pronouncements Adopted “ Revenue from Contracts with Customers ”). The Company earns management and development fees. Development and management services revenue is earned from unconsolidated joint venture entities and third-party property owners. The Company determined that the performance obligations associated with its development services contracts are satisfied over time and that the Company would recognize its development services revenue under the output method evenly over time from the development commencement date through the substantial completion date of the development management services project due to the stand-ready nature of the contracts. Significant judgments impacting the amount and timing of revenue recognized from the Company's development services contracts include estimates of total development project costs from which the fees are typically derived and estimates of the period of time until substantial completion of the development project, the period of time over which the development services are required to be performed. The Company recognizes development fees earned from unconsolidated joint venture projects equal to its cost plus profit to the extent of the third party partners’ ownership interest. Property management fees are recorded and earned based on a percentage of collected rents at the properties under management, and not on a straight-line basis, because such fees are contingent upon the collection of rents (see New Accounting Pronouncements Adopted “ Revenue from Contracts with Customers ”). Gains on sales of real estate are recognized pursuant to the provisions included in ASC 610-20. Under ASC 610-20, the Company must first determine whether the transaction is a sale to a customer or non-customer. The Company typically sells real estate on a selective basis and not within the ordinary course of its business and therefore expects that its sale transactions will not be contracts with customers. The Company next determines whether it has a controlling financial interest in the property after the sale, consistent with the consolidation model in ASC 810 "Consolidation" (“ASC 810”). If the Company determines that it does not have a controlling financial interest in the real estate, it evaluates whether a contract exists under ASC 606 and whether the buyer has obtained control of the asset that was sold. The Company recognizes a full gain on sale of real estate when the derecognition criteria under ASC 610-20 have been met (see New Accounting Pronouncements Adopted “ Sales of Real Estate ”). Ground Leases The Company has non-cancelable ground lease obligations with various initial term expiration dates through 2114 . The Company recognizes ground rent expense on a straight-line basis over the terms of the respective ground lease agreements. The future contractual minimum lease payments to be made by the Company as of December 31, 2018 , under non-cancelable ground leases which expire on various dates through 2114 , are as follows: Years Ending December 31, (in thousands) 2019 $ 11,425 2020 18,425 2021 25,310 2022 8,894 2023 9,084 Thereafter 567,232 Capital Leases The Company has four capital lease obligations with various initial term expiration dates through 2036. The following reflects the gross amount of assets recorded under capital leases by asset class at December 31, 2018 and December 31, 2017 (in thousands): December 31, 2018 2017 Land held for future development $ 12,397 $ — Buildings and improvements 23,636 23,636 Construction in progress 28,962 28,962 Total $ 64,995 $ 52,598 The future minimum lease payments, as of December 31, 2018, related to the four capital leases, through 2036 are as follows: Years Ending December 31, (in thousands) 2019 $ 1,441 2020 12,682 2021 2,123 2022 1,253 2023 944 Thereafter 73,241 Total expected minimum lease payments 91,684 Interest portion (27,497 ) Present value of expected net minimum lease payments $ 64,187 Earnings Per Share Basic earnings per share (“EPS”) is computed by dividing net income available to common shareholders, as adjusted for undistributed earnings (if any) of certain securities issued by Boston Properties Limited Partnership, by the weighted average number of shares of Common Stock outstanding during the year. Diluted EPS reflects the potential dilution that could occur from shares issuable in connection with awards under stock-based compensation plans, including upon the exercise of stock options, and securities of Boston Properties Limited Partnership that are exchangeable for Common Stock. Earnings Per Common Unit Basic earnings per common unit is computed by dividing net income available to common unitholders, as adjusted for undistributed earnings (if any) of certain securities issued by Boston Properties Limited Partnership, by the weighted average number of common units outstanding during the year. Diluted earnings per common unit reflects the potential dilution that could occur from units issuable in connection with awards under Boston Properties, Inc.’s stock-based compensation plans, including upon the exercise of stock options, and conversion of preferred units of Boston Properties Limited Partnership. Fair Value of Financial Instruments The carrying values of cash and cash equivalents, marketable securities, escrows, receivables, accounts payable, accrued expenses and other assets and liabilities are reasonable estimates of their fair values because of the short maturities of these instruments. The Company follows the authoritative guidance for fair value measurements when valuing its financial instruments for disclosure purposes. Boston Properties Limited Partnership determines the fair value of its unsecured senior notes using market prices. The inputs used in determining the fair value of Boston Properties Limited Partnership’s unsecured senior notes is categorized at a Level 1 basis (as defined in ASC 820 “Fair Value Measurements and Disclosures” (“ASC 820”)) due to the fact that it uses quoted market rates to value these instruments. However, the inputs used in determining the fair value could be categorized at a Level 2 basis (as defined in ASC 820) if trading volumes are low. The Company determines the fair value of its related party note receivable, note receivable and mortgage notes payable using discounted cash flow analysis by discounting the spread between the future contractual interest payments and hypothetical future interest payments on note receivables / mortgage debt 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. The inputs used in determining the fair value of the Company’s related party note receivable, note receivable, and mortgage notes payable are categorized at a Level 3 basis (as defined in ASC 820) due to the fact that the Company considers the rates used in the valuation techniques to be unobservable inputs. To the extent that there are outstanding borrowings under the unsecured line of credit or unsecured term loan, the Company utilizes a discounted cash flow methodology in order to estimate the fair value. To the extent that credit spreads have changed since the origination, the net present value of the difference between future contractual interest payments and future interest payments based on the Company’s estimate of a current market rate would represent the difference between the book value and the fair value. The Company’s estimate of a current market rate is based upon the rate, considering current market conditions and Boston Properties Limited Partnership's specific credit profile, at which it estimates it could obtain similar borrowings. To the extent there are outstanding borrowings, this current market rate is estimated and therefore would be primarily based upon a Level 3 input. 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, and the Company’s estimated fair values for these instruments as of the end of the applicable reporting period are not necessarily indicative of estimated or actual fair values in future reporting periods. The following table presents the aggregate carrying value of the Company’s related party note receivable, note receivable, mortgage notes payable, net, unsecured senior notes, net, unsecured line of credit and unsecured term loan, net and the Company’s corresponding estimate of fair value as of December 31, 2018 and December 31, 2017 (in thousands): December 31, 2018 December 31, 2017 Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Related party note receivable $ 80,000 $ 80,000 $ — $ — Note receivable 19,468 19,468 — — Total $ 99,468 $ 99,468 $ — $ — Mortgage notes payable, net $ 2,964,572 $ 2,903,925 $ 2,979,281 $ 3,042,920 Unsecured senior notes, net 7,544,697 7,469,338 7,247,330 7,461,615 Unsecured line of credit — — 45,000 45,000 Unsecured term loan, net 498,488 500,783 — — Total $ 11,007,757 $ 10,874,046 $ 10,271,611 $ 10,549,535 The Company uses interest rate swap agreements to manage its interest rate risk. The valuation of these instruments is determined using widely accepted valuation techniques, including discounted cash flow analysis on the expected cash flows of each derivative. This analysis reflects the contractual terms of the derivatives, including the period to maturity, and uses observable market-based inputs, including interest rate curves. To comply with the provisions of ASC 820, the Company incorporates credit valuation adjustments to appropriately reflect both its own nonperformance risk and the respective counterparty’s nonperformance risk in the fair value measurements. Although the Company determin

Real Estate

Real Estate	12 Months Ended
	Dec. 31, 2018
Real Estate [Abstract]
Real Estate	3. Real Estate Boston Properties, Inc. Real estate consisted of the following at December 31, 2018 and December 31, 2017 (in thousands): 2018 2017 Land $ 5,072,568 $ 5,080,679 Land held for future development (1) 200,498 204,925 Buildings and improvements 13,356,751 12,284,164 Tenant improvements 2,396,932 2,219,608 Furniture, fixtures and equipment 44,351 37,928 Construction in progress 578,796 1,269,338 Total 21,649,896 21,096,642 Less: Accumulated depreciation (4,897,777 ) (4,589,634 ) $ 16,752,119 $ 16,507,008 _______________ (1) Includes pre-development costs. Boston Properties Limited Partnership Real estate consisted of the following at December 31, 2018 and December 31, 2017 (in thousands): 2018 2017 Land $ 4,971,475 $ 4,976,303 Land held for future development (1) 200,498 204,925 Buildings and improvements 13,059,488 11,977,062 Tenant improvements 2,396,932 2,219,608 Furniture, fixtures and equipment 44,351 37,928 Construction in progress 578,796 1,269,338 Total 21,251,540 20,685,164 Less: Accumulated depreciation (4,800,475 ) (4,496,959 ) $ 16,451,065 $ 16,188,205 _______________ (1) Includes pre-development costs. Development/Redevelopment On January 24, 2018, the Company entered into a lease agreement with an affiliate of Leidos Holdings, Inc. for a build-to-suit project with approximately 276,000 net rentable square feet of Class A office space at the Company's 17Fifty Presidents Street development project located in Reston, Virginia. Concurrently with the execution of the lease, the Company commenced development of the project and expects the building to be completed and available for occupancy during the second quarter of 2020. On January 31, 2018, the Company partially placed in-service its Signature at Reston development project comprised of 508 apartment units and retail space aggregating approximately 518,000 square feet located in Reston, Virginia. This project was completed and fully placed in-service on June 7, 2018. On February 23, 2018, the Company entered into a lease agreement with Fannie Mae to lease approximately 850,000 net rentable square feet of Class A office space at the Company's Reston Gateway development project located in Reston, Virginia. The initial phase of the project will consist of two Class A office buildings aggregating approximately 1.1 million net rentable square feet. On August 31, 2018, the Company commenced development of the project. On June 20, 2018, the Company partially placed in-service its Proto Kendall Square development project comprised of 280 apartment units and retail space aggregating approximately 167,000 square feet located in Cambridge, Massachusetts. This project was completed and fully placed in-service on September 1, 2018. On August 7, 2018, the Company entered into an agreement with a third party to (1) share certain pre-development costs during the pre-lease period and (2) to form a joint venture to thereafter own and develop a leasehold interest in 343 Madison Avenue located in New York City, which will support a Class A office tower with approximately 850,000 net rentable square feet. The Company will serve as development manager of the project and will own a 55% interest in the joint venture. In 2016, the Company was selected by the Metropolitan Transportation Authority ("MTA") as the developer of the project and will enter into a pre-lease agreement and a 99 -year ground lease with the MTA for the site. There can be no assurances that the transaction will be completed on the terms currently contemplated, or at all. On November 9, 2018, the Company completed and fully placed in-service 191 Spring Street, a Class A office redevelopment project with approximately 171,000 square feet located in Lexington, Massachusetts. On December 1, 2018, a consolidated entity in which the Company has a 95% interest completed and fully placed in-service Salesforce Tower, a Class A office project with approximately 1,421,000 net rentable square feet located in San Francisco, California (See Notes 10 and 19 ). Ground Lease On November 29, 2018, the Company executed a 65 -year ground lease for land totaling approximately 5.6 acres at Platform 16 located in San Jose, California, which will support approximately 1.1 million square feet of commercial office space. The ground lease provides the Company with the right to purchase the land during a 12-month period commencing in the 13th month following the rent commencement date at a purchase price of approximately $134.8 million . The Company made a deposit totaling $15.0 million , which deposit may only be credited against the purchase price of the land. The Company’s option to purchase the land is considered a bargain purchase option and as a result, the Company has concluded that the lease should be accounted for as a capital lease. At the inception of the ground lease only a portion of the land was available for lease from the lessor (See Note 19 ). As a result, the Company recorded an approximately $12.4 million capital lease asset and liability, which is reflected within Real Estate (Land Held for Future Development) and Other Liabilities on the Company’s Consolidated Balance Sheets, reflecting the portion of the land available for lease from the lessor under the ground lease. Capital lease assets and liabilities are accounted for at the lower of fair market value or the present value of future minimum lease payments. The capital lease is for land only. Therefore, the Company will not depreciate the capital lease asset because land is assumed to have an indefinite life. As of November 29, 2018, future minimum lease payments related to the recognized portion of the capital lease are as follows (in thousands): Period from November 29, 2018 through December 31, 2018 $ 1,385 2019 427 2020 11,132 Total expected minimum lease payments 12,944 Interest portion (547 ) Present value of expected net minimum lease payments $ 12,397 Dispositions On January 9, 2018, the Company completed the sale of its 500 E Street, S.W. property located in Washington, DC for a net contract sale price of approximately $118.6 million . Net cash proceeds totaled approximately $116.1 million , resulting in a gain on sale of real estate totaling approximately $96.4 million for Boston Properties, Inc. and approximately $98.9 million for Boston Properties Limited Partnership. 500 E Street, S.W. is an approximately 262,000 net rentable square foot Class A office property. 500 E Street, S.W. contributed approximately $0.1 million of net income to the Company for the period from January 1, 2018 through January 8, 2018 and contributed approximately $6.5 million and $7.6 million of net income to the Company for the years ended December 31, 2017 and 2016, respectively. On May 24, 2018, the Company completed the sale of its 91 Hartwell Avenue property located in Lexington, Massachusetts for a gross sale price of approximately $22.2 million . Net cash proceeds totaled approximately $21.7 million , resulting in a gain on sale of real estate totaling approximately $15.5 million for Boston Properties, Inc. and approximately $15.9 million for Boston Properties Limited Partnership. 91 Hartwell Avenue is an approximately 119,000 net rentable square foot Class A office property. 91 Hartwell Avenue contributed approximately $0.3 million of net income to the Company for the period from January 1, 2018 through May 23, 2018 and contributed approximately $0.5 million and $0.4 million of net income to the Company for the years ended December 31, 2017 and 2016, respectively. On September 27, 2018, the Company completed the sale of its Quorum Office Park property located in Chelmsford, Massachusetts for a gross sale price of approximately $35.3 million . Net cash proceeds totaled approximately $34.3 million , resulting in a gain on sale of real estate totaling approximately $7.9 million for Boston Properties, Inc. and approximately $9.2 million for Boston Properties Limited Partnership. Quorum Office Park is an approximately 268,000 net rentable square foot Class A office property. Quorum Office Park contributed approximately $0.7 million of net income to the Company for the period from January 1, 2018 through September 26, 2018 and contributed approximately $0.9 million and $0.9 million of net income to the Company for the years ended December 31, 2017 and 2016, respectively. On November 30, 2018, the Company completed the sale of its 1333 New Hampshire Avenue property located in Washington, DC for a gross sale price of approximately $142.0 million , including the retention of a $5.5 million future payment by the anchor tenant. Net cash proceeds totaled approximately $133.7 million , resulting in a gain on sale of real estate totaling approximately $44.4 million for Boston Properties, Inc. and approximately $48.4 million for Boston Properties Limited Partnership. 1333 New Hampshire Avenue is an approximately 315,000 net rentable square foot Class A office property. 1333 New Hampshire Avenue contributed approximately $6.7 million of net income to the Company for the period from January 1, 2018 through November 29, 2018 and contributed approximately $7.4 million and $6.1 million of net income to the Company for the years ended December 31, 2017 and 2016, respectively. On December 13, 2018, the Company completed the sale of its 6595 Springfield Center Drive development project located in Springfield, Virginia, for a sale price of approximately $98.1 million , consisting of the land and project costs incurred through the closing date. Net cash proceeds totaled approximately $97.1 million . Concurrently with the sale, the Company agreed to act as development manager and has guaranteed the completion of the project. The book value of the property exceeded its estimated fair value prior to the sale, and as a result, the Company recognized an impairment loss totaling approximately $8.7 million during the three months ended December 31, 2018. 6595 Springfield Center Drive is an approximately 634,000 net rentable square foot Class A office project. On December 20, 2018, the Company completed the sale of a 41 -acre parcel of land at its Tower Oaks property located in Rockville, Maryland for a gross sale price of approximately $46.0 million . Net cash proceeds totaled approximately $25.9 million , resulting in a gain on sale of real estate totaling approximately $15.7 million . The Company agreed to provide seller financing to the buyer totaling $21.0 million , which is collateralized by a portion of the land parcel that secures the loan, bears interest at an effective rate of 1.92% per annum and matures on December 20, 2021. The loan has been reflected as Note Receivable on the Company’s Consolidated Balance Sheets. The Company's policy is to record notes receivable at their unamortized cost, net of any unamortized deferred fees or costs, premiums or discounts and an allowance for loan losses. Loan fees and direct costs associated with loans originated by the Company are deferred and amortized over the term of the note as a component of interest income. During the three months ended December 31, 2018, the Company reevaluated its strategy for the sale of its 2600 Tower Oaks Boulevard property. Based on a shorter than expected hold period, the Company reduced the carrying value of the property to its estimated fair value at December 31, 2018 and recognized an impairment loss totaling approximately $3.1 million for Boston Properties, Inc. and approximately $1.5 million for Boston Properties Limited Partnership. The Company’s estimated fair value was based on a pending offer for the sale of the property. 2600 Tower Oaks Boulevard is an approximately 179,000 net rentable square foot Class A office property (See Note 19 ).

Deferred Charges

Deferred Charges	12 Months Ended
	Dec. 31, 2018
Deferred Charges [Abstract]
Deferred Charges	4. Deferred Charges Deferred charges consisted of the following at December 31, 2018 and December 31, 2017 (in thousands): 2018 2017 Leasing costs, including lease related intangibles $ 1,191,297 $ 1,147,181 Financing costs 12,796 14,991 1,204,093 1,162,172 Less: Accumulated amortization (525,369 ) (483,134 ) $ 678,724 $ 679,038 The following table summarizes the scheduled amortization of the Company’s acquired in-place lease intangibles for each of the five succeeding years (in thousands). Acquired In-Place Lease Intangibles 2019 $ 25,690 2020 13,051 2021 8,610 2022 4,798 2023 4,107

Investments in Unconsolidated J

Investments in Unconsolidated Joint Ventures	12 Months Ended
	Dec. 31, 2018
Investments In Unconsolidated Joint Ventures [Abstract]
Investments In Unconsolidated Joint Ventures	5. Investments in Unconsolidated Joint Ventures The investments in unconsolidated joint ventures consist of the following at December 31, 2018 and 2017 : Carrying Value of Investment (1) Entity Properties Nominal % Ownership December 31, December 31, (in thousands) Square 407 Limited Partnership Market Square North 50.0 % $ (6,424 ) $ (8,258 ) The Metropolitan Square Associates LLC Metropolitan Square 20.0 % 2,644 3,339 BP/CRF 901 New York Avenue LLC 901 New York Avenue 25.0 % (2) (13,640 ) (13,811 ) WP Project Developer LLC Wisconsin Place Land and Infrastructure 33.3 % (3) 38,214 39,710 Annapolis Junction NFM LLC Annapolis Junction 50.0 % (4) 25,268 18,381 540 Madison Venture LLC 540 Madison Avenue 60.0 % 66,391 66,179 500 North Capitol Venture LLC 500 North Capitol Street, NW 30.0 % (5,026 ) (3,876 ) 501 K Street LLC 1001 6th Street 50.0 % (5) 42,557 42,657 Podium Developer LLC The Hub on Causeway - Podium 50.0 % 69,302 67,120 Residential Tower Developer LLC The Hub on Causeway - Residential 50.0 % 47,505 28,212 Hotel Tower Developer LLC The Hub on Causeway - Hotel Air Rights 50.0 % 3,022 1,690 Office Tower Developer LLC 100 Causeway Street 50.0 % (6) 23,804 — 1265 Main Office JV LLC 1265 Main Street 50.0 % 3,918 4,641 BNY Tower Holdings LLC Dock 72 50.0 % 82,520 72,104 CA-Colorado Center Limited Partnership Colorado Center 50.0 % 253,495 254,440 7750 Wisconsin Avenue LLC 7750 Wisconsin Avenue 50.0 % (6) 69,724 21,452 BP-M 3HB Venture LLC 3 Hudson Boulevard 25.0 % 46,993 — SMBP Venture LP Santa Monica Business Park 55.0 % 180,952 — $ 931,219 $ 593,980 _______________ (1) Investments with deficit balances aggregating approximately $25.1 million and $25.9 million at December 31, 2018 and 2017 , respectively, are included within Other Liabilities in the Company’s Consolidated Balance Sheets. (2) The Company’s economic ownership has increased based on the achievement of certain return thresholds. (3) The Company’s wholly-owned subsidiary that owns Wisconsin Place Office also owns a 33.3% interest in the joint venture entity that owns the land, parking garage and infrastructure of the project. (4) The joint venture owns three in-service buildings and two undeveloped land parcels. (5) Under the joint venture agreement for this land parcel, the partner will be entitled to up to two additional payments from the venture based on increases in total entitled square footage of the project above 520,000 square feet and achieving certain project returns at stabilization. (6) This entity is a VIE (See Note 1 ). Certain of the Company’s unconsolidated 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. With limited exceptions under these provisions, the Company is not compelled to purchase the interest of its outside joint venture partners. Under certain of the Company's joint venture agreements, if certain return thresholds are achieved the partners will be entitled to an additional promoted interest or payments. The combined summarized balance sheets of the Company’s unconsolidated joint ventures are as follows: December 31, December 31, (in thousands) ASSETS Real estate and development in process, net $ 3,545,906 $ 1,768,996 Other assets 543,512 367,743 Total assets $ 4,089,418 $ 2,136,739 LIABILITIES AND MEMBERS’/PARTNERS’ EQUITY Mortgage and notes payable, net $ 2,017,609 $ 1,437,440 Other liabilities 582,006 99,215 Members’/Partners’ equity 1,489,803 600,084 Total liabilities and members’/partners’ equity $ 4,089,418 $ 2,136,739 Company’s share of equity $ 622,498 $ 286,495 Basis differentials (1) 308,721 307,485 Carrying value of the Company’s investments in unconsolidated joint ventures (2) $ 931,219 $ 593,980 _______________ (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 result from impairments of investments, acquisitions through joint ventures with no change in control 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. At December 31, 2018 and 2017 , there was an aggregate basis differential of approximately $316.7 million and $322.5 million , respectively, between the carrying value of the Company’s investment in the joint venture that owns Colorado Center and the joint venture’s basis in the assets and liabilities, which differential (excluding land) shall be amortized over the remaining lives of the related assets and liabilities. (2) Investments with deficit balances aggregating approximately $25.1 million and $25.9 million at December 31, 2018 and 2017 , respectively, have been reflected within Other Liabilities in the Company’s Consolidated Balance Sheets. The combined summarized statements of operations of the Company’s unconsolidated joint ventures are as follows: For the year ended December 31, 2018 2017 2016 (in thousands) Total revenue (1) $ 271,951 $ 222,517 $ 177,182 Expenses Operating 106,610 90,542 76,741 Depreciation and amortization (2) 103,079 57,079 44,989 Total expenses 209,689 147,621 121,730 Other income (expense) Interest expense (71,308 ) (46,371 ) (34,016 ) Gain on sale of real estate 16,951 — — Net income $ 7,905 $ 28,525 $ 21,436 Company’s share of net income $ 8,084 $ 18,439 $ 9,873 Basis differential (3) (5,862 ) (7,207 ) (1,799 ) Income from unconsolidated joint ventures $ 2,222 $ 11,232 $ 8,074 Gain on sale of investment in unconsolidated joint venture $ — $ — $ 59,370 _______________ (1) Includes straight-line rent adjustments of approximately $15.9 million , $21.7 million and $18.1 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. (2) During the year ended December 31, 2018, the joint venture that owns Metropolitan Square in Washington, DC, commenced a renovation project and recorded accelerated depreciation expense of approximately $22.4 million related to the remaining book value of the assets to be replaced. The Company's share of the accelerated depreciation expense totaled approximately $4.5 million . (3) Includes straight-line rent adjustments of approximately $2.4 million , $1.9 million and $1.4 million for the years ended December 31, 2018, 2017 and 2016, respectively. Also includes net above-/below-market rent adjustments of approximately $1.6 million , $2.9 million and $0.9 million for the years ended December 31, 2018, 2017 and 2016, respectively. On April 19, 2018, a joint venture in which the Company has a 50% interest obtained construction financing with a total commitment of $180.0 million collateralized by its Hub on Causeway - Residential development project. The construction financing bears interest at a variable rate equal to LIBOR plus 2.00% per annum and matures on April 19, 2022, with two , one -year extension options, subject to certain conditions. As of December 31, 2018, approximately $40.5 million had been drawn under the loan. The Hub on Causeway - Residential is an approximately 320,000 square foot project comprised of 440 residential units located in Boston, Massachusetts. On April 27, 2018, a joint venture in which the Company has a 60% interest refinanced the mortgage loan collateralized by its 540 Madison Avenue property located in New York City totaling $120.0 million . The mortgage loan bears interest at a variable rate equal to LIBOR plus 1.10% per annum and matures on June 5, 2023. The previous mortgage loan bore interest at a variable rate equal to LIBOR plus 1.50% per annum and was scheduled to mature on June 5, 2018. 540 Madison Avenue is an approximately 284,000 net rentable square foot Class A office property. On July 13, 2018, the Company entered into a joint venture with a third party to acquire a development site at 3 Hudson Boulevard that, upon the future acquisition of additional available development rights, can accommodate a Class A office tower with up to 2.0 million net rentable square feet located on the entire square block between 11th Avenue and Hudson Boulevard Park from West 34th Street to West 35th Street in New York City. The Company owns a 25% interest in, and is the managing member of, the joint venture. The acquisition includes improvements consisting of excavation work and foundation elements that are currently being constructed on the site. The Company contributed cash totaling approximately $45.6 million at closing and will contribute approximately $62.2 million in the future for its initial capital contribution, a portion of which will fund the remaining costs to complete the foundation elements to grade for the future office building. In addition, the Company provided $80.0 million of mortgage financing to the joint venture that bears interest at a variable rate equal to LIBOR plus 3.50% per annum and matures on July 13, 2023, with extension options, subject to certain conditions. The loan has been reflected as a Related Party Note Receivable on the Company’s Consolidated Balance Sheets. The Company's policy is to record notes receivable at their unamortized cost, net of any unamortized deferred fees or costs, premiums or discounts and an allowance for loan losses. Loan fees and direct costs associated with loans originated by the Company are deferred and amortized over the term of the note as interest income. On July 19, 2018, the Company entered into a joint venture with Canada Pension Plan Investment Board (“CPPIB”) to acquire Santa Monica Business Park in the Ocean Park neighborhood of Santa Monica, California for a net purchase price of approximately $626.7 million , including $11.5 million of seller funded leasing costs after the effective date of the purchase and sale agreement. Santa Monica Business Park is a 47 -acre office park consisting of 21 buildings totaling approximately 1.2 million net rentable square feet. Approximately 70% of the rentable square footage is subject to a ground lease with 80 years remaining, including renewal periods. The ground lease provides the joint venture with the right to purchase the land underlying the properties in 2028 with subsequent purchase rights every 15 years. CPPIB invested approximately $147.0 million for a 45% ownership interest in the joint venture. The Company is providing customary operating, property management and leasing services to, and invested approximately $179.7 million in, the joint venture. The acquisition was completed with $300.0 million of financing. The mortgage financing bears interest at a variable rate equal to LIBOR plus 1.28% per annum and matures on July 19, 2025. At closing, the borrower under the loan, which is a subsidiary of the joint venture, entered into interest rate swap contracts with notional amounts aggregating $300.0 million through April 1, 2025, resulting in a fixed rate of approximately 4.063% per annum through the expiration of the interest rate swap contracts. At December 31, 2018 , the unconsolidated joint venture has recorded the changes in fair value of the interest rate swap contracts aggregating approximately $5.6 million as a liability and accumulated other comprehensive loss on its balance sheet. At December 31, 2018 , the Company has recognized its share of the fair value totaling approximately $3.1 million as a decrease to its Investments in Unconsolidated Joint Ventures and Accumulated Other Comprehensive Loss on the Company's Consolidated Balance Sheets. The following table summarizes the allocation of the joint venture's aggregate purchase price for Santa Monica Business Park at the date of acquisition (in thousands). Land and improvements $ 100,453 Leasehold interest in land 248,944 Site improvements 13,379 Building and improvements 593,669 Tenant improvements 31,329 In-place lease intangibles 47,955 Above-market lease intangible 4,495 Below-market lease intangible (17,503 ) Capital lease obligation (396,008 ) Net assets acquired $ 626,713 On July 27, 2018, the Company entered into a joint venture with its partner at The Hub on Causeway mixed-use development in Boston, Massachusetts to acquire the air rights for the development of an approximately 627,000 net rentable square foot Class A office tower at the site to be known as 100 Causeway Street. In addition, the joint venture entered into a lease agreement with an affiliate of Verizon Communications, Inc., under which Verizon will lease approximately 70% of the office tower for a term of 20 years. With the execution of the lease, the joint venture commenced development of the project. The Company serves as the co-development manager for the project. The joint venture partner contributed an air rights parcel and improvements, with a fair value of approximately $41.3 million , for its initial 50% interest in the joint venture. The Company contributed improvements totaling approximately $3.9 million and will contribute cash totaling approximately $37.4 million for its initial 50% interest. On November 16, 2018, a joint venture in which the Company has a 50% interest extended the loan collateralized by its Annapolis Junction Building Six property. At the time of the extension, the outstanding balance of the loan totaled approximately $13.1 million and was scheduled to mature on November 17, 2018. The extended loan has a total commitment amount of approximately $14.3 million , bears interest at a variable rate equal to LIBOR plus 2.00% per annum and matures on November 17, 2019, with one , one -year extension option, subject to certain conditions. Annapolis Junction Building Six is a Class A office property with approximately 119,000 net rentable square feet located in Annapolis, Maryland (See Note 19 ). On December 31, 2018, the Company entered into a distribution agreement with its partner in the joint venture in which the Company has a 50% interest and that owns Annapolis Junction. Under the agreement, the joint venture distributed its Annapolis Junction Building One property to the partner and the partner assumed the mortgage indebtedness collateralized by the property. The Company recognized a gain on sale of real estate totaling approximately $8.3 million , which is included within Income from Unconsolidated Joint Ventures in the Company's Consolidated Statements of Operations. Annapolis Junction Building One is an approximately 118,000 net rentable square foot Class A office property.

Mortgage Notes Payable, Net

Mortgage Notes Payable, Net	12 Months Ended
	Dec. 31, 2018
Loans Payable [Abstract]
6. Mortgage Notes Payable, Net	6. Mortgage Notes Payable, Net The Company had outstanding mortgage notes payable totaling approximately $3.0 billion and $3.0 billion as of December 31, 2018 and 2017 , respectively, each collateralized by one or more buildings and related land included in real estate assets. The mortgage notes payable are generally due in monthly installments and mature at various dates through June 9, 2027. Fixed rate mortgage notes payable totaled approximately $3.0 billion and $3.0 billion at December 31, 2018 and 2017 , respectively, with contractual interest rates ranging from 3.43% to 7.69% per annum at December 31, 2018 and December 31, 2017 (with a weighted-average interest rate of 3.77% and 3.78% per annum at December 31, 2018 and 2017 , respectively). There were no variable rate mortgage loans at December 31, 2018 and 2017 . No mortgage loans at December 31, 2018 and December 31, 2017 had been accounted for at fair value. Prior to December 31, 2017, the Company had mortgage loans that were accounted for at fair value and the impact of recording them at fair value resulted in a decrease to interest expense of approximately $19.6 million and $46.4 million for the years ended December 31, 2017 and 2016 , respectively. Contractual aggregate principal payments of mortgage notes payable at December 31, 2018 are as follows (in thousands): Principal Payments 2019 $ 19,670 2020 20,766 2021 40,182 2022 614,710 2023 — Thereafter 2,300,000 Total aggregate principal payments 2,995,328 Deferred financing costs, net (30,756 ) Total carrying value of mortgage notes payable, net $ 2,964,572

Unsecured Senior Notes

Unsecured Senior Notes	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Unsecured Senior Notes	7. Unsecured Senior Notes The following summarizes the unsecured senior notes outstanding as of December 31, 2018 (dollars in thousands): Coupon/ Stated Rate Effective Rate(1) Principal Amount Maturity Date(2) 10 Year Unsecured Senior Notes 5.625 % 5.708 % $ 700,000 November 15, 2020 10 Year Unsecured Senior Notes 4.125 % 4.289 % 850,000 May 15, 2021 11 Year Unsecured Senior Notes 3.850 % 3.954 % 1,000,000 February 1, 2023 10.5 Year Unsecured Senior Notes 3.125 % 3.279 % 500,000 September 1, 2023 10.5 Year Unsecured Senior Notes 3.800 % 3.916 % 700,000 February 1, 2024 7 Year Unsecured Senior Notes 3.200 % 3.350 % 850,000 January 15, 2025 10 Year Unsecured Senior Notes 3.650 % 3.766 % 1,000,000 February 1, 2026 10 Year Unsecured Senior Notes 2.750 % 3.495 % 1,000,000 October 1, 2026 10 Year Unsecured Senior Notes 4.500 % 4.628 % 1,000,000 December 1, 2028 Total principal 7,600,000 Net unamortized discount (18,722 ) Deferred financing costs, net (36,581 ) Total $ 7,544,697 _______________ (1) Yield on issuance date including the effects of discounts on the notes, settlements of interest rate contracts and the amortization of financing costs. (2) No principal amounts are due prior to maturity. On November 28, 2018, Boston Properties Limited Partnership completed a public offering of $1.0 billion in aggregate principal amount of its 4.500% unsecured senior notes due 2028. The notes were priced at 99.641% of the principal amount to yield an effective rate (including financing fees) of approximately 4.628% per annum to maturity. The notes will mature on December 1, 2028, unless earlier redeemed. The aggregate net proceeds from the offering were approximately $988.1 million after deducting underwriting discounts and transaction expenses. On December 13, 2018, Boston Properties Limited Partnership completed the redemption of $700.0 million in aggregate principal amount of its 5.875% senior notes due October 15, 2019. The redemption price was approximately $722.6 million . The redemption price included approximately $6.6 million of accrued and unpaid interest to, but not including, the redemption date. Excluding the accrued and unpaid interest, the redemption price was approximately 102.28% of the principal amount being redeemed. The Company recognized a loss from early extinguishment of debt totaling approximately $16.5 million , which amount included the payment of the redemption premium totaling approximately $16.0 million . The indenture relating to the unsecured senior notes contains certain financial restrictions and requirements, including (1) a leverage ratio not to exceed 60% , (2) a secured debt leverage ratio not to exceed 50% , (3) an interest coverage ratio of greater than 1.50 , and (4) an unencumbered asset value of not less than 150% of unsecured debt. At December 31, 2018 , Boston Properties Limited Partnership was in compliance with each of these financial restrictions and requirements.

Unsecured Credit Facility

Unsecured Credit Facility	12 Months Ended
	Dec. 31, 2018
Unsecured Line of Credit [Abstract]
Unsecured Credit Facility [Text Block]	8. Unsecured Credit Facility On April 24, 2017, Boston Properties Limited Partnership amended and restated its unsecured revolving credit agreement (as amended and restated, the “2017 Credit Facility”). Among other things, the 2017 Credit Facility (1) increased the total commitment of the revolving line of credit (the “Revolving Facility”) from $1.0 billion to $1.5 billion , (2) extended the maturity date from July 26, 2018 to April 24, 2022, (3) reduced the per annum variable interest rates, and (4) added a $500.0 million delayed draw term loan facility (the “Delayed Draw Facility”) that permitted Boston Properties Limited Partnership, until the first anniversary of the closing date, to draw upon up to four times a minimum of $50.0 million (or, if less, the remaining unused delayed draw term commitments), provided that amounts drawn under the Delayed Draw Facility and subsequently repaid may not be borrowed again. In addition, Boston Properties Limited Partnership may increase the total commitment under the 2017 Credit Facility by up to $500.0 million through increases in the Revolving Facility or the Delayed Draw Facility, or both, subject to syndication of the increase and other conditions. On April 24, 2018, Boston Properties Limited Partnership exercised its option to draw $500.0 million on its Delayed Draw Facility. The Delayed Draw Facility bears interest at a variable rate equal to LIBOR plus 0.90% per annum based on Boston Properties Limited Partnership's current credit rating and matures on April 24, 2022. At Boston Properties Limited Partnership’s option, loans under the Revolving Facility and Delayed Draw Facility will bear interest at a rate per annum equal to (1) (a) in the case of loans denominated in Dollars, Euro or Sterling, LIBOR, and (b) in the case of loans denominated in Canadian Dollars, CDOR, in each case, plus a margin ranging from 77.5 to 155 basis points for the Revolving Commitment and 85 to 175 basis points for the Delayed Draw Facility, based on Boston Properties Limited Partnership’s credit rating or (2) an alternate base rate equal to the greatest of (x) the Administrative Agent’s prime rate, (y) the Federal Funds rate plus 0.50% or (z) LIBOR for a one -month period plus 1.00% , in each case, plus a margin ranging from 0 to 55 basis points for the Revolving Facility and 0 to 75 basis points for the Delayed Draw Facility, based on Boston Properties Limited Partnership’s credit rating. The 2017 Credit Facility also contains a competitive bid option for up to 65% of the Revolving Facility that allows banks that are part of the lender consortium to bid to make loan advances to Boston Properties Limited Partnership at a reduced interest rate. In addition, Boston Properties Limited Partnership is obligated to pay (1) in quarterly installments a facility fee on the total commitment under the Revolving Facility at a rate per annum ranging from 0.10% to 0.30% based on Boston Properties Limited Partnership’s credit rating, (2) an annual fee on the undrawn amount of each letter of credit equal to the LIBOR margin on the Revolving Facility and (3) a fee on the unused commitments under the Delayed Draw Facility equal to 0.15% per annum. Based on Boston Properties Limited Partnership’s December 31, 2018 credit rating, (1) the applicable Eurocurrency margins for the Revolving Facility and Delayed Draw Facility are 82.5 basis points and 90 basis points, respectively, (2) the alternate base rate margin is zero basis points for each of the Revolving Facility and Delayed Draw Facility and (3) the facility fee on the Revolving Facility commitment is 0.125% per annum. At December 31, 2018, Boston Properties Limited Partnership had $500.0 million of borrowings outstanding under its Delayed Draw Facility and no amounts outstanding under its Revolving Facility. At December 31, 2017, there was $45.0 million outstanding under its Revolving Facility. The 2017 Credit Facility contains customary representations and warranties, affirmative and negative covenants and events of default provisions, including failure to pay indebtedness, breaches of covenants, and bankruptcy and other insolvency events, which could result in the acceleration of all amounts and cancellation of all commitments outstanding under the Credit Agreement. Among other covenants, the 2017 Credit Facility requires that Boston Properties Limited Partnership maintain on an ongoing basis: (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 to 60% within one year, (5) an unsecured debt interest coverage ratio of at least 1.75 and (6) limitations on permitted investments. At December 31, 2018 , Boston Properties Limited Partnership was in compliance with each of these financial and other covenant requirements.

Commitments And Contingencies

Commitments And Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments And Contingencies	9. Commitments and Contingencies General In the normal course of business, the Company guarantees its performance of services or indemnifies third parties against its negligence. In addition, in the normal course of business, the Company guarantees to certain tenants the obligations of its subsidiaries for the payment of tenant improvement allowances and brokerage commissions in connection with their leases and limited costs arising from delays in delivery of their premises. The Company has letter of credit and performance obligations related to lender and development requirements that total approximately $7.8 million . 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. With limited exception, under these provisions, the Company is not compelled to purchase the interest of its outside joint venture partners. From time to time, under certain of the Company’s joint venture agreements, if certain return thresholds are achieved, either the Company or its partners will be entitled to an additional promoted interest or payments. See also Note 10 . From time to time, the Company (or ventures in which the Company has an ownership interest) has agreed, and may in the future agree, to (1) guarantee portions of the principal, interest and other amounts in connection with their borrowings, (2) provide customary environmental indemnifications and nonrecourse carve-outs (e.g., guarantees against fraud, misrepresentation and bankruptcy) in connection with their borrowings and (3) provide guarantees to lenders, tenants and other third parties for the completion of development projects. The Company has agreements with its outside partners whereby the partners agree to reimburse the joint venture for their share of any payments made under the guarantee. In some cases, the Company earns a fee from the applicable joint venture for providing the guarantee. In connection with the refinancing of 767 Fifth Avenue’s (the General Motors Building) secured loan by the Company’s consolidated joint venture entity, 767 Venture, LLC, the Company guaranteed the consolidated entity’s obligation to fund various reserves for tenant improvement costs and allowances, leasing commissions and free rent obligations in lieu of cash deposits. As of December 31, 2018 , the maximum funding obligation under the guarantee was approximately $116.1 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. As of December 31, 2018 , no amounts related to the guarantee are recorded as liabilities in the Company’s consolidated financial statements. Pursuant to the lease agreement with Marriott, the Company has guaranteed the completion of the office building and parking garage on behalf of its 7750 Wisconsin Avenue joint venture and has also agreed to provide any financing guaranty that may be required with respect to third-party construction financing. The Company earns fees from the joint venture for providing the guarantees and any amounts the Company pays under the guarantee(s) will be deemed to be capital contributions by the Company to the joint venture. The Company has also agreed to fund construction costs through capital contributions to the joint venture in the event of unavailability or insufficiency of third-party construction financing. In addition, the Company has guaranteed to Marriott, as hotel manager, the completion of a hotel being developed by an affiliate of The Bernstein Companies (the Company's partner in the 7750 Wisconsin Avenue joint venture) adjacent to the office property, for which the Company earns a fee from the affiliate of The Bernstein Companies. In addition, the Company entered into agreements with affiliates of The Bernstein Companies whereby the Company could be required to act as a mezzanine and/or mortgage lender and finance the construction of the hotel property. To secure such financing arrangements, affiliates of The Bernstein Companies are required to provide certain security, which varies depending on the specific loan, by pledges of their equity interest in the office property or, a fee mortgage on the hotel property, or both. As of December 31, 2018 , no amounts related to the contingent aspect of any of the guarantees are recorded as liabilities in the Company’s consolidated financial statements. In connection with the sale and development of the Company's 6595 Springfield Center Drive development project, the Company has guaranteed the completion of the project and the payment of certain cost overruns in accordance with the development management agreement with the buyer. Although the project has been sold and the lease with the federal government tenant has been assigned to the buyer, pursuant to the terms of the federal government lease, the federal government tenant is not obligated to release the prior owner/landlord from such landlord’s obligations under the lease until completion of the construction. As a result, the entity which previously owned the land remains liable to the federal government tenant for the completion of the construction obligations under the lease. The buyer is obligated to fund the balance of the costs to meet such construction obligations, subject to the Company’s obligation to fund cost overruns (if any), as noted above. An affiliate of the buyer has provided a guaranty of the obligations of the buyer to fund such construction costs and the buyer has agreed to use commercially reasonable efforts to require the construction lender to provide certain remedies to the Company in the event the buyer does not fund such construction obligations. As of December 31, 2018 , no amounts related to the contingent aspect of the guarantee are recorded as a liability in the Company’s consolidated financial statements (See Note 3 ). In 2009, the Company filed a general unsecured creditor’s claim against Lehman Brothers, Inc. for approximately $45.3 million related to its rejection of a lease at 399 Park Avenue in New York City. On January 10, 2014, the trustee for the liquidation of the business of Lehman Brothers allowed the Company’s claim in the amount of approximately $45.2 million . During 2014, 2015, 2016, 2017 and 2018, the Company received distributions totaling approximately $7.7 million , $8.1 million , $1.4 million , $0.4 million and $0.3 million , respectively, which are included in Base Rent in the Consolidated Statements of Operations, leaving a remaining claim of approximately $27.2 million . The Company will continue to evaluate whether to attempt to sell the remaining claim or wait until the trustee distributes proceeds from the Lehman Brothers estate. Given the inherent uncertainties in bankruptcy proceedings, there can be no assurance as to the timing or amount of additional proceeds, if any, that the Company may ultimately realize on the remaining claim, whether by sale to a third party or by one or more distributions from the trustee. Accordingly, the Company has not recorded any estimated recoveries associated with this gain contingency within its Consolidated Financial Statements at December 31, 2018 . Concentrations of Credit Risk Management of the Company performs ongoing credit evaluations of tenants and may require tenants to provide some form of credit support such as corporate guarantees and/or other financial guarantees. Although the Company’s properties are geographically diverse and the tenants operate in a variety of industries, to the extent the Company has a significant concentration of rental revenue from any single tenant, the inability of that tenant to make its lease payments could have an adverse effect on the Company. Insurance The Company’s property insurance program per occurrence limits are $1.0 billion for its portfolio insurance program, including coverage for acts of terrorism 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. Certain properties, including the General Motors Building located at 767 Fifth Avenue in New York, New York (“767 Fifth Avenue”), are currently insured in separate insurance programs. The property insurance program per occurrence limits for 767 Fifth Avenue are $1.625 billion , including Terrorism Coverage. The Company also currently carries nuclear, biological, chemical and radiological terrorism insurance coverage for acts of terrorism certified under the Federal Terrorism Risk Insurance Act (as amended, “TRIA”) (“NBCR Coverage”), which is provided by IXP as a direct insurer, for the properties in the Company's portfolio, including 767 Fifth Avenue, but excluding 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 NBCR Coverage provided by IXP is backstopped by the Federal Government if the aggregate industry insured losses resulting from a certified act of terrorism exceed a “program trigger.” In 2018, the program trigger was $160 million and the coinsurance was 18% , however, both will increase in subsequent years pursuant to TRIA. 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 TRIA. The Company may elect to terminate the NBCR Coverage if the Federal Government seeks recoupment for losses paid under TRIA, if TRIA is not extended after its expiration on December 31, 2020, 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. The Company also currently carries earthquake insurance on its properties located in areas known to be subject to earthquakes. In addition, this insurance is subject to a deductible in the amount of 3% of the value of the affected property. Specifically, the Company currently carries earthquake insurance which covers its San Francisco and Los Angeles regions with a $240 million per occurrence limit and a $240 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 or change the structure of its earthquake insurance program 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 and Los Angeles properties and the Company’s NBCR Coverage. Insofar as the Company owns IXP, it is responsible for its liquidity and capital resources, and the accounts of IXP 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 would also be responsible for any recoupment charges by the Federal Government in the event losses are paid out and its insurance policy is maintained after the payout by the Federal Government. If the Company experiences a loss and IXP is required to pay under its insurance policy, the Company would ultimately record the loss to the extent of the required payment. Therefore, insurance coverage provided by IXP should not be considered as the equivalent of third-party insurance, but rather as a modified form of self-insurance. In addition, Boston Properties Limited Partnership has issued a guarantee to cover liabilities of IXP in the amount of $20.0 million . 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 that 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, for which the Company cannot obtain insurance at all or at a reasonable cost. With respect to such losses and losses from acts of terrorism, earthquakes or other catastrophic events, if the Company experiences a loss that is uninsured or that exceeds policy limits, the Company could lose the capital invested in the damaged properties, as well as the anticipated future revenues from those properties. Depending on the specific circumstances of each affected property, it is possible that the Company could be liable for mortgage indebtedness or other obligations related to the property. Any such loss could materially and adversely affect the Company’s business and financial condition and results of operations. Legal Matters The Company is subject to various legal proceedings and claims that arise in the ordinary course of business. These matters are generally covered by insurance. Management believes that the final outcome of such matters will not have a material adverse effect on the financial position, results of operations or liquidity of the Company. State and Local Tax Matters Because Boston Properties, Inc. is organized and qualifies as a REIT, it is generally not subject to federal income taxes, but is subject to certain state and local taxes. In the normal course of business, certain entities through which the Company owns real estate either have undergone, or are currently undergoing, tax audits. Although the Company believes that it has substantial arguments in favor of its positions in the ongoing audits, in some instances there is no controlling precedent or interpretive guidance on the specific point at issue. Collectively, tax deficiency notices received to date from the jurisdictions conducting the ongoing audits have not been material. However, there can be no assurance that future audits will not occur with increased frequency or that the ultimate result of such audits will not have a material adverse effect on the Company’s results of operations. Environmental Matters It is the Company’s policy to retain independent environmental consultants to conduct or update Phase I environmental assessments (which generally do not involve invasive techniques such as soil or ground water sampling) and asbestos surveys in connection with the Company’s acquisition of properties. These pre-purchase environmental assessments have not revealed environmental conditions that the Company believes will have a material adverse effect on its business, assets, financial condition, results of operations or liquidity, and the Company is not otherwise aware of environmental conditions with respect to its properties that the Company believes would have such a material adverse effect. However, from time to time environmental conditions at the Company’s properties have required and may in the future require environmental testing and/or regulatory filings, as well as remedial action. In February 1999, the Company (through a joint venture) acquired from Exxon Corporation a property in Massachusetts that was formerly used as a petroleum bulk storage and distribution facility and was known by the state regulatory authority to contain soil and groundwater contamination. The Company developed an office park on the property. The Company engaged a specially licensed environmental consultant to oversee the management of contaminated soil and groundwater that was disturbed in the course of construction. Under the property acquisition agreement, Exxon agreed to (1) bear the liability arising from releases or discharges of oil and hazardous substances which occurred at the site prior to the Company’s ownership, (2) continue monitoring and/or remediating such releases and discharges as necessary and appropriate to comply with applicable requirements, and (3) indemnify the Company for certain losses arising from preexisting site conditions. Any indemnity claim may be subject to various defenses, and there can be no assurance that the amounts paid under the indemnity, if any, would be sufficient to cover the liabilities arising from any such releases and discharges. Environmental investigations at some of the Company’s properties and certain properties owned by affiliates of the Company have identified groundwater contamination migrating from off-site source properties. In each case the Company engaged a licensed environmental consultant to perform the necessary investigations and assessments and to prepare any required submittals to the regulatory authorities. In each case the environmental consultant concluded that the properties qualify under the regulatory program or the regulatory practice for a status which eliminates certain deadlines for conducting response actions at a site. The Company also believes that these properties qualify for liability relief under certain statutory provisions or regulatory practices regarding upgradient releases. Although the Company believes that the current or former owners of the upgradient source properties may bear responsibility for some or all of the costs of addressing the identified groundwater contamination, the Company will take such further response actions (if any) that it deems necessary or advisable. Other than periodic testing at some of these properties, no such additional response actions are anticipated at this time. Some of the Company’s properties and certain properties owned by the Company’s affiliates are located in urban, industrial and other previously developed areas where fill or current or historical uses of the areas have caused site contamination. Accordingly, it is sometimes necessary to institute special soil and/or groundwater handling procedures and/or include particular building design features in connection with development, construction and other property operations in order to achieve regulatory closure and/or ensure that contaminated materials are addressed in an appropriate manner. In these situations, it is the Company’s practice to investigate the nature and extent of detected contamination, including potential issues associated with contaminant migration, assess potential liability risks and estimate the costs of required response actions and special handling procedures. The Company then uses this information as part of its decision-making process with respect to the acquisition, deal structure and/or development of the property. For example, the Company owns a parcel in Massachusetts which was formerly used as a quarry/asphalt batching facility. Pre-purchase testing indicated that the site contained relatively low levels of certain contaminants. The Company has developed an office park on this property. Prior to and during redevelopment activities, the Company engaged a specially licensed environmental consultant to monitor environmental conditions at the site and prepare necessary regulatory submittals based on the results of an environmental risk characterization. A submittal has been made to the regulatory authorities in order to achieve regulatory closure at this site. The submittal included an environmental deed restriction that mandates compliance with certain protective measures in a portion of the site where low levels of residual soil contamination have been left in place in accordance with applicable laws. The Company expects that resolution of the environmental matters relating to the above will not have a material impact on its business, assets, financial condition, results of operations or liquidity. However, the Company cannot assure you that it has identified all environmental liabilities at its properties, that all necessary remediation actions have been or will be undertaken at the Company’s properties or that the Company will be indemnified, in full or at all, in the event that such environmental liabilities arise.

Noncontrolling Interests

Noncontrolling Interests	12 Months Ended
	Dec. 31, 2018
Noncontrolling Interest [Abstract]
Noncontrolling Interests	10. Noncontrolling Interests Noncontrolling interests relate to the interests in Boston Properties Limited Partnership not owned by Boston Properties, Inc. and interests in consolidated property partnerships not wholly-owned by the Company. As of December 31, 2018 , the noncontrolling interests in Boston Properties Limited Partnership consisted of 16,783,558 OP Units, 991,577 LTIP Units (including 118,067 2012 OPP Units, 68,889 2013 MYLTIP Units, 23,187 2014 MYLTIP Units and 28,724 2015 MYLTIP Units), 471,579 2016 MYLTIP Units, 398,871 2017 MYLTIP Units and 341,366 2018 MYLTIP Units held by parties other than Boston Properties, Inc. Noncontrolling Interest—Common Units During the years ended December 31, 2018 and 2017 , 83,136 and 495,637 OP Units, respectively, were presented by the holders for redemption (including 48,389 and 36,486 OP Units, respectively, issued upon conversion of LTIP Units, 2012 OPP Units, 2013 MYLTIP Units and 2014 MYLTIP Units) and were redeemed by Boston Properties, Inc. in exchange for an equal number of shares of Common Stock. Boston Properties Limited Partnership exercised its right under the terms of its partnership agreement to convert an aggregate of 625,043 eligible LTIP Units (including an aggregate of 32,349 2012 OPP Units and 2013 MYLTIP Units) into Common Units effective as of May 2, 2016. These conversions were effected solely for administrative efficiency and had no substantive impact on the rights of Boston Properties Limited Partnership or the holders of these LTIP Units, as the economic and other rights of the LTIP Units converted were substantively identical to those of the Common Units. In the future, Boston Properties Limited Partnership intends to convert LTIP Units (including 2012 OPP Units and MYLTIP Units) into Common Units promptly after they become eligible for conversion. The May 2016 conversions were, and future conversions will be, effected at the election of Boston Properties Limited Partnership and are without regard to the investment intentions of the holders of the units. At December 31, 2018 , Boston Properties Limited Partnership had outstanding 471,579 2016 MYLTIP Units, 398,871 2017 MYLTIP Units and 341,366 2018 MYLTIP Units (See Note 16 ). Prior to the applicable measurement date (February 9, 2019 for 2016 MYLTIP Units (See Note 19 ), February 6, 2020 for 2017 MYLTIP Units and February 5, 2021 for 2018 MYLTIP Units), holders of MYLTIP 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 MYLTIP Units, both vested and unvested, that MYLTIP award recipients have earned, if any, based on the establishment of a performance 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 4, 2016, the measurement period for the Company’s 2013 MYLTIP awards ended and, based on Boston Properties, Inc.’s relative TSR performance, the final awards were determined to be 109.5% of target, or an aggregate of approximately $13.5 million . As a result, 205,762 2013 MYLTIP Units were automatically forfeited. On February 3, 2017, the measurement period for the Company’s 2014 MYLTIP awards ended and, based on Boston Properties, Inc.’s relative TSR performance, the final awards were determined to be 27.7% of target or an aggregate of approximately $3.5 million (after giving effect to voluntary employee separations and the unallocated reserve). As a result, an aggregate of 447,386 2014 MYLTIP Units that had been previously granted were automatically forfeited. On February 4, 2018, the measurement period for the Company’s 2015 MYLTIP awards ended and, based on Boston Properties, Inc.’s relative TSR performance, the final awards were determined to be 22.0% of target or an aggregate of approximately $3.6 million (after giving effect to voluntary employee separations). As a result, an aggregate of 337,847 2015 MYLTIP Units that had been previously granted were automatically forfeited. The following table presents Boston Properties Limited Partnership’s distributions on the OP Units and LTIP Units (including the 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units and, after the February 4, 2018 measurement date, the 2015 MYLTIP Units) and its distributions on the 2015 MYLTIP Units (prior to the February 4, 2018 measurement date), 2016 MYLTIP Units, 2017 MYLTIP Units and 2018 MYLTIP Units (after the February 5, 2018 issuance date) paid in 2018: Record Date Payment Date Distributions per OP Unit and LTIP Unit Distributions per MYLTIP Unit December 31, 2018 January 30, 2019 $0.95 $0.095 September 28, 2018 October 31, 2018 $0.95 $0.095 June 29, 2018 July 31, 2018 $0.80 $0.080 March 29, 2018 April 30, 2018 $0.80 $0.080 December 29, 2017 January 30, 2018 $0.80 $0.080 A holder of an OP Unit may present the OP Unit to Boston Properties Limited 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, Boston Properties Limited Partnership must redeem the OP Unit for cash equal to the then value of a share of common stock of Boston Properties, Inc. Boston Properties, Inc. 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 Boston Properties, Inc. and LTIP Units (including the 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units and 2015 MYLTIP Units) assuming that all conditions had been met for the conversion thereof) had all of such units been redeemed at December 31, 2018 was approximately $2.0 billion based on the last reported price of a share of Common Stock on the New York Stock Exchange of $112.55 per share on December 31, 2018. Boston Properties Limited Partnership The following table reflects the activity of noncontrolling interests—redeemable common units of Boston Properties Limited Partnership for the years ended December 31, 2018 , 2017 and 2016 (in thousands): Balance at December 31, 2015 $ 2,286,689 Contributions 31,395 Net income 59,260 Distributions (49,087 ) Conversion of redeemable partnership units (6,461 ) Unearned compensation (3,464 ) Other comprehensive loss (4,379 ) Adjustment to reflect redeemable partnership units at redemption value (51,913 ) Balance at December 31, 2016 2,262,040 Contributions 31,743 Net income 52,210 Distributions (54,494 ) Conversion of redeemable partnership units (16,916 ) Unearned compensation 1,650 Cumulative effect of a change in accounting principle (1,763 ) Other comprehensive income 206 Adjustment to reflect redeemable partnership units at redemption value 17,587 Balance at December 31, 2017 2,292,263 Contributions 34,680 Net income 66,807 Distributions (62,731 ) Conversion of redeemable partnership units (2,880 ) Unearned compensation 2,181 Cumulative effect of a change in accounting principle 563 Other comprehensive income 304 Adjustment to reflect redeemable partnership units at redemption value (330,596 ) Balance at December 31, 2018 $ 2,000,591 Noncontrolling Interests—Property Partnerships The noncontrolling interests in property partnerships consist of the outside equity interests 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 $1.7 billion at December 31, 2018 and 2017 , are included in Noncontrolling Interests—Property Partnerships on the accompanying Consolidated Balance Sheets. On May 12, 2016, the partners in the Company’s consolidated entity that owns Salesforce Tower located in San Francisco, California amended the venture agreement. Under the original venture agreement, if the Company elects to fund the construction of Salesforce Tower without a construction loan (or a construction loan of less than 50% of project costs) and the venture has commenced vertical construction of the project, then the partner’s capital funding obligation shall be limited, in which event the Company shall fund up to 2.5% of the total project costs (i.e., 50% of the partner’s 5% interest in the venture) in the form of a loan to the partner. This loan would bear interest at the then prevailing market interest rates for construction loans. Under the amended agreement, the partners have agreed to structure this funding by the Company as preferred equity rather than a loan. The preferred equity contributed by the Company earns a preferred return equal to LIBOR plus 3.00% per annum and is payable to the Company out of any distributions to which the partner would otherwise be entitled until such preferred equity and preferred return have been repaid to the Company. As of December 31, 2018 , the Company had contributed an aggregate of approximately $22.6 million of preferred equity to the venture. Also, under the joint venture agreement, (a) from and after the stabilization date, the partner has the right to cause the Company to purchase all (but not less than all) of the partner’s interest and (b) from and after the third anniversary of the stabilization date, the Company has the right to acquire all (but not less than all) of the partner’s interest, in each case at an agreed upon purchase price or appraised value. In addition, if certain threshold returns are achieved the partner will be entitled to receive an additional promoted interest with respect to cash flow distributions. The term stabilization date is defined in the agreement to generally mean the first date after completion upon which Salesforce Tower is (1) at least 90% leased and (2) 50% occupied by tenants that are paying rent (See Note 19 ). On June 6, 2017, in conjunction with the refinancing of the indebtedness of the Company’s consolidated entity in which it has a 60% interest and that owns 767 Fifth Avenue (the General Motors Building) located in New York City, the members of the consolidated entity amended the limited liability company agreement to provide for the contribution of the remaining unpaid principal balance of the members’ notes payable totaling approximately $273.9 million (of which the Company’s share of approximately $164.4 million is eliminated in consolidation) to equity in the consolidated entity, resulting in an increase of approximately $109.6 million to Noncontrolling Interests in Property Partnerships on the Company’s Consolidated Balance Sheets. There were no changes to the ownership interests or rights of the members as a result of the amendment. The following table reflects the activity of the noncontrolling interests—property partnerships for the years ended December 31, 2018 , 2017 and 2016 (in thousands): Balance at December 31, 2015 $ 1,574,400 Capital contributions 10,756 Net loss (2,068 ) Accumulated other comprehensive loss (877 ) Distributions (51,564 ) Balance at December 31, 2016 1,530,647 Capital contributions (1) 161,585 Net income 47,832 Accumulated other comprehensive loss (2,128 ) Distributions (54,176 ) Balance at December 31, 2017 1,683,760 Capital contributions 46,701 Net income 62,909 Accumulated other comprehensive income 576 Distributions (82,501 ) Balance at December 31, 2018 $ 1,711,445 _______________ (1) Includes the contribution of the remaining unpaid principal balance of the members’ notes payable totaling $109,576 to equity in the consolidated entity that owns 767 Fifth Avenue (the General Motors Building).

Stockholders' Equity _ Partners

Stockholders' Equity / Partners' Capital	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Stockholders' Equity	11. Stockholders’ Equity / Partners’ Capital Boston Properties, Inc. As of December 31, 2018 , Boston Properties, Inc. had 154,458,478 shares of Common Stock outstanding. On June 2, 2017, Boston Properties, Inc. renewed its “at the market” (“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. This program replaced the Company’s prior $600.0 million ATM stock offering program that was scheduled to expire on June 3, 2017. The Company intends to use the net proceeds from any offering for general business purposes, which may include investment opportunities and debt reduction. No shares of common stock have been issued under this ATM stock offering program. During the year ended December 31, 2018, there were no options to purchase Common Stock exercised. During the year ended December 31, 2017, Boston Properties, Inc. issued 6,688 shares of Common Stock upon the exercise of options to purchase Common Stock. During the years ended December 31, 2018 and 2017 , Boston Properties, Inc. issued 83,136 and 495,637 shares of Common Stock, respectively, in connection with the redemption of an equal number of redeemable OP Units from limited partners. The following table presents Boston Properties, Inc.’s dividends per share and Boston Properties Limited Partnership’s distributions per OP Unit and LTIP Unit paid or payable in 2018 : Record Date Payment Date Dividend (Per Share) Distribution (Per Unit) December 31, 2018 January 30, 2019 $0.95 $0.95 September 28, 2018 October 31, 2018 $0.95 $0.95 June 29, 2018 July 31, 2018 $0.80 $0.80 March 29, 2018 April 30, 2018 $0.80 $0.80 December 29, 2017 January 30, 2018 $0.80 $0.80 Preferred Stock As of December 31, 2018 , Boston Properties, Inc. had 80,000 shares ( 8,000,000 depositary shares each representing 1/100th of a share) outstanding of its 5.25% Series B Cumulative Redeemable Preferred Stock with a liquidation preference of $2,500.00 per share ( $25.00 per depositary share). Boston Properties, Inc. pays cumulative cash dividends on the Series B Preferred Stock at a rate of 5.25% per annum of the $2,500.00 liquidation preference per share. Boston Properties, Inc. did not redeem the Series B Preferred Stock prior to March 27, 2018, except in certain circumstances relating to the preservation of Boston Properties, Inc.’s REIT status. On and after March 27, 2018, Boston Properties, Inc., at its option, may redeem the Series B Preferred Stock for a cash redemption price of $2,500.00 per share ( $25.00 per depositary share), plus all accrued and unpaid dividends. The Series B Preferred Stock is not redeemable by the holders, has no maturity date and is not convertible into any other security of Boston Properties, Inc. or its affiliates. The following table presents Boston Properties Inc.’s dividends per share on its outstanding Series B Preferred Stock paid or payable in 2018 : Record Date Payment Date Dividend (Per Share) February 4, 2019 February 15, 2019 $32.8125 November 2, 2018 November 15, 2018 $32.8125 August 3, 2018 August 15, 2018 $32.8125 May 4, 2018 May 15, 2018 $32.8125 February 2, 2018 February 15, 2018 $32.8125 Boston Properties Limited Partnership The following table presents the changes in the issued and outstanding partners’ capital units since January 1, 2016 : General Partner Units Limited Partner Units Total Partners’ Outstanding at December 31, 2015 1,715,092 151,864,874 153,579,966 Units issued to Boston Properties, Inc. related to Common Stock issued under the Employee Stock Purchase Plan 72 5,623 5,695 Units issued to Boston Properties, Inc. related to Common Stock issued under the Stock Option and Incentive Plan, net 172 13,485 13,657 Units issued to Boston Properties, Inc. related to Common Stock issued in exchange for OP Units 2,407 188,450 190,857 Outstanding at December 31, 2016 1,717,743 152,072,432 153,790,175 Units issued to Boston Properties, Inc. related to Common Stock issued under the Employee Stock Purchase Plan 21 6,296 6,317 Units issued to Boston Properties, Inc. related to Common Stock issued under the Stock Option and Incentive Plan, net 111 33,046 33,157 Units issued to Boston Properties, Inc. related to Common Stock issued in exchange for OP Units 1,665 493,972 495,637 Outstanding at December 31, 2017 1,719,540 152,605,746 154,325,286 Units issued to Boston Properties, Inc. related to Common Stock issued under the Employee Stock Purchase Plan 132 6,136 6,268 Units issued to Boston Properties, Inc. related to Common Stock issued under the Stock Option and Incentive Plan, net 919 42,869 43,788 Units issued to Boston Properties, Inc. related to Common Stock issued in exchange for OP Units 1,745 81,391 83,136 Outstanding at December 31, 2018 1,722,336 152,736,142 154,458,478 As of December 31, 2018 , Boston Properties, Inc. owned 1,722,336 general partnership units and 152,736,142 limited partnership units. The following table reflects the activity of the Series B Preferred Units for the years ended December 31, 2018 , 2017 and 2016 (in thousands), which activity is included within Boston Properties Limited Partnership’s Consolidated Statements of Partners’ Capital: Balance at December 31, 2015 $ 193,623 Net income 10,500 Distributions (10,500 ) Balance at December 31, 2016 193,623 Net income 10,500 Distributions (10,500 ) Balance at December 31, 2017 193,623 Net income 10,500 Distributions (10,500 ) Balance at December 31, 2018 $ 193,623

Future Minimum Rents

Future Minimum Rents	12 Months Ended
	Dec. 31, 2018
Future Minimum Rents [Abstract]
Future Minimum Rents [Text Block]	12. Future Minimum Rents The properties are leased to tenants under net operating leases with initial term expiration dates ranging from 2019 to 2049 . The future contractual minimum lease payments to be received (excluding operating expense reimbursements) by the Company as of December 31, 2018 , under non-cancelable operating leases which expire on various dates through 2049 , are as follows: Years Ending December 31, (in thousands) 2019 $ 2,088,171 2020 2,106,963 2021 2,015,031 2022 1,838,699 2023 1,736,636 Thereafter 12,295,464 No single tenant represented more than 10.0% of the Company’s total rental revenue for the years ended December 31, 2018 , 2017 and 2016 .

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Segment Reporting Disclosure [Text Block]	13. Segment Information The following tables present reconciliations of Net Income Attributable to Boston Properties, Inc. Common Shareholders to Net Operating Income and Net Income Attributable to Boston Properties Limited Partnership Common Unitholders to Net Operating Income for the years ended December 31, 2018 , 2017 and 2016 . Boston Properties, Inc. Year ended December 31, 2018 2017 2016 (in thousands) Net income attributable to Boston Properties, Inc. common shareholders $ 572,347 $ 451,939 $ 502,285 Add: Preferred dividends 10,500 10,500 10,500 Noncontrolling interest—common units of the Operating Partnership 66,807 52,210 59,260 Noncontrolling interests in property partnerships 62,909 47,832 (2,068 ) Losses from interest rate contracts — — 140 Interest expense 378,168 374,481 412,849 Impairment losses 11,812 — 1,783 Depreciation and amortization expense 645,649 617,547 694,403 Transaction costs 1,604 668 2,387 Payroll and related costs from management services contracts 9,590 — — General and administrative expense 121,722 113,715 105,229 Less: Gains (losses) from early extinguishments of debt (16,490 ) 496 (371 ) Gains (losses) from investments in securities (1,865 ) 3,678 2,273 Interest and other income 10,823 5,783 7,230 Gains on sales of real estate 182,356 7,663 80,606 Gain on sale of investment in unconsolidated joint venture — — 59,370 Income from unconsolidated joint ventures 2,222 11,232 8,074 Direct reimbursements of payroll and related costs from management services contracts 9,590 — — Development and management services revenue 45,158 34,605 28,284 Net Operating Income $ 1,649,314 $ 1,605,435 $ 1,601,302 Boston Properties Limited Partnership Year ended December 31, 2018 2017 2016 (in thousands) Net income attributable to Boston Properties Limited Partnership common unitholders $ 656,903 $ 512,866 $ 575,341 Add: Preferred distributions 10,500 10,500 10,500 Noncontrolling interests in property partnerships 62,909 47,832 (2,068 ) Losses from interest rate contracts — — 140 Interest expense 378,168 374,481 412,849 Impairment losses 10,181 — 1,783 Depreciation and amortization expense 637,891 609,407 682,776 Transaction costs 1,604 668 2,387 Payroll and related costs from management services contracts 9,590 — — General and administrative expense 121,722 113,715 105,229 Less: Gains (losses) from early extinguishments of debt (16,490 ) 496 (371 ) Gains (losses) from investments in securities (1,865 ) 3,678 2,273 Interest and other income 10,823 5,783 7,230 Gains on sales of real estate 190,716 8,240 82,775 Gain on sale of investment in unconsolidated joint venture — — 59,370 Income from unconsolidated joint ventures 2,222 11,232 8,074 Direct reimbursements of payroll and related costs from management services contracts 9,590 — — Development and management services revenue 45,158 34,605 28,284 Net Operating Income $ 1,649,314 $ 1,605,435 $ 1,601,302 Net operating income (“NOI”) is a non-GAAP financial measure equal to net income attributable to Boston Properties, Inc. common shareholders and net income attributable to Boston Properties Limited Partnership common unitholders, as applicable, the most directly comparable GAAP financial measures, plus (1) preferred dividends/distributions, net income attributable to noncontrolling interests, losses from interest rate contracts, interest expense, impairment losses, depreciation and amortization expense, transaction costs, payroll and related costs from management services contracts and corporate general and administrative expense less (2) gains (losses) from early extinguishments of debt, gains (losses) from investments in securities, interest and other income, gains on sales of real estate, gain on sale of investment in unconsolidated joint venture, income from unconsolidated joint ventures, direct reimbursements of payroll and related costs from management services contracts and development and management services revenue. The Company believes NOI is useful to investors as a performance measure and believes it provides useful information to investors regarding its results of operations and financial condition because, when compared across periods, it reflects the impact on operations from trends in occupancy rates, rental rates, operating costs and acquisition and development activity on an unleveraged basis, providing perspective not immediately apparent from net income attributable to Boston Properties, Inc. common shareholders and net income attributable to Boston Properties Limited Partnership common unitholders. For example, interest expense is not necessarily linked to the operating performance of a real estate asset and is often incurred at the corporate level as opposed to the property level. Similarly, interest expense may be incurred at the property level even though the financing proceeds may be used at the corporate level (e.g., used for other investment activity). In addition, depreciation and amortization expense, because of historical cost accounting and useful life estimates, may distort operating performance measures at the property level. NOI presented by the Company may not be comparable to NOI reported by other REITs or real estate companies that define NOI differently. 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. Preferred dividends/distributions, net income attributable noncontrolling interests, losses from interest rate contracts, interest expense, impairment losses, depreciation and amortization expense, transactions costs, payroll and related costs from management services contracts, corporate general and administrative expense, gains (losses) from early extinguishments of debt, gains (losses) from investments in securities, gains on sales of real estate, interest and other income, gain on sale of investment in unconsolidated joint venture, income from unconsolidated joint ventures, direct reimbursements of payroll and related costs from management services contracts and development and management services revenue are not included in NOI as internal reporting addresses these items on a corporate level. The Company’s segments are based on the Company’s method of internal reporting which classifies its operations by both geographic area and property type. The Company’s segments by geographic area are Boston, New York, San Francisco and Washington, DC. Segments by property type include: Office, Residential and Hotel. Information by geographic area and property type (dollars in thousands): For the year ended December 31, 2018 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 838,341 $ 959,050 $ 397,180 $ 396,088 $ 2,590,659 Residential 6,694 — — 15,857 22,551 Hotel 49,118 — — — 49,118 Total 894,153 959,050 397,180 411,945 2,662,328 % of Grand Totals 33.59 % 36.02 % 14.92 % 15.47 % 100.00 % Rental Expenses: Office 315,653 377,992 130,016 142,886 966,547 Residential 3,632 — — 8,972 12,604 Hotel 33,863 — — — 33,863 Total 353,148 377,992 130,016 151,858 1,013,014 % of Grand Totals 34.86 % 37.32 % 12.83 % 14.99 % 100.00 % Net operating income $ 541,005 $ 581,058 $ 267,164 $ 260,087 $ 1,649,314 % of Grand Totals 32.80 % 35.23 % 16.20 % 15.77 % 100.00 % For the year ended December 31, 2017 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 776,279 $ 969,371 $ 345,519 $ 414,103 $ 2,505,272 Residential 4,745 — — 11,851 16,596 Hotel 45,603 — — — 45,603 Total 826,627 969,371 345,519 425,954 2,567,471 % of Grand Totals 32.20 % 37.75 % 13.46 % 16.59 % 100.00 % Rental Expenses: Office 301,097 372,810 105,253 144,515 923,675 Residential 2,044 — — 4,258 6,302 Hotel 32,059 — — — 32,059 Total 335,200 372,810 105,253 148,773 962,036 % of Grand Totals 34.84 % 38.76 % 10.94 % 15.46 % 100.00 % Net operating income $ 491,427 $ 596,561 $ 240,266 $ 277,181 $ 1,605,435 % of Grand Totals 30.61 % 37.15 % 14.97 % 17.27 % 100.00 % For the year ended December 31, 2016 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 727,265 $ 1,012,518 $ 318,609 $ 402,561 $ 2,460,953 Residential 4,812 — — 11,887 16,699 Hotel 44,884 — — — 44,884 Total 776,961 1,012,518 318,609 414,448 2,522,536 % of Grand Totals 30.80 % 40.14 % 12.63 % 16.43 % 100.00 % Rental Expenses: Office 282,827 363,188 100,787 135,890 882,692 Residential 2,708 — — 4,368 7,076 Hotel 31,466 — — — 31,466 Total 317,001 363,188 100,787 140,258 921,234 % of Grand Totals 34.41 % 39.42 % 10.94 % 15.23 % 100.00 % Net operating income $ 459,960 $ 649,330 $ 217,822 $ 274,190 $ 1,601,302 % of Grand Totals 28.73 % 40.55 % 13.60 % 17.12 % 100.00 %

Earnings Per Share _ Common Uni

Earnings Per Share / Common Unit	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Earnings Per Share	14. Earnings Per Share / Common Unit Boston Properties, Inc. The following table provides a reconciliation of both the net income attributable to Boston Properties, Inc. common shareholders 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. common shareholders by the weighted-average number of common shares outstanding during the period. Unvested share-based payment awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid) are also participating securities. As such, unvested restricted common stock of Boston Properties, Inc. and Boston Properties Limited Partnership's LTIP Units, 2012 OPP Units and MYLTIP Units are considered participating securities. Participating securities are included in the computation of basic EPS of Boston Properties, Inc. using the two -class method. Participating securities are included in the computation of diluted EPS of Boston Properties, Inc. using the if-converted method if the impact is dilutive. Because the 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units and 2015 MYLTIP Units required, and the 2016-2018 MYLTIP Units require, Boston Properties, Inc. to outperform absolute and relative return thresholds, unless such thresholds have been met by the end of the applicable reporting period, Boston Properties, Inc. excludes such units from the diluted EPS calculation. Other potentially dilutive common shares, including stock options, restricted stock and other securities of Boston Properties Limited Partnership that are exchangeable for the Boston Properties, Inc.’s Common Stock, and the related impact on earnings, are considered when calculating diluted EPS. For the Year Ended December 31, 2018 Income (Numerator) Shares (Denominator) Per Share Amount (in thousands, except for per share amounts) Basic Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 572,347 154,427 $ 3.71 Allocation of undistributed earnings to participating securities (101 ) — — Net income attributable to Boston Properties, Inc. common shareholders $ 572,246 154,427 $ 3.71 Effect of Dilutive Securities: Stock Based Compensation — 255 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 572,246 154,682 $ 3.70 For the Year Ended December 31, 2017 Income (Numerator) Shares (Denominator) Per Share Amount (in thousands, except for per share amounts) Basic Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 451,939 154,190 $ 2.93 Effect of Dilutive Securities: Stock Based Compensation — 200 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 451,939 154,390 $ 2.93 For the Year Ended December 31, 2016 Income (Numerator) Shares (Denominator) Per Share Amount (in thousands, except for per share amounts) Basic Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 502,285 153,715 $ 3.27 Allocation of undistributed earnings to participating securities (283 ) — — Net income attributable to Boston Properties, Inc. common shareholders $ 502,002 153,715 $ 3.27 Effect of Dilutive Securities: Stock Based Compensation — 262 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 502,002 153,977 $ 3.26 Boston Properties Limited Partnership The following table provides a reconciliation of both the net income attributable to Boston Properties Limited Partnership common unitholders and the number of common units used in the computation of basic earnings per common unit, which is calculated by dividing net income attributable to Boston Properties Limited Partnership common unitholders by the weighted-average number of common units outstanding during the period. Unvested share-based payment awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid) are also participating securities. As such, unvested restricted common stock of Boston Properties, Inc. and Boston Properties Limited Partnership’s LTIP Units, 2012 OPP Units and MYLTIP Units are considered participating securities. Participating securities are included in the computation of basic earnings per common unit using the two -class method. Participating securities are included in the computation of diluted earnings per common unit using the if-converted method if the impact is dilutive. Because the 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units and 2015 MYLTIP Units required, and the 2016-2018 MYLTIP Units require, Boston Properties, Inc. to outperform absolute and relative return thresholds, unless such thresholds have been met by the end of the applicable reporting period, Boston Properties Limited Partnership excludes such units from the diluted earnings per common unit calculation. Other potentially dilutive common units and the related impact on earnings are considered when calculating diluted earnings per common unit. Included in the number of units (the denominator) below are approximately 17,485,000 , 17,471,000 and 17,646,000 redeemable common units for the years ended December 31, 2018 , 2017 and 2016 , respectively. For the Year Ended December 31, 2018 Income (Numerator) Units (Denominator) Per Unit Amount (in thousands, except for per unit amounts) Basic Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 656,903 171,912 $ 3.82 Allocation of undistributed earnings to participating securities (113 ) — — Net income attributable to Boston Properties Limited Partnership common unitholders $ 656,790 171,912 $ 3.82 Effect of Dilutive Securities: Stock Based Compensation — 255 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 656,790 172,167 $ 3.81 For the Year Ended December 31, 2017 Income (Numerator) Units (Denominator) Per Unit Amount (in thousands, except for per unit amounts) Basic Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 512,866 171,661 $ 2.99 Effect of Dilutive Securities: Stock Based Compensation — 200 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 512,866 171,861 $ 2.98 For the Year Ended December 31, 2016 Income (Numerator) Units (Denominator) Per Unit Amount (in thousands, except for per unit amounts) Basic Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 575,341 171,361 $ 3.36 Allocation of undistributed earnings to participating securities (316 ) — — Net income attributable to Boston Properties Limited Partnership common unitholders $ 575,025 171,361 $ 3.36 Effect of Dilutive Securities: Stock Based Compensation — 262 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 575,025 171,623 $ 3.35

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2018
Employee Benefit Plans [Abstract]
Compensation and Employee Benefit Plans [Text Block]	15. Employee Benefit Plans Effective January 1, 1985, the predecessor of the Company adopted a 401(k) Savings Plan (the “Plan”) for its employees. Under the Plan, as amended, employees, as defined, are eligible to participate in the Plan after they have completed three months of service. Upon formation, the Company adopted the Plan and the terms of the Plan. Under the Plan, as amended, the Company’s matching contribution equals 200% of the first 3% of participant’s eligible earnings contributed (utilizing earnings that are not in excess of an amount established by the IRS ( $275,000 , $270,000 and $265,000 in 2018 , 2017 and 2016 , respectively), indexed for inflation) with no vesting requirement. The Company’s aggregate matching contribution for the years ended December 31, 2018 , 2017 and 2016 was approximately $4.1 million , $4.1 million and $4.0 million , respectively. The Plan also provides for supplemental retirement contributions to certain employees who had at least ten years of service on January 1, 2001, and who were 40 years of age or older as of January 1, 2001. The maximum supplemental retirement contribution will not exceed the annual limit on contributions established by the IRS. The Company will record an annual supplemental retirement credit for the benefit of each participant. The Company’s supplemental retirement contribution and credit for the years ended December 31, 2018 , 2017 and 2016 was approximately $18,000 , $18,000 and $21,000 , respectively. The Company also maintains a deferred compensation plan that is designed to allow officers of Boston Properties, Inc. to defer a portion of their current income on a pre-tax basis and receive a tax-deferred return on these deferrals. The Company’s obligation under the plan is that of an unsecured promise to pay the deferred compensation to the plan participants in the future. At December 31, 2018 and 2017 , the Company had maintained approximately $28.2 million and $29.2 million , respectively, in a separate account, which is not restricted as to its use. The Company’s liability under the plan is equal to the total amount of compensation deferred by the plan participants and earnings on the deferred compensation pursuant to investments elected by the plan participants. The Company’s liability as of December 31, 2018 and 2017 was approximately $28.2 million and $29.2 million , respectively, which are included in the accompanying Consolidated Balance Sheets.

Stock Option and Incentive Plan

Stock Option and Incentive Plan	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Option and Incentive Plan	16. Stock Option and Incentive Plan At Boston Properties, Inc.’s 2012 annual meeting of stockholders held on May 15, 2012, its stockholders approved the Boston Properties, Inc. 2012 Stock Option and Incentive Plan (the “2012 Plan”). The 2012 Plan replaced the 1997 Stock Option and Incentive Plan (the “1997 Plan”). The material terms of the 2012 Plan include, among other things: (1) the maximum number of shares of common stock reserved and available for issuance under the 2012 Plan is the sum of (i) 13,000,000 newly authorized shares, plus (ii) the number of shares available for grant under the 1997 Stock Plan immediately prior to the effective date of the 2012 Plan, plus (iii) any shares underlying grants under the 1997 Plan that are forfeited, canceled or terminated (other than by exercise) in the future; (2) “full-value” awards (i.e., awards other than stock options) are multiplied by a 2.32 conversion ratio to calculate the number of shares available under the 2012 Plan that are used for each full-value award, as opposed to a 1.0 conversion ratio for each stock option awarded under the 2012 Plan; (3) shares tendered or held back for taxes will not be added back to the reserved pool under the 2012 Plan; (4) stock options may not be re-priced without stockholder approval; and (5) the term of the 2012 Plan is for ten years from the date of stockholder approval. On February 6, 2018, Boston Properties, Inc.’s Compensation Committee approved the 2018 MYLTIP awards under Boston Properties, Inc.’s 2012 Stock Option and Incentive Plan (the “2012 Plan”) to certain officers and employees of Boston Properties, Inc. The 2018 MYLTIP awards utilize Boston Properties, Inc.’s TSR over a three -year measurement period, on an annualized, compounded basis, as the performance metric. Earned awards will be based on Boston Properties, Inc.’s TSR relative to (i) the Cohen & Steers Realty Majors Portfolio Index ( 50% weight) and (ii) the Nareit Office Index adjusted to include Vornado Realty Trust ( 50% weight). For 2018 MYLTIP awards, levels of payout opportunity will range from zero for relative TSR performance that is 1,000 basis points or more below the index to a maximum of 200% of target if the Company's TSR is equal to or greater than 1,000 basis points above the index, on a straight-line basis, depending on the value and linear interpolation between zero and maximum. Earned awards measured on the basis of relative TSR performance are subject to an absolute TSR component in the form of modifiers that (A) reduce the level of earned awards in the event Boston Properties, Inc.’s annualized TSR is 0% or less and (B) cause some awards to be earned in the event Boston Properties, Inc.’s annualized TSR is 12% or more even though on a relative basis alone Boston Properties, Inc.’s TSR would not result in any earned awards. Earned awards (if any) will vest 50% on February 5, 2021 and 50% on February 5, 2022, based on continued employment. Vesting will be accelerated in the event of a change in control, termination of employment by Boston Properties, Inc. without cause, or termination of employment by the award recipient for good reason, death, disability or retirement. If there is a change of control prior to February 5, 2021, earned awards will be calculated based on TSR performance up to the date of the change of control. The 2018 MYLTIP awards are in the form of LTIP Units issued on the grant date which (i) are subject to forfeiture to the extent awards are not earned and (ii) prior to the performance measurement date are only entitled to one-tenth ( 10% ) of the regular quarterly distributions payable on common partnership units. Under ASC 718, the 2018 MYLTIP awards have an aggregate value of approximately $13.3 million , which amount will generally be amortized into earnings over the four -year plan period under the graded vesting method. On February 4, 2018, the measurement period for the Company’s 2015 MYLTIP awards ended and, based on Boston Properties, Inc.’s relative TSR performance, the final awards were determined to be 22.0% of target or an aggregate of approximately $3.6 million (after giving effect to voluntary employee separations). As a result, an aggregate of 337,847 2015 MYLTIP Units that had been previously granted were automatically forfeited. On February 3, 2017, the measurement period for the Company’s 2014 MYLTIP awards ended and, based on Boston Properties, Inc.’s relative TSR performance, the final awards were determined to be 27.7% of target or an aggregate of approximately $3.5 million (after giving effect to voluntary employee separations and the unallocated reserve). As a result, an aggregate of 447,386 2014 MYLTIP Units that had been previously granted were automatically forfeited. On February 4, 2016, the measurement period for the Company’s 2013 MYLTIP awards ended and, based on Boston Properties, Inc.’s relative TSR performance, the final awards were determined to be 109.5% of target or an aggregate of approximately $13.5 million . As a result, 205,762 2013 MYLTIP Units were automatically forfeited. Boston Properties, Inc. issued 20,320 , 37,414 and 22,067 shares of restricted common stock and Boston Properties Limited Partnership issued 205,838 , 113,918 and 147,872 LTIP Units to employees and non-employee directors under the 2012 Plan during the years ended December 31, 2018 , 2017 and 2016 , respectively. Boston Properties, Inc. did not issue any non-qualified stock options under the 2012 Plan during the years ended December 31, 2018 , 2017 and 2016. Boston Properties Limited Partnership issued 342,659 2018 MYLTIP Units, 400,000 2017 MYLTIP Units and 475,004 2016 MYLTIP Units to employees under the 2012 Plan during the years ended December 31, 2018, 2017 and 2016, respectively. Employees and non-employee directors paid $0.01 per share of restricted common stock and $0.25 per LTIP Unit, OPP Unit and MYLTIP Unit. When issued, LTIP Units are not economically equivalent in value to a share of Common Stock, but over time can increase in value to one-for-one parity with Common Stock if there is sufficient appreciation in the value of the Company’s assets. The aggregate value of the LTIP Units is included in noncontrolling interests in the Consolidated Balance Sheets. Grants of restricted stock and LTIP Units to employees vest in four equal annual installments. Restricted stock is measured at fair value on the date of grant based on the number of shares granted and the closing price of Boston Properties, Inc.’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. Non-qualified stock options, which are valued using the Black-Scholes option-pricing model, are recognized as an expense ratably over the corresponding employee service period. As the 2012 OPP Awards, 2013 MYLTIP Awards, 2014 MYLTIP Awards, 2015 MYLTIP Awards, 2016 MYLTIP Awards, 2017 MYLTIP Awards and 2018 MYLTIP Awards are subject to both a service condition and a market condition, the Company recognizes the compensation expense related to the 2012 OPP Awards, 2013 MYLTIP Awards, 2014 MYLTIP Awards, 2015 MYLTIP Awards 2016 MYLTIP Awards, 2017 MYLTIP Awards and 2018 MYLTIP 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. The Company recognizes forfeitures as they occur on its awards of stock-based compensation (See Note 2 ). Dividends paid on both vested and unvested shares of restricted stock are charged directly to Dividends in Excess of Earnings in Boston Properties, Inc.’s Consolidated Balance Sheets and Partners’ Capital in Boston Properties Limited Partnership’s Consolidated Balance Sheets. Aggregate stock-based compensation expense associated with restricted stock, non-qualified stock options, LTIP Units, 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units, 2015 MYLTIP Units, 2016 MYLTIP Units, 2017 MYLTIP Units and 2018 MYLTIP Units was approximately $38.0 million , $33.2 million and $30.6 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. At December 31, 2018 , there was (1) an aggregate of approximately $22.7 million of unrecognized compensation expense related to unvested restricted stock and LTIP Units and (2) an aggregate of approximately $15.2 million of unrecognized compensation expense related to unvested 2016 MYLTIP Units, 2017 MYLTIP Units and 2018 MYLTIP Units that is expected to be recognized over a weighted-average period of approximately 2.4 years . The shares of restricted stock were valued at approximately $2.4 million ( $119.27 per share weighted-average), $4.9 million ( $130.32 per share weighted-average) and $2.5 million ( $113.51 per share weighted-average) for the years ended December 31, 2018 , 2017 and 2016 , respectively. LTIP Units were valued using a Monte Carlo simulation method model in accordance with the provisions of ASC 718. LTIP Units issued during the years ended December 31, 2018 , 2017 and 2016 were valued at approximately $22.7 million , $13.6 million and $15.4 million , respectively. The weighted-average per unit fair value of LTIP Unit grants in 2018 , 2017 and 2016 was $110.29 , $119.41 and $103.83 , respectively. The per unit fair value of each LTIP Unit granted in 2018 , 2017 and 2016 was estimated on the date of grant using the following assumptions; an expected life of 5.7 years , 5.7 years and 5.7 years , a risk-free interest rate of 2.63% , 2.14% and 1.61% and an expected price volatility of 27.0% , 28.0% and 33.0% , respectively. There were no non-qualified stock options granted during the years ended December 31, 2018 , 2017 and 2016 . A summary of the status of Boston Properties, Inc.’s stock options as of December 31, 2018 , 2017 and 2016 and changes during the years then ended are presented below: Shares Weighted-Average Exercise Price Outstanding at December 31, 2015 547,129 $ 96.38 Exercised — $ — Outstanding at December 31, 2016 547,129 $ 96.38 Exercised (6,688 ) $ 99.15 Outstanding at December 31, 2017 540,441 $ 96.35 Exercised — $ — Outstanding at December 31, 2018 540,441 $ 96.35 The following table summarizes information about Boston Properties, Inc.’s stock options outstanding at December 31, 2018 : Options Outstanding Options Exercisable Number Outstanding at 12/31/18 Weighted-Average Remaining Contractual Life Exercise Price Number Exercisable at 12/31/18 Exercise Price 118,502 2.1 years $ 86.86 118,502 $ 86.86 54,282 4.3 years $ 95.69 54,282 $ 95.69 202,030 4.1 years $ 98.46 202,030 $ 98.46 165,627 3.1 years $ 100.77 165,627 $ 100.77 The total intrinsic value of the outstanding and exercisable stock options as of December 31, 2018 was approximately $8.8 million . In addition, Boston Properties, Inc. had 540,441 and 514,360 options exercisable at a weighted-average exercise price of $96.35 and $96.32 at December 31, 2017 and 2016, respectively. Boston Properties, Inc. adopted the 1999 Non-Qualified Employee Stock Purchase Plan (the “Stock Purchase Plan”) to encourage the ownership of Common Stock by eligible employees. The Stock Purchase Plan became effective on January 1, 1999 with an aggregate maximum of 250,000 shares of Common Stock available for issuance. The Stock Purchase Plan provides for eligible employees to purchase on the business day immediately following the end of the biannual purchase periods (i.e., January 1-June 30 and July 1-December 31) shares of Common Stock at a purchase price equal to 85% of the average closing prices of the Common Stock during the last ten business days of the purchase period. Boston Properties, Inc. issued 6,268 , 6,317 and 5,695 shares with the weighted-average purchase price equal to $107.20 per share, $105.97 per share and $109.27 per share under the Stock Purchase Plan during the years ended December 31, 2018 , 2017 and 2016 , respectively.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2018
Related Party Transaction [Line Items]
Related Party Transactions Disclosure [Text Block]	17. Related Party Transactions A firm controlled by Mr. Raymond A. Ritchey’s brother was paid aggregate leasing commissions of approximately $921,000 , $368,000 and $374,000 for the years ended December 31, 2018 , 2017 and 2016 , respectively, related to certain exclusive leasing arrangements for certain Northern Virginia properties. Mr. Ritchey is a Senior Executive Vice President of Boston Properties, Inc. In accordance with Boston Properties, Inc.’s 2012 Plan, and as approved by its Board of Directors, four non-employee directors made elections to receive deferred stock units in lieu of cash fees for 2018 . The deferred stock units will be settled in shares of common stock upon the cessation of such director’s service on the Board of Directors of Boston Properties, Inc. As a result of these elections, the aggregate cash fees otherwise payable to a non-employee director during a fiscal quarter are converted into a number of deferred stock units equal to the aggregate cash fees divided by the last reported sales price of a share of Boston Properties, Inc.’s common stock on the last trading of the applicable fiscal quarter. The deferred stock units are also credited with dividend equivalents as dividends are paid by Boston Properties, Inc. On May 23, 2018, in connection with the cessation of a director’s service on the Board of Directors of Boston Properties, Inc., Boston Properties, Inc. issued 36,836 shares of common stock in settlement of the director’s outstanding deferred stock units. At December 31, 2018 and 2017 , Boston Properties, Inc. had outstanding 74,966 and 105,479 deferred stock units, respectively.

Selected Interim Financial Info

Selected Interim Financial Information (unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information [Text Block]	18. Selected Interim Financial Information (unaudited) Boston Properties, Inc. The tables below reflect Boston Properties, Inc.’s selected quarterly information for the years ended December 31, 2018 and 2017 . 2018 Quarter Ended March 31, June 30, September 30, December 31, (in thousands, except for per share amounts) Total revenue $ 661,151 $ 664,484 $ 686,284 $ 705,157 Net income $ 216,312 $ 160,565 $ 150,445 $ 185,241 Net income attributable to Boston Properties, Inc. common shareholders $ 176,021 $ 128,681 $ 119,118 $ 148,529 Income attributable to Boston Properties, Inc. per share—basic $ 1.14 $ 0.83 $ 0.77 $ 0.96 Income attributable to Boston Properties, Inc. per share—diluted $ 1.14 $ 0.83 $ 0.77 $ 0.96 2017 Quarter Ended March 31, June 30, September 30, December 31, (in thousands, except for per share amounts) Total revenue $ 632,228 $ 656,907 $ 657,712 $ 655,229 Net income $ 115,564 $ 167,010 $ 147,704 $ 132,203 Net income attributable to Boston Properties, Inc. common shareholders $ 97,083 $ 133,709 $ 117,337 $ 103,829 Income attributable to Boston Properties, Inc. per share—basic $ 0.63 $ 0.87 $ 0.76 $ 0.67 Income attributable to Boston Properties, Inc. per share—diluted $ 0.63 $ 0.87 $ 0.76 $ 0.67 Boston Properties Limited Partnership The tables below reflect Boston Properties Limited Partnership’s selected quarterly information for the years ended December 31, 2018 and 2017 . 2018 Quarter Ended March 31, June 30, September 30, December 31, (in thousands, except for per unit amounts) Total revenue $ 661,151 $ 664,484 $ 686,284 $ 705,157 Net income $ 220,766 $ 162,986 $ 153,676 $ 192,884 Net income attributable to Boston Properties Limited Partnership common unitholders $ 200,907 $ 145,961 $ 136,201 $ 173,834 Income attributable to Boston Properties Limited Partnership per unit—basic $ 1.17 $ 0.85 $ 0.79 $ 1.01 Income attributable to Boston Properties Limited Partnership per unit—diluted $ 1.17 $ 0.85 $ 0.79 $ 1.01 2017 Quarter Ended March 31, June 30, September 30, December 31, (in thousands, except for per unit amounts) Total revenue $ 632,228 $ 656,907 $ 657,712 $ 655,229 Net income $ 117,711 $ 169,672 $ 149,658 $ 134,157 Net income attributable to Boston Properties Limited Partnership common unitholders $ 110,662 $ 151,844 $ 132,693 $ 117,667 Income attributable to Boston Properties Limited Partnership per unit—basic $ 0.64 $ 0.88 $ 0.77 $ 0.69 Income attributable to Boston Properties Limited Partnership per unit—diluted $ 0.64 $ 0.88 $ 0.77 $ 0.68

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	19. Subsequent Events On January 10, 2019, the Company acquired land parcels at its Carnegie Center property located in Princeton, New Jersey for a purchase price of approximately $42.9 million . The Company also agreed to pay the seller additional amounts aggregating approximately $8.6 million , which are payable in the future and contingent on the development or sale of each of the parcels. The land parcels will support approximately 1.7 million square feet of development. On January 18, 2019, the Company and its partner in the consolidated entity that owns Salesforce Tower located in San Francisco, California amended the venture agreement. Per the amendment, the partner exercised its right to cause the Company to purchase on April 1, 2019 its 5% ownership interest and promoted profits interest in the venture for cash totaling approximately $210.9 million , which amount shall be reduced by approximately $24.1 million consisting of the repayment of the Company's preferred equity and preferred return as provided for in the venture agreement. As part of the original agreement, the partner was required to contribute 5% of the equity and was entitled to receive an additional promoted payment based on the success of the property (See Note 10 ). On January 24, 2019, the Company completed the sale of its 2600 Tower Oaks Boulevard property located in Rockville, Maryland for a gross sales price of approximately $22.7 million . 2600 Tower Oaks Boulevard is an approximately 179,000 net rentable square foot Class A office property (See Note 3 ). On January 24, 2019, a joint venture in which the Company has a 50% interest extended the loan collateralized by its Annapolis Junction Building Six property. At the time of the extension, the outstanding balance of the loan totaled approximately $13.0 million and was scheduled to mature on November 17, 2019, with one , one -year extension option, subject to certain conditions. The extended loan has a total commitment amount of approximately $14.3 million , bears interest at a variable rate equal to LIBOR plus 2.00% per annum and matures on November 17, 2020. Annapolis Junction Building Six is a Class A office property with approximately 119,000 net rentable square feet located in Annapolis, Maryland (See Note 5 ). On January 24, 2019, the ground lessor under the Company's 65 -year ground lease for land totaling approximately 5.6 acres at Platform 16 located in San Jose, California made available for lease to the Company the remaining land parcels. As a result, the Company recognized the remaining portion of the capital lease asset and liability (See Note 3 ). On February 1, 2019 and February 5, 2019, Boston Properties, Inc. issued an aggregate of 23,083 shares of restricted common stock and Boston Properties Limited Partnership issued an aggregate of 172,166 LTIP units under the 2012 Plan to certain employees of Boston Properties, Inc. On February 5, 2019, Boston Properties, Inc.’s Compensation Committee approved the 2019 Multi-Year Long-Term Incentive Program (the “2019 MYLTIP”) awards under Boston Properties, Inc.’s 2012 Plan to certain officers and employees of Boston Properties, Inc. Earned awards will range from zero to a maximum of 220,734 LTIP Units depending on Boston Properties, Inc.’s TSR relative to the FTSE Nareit Office Index, adjusted to include Vornado Realty Trust, with a target of approximately 110,367 LTIP Units and linear interpolation between zero and maximum. Under ASC 718, the 2019 MYLTIP awards have an aggregate value of approximately $13.5 million , which amount will generally be amortized into earnings over the four-year plan period under the graded vesting method. On February 9, 2019, the measurement period for the Company’s 2016 MYLTIP awards ended and, based on Boston Properties, Inc.’s relative TSR performance, the final awards were determined to be 69.5% of target or an aggregate of approximately $13.6 million (after giving effect to voluntary employee separations). As a result, an aggregate of 364,980 2016 MYLTIP Units that had been previously granted were automatically forfeited. On February 14, 2019, the Company announced that it had entered into a 15 -year lease with Google, LLC for approximately 362,000 net rentable square feet of Class A office space in a build-to-suit development project to be located at the Company’s 325 Main Street property at Kendall Center in Cambridge, Massachusetts. 325 Main Street currently consists of an approximately 115,000 net rentable square foot Class A office property that will be demolished and developed into an approximately 400,000 net rentable square foot Class A office property, including approximately 38,000 net rentable square feet of retail space. There can be no assurance that the project will commence.

Real Estate and Accumulated Dep

Real Estate and Accumulated Depreciation	12 Months Ended
	Dec. 31, 2018
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate and Accumulated Depreciation Disclosure [Text Block]	Item 15. Exhibits and Financial Statement Schedules (a) Financial Statement Schedule Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2018 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building 767 Fifth Avenue (the General Motors Building) Office New York, NY $ 2,270,534 $ 1,796,252 $ 1,532,654 $ 189,657 $ 1,796,252 $ 1,722,311 $ — $ — $ 3,518,563 $ 271,534 1968 2013 (1) Prudential Center Office Boston, MA — 92,077 948,357 532,802 115,638 1,457,494 104 — 1,573,236 550,109 1965/1993/2002/2016-2017 1998/1999/2000 (1) Embarcadero Center Office San Francisco, CA — 179,697 847,410 368,967 195,987 1,200,087 — — 1,396,074 612,981 1970/1989 1998-1999 (1) 399 Park Avenue Office New York, NY — 339,200 700,358 247,092 354,107 932,543 — — 1,286,650 332,911 1961/2018 2002 (1) Salesforce Tower Office San Francisco, CA — 200,349 919,565 — 200,349 919,565 — — 1,119,914 9,509 2018 2013 (1) 601 Lexington Avenue Office New York, NY 658,792 241,600 494,782 361,985 289,639 637,044 — 171,684 1,098,367 272,936 1977/1997 2001 (1) 200 Clarendon Street and Garage Office Boston, MA — 219,543 667,884 164,073 219,616 822,218 9,666 — 1,051,500 192,137 1976 2010 (1) 250 West 55th Street Office New York, NY — 285,263 603,167 48,642 285,263 651,809 — — 937,072 94,434 2014 2007 (1) 100 Federal Street Office Boston, MA — 131,067 435,954 99,702 131,067 535,656 — — 666,723 105,536 1971-1975/2017 2012 (1) Carnegie Center Office Princeton, NJ — 107,997 389,359 158,752 108,948 543,974 3,186 — 656,108 241,570 1983-2016 1998/1999/2000/2007/2014/2017 (1) Times Square Tower Office New York, NY — 165,413 380,438 94,451 169,193 471,109 — — 640,302 206,067 2004 2000 (1) Atlantic Wharf Office Boston, MA — 63,988 454,537 17,184 63,988 471,721 — — 535,709 116,238 2011 2007 (1) 510 Madison Avenue Office New York, NY — 103,000 253,665 24,992 103,000 278,657 — — 381,657 62,507 2012 2010 (1) Fountain Square Office Reston, VA — 56,853 306,298 3,170 56,853 309,468 — — 366,321 68,390 1986-1990 2012 (1) 599 Lexington Avenue Office New York, NY — 81,040 100,507 174,213 87,852 267,908 — — 355,760 170,678 1986 1997 (1) 680 Folsom Street Office San Francisco, CA — 72,545 219,766 7,829 72,545 227,595 — — 300,140 38,230 2014 2012 (1) 601 Massachusetts Avenue Office Washington, DC — 95,310 165,173 3,900 95,322 169,061 — — 264,383 18,263 2016 2008 (1) South of Market and Democracy Tower Office Reston, VA — 13,603 237,479 12,428 13,687 249,823 — — 263,510 91,072 2008-2009 2003 (1) Bay Colony Corporate Center Office Waltham, MA — 18,789 148,451 77,133 18,789 225,584 — — 244,373 68,903 1985-1989 2011 (1) Gateway Center Office San Francisco, CA — 28,255 139,245 64,831 30,627 201,704 — — 232,331 107,640 1984/1986/2002 1999 (1) 535 Mission Street Office San Francisco, CA — 40,933 148,378 3,259 40,933 151,637 — — 192,570 20,576 2015 2013 (1) 2200 Pennsylvania Avenue Office Washington, DC — — 183,541 4,535 — 188,076 — — 188,076 52,280 2011 2008 (1) Mountain View Research Park Office Mountain View, CA — 95,066 68,373 9,988 95,066 78,361 — — 173,427 17,866 1977-1981/2007-2013 2013 (1) Reservoir Place Office Waltham, MA — 18,605 104,124 45,144 20,108 147,765 — — 167,873 64,683 1955/1987/2017 1997/1998 (1) 1330 Connecticut Avenue Office Washington, DC — 25,982 82,311 36,089 27,135 117,247 — — 144,382 27,535 1984/2018 2004 (1) Kingstowne Towne Center Office Alexandria, VA — 18,021 109,038 2,098 18,062 111,095 — — 129,157 41,469 2003-2006 2007 (1) Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2018 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building One Freedom Square Office Reston, VA — 9,929 84,504 32,256 11,293 115,396 — — 126,689 54,652 2000 2003 (1) Capital Gallery Office Washington, DC — 4,725 29,565 87,231 8,662 112,859 — — 121,521 67,759 1981/2006 2007 (1) Weston Corporate Center Office Weston, MA — 25,753 92,312 (123 ) 25,854 92,088 — — 117,942 26,176 2010 2001 (1) Two Freedom Square Office Reston, VA — 13,930 77,739 23,427 15,420 99,676 — — 115,096 51,291 2001 2003 (1) One and Two Reston Overlook Office Reston, VA — 16,456 66,192 24,181 16,179 90,650 — — 106,829 47,668 1999 2000 (1) 140 Kendrick Street Office Needham, MA — 18,095 66,905 17,553 19,092 83,461 — — 102,553 32,360 2000 2004 (1) Discovery Square Office Reston, VA — 11,198 71,782 17,753 12,533 88,200 — — 100,733 39,574 2001 2003 (1) 355 Main Street Office Cambridge, MA — 18,863 53,346 23,701 21,173 74,737 — — 95,910 23,691 1981/1996/2013 2006 (1) 10 CityPoint Office Waltham, MA — 1,953 85,752 4,515 2,116 90,104 — — 92,220 7,772 2016 1997 (1) 90 Broadway Office Cambridge, MA — 19,104 52,078 18,363 20,785 68,760 — — 89,545 21,302 1983/1998/2013 2006 (1) 230 CityPoint Office Waltham, MA — 13,189 49,823 21,914 13,593 71,333 — — 84,926 26,357 1992 2005 (1) Waltham Weston Corporate Center Office Waltham, MA — 10,385 60,694 11,449 11,097 71,431 — — 82,528 32,739 2003 1999 (1) 77 CityPoint Office Waltham, MA — 13,847 60,383 5,858 13,873 66,215 — — 80,088 25,107 2008 2001 (1) 3625-3635 Peterson Way Office Santa Clara, CA — 63,206 14,879 673 63,206 14,879 673 — 78,758 8,146 1979 2016 (1) 2440 West El Camino Real Office Mountain View, CA — 16,741 51,285 3,411 16,741 54,696 — — 71,437 12,562 1987/2003 2011 (1) 300 Binney Street Office Cambridge, MA — 18,080 51,262 140 18,080 51,402 — — 69,482 9,450 2013 2009 (1) 191 Spring Street Office Lexington, MA — 2,850 59,751 6,235 3,151 65,685 — — 68,836 19,543 1971/1995/2018 1997 (1) Wisconsin Place Office Chevy Chase, MD — — 53,349 14,889 — 68,238 — — 68,238 22,936 2009 2004 (1) Reston Corporate Center Office Reston, VA — 9,135 50,857 6,236 10,148 56,080 — — 66,228 28,315 1984 1998 (1) New Dominion Technology Park, Bldg. Two Office Herndon, VA — 5,584 51,868 4,157 6,510 55,099 — — 61,609 25,421 2004 1998 (1) 255 Main Street Office Cambridge, MA — 134 25,110 29,672 548 54,368 — — 54,916 30,180 1987 1997 (1) 200 West Street Office Waltham, MA — 16,148 24,983 11,120 16,813 35,438 — — 52,251 22,544 1999 1997 (1) New Dominion Technology Park, Bldg. One Office Herndon, VA 29,675 3,880 43,227 3,927 4,583 46,451 — — 51,034 27,542 2001 1998 (1) Sumner Square Office Washington, DC — 624 28,745 19,054 1,478 46,945 — — 48,423 25,384 1985 1999 (1) University Place Office Cambridge, MA 5,571 — 37,091 9,001 390 45,702 — — 46,092 27,871 1985 1998 (1) 2600 Tower Oaks Boulevard Office Rockville, MD — 4,243 31,125 6,517 4,244 37,641 — — 41,885 21,426 2001 1998 (1) North First Business Park Office San Jose, CA — 23,398 13,069 4,613 23,377 17,703 — — 41,080 16,076 1981 2007 (1) 150 Broadway Office Cambridge, MA — 850 25,042 8,540 1,323 33,109 — — 34,432 18,404 1999 1997 (1) 325 Main Street Office Cambridge, MA — 174 12,200 16,437 965 23,319 4,527 — 28,811 13,676 1987/2013 1997 (1) 105 Broadway Office Cambridge, MA — 1,299 12,943 9,401 2,395 21,248 — — 23,643 13,950 1990 1997 (1) Lexington Office Park Office Lexington, MA — 998 1,426 18,700 1,264 19,860 — — 21,124 13,614 1982 1997 (1) 201 Spring Street Office Lexington, MA — 2,849 15,303 1,390 3,124 16,418 — — 19,542 8,344 1997 1997 (1) The Point Office Waltham, MA — 6,395 10,040 431 6,480 10,386 — — 16,866 1,031 2015 2007 (1) 690 Folsom Street Office San Francisco, CA — 3,219 11,038 1,157 3,219 12,195 — — 15,414 1,790 2015 2012 (1) 92-100 Hayden Avenue Office Lexington, MA — 594 6,748 7,255 802 13,795 — — 14,597 11,809 1985 1997 (1) Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2018 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building 181 Spring Street Office Lexington, MA — 1,066 9,520 2,230 1,160 11,656 — — 12,816 5,424 1999 1997 (1) 195 West Street Office Waltham, MA — 1,611 6,652 4,270 1,858 10,675 — — 12,533 8,330 1990 1997 (1) 33 Hayden Avenue Office Lexington, MA — 266 3,234 8,223 425 11,298 — — 11,723 9,033 1979 1997 (1) 7501 Boston Boulevard, Building Seven Office Springfield, VA — 665 9,273 819 791 9,966 — — 10,757 5,121 1997 1997 (1) 7450 Boston Boulevard, Building Three Office Springfield, VA — 1,165 4,681 3,278 1,430 7,694 — — 9,124 3,733 1987 1998 (1) 7435 Boston Boulevard, Building One Office Springfield, VA — 392 3,822 4,737 659 8,292 — — 8,951 5,917 1982 1997 (1) 250 Binney Street Office Cambridge, MA — 110 4,483 3,593 273 7,913 — — 8,186 5,448 1983 1997 (1) 8000 Grainger Court, Building Five Office Springfield, VA — 366 4,282 3,536 601 7,583 — — 8,184 5,864 1984 1997 (1) 453 Ravendale Drive Office Mountain View, CA — 5,477 1,090 676 5,477 1,766 — — 7,243 558 1977 2012 (1) 7300 Boston Boulevard, Building Thirteen Office Springfield, VA — 608 4,773 1,438 661 6,158 — — 6,819 3,011 2002 1997 (1) 7601 Boston Boulevard, Building Eight Office Springfield, VA — 200 878 5,373 551 5,900 — — 6,451 4,487 1986 1997 (1) 17 Hartwell Avenue Office Lexington, MA — 26 150 6,064 65 6,175 — — 6,240 1,445 1968 1997 (1) 7500 Boston Boulevard, Building Six Office Springfield, VA — 138 3,749 1,673 406 5,154 — — 5,560 4,121 1985 1997 (1) 8000 Corporate Court, Building Eleven Office Springfield, VA — 136 3,071 1,596 774 4,029 — — 4,803 3,051 1989 1997 (1) 7375 Boston Boulevard, Building Ten Office Springfield, VA — 23 2,685 992 93 3,607 — — 3,700 2,593 1988 1997 (1) 7374 Boston Boulevard, Building Four Office Springfield, VA — 241 1,605 1,828 398 3,276 — — 3,674 2,685 1984 1997 (1) 7451 Boston Boulevard, Building Two Office Springfield, VA — 249 1,542 1,659 613 2,837 — — 3,450 2,527 1982 1997 (1) 32 Hartwell Avenue Office Lexington, MA — 168 1,943 817 314 2,614 — — 2,928 1,821 1968/1979/1987 1997 (1) 164 Lexington Road Office Billerica, MA — 592 1,370 319 643 1,638 — — 2,281 906 1982 1997 (1) Signature at Reston Residential Reston, VA — 27,076 190,580 — 27,076 190,580 — — 217,656 3,938 2018 2013 (1) Proto Kendall Square Residential Cambridge, MA — 9,243 127,248 — 9,243 127,248 — — 136,491 1,324 2018 2015 (1) The Avant at Reston Town Center Residential Reston, VA — 20,350 91,995 830 20,350 92,825 — — 113,175 12,254 2014 2010 (1) The Lofts at Atlantic Wharf Residential Boston, MA — 3,529 54,891 1,768 3,529 56,659 — — 60,188 11,131 2011 2007 (1) Boston Marriott Cambridge Hotel Cambridge, MA — 478 37,918 36,697 1,201 73,892 — — 75,093 46,576 1986/2017 1997 (1) Kendall Center Green Garage Garage Cambridge, MA — — 35,035 7,448 103 42,380 — — 42,483 12,208 1984 2006 (1) Kendall Center Yellow Garage Garage Cambridge, MA — 1,256 15,697 1,621 1,434 17,140 — — 18,574 5,643 2006 2004 (1) Kendall Center Blue Garage Garage Cambridge, MA — 1,163 11,633 2,145 1,579 13,362 — — 14,941 9,437 1990 1997 (1) 145 Broadway Development Cambridge, MA — 121 — 223,845 324 — — 223,642 223,966 — N/A 1997 N/A MacArthur Station Residences Development Oakland, CA — — — 87,159 — — — 87,159 87,159 — N/A N/A N/A 20 CityPoint Development Waltham, MA — — 6,287 46,024 — 6,287 — 46,024 52,311 — N/A 2007 N/A Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2018 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building Reston Gateway Development Reston, VA — — — 25,167 — — — 25,167 25,167 — N/A 1998 N/A 17Fifty Presidents Street Development Reston, VA — — — 25,120 — — — 25,120 25,120 — N/A 2013 N/A North First Master Plan Land San Jose, CA — 35,004 — 3,932 — — 38,936 — 38,936 — N/A 2007 N/A Plaza at Almaden Land San Jose, CA — — — 29,928 — — 29,928 — 29,928 — N/A 2006 N/A Springfield Metro Center Land Springfield, VA — — — 19,823 — — 19,823 — 19,823 — N/A 2007 N/A 214 Third Avenue Land Waltham, MA — — — 15,233 — — 15,233 — 15,233 — N/A 2006 N/A Platform 16 Land San Jose, CA — — — 12,962 — — 12,962 — 12,962 — N/A 2018 N/A 103 Fourth Avenue Land Waltham, MA — — — 12,208 — — 12,208 — 12,208 — N/A 2007 N/A Reston Gateway Master Plan Land Reston, VA — — — 11,014 — — 11,014 — 11,014 — N/A 1998 N/A Fourth and Harrison Land San Francisco, CA — — — 10,350 — — 10,350 — 10,350 — N/A N/A N/A 2100 Pennsylvania Avenue Land Washington, DC — — — 9,700 — — 9,700 — 9,700 — N/A N/A N/A Crane Meadow Land Marlborough, MA — — — 8,852 — — 8,852 — 8,852 — N/A 2000 N/A Washingtonian North Land Gaithersburg, MD — — — 7,473 — — 7,473 — 7,473 — N/A 1998 N/A Broad Run Business Park Land Loudoun County, VA — — — 2,388 — — 2,388 — 2,388 — N/A 1998 N/A Kendall Center Master Plan Land Cambridge, MA — — — 2,199 — — 2,199 — 2,199 — N/A 1997 N/A Weston Quarry Land Weston, MA — — — 1,237 — — 1,237 — 1,237 — N/A 2001 N/A Reston Overlook Master Plan Land Reston, VA — — — 39 — — 39 — 39 — N/A 2000 N/A $ 2,964,572 (2 ) $ 4,959,995 $ 12,763,317 $ 3,882,233 $ 5,072,568 $ 15,753,683 $ 200,498 (3 ) $ 578,796 $ 21,605,545 $ 4,871,102 Note: Total Real Estate does not include Furniture, Fixtures and Equipment totaling approximately $44,351 . Accumulated Depreciation does not include approximately $26,675 of accumulated depreciation related to Furniture, Fixtures and Equipment. The aggregate cost and accumulated depreciation for tax purposes was approximately $17.9 billion and $3.9 billion , respectively. (1) Depreciation of the buildings and improvements are calculated over lives ranging from the life of the lease to 40 years. (2) Includes unamortized deferred financing costs totaling approximately $(30.8) million . (3) Includes pre-development costs. Boston Properties, Inc. Real Estate and Accumulated Depreciation December 31, 2018 , 2017 and 2016 (dollars in thousands) A summary of activity for real estate and accumulated depreciation is as follows: 2018 2017 2016 Real Estate: Balance at the beginning of the year $ 21,058,714 $ 20,114,576 $ 19,451,683 Additions to/improvements of real estate 1,043,379 1,099,286 977,287 Assets sold/written-off (496,548 ) (155,148 ) (314,394 ) Balance at the end of the year $ 21,605,545 $ 21,058,714 $ 20,114,576 Accumulated Depreciation: Balance at the beginning of the year $ 4,566,570 $ 4,201,891 $ 3,905,940 Depreciation expense 533,342 497,059 560,024 Assets sold/written-off (228,810 ) (132,380 ) (264,073 ) Balance at the end of the year $ 4,871,102 $ 4,566,570 $ 4,201,891 Note: Real Estate and Accumulated Depreciation amounts do not include Furniture, Fixtures and Equipment.
Boston Properties Limited Partnership
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate and Accumulated Depreciation Disclosure [Text Block]	Boston Properties Limited Partnership Schedule 3—Real Estate and Accumulated Depreciation December 31, 2018 (dollars in thousands) Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Property Name Type Location Encumbrances Land Building 767 Fifth Avenue (the General Motors Building) Office New York, NY $ 2,270,534 $ 1,796,252 $ 1,532,654 $ 189,657 $ 1,796,252 $ 1,722,311 $ — $ — $ 3,518,563 $ 271,534 1968 2013 (1) Prudential Center Office Boston, MA — 92,077 948,357 472,432 100,540 1,412,222 104 — 1,512,866 535,305 1965/1993/2002/2016-2017 1998/1999/2000 (1) Embarcadero Center Office San Francisco, CA — 179,697 847,410 306,586 180,420 1,153,273 — — 1,333,693 597,613 1970/1989 1998-1999 (1) 399 Park Avenue Office New York, NY — 339,200 700,358 187,484 339,200 887,842 — — 1,227,042 318,267 1961/2018 2002 (1) Salesforce Tower Office San Francisco, CA — 200,349 919,565 — 200,349 919,565 — — 1,119,914 9,509 2018 2013 (1) 601 Lexington Avenue Office New York, NY 658,792 241,600 494,782 324,899 279,281 610,316 — 171,684 1,061,281 264,150 1977/1997 2001 (1) 200 Clarendon Street and Garage Office Boston, MA — 219,543 667,884 164,073 219,616 822,218 9,666 — 1,051,500 192,137 1976 2010 (1) 250 West 55th Street Office New York, NY — 285,263 603,167 48,642 285,263 651,809 — — 937,072 94,434 2014 2007 (1) 100 Federal Street Office Boston, MA — 131,067 435,954 99,702 131,067 535,656 — — 666,723 105,536 1971-1975/2017 2012 (1) Carnegie Center Office Princeton, NJ — 107,997 389,359 141,434 104,617 530,987 3,186 — 638,790 237,322 1983-2016 1998/1999/2000/2007/2014/2017 (1) Times Square Tower Office New York, NY — 165,413 380,438 56,472 159,694 442,629 — — 602,323 196,753 2004 2000 (1) Atlantic Wharf Office Boston, MA — 63,988 454,537 17,184 63,988 471,721 — — 535,709 116,238 2011 2007 (1) 510 Madison Avenue Office New York, NY — 103,000 253,665 24,992 103,000 278,657 — — 381,657 62,507 2012 2010 (1) Fountain Square Office Reston, VA — 56,853 306,298 3,170 56,853 309,468 — — 366,321 68,390 1986-1990 2012 (1) 599 Lexington Avenue Office New York, NY — 81,040 100,507 146,971 81,040 247,478 — — 328,518 164,002 1986 1997 (1) 680 Folsom Street Office San Francisco, CA — 72,545 219,766 7,829 72,545 227,595 — — 300,140 38,230 2014 2012 (1) 601 Massachusetts Avenue Office Washington, DC — 95,310 165,173 3,888 95,310 169,061 — — 264,371 18,263 2016 2008 (1) South of Market and Democracy Tower Office Reston, VA — 13,603 237,479 12,092 13,603 249,571 — — 263,174 91,006 2008-2009 2003 (1) Bay Colony Corporate Center Office Waltham, MA — 18,789 148,451 77,133 18,789 225,584 — — 244,373 68,903 1985-1989 2011 (1) Gateway Center Office San Francisco, CA — 28,255 139,245 58,442 29,029 196,913 — — 225,942 106,074 1984/1986/2002 1999 (1) 535 Mission Street Office San Francisco, CA — 40,933 148,378 3,259 40,933 151,637 — — 192,570 20,576 2015 2013 (1) 2200 Pennsylvania Avenue Office Washington, DC — — 183,541 4,535 — 188,076 — — 188,076 52,280 2011 2008 (1) Mountain View Research Park Office Mountain View, CA — 95,066 68,373 9,988 95,066 78,361 — — 173,427 17,866 1977-1981/2007-2013 2013 (1) Reservoir Place Office Waltham, MA — 18,605 104,124 41,069 19,089 144,709 — — 163,798 63,684 1955/1987/2017 1997/1998 (1) 1330 Connecticut Avenue Office Washington, DC — 25,982 82,311 31,476 25,982 113,787 — — 139,769 26,400 1984/2018 2004 (1) Kingstowne Towne Center Office Alexandria, VA — 18,021 109,038 1,934 18,021 110,972 — — 128,993 41,436 2003-2006 2007 (1) One Freedom Square Office Reston, VA — 9,929 84,504 26,619 9,883 111,169 — — 121,052 53,268 2000 2003 (1) Weston Corporate Center Office Weston, MA — 25,753 92,312 (123 ) 25,854 92,088 — — 117,942 26,176 2010 2001 (1) Capital Gallery Office Washington, DC — 4,725 29,565 77,100 6,128 105,262 — — 111,390 65,272 1981/2006 2007 (1) Two Freedom Square Office Reston, VA — 13,930 77,739 17,215 13,866 95,018 — — 108,884 49,768 2001 2003 (1) One and Two Reston Overlook Office Reston, VA — 16,456 66,192 19,763 15,074 87,337 — — 102,411 46,584 1999 2000 (1) Boston Properties Limited Partnership Schedule 3—Real Estate and Accumulated Depreciation December 31, 2018 (dollars in thousands) Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Property Name Type Location Encumbrances Land Building 140 Kendrick Street Office Needham, MA — 18,095 66,905 13,563 18,095 80,468 — — 98,563 31,381 2000 2004 (1) 355 Main Street Office Cambridge, MA — 18,863 53,346 23,403 21,098 74,514 — — 95,612 23,620 1981/1996/2013 2006 (1) Discovery Square Office Reston, VA — 11,198 71,782 12,208 11,146 84,042 — — 95,188 38,212 2001 2003 (1) 10 CityPoint Office Waltham, MA — 1,953 85,752 4,352 1,953 90,104 — — 92,057 7,772 2016 1997 (1) 90 Broadway Office Cambridge, MA — 19,104 52,078 18,184 20,741 68,625 — — 89,366 21,265 1983/1998/2013 2006 (1) 230 CityPoint Office Waltham, MA — 13,189 49,823 20,297 13,189 70,120 — — 83,309 25,964 1992 2005 (1) 77 CityPoint Office Waltham, MA — 13,847 60,383 5,753 13,847 66,136 — — 79,983 25,085 2008 2001 (1) Waltham Weston Corporate Center Office Waltham, MA — 10,385 60,694 8,462 10,350 69,191 — — 79,541 32,005 2003 1999 (1) 3625-3635 Peterson Way Office Santa Clara, CA — 63,206 14,879 673 63,206 14,879 673 — 78,758 8,146 1979 2016 (1) 2440 West El Camino Real Office Mountain View, CA — 16,741 51,285 3,411 16,741 54,696 — — 71,437 12,562 1987/2003 2011 (1) 300 Binney Street Office Cambridge, MA — 18,080 51,262 140 18,080 51,402 — — 69,482 9,450 2013 2009 (1) Wisconsin Place Office Chevy Chase, MD — — 53,349 14,889 — 68,238 — — 68,238 22,936 2009 2004 (1) 191 Spring Street Office Lexington, MA — 2,850 59,751 5,603 2,850 65,354 — — 68,204 19,435 1971/1995/2018 1997 (1) Reston Corporate Center Office Reston, VA — 9,135 50,857 3,625 9,496 54,121 — — 63,617 27,674 1984 1998 (1) New Dominion Technology Park, Bldg. Two Office Herndon, VA — 5,584 51,868 412 5,574 52,290 — — 57,864 24,498 2004 1998 (1) 255 Main Street Office Cambridge, MA — 134 25,110 28,016 134 53,126 — — 53,260 29,776 1987 1997 (1) 200 West Street Office Waltham, MA — 16,148 24,983 8,459 16,148 33,442 — — 49,590 21,891 1999 1997 (1) New Dominion Technology Park, Bldg. One Office Herndon, VA 29,675 3,880 43,227 1,117 3,880 44,344 — — 48,224 26,852 2001 1998 (1) Sumner Square Office Washington, DC — 624 28,745 16,974 958 45,385 — — 46,343 24,877 1985 1999 (1) University Place Office Cambridge, MA 5,571 — 37,091 7,551 27 44,615 — — 44,642 27,519 1985 1998 (1) 2600 Tower Oaks Boulevard Office Rockville, MD — 4,243 31,125 6,517 4,244 37,641 — — 41,885 21,426 2001 1998 (1) North First Business Park Office San Jose, CA — 23,398 13,069 4,590 23,371 17,686 — — 41,057 16,076 1981 2007 (1) 150 Broadway Office Cambridge, MA — 850 25,042 6,535 822 31,605 — — 32,427 17,909 1999 1997 (1) 325 Main Street Office Cambridge, MA — 174 12,200 15,666 772 22,741 4,527 — 28,040 13,484 1987/2013 1997 (1) 105 Broadway Office Cambridge, MA — 1,299 12,943 7,295 1,868 19,669 — — 21,537 13,432 1990 1997 (1) Lexington Office Park Office Lexington, MA — 998 1,426 17,936 1,073 19,287 — — 20,360 13,430 1982 1997 (1) 201 Spring Street Office Lexington, MA — 2,849 15,303 291 2,849 15,594 — — 18,443 8,073 1997 1997 (1) The Point Office Waltham, MA — 6,395 10,040 431 6,480 10,386 — — 16,866 1,031 2015 2007 (1) 690 Folsom Street Office San Francisco, CA — 3,219 11,038 1,157 3,219 12,195 — — 15,414 1,790 2015 2012 (1) 92-100 Hayden Avenue Office Lexington, MA — 594 6,748 6,526 619 13,249 — — 13,868 11,629 1985 1997 (1) 181 Spring Street Office Lexington, MA — 1,066 9,520 1,853 1,066 11,373 — — 12,439 5,332 1999 1997 (1) 195 West Street Office Waltham, MA — 1,611 6,652 3,281 1,611 9,933 — — 11,544 8,084 1990 1997 (1) 33 Hayden Avenue Office Lexington, MA — 266 3,234 7,586 266 10,820 — — 11,086 8,877 1979 1997 (1) 7501 Boston Boulevard, Building Seven Office Springfield, VA — 665 9,273 314 665 9,587 — — 10,252 4,995 1997 1997 (1) Boston Properties Limited Partnership Schedule 3—Real Estate and Accumulated Depreciation December 31, 2018 (dollars in thousands) Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Property Name Type Location Encumbrances Land Building 7450 Boston Boulevard, Building Three Office Springfield, VA — 1,165 4,681 2,864 1,327 7,383 — — 8,710 3,628 1987 1998 (1) 7435 Boston Boulevard, Building One Office Springfield, VA — 392 3,822 4,044 486 7,772 — — 8,258 5,748 1982 1997 (1) 8000 Grainger Court, Building Five Office Springfield, VA — 366 4,282 2,942 453 7,137 — — 7,590 5,720 1984 1997 (1) 250 Binney Street Office Cambridge, MA — 110 4,483 2,939 110 7,422 — — 7,532 5,291 1983 1997 (1) 453 Ravendale Drive Office Mountain View, CA — 5,477 1,090 676 5,477 1,766 — — 7,243 558 1977 2012 (1) 7300 Boston Boulevard, Building Thirteen Office Springfield, VA — 608 4,773 1,226 608 5,999 — — 6,607 2,959 2002 1997 (1) 17 Hartwell Avenue Office Lexington, MA — 26 150 5,907 26 6,057 — — 6,083 1,406 1968 1997 (1) 7601 Boston Boulevard, Building Eight Office Springfield, VA — 200 878 4,680 378 5,380 — — 5,758 4,318 1986 1997 (1) 7500 Boston Boulevard, Building Six Office Springfield, VA — 138 3,749 1,140 273 4,754 — — 5,027 3,991 1985 1997 (1) 8000 Corporate Court, Building Eleven Office Springfield, VA — 136 3,071 1,245 686 3,766 — — 4,452 2,961 1989 1997 (1) 7375 Boston Boulevard, Building Ten Office Springfield, VA — 23 2,685 811 47 3,472 — — 3,519 2,552 1988 1997 (1) 7374 Boston Boulevard, Building Four Office Springfield, VA — 241 1,605 1,445 303 2,988 — — 3,291 2,594 1984 1997 (1) 7451 Boston Boulevard, Building Two Office Springfield, VA — 249 1,542 1,346 535 2,602 — — 3,137 2,449 1982 1997 (1) 32 Hartwell Avenue Office Lexington, MA — 168 1,943 231 168 2,174 — — 2,342 1,676 1968/1979/1987 1997 (1) 164 Lexington Road Office Billerica, MA — 592 1,370 117 592 1,487 — — 2,079 853 1982 1997 (1) Signature at Reston Residential Reston, VA — 27,076 190,580 — 27,076 190,580 — — 217,656 3,938 2018 2013 (1) Proto Kendall Square Residential Cambridge, MA — 9,243 127,248 — 9,243 127,248 — — 136,491 1,324 2018 2015 (1) The Avant at Reston Town Center Residential Reston, VA — 20,350 91,995 830 20,350 92,825 — — 113,175 12,254 2014 2010 (1) The Lofts at Atlantic Wharf Residential Boston, MA — 3,529 54,891 1,768 3,529 56,659 — — 60,188 11,131 2011 2007 (1) Boston Marriott Cambridge Hotel Cambridge, MA — 478 37,918 33,806 478 71,724 — — 72,202 45,868 1986/2017 1997 (1) Kendall Center Green Garage Garage Cambridge, MA — — 35,035 7,034 — 42,069 — — 42,069 12,108 1984 2006 (1) Kendall Center Yellow Garage Garage Cambridge, MA — 1,256 15,697 909 1,256 16,606 — — 17,862 5,472 2006 2004 (1) Kendall Center Blue Garage Garage Cambridge, MA — 1,163 11,633 480 1,163 12,113 — — 13,276 9,030 1990 1997 (1) 145 Broadway Development Cambridge, MA — 121 — 223,642 121 — — 223,642 223,763 — N/A 1997 N/A MacArthur Station Residences Development Oakland, CA — — — 87,159 — — — 87,159 87,159 — N/A N/A N/A 20 CityPoint Development Waltham, MA — — 6,287 46,024 — 6,287 — 46,024 52,311 — N/A 2007 N/A Reston Gateway Development Reston, VA — — — 25,167 — — — 25,167 25,167 — N/A 1998 N/A 17Fifty Presidents Street Development Reston, VA — — — 25,120 — — — 25,120 25,120 — N/A 2013 N/A North First Master Plan Land San Jose, CA — 35,004 — 3,932 — — 38,936 — 38,936 — N/A 2007 N/A Plaza at Almaden Land San Jose, CA — — — 29,928 — — 29,928 — 29,928 — N/A 2006 N/A Boston Properties Limited Partnership Schedule 3—Real Estate and Accumulated Depreciation December 31, 2018 (dollars in thousands) Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Property Name Type Location Encumbrances Land Building Springfield Metro Center Land Springfield, VA — — — 19,823 — — 19,823 — 19,823 — N/A 2007 N/A 214 Third Avenue Land Waltham, MA — — — 15,233 — — 15,233 — 15,233 — N/A 2006 N/A Platform 16 Land San Jose, CA — — — 12,962 — — 12,962 — 12,962 — N/A 2018 N/A 103 Fourth Avenue Land Waltham, MA — — — 12,208 — — 12,208 — 12,208 — N/A 2007 N/A Reston Gateway Master Plan Land Reston, VA — — — 11,014 — — 11,014 — 11,014 — N/A 1998 N/A Fourth and Harrison Land San Francisco, CA — — — 10,350 — — 10,350 — 10,350 — N/A N/A N/A 2100 Pennsylvania Avenue Land Washington, DC — — — 9,700 — — 9,700 — 9,700 — N/A N/A N/A Crane Meadow Land Marlborough, MA — — — 8,852 — — 8,852 — 8,852 — N/A 2000 N/A Washingtonian North Land Gaithersburg, MD — — — 7,473 — — 7,473 — 7,473 — N/A 1998 N/A Broad Run Business Park Land Loudoun County, VA — — — 2,388 — — 2,388 — 2,388 — N/A 1998 N/A Kendall Center Master Plan Land Cambridge, MA — — — 2,199 — — 2,199 — 2,199 — N/A 1997 N/A Weston Quarry Land Weston, MA — — — 1,237 — — 1,237 — 1,237 — N/A 2001 N/A Reston Overlook Master Plan Land Reston, VA — — — 39 — — 39 — 39 — N/A 2000 N/A $ 2,964,572 (2 ) $ 4,959,995 $ 12,763,317 $ 3,483,877 $ 4,971,475 $ 15,456,420 $ 200,498 (3 ) $ 578,796 $ 21,207,189 $ 4,773,800 Note: Total Real Estate does not include Furniture, Fixtures and Equipment totaling approximately $44,351 . Accumulated Depreciation does not include approximately $26,675 of accumulated depreciation related to Furniture, Fixtures and Equipment. The aggregate cost and accumulated depreciation for tax purposes was approximately $19.9 billion and $4.3 billion , respectively. (1) Depreciation of the buildings and improvements are calculated over lives ranging from the life of the lease to 40 years. (2) Includes unamortized deferred financing costs totaling approximately $(30.8) million . (3) Includes pre-development costs. Boston Properties Limited Partnership Real Estate and Accumulated Depreciation December 31, 2018 , 2017 and 2016 (dollars in thousands) A summary of activity for real estate and accumulated depreciation is as follows: 2018 2017 2016 Real Estate: Balance at the beginning of the year $ 20,647,236 $ 19,701,185 $ 19,031,289 Additions to/improvements of real estate 1,043,379 1,099,286 977,287 Assets sold/written-off (483,426 ) (153,235 ) (307,391 ) Balance at the end of the year $ 21,207,189 $ 20,647,236 $ 19,701,185 Accumulated Depreciation: Balance at the beginning of the year $ 4,473,895 $ 4,116,020 $ 3,826,862 Depreciation expense 525,584 488,919 548,397 Assets sold/written-off (225,679 ) (131,044 ) (259,239 ) Balance at the end of the year $ 4,773,800 $ 4,473,895 $ 4,116,020 Note: Real Estate and Accumulated Depreciation amounts do not include Furniture, Fixtures and Equipment.

Real Estate and Accumulated D_2

Real Estate and Accumulated Depreciation Activity of Real Estate and Accumulated Depreciation (Notes)	12 Months Ended
	Dec. 31, 2018
SEC Schedule III, Real Estate and Accumulated Depreciation Disclosure [Abstract]
SEC Schedule III, Real Estate and Accumulated Depreciation Disclosure [Text Block]	Item 15. Exhibits and Financial Statement Schedules (a) Financial Statement Schedule Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2018 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building 767 Fifth Avenue (the General Motors Building) Office New York, NY $ 2,270,534 $ 1,796,252 $ 1,532,654 $ 189,657 $ 1,796,252 $ 1,722,311 $ — $ — $ 3,518,563 $ 271,534 1968 2013 (1) Prudential Center Office Boston, MA — 92,077 948,357 532,802 115,638 1,457,494 104 — 1,573,236 550,109 1965/1993/2002/2016-2017 1998/1999/2000 (1) Embarcadero Center Office San Francisco, CA — 179,697 847,410 368,967 195,987 1,200,087 — — 1,396,074 612,981 1970/1989 1998-1999 (1) 399 Park Avenue Office New York, NY — 339,200 700,358 247,092 354,107 932,543 — — 1,286,650 332,911 1961/2018 2002 (1) Salesforce Tower Office San Francisco, CA — 200,349 919,565 — 200,349 919,565 — — 1,119,914 9,509 2018 2013 (1) 601 Lexington Avenue Office New York, NY 658,792 241,600 494,782 361,985 289,639 637,044 — 171,684 1,098,367 272,936 1977/1997 2001 (1) 200 Clarendon Street and Garage Office Boston, MA — 219,543 667,884 164,073 219,616 822,218 9,666 — 1,051,500 192,137 1976 2010 (1) 250 West 55th Street Office New York, NY — 285,263 603,167 48,642 285,263 651,809 — — 937,072 94,434 2014 2007 (1) 100 Federal Street Office Boston, MA — 131,067 435,954 99,702 131,067 535,656 — — 666,723 105,536 1971-1975/2017 2012 (1) Carnegie Center Office Princeton, NJ — 107,997 389,359 158,752 108,948 543,974 3,186 — 656,108 241,570 1983-2016 1998/1999/2000/2007/2014/2017 (1) Times Square Tower Office New York, NY — 165,413 380,438 94,451 169,193 471,109 — — 640,302 206,067 2004 2000 (1) Atlantic Wharf Office Boston, MA — 63,988 454,537 17,184 63,988 471,721 — — 535,709 116,238 2011 2007 (1) 510 Madison Avenue Office New York, NY — 103,000 253,665 24,992 103,000 278,657 — — 381,657 62,507 2012 2010 (1) Fountain Square Office Reston, VA — 56,853 306,298 3,170 56,853 309,468 — — 366,321 68,390 1986-1990 2012 (1) 599 Lexington Avenue Office New York, NY — 81,040 100,507 174,213 87,852 267,908 — — 355,760 170,678 1986 1997 (1) 680 Folsom Street Office San Francisco, CA — 72,545 219,766 7,829 72,545 227,595 — — 300,140 38,230 2014 2012 (1) 601 Massachusetts Avenue Office Washington, DC — 95,310 165,173 3,900 95,322 169,061 — — 264,383 18,263 2016 2008 (1) South of Market and Democracy Tower Office Reston, VA — 13,603 237,479 12,428 13,687 249,823 — — 263,510 91,072 2008-2009 2003 (1) Bay Colony Corporate Center Office Waltham, MA — 18,789 148,451 77,133 18,789 225,584 — — 244,373 68,903 1985-1989 2011 (1) Gateway Center Office San Francisco, CA — 28,255 139,245 64,831 30,627 201,704 — — 232,331 107,640 1984/1986/2002 1999 (1) 535 Mission Street Office San Francisco, CA — 40,933 148,378 3,259 40,933 151,637 — — 192,570 20,576 2015 2013 (1) 2200 Pennsylvania Avenue Office Washington, DC — — 183,541 4,535 — 188,076 — — 188,076 52,280 2011 2008 (1) Mountain View Research Park Office Mountain View, CA — 95,066 68,373 9,988 95,066 78,361 — — 173,427 17,866 1977-1981/2007-2013 2013 (1) Reservoir Place Office Waltham, MA — 18,605 104,124 45,144 20,108 147,765 — — 167,873 64,683 1955/1987/2017 1997/1998 (1) 1330 Connecticut Avenue Office Washington, DC — 25,982 82,311 36,089 27,135 117,247 — — 144,382 27,535 1984/2018 2004 (1) Kingstowne Towne Center Office Alexandria, VA — 18,021 109,038 2,098 18,062 111,095 — — 129,157 41,469 2003-2006 2007 (1) Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2018 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building One Freedom Square Office Reston, VA — 9,929 84,504 32,256 11,293 115,396 — — 126,689 54,652 2000 2003 (1) Capital Gallery Office Washington, DC — 4,725 29,565 87,231 8,662 112,859 — — 121,521 67,759 1981/2006 2007 (1) Weston Corporate Center Office Weston, MA — 25,753 92,312 (123 ) 25,854 92,088 — — 117,942 26,176 2010 2001 (1) Two Freedom Square Office Reston, VA — 13,930 77,739 23,427 15,420 99,676 — — 115,096 51,291 2001 2003 (1) One and Two Reston Overlook Office Reston, VA — 16,456 66,192 24,181 16,179 90,650 — — 106,829 47,668 1999 2000 (1) 140 Kendrick Street Office Needham, MA — 18,095 66,905 17,553 19,092 83,461 — — 102,553 32,360 2000 2004 (1) Discovery Square Office Reston, VA — 11,198 71,782 17,753 12,533 88,200 — — 100,733 39,574 2001 2003 (1) 355 Main Street Office Cambridge, MA — 18,863 53,346 23,701 21,173 74,737 — — 95,910 23,691 1981/1996/2013 2006 (1) 10 CityPoint Office Waltham, MA — 1,953 85,752 4,515 2,116 90,104 — — 92,220 7,772 2016 1997 (1) 90 Broadway Office Cambridge, MA — 19,104 52,078 18,363 20,785 68,760 — — 89,545 21,302 1983/1998/2013 2006 (1) 230 CityPoint Office Waltham, MA — 13,189 49,823 21,914 13,593 71,333 — — 84,926 26,357 1992 2005 (1) Waltham Weston Corporate Center Office Waltham, MA — 10,385 60,694 11,449 11,097 71,431 — — 82,528 32,739 2003 1999 (1) 77 CityPoint Office Waltham, MA — 13,847 60,383 5,858 13,873 66,215 — — 80,088 25,107 2008 2001 (1) 3625-3635 Peterson Way Office Santa Clara, CA — 63,206 14,879 673 63,206 14,879 673 — 78,758 8,146 1979 2016 (1) 2440 West El Camino Real Office Mountain View, CA — 16,741 51,285 3,411 16,741 54,696 — — 71,437 12,562 1987/2003 2011 (1) 300 Binney Street Office Cambridge, MA — 18,080 51,262 140 18,080 51,402 — — 69,482 9,450 2013 2009 (1) 191 Spring Street Office Lexington, MA — 2,850 59,751 6,235 3,151 65,685 — — 68,836 19,543 1971/1995/2018 1997 (1) Wisconsin Place Office Chevy Chase, MD — — 53,349 14,889 — 68,238 — — 68,238 22,936 2009 2004 (1) Reston Corporate Center Office Reston, VA — 9,135 50,857 6,236 10,148 56,080 — — 66,228 28,315 1984 1998 (1) New Dominion Technology Park, Bldg. Two Office Herndon, VA — 5,584 51,868 4,157 6,510 55,099 — — 61,609 25,421 2004 1998 (1) 255 Main Street Office Cambridge, MA — 134 25,110 29,672 548 54,368 — — 54,916 30,180 1987 1997 (1) 200 West Street Office Waltham, MA — 16,148 24,983 11,120 16,813 35,438 — — 52,251 22,544 1999 1997 (1) New Dominion Technology Park, Bldg. One Office Herndon, VA 29,675 3,880 43,227 3,927 4,583 46,451 — — 51,034 27,542 2001 1998 (1) Sumner Square Office Washington, DC — 624 28,745 19,054 1,478 46,945 — — 48,423 25,384 1985 1999 (1) University Place Office Cambridge, MA 5,571 — 37,091 9,001 390 45,702 — — 46,092 27,871 1985 1998 (1) 2600 Tower Oaks Boulevard Office Rockville, MD — 4,243 31,125 6,517 4,244 37,641 — — 41,885 21,426 2001 1998 (1) North First Business Park Office San Jose, CA — 23,398 13,069 4,613 23,377 17,703 — — 41,080 16,076 1981 2007 (1) 150 Broadway Office Cambridge, MA — 850 25,042 8,540 1,323 33,109 — — 34,432 18,404 1999 1997 (1) 325 Main Street Office Cambridge, MA — 174 12,200 16,437 965 23,319 4,527 — 28,811 13,676 1987/2013 1997 (1) 105 Broadway Office Cambridge, MA — 1,299 12,943 9,401 2,395 21,248 — — 23,643 13,950 1990 1997 (1) Lexington Office Park Office Lexington, MA — 998 1,426 18,700 1,264 19,860 — — 21,124 13,614 1982 1997 (1) 201 Spring Street Office Lexington, MA — 2,849 15,303 1,390 3,124 16,418 — — 19,542 8,344 1997 1997 (1) The Point Office Waltham, MA — 6,395 10,040 431 6,480 10,386 — — 16,866 1,031 2015 2007 (1) 690 Folsom Street Office San Francisco, CA — 3,219 11,038 1,157 3,219 12,195 — — 15,414 1,790 2015 2012 (1) 92-100 Hayden Avenue Office Lexington, MA — 594 6,748 7,255 802 13,795 — — 14,597 11,809 1985 1997 (1) Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2018 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building 181 Spring Street Office Lexington, MA — 1,066 9,520 2,230 1,160 11,656 — — 12,816 5,424 1999 1997 (1) 195 West Street Office Waltham, MA — 1,611 6,652 4,270 1,858 10,675 — — 12,533 8,330 1990 1997 (1) 33 Hayden Avenue Office Lexington, MA — 266 3,234 8,223 425 11,298 — — 11,723 9,033 1979 1997 (1) 7501 Boston Boulevard, Building Seven Office Springfield, VA — 665 9,273 819 791 9,966 — — 10,757 5,121 1997 1997 (1) 7450 Boston Boulevard, Building Three Office Springfield, VA — 1,165 4,681 3,278 1,430 7,694 — — 9,124 3,733 1987 1998 (1) 7435 Boston Boulevard, Building One Office Springfield, VA — 392 3,822 4,737 659 8,292 — — 8,951 5,917 1982 1997 (1) 250 Binney Street Office Cambridge, MA — 110 4,483 3,593 273 7,913 — — 8,186 5,448 1983 1997 (1) 8000 Grainger Court, Building Five Office Springfield, VA — 366 4,282 3,536 601 7,583 — — 8,184 5,864 1984 1997 (1) 453 Ravendale Drive Office Mountain View, CA — 5,477 1,090 676 5,477 1,766 — — 7,243 558 1977 2012 (1) 7300 Boston Boulevard, Building Thirteen Office Springfield, VA — 608 4,773 1,438 661 6,158 — — 6,819 3,011 2002 1997 (1) 7601 Boston Boulevard, Building Eight Office Springfield, VA — 200 878 5,373 551 5,900 — — 6,451 4,487 1986 1997 (1) 17 Hartwell Avenue Office Lexington, MA — 26 150 6,064 65 6,175 — — 6,240 1,445 1968 1997 (1) 7500 Boston Boulevard, Building Six Office Springfield, VA — 138 3,749 1,673 406 5,154 — — 5,560 4,121 1985 1997 (1) 8000 Corporate Court, Building Eleven Office Springfield, VA — 136 3,071 1,596 774 4,029 — — 4,803 3,051 1989 1997 (1) 7375 Boston Boulevard, Building Ten Office Springfield, VA — 23 2,685 992 93 3,607 — — 3,700 2,593 1988 1997 (1) 7374 Boston Boulevard, Building Four Office Springfield, VA — 241 1,605 1,828 398 3,276 — — 3,674 2,685 1984 1997 (1) 7451 Boston Boulevard, Building Two Office Springfield, VA — 249 1,542 1,659 613 2,837 — — 3,450 2,527 1982 1997 (1) 32 Hartwell Avenue Office Lexington, MA — 168 1,943 817 314 2,614 — — 2,928 1,821 1968/1979/1987 1997 (1) 164 Lexington Road Office Billerica, MA — 592 1,370 319 643 1,638 — — 2,281 906 1982 1997 (1) Signature at Reston Residential Reston, VA — 27,076 190,580 — 27,076 190,580 — — 217,656 3,938 2018 2013 (1) Proto Kendall Square Residential Cambridge, MA — 9,243 127,248 — 9,243 127,248 — — 136,491 1,324 2018 2015 (1) The Avant at Reston Town Center Residential Reston, VA — 20,350 91,995 830 20,350 92,825 — — 113,175 12,254 2014 2010 (1) The Lofts at Atlantic Wharf Residential Boston, MA — 3,529 54,891 1,768 3,529 56,659 — — 60,188 11,131 2011 2007 (1) Boston Marriott Cambridge Hotel Cambridge, MA — 478 37,918 36,697 1,201 73,892 — — 75,093 46,576 1986/2017 1997 (1) Kendall Center Green Garage Garage Cambridge, MA — — 35,035 7,448 103 42,380 — — 42,483 12,208 1984 2006 (1) Kendall Center Yellow Garage Garage Cambridge, MA — 1,256 15,697 1,621 1,434 17,140 — — 18,574 5,643 2006 2004 (1) Kendall Center Blue Garage Garage Cambridge, MA — 1,163 11,633 2,145 1,579 13,362 — — 14,941 9,437 1990 1997 (1) 145 Broadway Development Cambridge, MA — 121 — 223,845 324 — — 223,642 223,966 — N/A 1997 N/A MacArthur Station Residences Development Oakland, CA — — — 87,159 — — — 87,159 87,159 — N/A N/A N/A 20 CityPoint Development Waltham, MA — — 6,287 46,024 — 6,287 — 46,024 52,311 — N/A 2007 N/A Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2018 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building Reston Gateway Development Reston, VA — — — 25,167 — — — 25,167 25,167 — N/A 1998 N/A 17Fifty Presidents Street Development Reston, VA — — — 25,120 — — — 25,120 25,120 — N/A 2013 N/A North First Master Plan Land San Jose, CA — 35,004 — 3,932 — — 38,936 — 38,936 — N/A 2007 N/A Plaza at Almaden Land San Jose, CA — — — 29,928 — — 29,928 — 29,928 — N/A 2006 N/A Springfield Metro Center Land Springfield, VA — — — 19,823 — — 19,823 — 19,823 — N/A 2007 N/A 214 Third Avenue Land Waltham, MA — — — 15,233 — — 15,233 — 15,233 — N/A 2006 N/A Platform 16 Land San Jose, CA — — — 12,962 — — 12,962 — 12,962 — N/A 2018 N/A 103 Fourth Avenue Land Waltham, MA — — — 12,208 — — 12,208 — 12,208 — N/A 2007 N/A Reston Gateway Master Plan Land Reston, VA — — — 11,014 — — 11,014 — 11,014 — N/A 1998 N/A Fourth and Harrison Land San Francisco, CA — — — 10,350 — — 10,350 — 10,350 — N/A N/A N/A 2100 Pennsylvania Avenue Land Washington, DC — — — 9,700 — — 9,700 — 9,700 — N/A N/A N/A Crane Meadow Land Marlborough, MA — — — 8,852 — — 8,852 — 8,852 — N/A 2000 N/A Washingtonian North Land Gaithersburg, MD — — — 7,473 — — 7,473 — 7,473 — N/A 1998 N/A Broad Run Business Park Land Loudoun County, VA — — — 2,388 — — 2,388 — 2,388 — N/A 1998 N/A Kendall Center Master Plan Land Cambridge, MA — — — 2,199 — — 2,199 — 2,199 — N/A 1997 N/A Weston Quarry Land Weston, MA — — — 1,237 — — 1,237 — 1,237 — N/A 2001 N/A Reston Overlook Master Plan Land Reston, VA — — — 39 — — 39 — 39 — N/A 2000 N/A $ 2,964,572 (2 ) $ 4,959,995 $ 12,763,317 $ 3,882,233 $ 5,072,568 $ 15,753,683 $ 200,498 (3 ) $ 578,796 $ 21,605,545 $ 4,871,102 Note: Total Real Estate does not include Furniture, Fixtures and Equipment totaling approximately $44,351 . Accumulated Depreciation does not include approximately $26,675 of accumulated depreciation related to Furniture, Fixtures and Equipment. The aggregate cost and accumulated depreciation for tax purposes was approximately $17.9 billion and $3.9 billion , respectively. (1) Depreciation of the buildings and improvements are calculated over lives ranging from the life of the lease to 40 years. (2) Includes unamortized deferred financing costs totaling approximately $(30.8) million . (3) Includes pre-development costs. Boston Properties, Inc. Real Estate and Accumulated Depreciation December 31, 2018 , 2017 and 2016 (dollars in thousands) A summary of activity for real estate and accumulated depreciation is as follows: 2018 2017 2016 Real Estate: Balance at the beginning of the year $ 21,058,714 $ 20,114,576 $ 19,451,683 Additions to/improvements of real estate 1,043,379 1,099,286 977,287 Assets sold/written-off (496,548 ) (155,148 ) (314,394 ) Balance at the end of the year $ 21,605,545 $ 21,058,714 $ 20,114,576 Accumulated Depreciation: Balance at the beginning of the year $ 4,566,570 $ 4,201,891 $ 3,905,940 Depreciation expense 533,342 497,059 560,024 Assets sold/written-off (228,810 ) (132,380 ) (264,073 ) Balance at the end of the year $ 4,871,102 $ 4,566,570 $ 4,201,891 Note: Real Estate and Accumulated Depreciation amounts do not include Furniture, Fixtures and Equipment.

Summary Of Significant Accoun_2

Summary Of Significant Accounting Policies Summary Of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Real Estate	Real Estate Upon acquisitions of real estate, which includes the consolidation of previously unconsolidated joint ventures, the Company assesses the fair value of acquired tangible and intangible assets (including land, buildings, tenant improvements, “above-” and “below-market” leases, leasing and assumed financing origination costs, acquired in-place leases, other identified intangible assets and assumed liabilities) and allocates the purchase price to the acquired assets and assumed liabilities, including land and buildings as if vacant. The Company assesses and considers fair value based on estimated cash flow projections that utilize discount and/or capitalization rates that it deems appropriate, as well as available market information. Estimates of future cash flows are based on a number of factors including the historical operating results, known and anticipated trends, and market and economic conditions. The fair value of the tangible assets of an acquired property considers the value of the property as if it were vacant. The Company also considers an allocation of purchase price of other acquired intangibles, including acquired in-place leases that may have a customer relationship intangible value, including (but not limited to) the nature and extent of the existing relationship with the tenants, the tenants’ credit quality and expectations of lease renewals. Based on its acquisitions to date, the Company’s allocation to customer relationship intangible assets has been immaterial. The Company records acquired “above-” and “below-market” leases at their fair values (using a discount rate which reflects the risks associated with the leases acquired) equal to the difference between (1) the contractual amounts to be paid pursuant to each in-place lease and (2) management’s estimate of fair market lease rates for each corresponding in-place lease, measured over a period equal to the remaining term of the lease for above-market leases and the initial term plus the term of any below-market fixed rate renewal options for below-market leases. Acquired “above-” and “below-market” lease values have been reflected within Prepaid Expenses and Other Assets and Other Liabilities, respectively, in the Company’s Consolidated Balance Sheets. Other intangible assets acquired include amounts for in-place lease values that are based on the Company’s evaluation of the specific characteristics of each tenant’s lease. Factors to be considered include estimates of carrying costs during hypothetical expected lease-up periods considering current market conditions, and costs to execute similar leases. In estimating carrying costs, the Company includes real estate taxes, insurance and other operating expenses and estimates of lost rentals at market rates during the expected lease-up periods, depending on local market conditions. In estimating costs to execute similar leases, the Company considers leasing commissions, legal and other related expenses. Management reviews its long-lived assets for impairment following the end of each quarter and when there is an event or change in circumstances that indicates an impairment in value. An impairment loss is recognized if the carrying amount of an asset is not recoverable and exceeds its fair value. The evaluation of anticipated cash flows is highly subjective and is based in part on assumptions regarding anticipated hold periods, future occupancy, rental rates and capital requirements that could differ materially from actual results in future periods. Because cash flows on properties considered to be “long-lived assets to be held and used” are considered on an undiscounted basis to determine whether an asset has been impaired, the Company’s established strategy of holding properties over the long term directly decreases the likelihood of recording an impairment loss. If the Company’s strategy changes or market conditions otherwise dictate an earlier sale date, an impairment loss may be recognized and such loss could be material. If the Company determines that an impairment has occurred, the affected assets must be reduced to their fair value. Guidance in Accounting Standards Codification (“ASC”) 360 “Property Plant and Equipment” (“ASC 360”) requires that qualifying assets and liabilities and the results of operations that have been sold, or otherwise qualify as “held for sale,” be presented as discontinued operations in all periods presented if the property operations are expected to be eliminated and the Company will not have significant continuing involvement following the sale. Discontinued operations presentation applies only to disposals representing a strategic shift that has (or will have) a major effect on an entity’s operations and financial results (e.g., a disposal of a major geographical area, a major line of business, a major equity method investment or other major parts of an entity). The components of the property’s net income that are reflected as discontinued operations include the net gain (or loss) upon the disposition of the property held for sale, operating results, depreciation and interest expense (if the property is subject to a secured loan). The Company generally considers assets to be “held for sale” when the transaction has been approved by Boston Properties, Inc.’s Board of Directors, or a committee thereof, and there are no known significant contingencies relating to the sale, such that a sale of the property within one year is considered probable. Following the classification of a property as “held for sale,” no further depreciation is recorded on the assets, and the asset is written down to the lower of carrying value or fair market value, less cost to sell. Real estate is stated at depreciated cost. A variety of costs are incurred in the acquisition, development and leasing of properties. The cost of buildings and improvements includes the purchase price of property, legal fees and other acquisition costs. The Company capitalizes acquisition costs that it incurs to effect an asset acquisition and expenses acquisition costs that it incurs to effect a business combination, including legal, due diligence and other closing related costs. Costs directly related to the development of properties are capitalized. Capitalized development costs include interest, internal wages, property taxes, insurance, and other project costs incurred during the period of development. After the determination is made to capitalize a cost, it is allocated to the specific component of the project that benefited from the investment. Determination of when a development project commences and capitalization begins, and when a development project is substantially complete and held available for occupancy and capitalization must cease, involves a degree of judgment. The Company’s capitalization policy on development properties follows the guidance in ASC 835-20 “Capitalization of Interest” and ASC 970 “Real Estate-General.” The costs of land and buildings under development include specifically identifiable costs. Capitalized costs include pre-construction costs necessary to the development of the property, development costs, construction costs, interest costs, real estate taxes, salaries and related costs and other costs incurred during the period of development. The Company begins the capitalization of costs during the pre-construction period, which it defines as activities that are necessary for the development of the property. The Company considers a construction project as substantially complete and held available for occupancy upon the completion of tenant improvements, but no later than one year from cessation of major construction activity. The Company ceases capitalization on the portion (1) substantially completed, (2) occupied or held available for occupancy, and capitalizes only those costs associated with the portion under construction or (3) if activities necessary for the development of the property have been suspended. Interest costs capitalized for the years ended December 31, 2018 , 2017 and 2016 were approximately $65.8 million , $61.1 million and $39.2 million , respectively. Salaries and related costs capitalized for the years ended December 31, 2018 , 2017 and 2016 were approximately $12.5 million , $13.2 million and $11.1 million , respectively. Expenditures for repairs and maintenance are charged to operations as incurred. Significant betterments are capitalized. When assets are sold or retired, their costs and related accumulated depreciation are removed from the accounts with the resulting gains or losses reflected in net income or loss for the period. The Company computes depreciation and amortization on properties using the straight-line method based on estimated useful asset lives. In accordance with ASC 805 “Business Combinations,” the Company allocates the acquisition cost of real estate to its components and depreciates or amortizes these assets (or liabilities) over their useful lives. The amortization of acquired “above-” and “below-market” leases and acquired in-place leases is recorded as an adjustment to revenue and depreciation and amortization, respectively, in the Consolidated Statements of Operations. Depreciation is computed on a straight-line basis over the estimated useful lives of the assets as follows: Land improvements 25 to 40 years Buildings and improvements 10 to 40 years Tenant improvements Shorter of useful life or terms of related lease Furniture, fixtures, and equipment 3 to 7 years
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents consist of cash on hand and investments with maturities of three months or less from the date of purchase. The majority of the Company’s cash and cash equivalents are held at major commercial banks which may at times exceed the Federal Deposit Insurance Corporation limit of $250,000 .
Cash Held in Escrows	Cash Held in Escrows Escrows include amounts established pursuant to various agreements for security deposits, property taxes, insurance and other costs. Escrows also include cash held by qualified intermediaries for possible investments in like-kind exchanges in accordance with Section 1031 of the Internal Revenue Code in connection with sales of the Company’s properties.
Investments in Securities	Investments in Securities The Company accounts for investments in trading securities at fair value, with gains or losses resulting from changes in fair value recognized currently in earnings. The designation of trading securities is generally determined at acquisition. The Company maintains a deferred compensation plan that is designed to allow officers of Boston Properties, Inc. to defer a portion of their current income on a pre-tax basis and receive a tax-deferred return on these deferrals. The Company’s obligation under the plan is that of an unsecured promise to pay the deferred compensation to the plan participants in the future. At December 31, 2018 and 2017 , the Company had maintained approximately $28.2 million and $29.2 million , respectively, in a separate account, which is not restricted as to its use. The Company recognized gains (losses) of approximately $(1.9) million , $3.7 million and $2.3 million on its investments in the account associated with the Company’s deferred compensation plan during the years ended December 31, 2018 , 2017 and 2016 , respectively.
Tenant and Other Receivables and Note Receivables	Tenant and Other Receivables Tenant and other accounts receivable, other than accrued rents receivable, are expected to be collected within one year. Notes Receivable The Company accounts for notes receivable at their unamortized cost, net of any unamortized deferred fees or costs, premiums or discounts and an allowance for loan losses. Loan fees and direct costs associated with loans originated by the Company are deferred and amortized over the term of the note as interest income.
Deferred Charges	Deferred Charges Deferred charges include leasing costs and certain financing fees. Leasing costs include acquired intangible in-place lease values and direct and incremental fees and costs incurred in the successful negotiation of leases, including brokerage, legal, internal leasing employee salaries and other costs which have been deferred and are being amortized on a straight-line basis over the terms of the respective leases. Unamortized leasing costs are charged to expense upon the early termination of the lease. Fully amortized deferred leasing costs are removed from the books upon the expiration of the lease. Internal leasing salaries and related costs capitalized for the years ended December 31, 2018 , 2017 and 2016 were approximately $5.4 million , $5.0 million and $7.2 million , respectively (see New Accounting Pronouncements Issued but not yet Adopted “ Leases ”). Financing fees included in deferred charges consist of external fees and costs incurred to obtain the Company's revolving facility and if applicable, the delayed draw facility and construction financing arrangements where there are not sufficient amounts outstanding. Such financing costs have been deferred and are being amortized over the terms of the respective financing and included within interest expense. Unamortized financing costs are charged to expense upon the early repayment or significant modification of the financing. Fully amortized deferred financing costs are removed from the books upon the maturity of the debt. External fees and costs incurred to obtain mortgage financings and unsecured senior notes have been deferred and are presented as direct deductions from the carrying amounts of the corresponding debt liability. Such financing costs are being amortized over the terms of the respective financing and included within interest expense. Unamortized financing costs are charged to expense upon the early repayment or significant modification of the financing.
Investments in Unconsolidated Joint Ventures	Investments in Unconsolidated Joint Ventures The Company consolidates VIEs in which it is considered to be the primary beneficiary. VIEs are entities in which the equity investors do not have sufficient equity at risk to finance their endeavors without additional financial support or that the holders of the equity investment at risk do not have substantive participating rights. The primary beneficiary is defined by the entity having both of the following characteristics: (1) the power to direct the activities that, when taken together, most significantly impact the variable interest entity’s performance, and (2) the obligation to absorb losses and the right to receive the returns from the variable interest entity that could potentially be significant to the VIE. For ventures that are not VIEs, the Company consolidates entities for which it has significant decision making control over the ventures’ operations. The Company’s judgment with respect to its level of influence or control of an entity involves the consideration of various factors including the form of the Company’s ownership interest, its representation in the entity’s governance, the size of its investment (including loans), estimates of future cash flows, its ability to participate in policy making decisions and the rights of the other investors to participate in the decision making process and to replace the Company as manager and/or liquidate the venture, if applicable. The Company’s assessment of its influence or control over an entity affects the presentation of these investments in the Company’s consolidated financial statements. In addition to evaluating control rights, the Company consolidates entities in which the outside partner has no substantive kick-out rights to remove the Company as the managing member. Accounts of the consolidated entity are included in the accounts of the Company and the noncontrolling interest is reflected on the Consolidated Balance Sheets as a component of equity or in temporary equity between liabilities and equity. Investments in unconsolidated joint ventures are recorded initially at cost, and subsequently adjusted for equity in earnings and cash contributions and distributions. Any difference between the carrying amount of these investments on the balance sheet and the underlying equity in net assets is amortized as an adjustment to equity in earnings of unconsolidated joint ventures over the life of the related asset. Under the equity method of accounting, the net equity investment of the Company is reflected within the Consolidated Balance Sheets, and the Company’s share of net income or loss from the joint ventures is included within the Consolidated Statements of Operations. The joint venture agreements may designate different percentage allocations among investors for profits and losses; however, the Company’s recognition of joint venture income or loss generally follows the joint venture’s distribution priorities, which may change upon the achievement of certain investment return thresholds. The Company may account for cash distributions in excess of its investment in an unconsolidated joint venture as income when the Company is not the general partner in a limited partnership and when the Company has neither the requirement nor the intent to provide financial support to the joint venture. The Company’s investments in unconsolidated joint ventures are reviewed for impairment periodically and the Company records impairment charges when events or circumstances change indicating that a decline in the fair values below the carrying values has occurred and such decline is other-than-temporary. The ultimate realization of the investment in unconsolidated joint ventures is dependent on a number of factors, including the performance of each investment and market conditions. The Company will record an impairment charge if it determines that a decline in the value below the carrying value of an investment in an unconsolidated joint venture is other-than-temporary. To the extent that the Company contributed assets to a joint venture, the Company’s investment in the joint venture was recorded at the Company’s cost basis in the assets that were contributed to the joint venture. To the extent that the Company’s cost basis is different than the basis reflected at the joint venture level, the basis difference is amortized over the life of the related asset and included in the Company’s share of equity in net income of the joint venture. In accordance with the provisions of ASC 610-20 “Gains and Losses from the Derecognition of Nonfinancial Assets” (“ASC 610-20”), the Company will recognize a full gain on both the retained and sold portions of real estate contributed or sold to a joint venture by recognizing its new equity method investment interest at fair value. The combined summarized financial information of the unconsolidated joint ventures is disclosed in Note 5 .
Revenue Recognition	Revenue Recognition In general, the Company commences rental revenue recognition when the tenant takes possession of the leased space and the leased space is substantially ready for its intended use. Contractual rental revenue is reported on a straight-line basis over the terms of the respective leases. The impact of the straight-line rent adjustment increased revenue by approximately $51.9 million , $54.8 million and $31.7 million for the years ended December 31, 2018 , 2017 and 2016 , respectively, as the revenue recorded exceeded amounts billed. Accrued rental income, as reported on the Consolidated Balance Sheets, represents cumulative rental income earned in excess of rent payments received pursuant to the terms of the individual lease agreements. The Company maintains an allowance against accrued rental income for future potential tenant credit losses. The credit assessment is based on the estimated accrued rental income that is recoverable over the term of the lease. The Company also maintains an allowance for doubtful accounts for estimated losses resulting from the inability of tenants to make required rent payments. The computation of this allowance is based on the tenants’ payment history and current credit status, as well as certain industry or geographic specific credit considerations. If the Company’s estimates of collectability differ from the cash received, then the timing and amount of the Company’s reported revenue could be impacted. The credit risk is mitigated by the high quality of the Company’s existing tenant base, reviews of prospective tenants’ risk profiles prior to lease execution and consistent monitoring of the Company’s portfolio to identify potential problem tenants. In accordance with ASC 805, the Company recognizes acquired in-place “above-” and “below-market” leases at their fair values as rental revenue over the original term of the respective leases. The impact of the acquired in-place “above-” and “below-market” leases increased revenue by approximately $23.8 million , $23.5 million and $30.2 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. The following table summarizes the scheduled amortization of the Company’s acquired “above-” and “below-market” lease intangibles for each of the five succeeding years (in thousands). Acquired Above-Market Lease Intangibles Acquired Below-Market Lease Intangibles 2019 $ 7,099 $ 27,327 2020 5,394 10,462 2021 2,988 6,348 2022 314 5,669 2023 168 5,558 Recoveries from tenants, consisting of amounts due from tenants for common area maintenance, real estate taxes and other recoverable costs, are recognized as revenue in the period during which the expenses are incurred. The Company recognizes these reimbursements on a gross basis, as the Company obtains control of the goods and services before they are transferred to the tenant. The Company also receives reimbursements of payroll and payroll related costs from third parties that the Company reflects on a gross basis. The Company’s parking revenue is derived primarily from monthly and transient daily parking. In addition, the Company has certain lease arrangements for parking accounted for under the guidance in ASC 840 “Leases” (“ASC 840”). The monthly and transient daily parking revenue falls within the scope of ASC 606 “Revenue from Contracts with Customers” (“ASC 606”) and is accounted for at the point in time when control of the goods or services transfers to the customer and the Company’s performance obligation is satisfied (see New Accounting Pronouncements Adopted “ Revenue from Contracts with Customers ”). The Company’s hotel revenue is derived from room rentals and other sources such as charges to guests for telephone service, movie and vending commissions, meeting and banquet room revenue and laundry services. Hotel revenue is recognized as the hotel rooms are occupied and the services are rendered to the hotel customers (see New Accounting Pronouncements Adopted “ Revenue from Contracts with Customers ”). The Company earns management and development fees. Development and management services revenue is earned from unconsolidated joint venture entities and third-party property owners. The Company determined that the performance obligations associated with its development services contracts are satisfied over time and that the Company would recognize its development services revenue under the output method evenly over time from the development commencement date through the substantial completion date of the development management services project due to the stand-ready nature of the contracts. Significant judgments impacting the amount and timing of revenue recognized from the Company's development services contracts include estimates of total development project costs from which the fees are typically derived and estimates of the period of time until substantial completion of the development project, the period of time over which the development services are required to be performed. The Company recognizes development fees earned from unconsolidated joint venture projects equal to its cost plus profit to the extent of the third party partners’ ownership interest. Property management fees are recorded and earned based on a percentage of collected rents at the properties under management, and not on a straight-line basis, because such fees are contingent upon the collection of rents (see New Accounting Pronouncements Adopted “ Revenue from Contracts with Customers ”). Gains on sales of real estate are recognized pursuant to the provisions included in ASC 610-20. Under ASC 610-20, the Company must first determine whether the transaction is a sale to a customer or non-customer. The Company typically sells real estate on a selective basis and not within the ordinary course of its business and therefore expects that its sale transactions will not be contracts with customers. The Company next determines whether it has a controlling financial interest in the property after the sale, consistent with the consolidation model in ASC 810 "Consolidation" (“ASC 810”). If the Company determines that it does not have a controlling financial interest in the real estate, it evaluates whether a contract exists under ASC 606 and whether the buyer has obtained control of the asset that was sold. The Company recognizes a full gain on sale of real estate when the derecognition criteria under ASC 610-20 have been met (see New Accounting Pronouncements Adopted “ Sales of Real Estate ”).
Ground Leases	Ground Leases The Company has non-cancelable ground lease obligations with various initial term expiration dates through 2114 . The Company recognizes ground rent expense on a straight-line basis over the terms of the respective ground lease agreements. The future contractual minimum lease payments to be made by the Company as of December 31, 2018 , under non-cancelable ground leases which expire on various dates through 2114 , are as follows: Years Ending December 31, (in thousands) 2019 $ 11,425 2020 18,425 2021 25,310 2022 8,894 2023 9,084 Thereafter 567,232
Capital Leases	Capital Leases The Company has four capital lease obligations with various initial term expiration dates through 2036. The following reflects the gross amount of assets recorded under capital leases by asset class at December 31, 2018 and December 31, 2017 (in thousands): December 31, 2018 2017 Land held for future development $ 12,397 $ — Buildings and improvements 23,636 23,636 Construction in progress 28,962 28,962 Total $ 64,995 $ 52,598 The future minimum lease payments, as of December 31, 2018, related to the four capital leases, through 2036 are as follows: Years Ending December 31, (in thousands) 2019 $ 1,441 2020 12,682 2021 2,123 2022 1,253 2023 944 Thereafter 73,241 Total expected minimum lease payments 91,684 Interest portion (27,497 ) Present value of expected net minimum lease payments $ 64,187
Earnings Per Share and Earnings Per Common Unit	Earnings Per Share Basic earnings per share (“EPS”) is computed by dividing net income available to common shareholders, as adjusted for undistributed earnings (if any) of certain securities issued by Boston Properties Limited Partnership, by the weighted average number of shares of Common Stock outstanding during the year. Diluted EPS reflects the potential dilution that could occur from shares issuable in connection with awards under stock-based compensation plans, including upon the exercise of stock options, and securities of Boston Properties Limited Partnership that are exchangeable for Common Stock. Earnings Per Common Unit Basic earnings per common unit is computed by dividing net income available to common unitholders, as adjusted for undistributed earnings (if any) of certain securities issued by Boston Properties Limited Partnership, by the weighted average number of common units outstanding during the year. Diluted earnings per common unit reflects the potential dilution that could occur from units issuable in connection with awards under Boston Properties, Inc.’s stock-based compensation plans, including upon the exercise of stock options, and conversion of preferred units of Boston Properties Limited Partnership.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying values of cash and cash equivalents, marketable securities, escrows, receivables, accounts payable, accrued expenses and other assets and liabilities are reasonable estimates of their fair values because of the short maturities of these instruments. The Company follows the authoritative guidance for fair value measurements when valuing its financial instruments for disclosure purposes. Boston Properties Limited Partnership determines the fair value of its unsecured senior notes using market prices. The inputs used in determining the fair value of Boston Properties Limited Partnership’s unsecured senior notes is categorized at a Level 1 basis (as defined in ASC 820 “Fair Value Measurements and Disclosures” (“ASC 820”)) due to the fact that it uses quoted market rates to value these instruments. However, the inputs used in determining the fair value could be categorized at a Level 2 basis (as defined in ASC 820) if trading volumes are low. The Company determines the fair value of its related party note receivable, note receivable and mortgage notes payable using discounted cash flow analysis by discounting the spread between the future contractual interest payments and hypothetical future interest payments on note receivables / mortgage debt 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. The inputs used in determining the fair value of the Company’s related party note receivable, note receivable, and mortgage notes payable are categorized at a Level 3 basis (as defined in ASC 820) due to the fact that the Company considers the rates used in the valuation techniques to be unobservable inputs. To the extent that there are outstanding borrowings under the unsecured line of credit or unsecured term loan, the Company utilizes a discounted cash flow methodology in order to estimate the fair value. To the extent that credit spreads have changed since the origination, the net present value of the difference between future contractual interest payments and future interest payments based on the Company’s estimate of a current market rate would represent the difference between the book value and the fair value. The Company’s estimate of a current market rate is based upon the rate, considering current market conditions and Boston Properties Limited Partnership's specific credit profile, at which it estimates it could obtain similar borrowings. To the extent there are outstanding borrowings, this current market rate is estimated and therefore would be primarily based upon a Level 3 input. 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, and the Company’s estimated fair values for these instruments as of the end of the applicable reporting period are not necessarily indicative of estimated or actual fair values in future reporting periods. The following table presents the aggregate carrying value of the Company’s related party note receivable, note receivable, mortgage notes payable, net, unsecured senior notes, net, unsecured line of credit and unsecured term loan, net and the Company’s corresponding estimate of fair value as of December 31, 2018 and December 31, 2017 (in thousands): December 31, 2018 December 31, 2017 Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Related party note receivable $ 80,000 $ 80,000 $ — $ — Note receivable 19,468 19,468 — — Total $ 99,468 $ 99,468 $ — $ — Mortgage notes payable, net $ 2,964,572 $ 2,903,925 $ 2,979,281 $ 3,042,920 Unsecured senior notes, net 7,544,697 7,469,338 7,247,330 7,461,615 Unsecured line of credit — — 45,000 45,000 Unsecured term loan, net 498,488 500,783 — — Total $ 11,007,757 $ 10,874,046 $ 10,271,611 $ 10,549,535 The Company uses interest rate swap agreements to manage its interest rate risk. The valuation of these instruments is determined using widely accepted valuation techniques, including discounted cash flow analysis on the expected cash flows of each derivative. This analysis reflects the contractual terms of the derivatives, including the period to maturity, and uses observable market-based inputs, including interest rate curves. To comply with the provisions of ASC 820, the Company incorporates credit valuation adjustments to appropriately reflect both its own nonperformance risk and the respective counterparty’s nonperformance risk in the fair value measurements. Although the Company determined that the majority of the inputs used to value its derivatives fall within Level 2 of the fair value hierarchy, the credit valuation adjustments associated with its derivatives utilize Level 3 inputs, such as estimates of current credit spreads to evaluate the likelihood of default by the Company and its counterparties. The Company assessed the significance of the impact of the credit valuation adjustments on the overall valuation of its derivative positions and determined that the credit valuation adjustments were not significant to the overall valuation of its derivatives. As a result, the Company has determined that its derivative valuations in their entirety are classified in Level 2 of the fair value hierarchy.
Derivative Instruments and Hedging Activities	Derivative Instruments and Hedging Activities Derivative instruments and hedging activities require management to make judgments on the nature of its derivatives and their effectiveness as hedges. These judgments determine if the changes in fair value of the derivative instruments are reported in the Consolidated Statements of Operations as a component of net income or as a component of comprehensive income and as a component of equity on the Consolidated Balance Sheets. While management believes its judgments are reasonable, a change in a derivative’s effectiveness as a hedge could materially affect expenses, net income and equity. The Company accounts for both the effective and ineffective portions of changes in the fair value of a derivative in other comprehensive income (loss) and subsequently reclassifies the fair value of the derivative to earnings over the term that the hedged transaction affects earnings and in the same line item as the hedged transaction within the statements of operations (see New Accounting Pronouncements Adopted “ Derivatives and Hedging ”).
Stock-Based Employee Compensation Plans	Stock-Based Employee Compensation Plans At December 31, 2018 , the Company has a stock-based employee compensation plan. The Company accounts for the plan under the guidance in ASC 718 “Compensation – Stock Compensation” (“ASC 718”), which revised the fair value based method of accounting for share-based payment liabilities, forfeitures and modifications of stock-based awards and clarified previous guidance in several areas, including measuring fair value, classifying an award as equity or as a liability and attributing compensation cost to reporting periods.
Use of Estimates in the Preparation of Financial Statements	Use of Estimates in the Preparation of Financial Statements The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America (“GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. These estimates include such items as depreciation and allowances for doubtful accounts. Actual results could differ from those estimates.
Recent Accounting Pronouncements	New Accounting Pronouncements Adopted Revenue from Contracts with Customers In May 2014, the Financial Accounting Standards Board (“FASB”) issued ASU 2014-09, “Revenue from Contracts with Customers (Topic 606)” (“ASU 2014-09”). The objective of ASU 2014-09 is to establish a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers, which supersedes most of the existing revenue recognition guidance, including industry-specific guidance. The core principle is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In applying ASU 2014-09, companies will perform a five-step analysis of transactions to determine when and how revenue is recognized. The five-step analysis consists of the following: (i) identifying the contract with a customer, (ii) identifying the performance obligations in the contract, (iii) determining the transaction price, (iv) allocating the transaction price to the performance obligations in the contract and (v) recognizing revenue when (or as) the entity satisfies a performance obligation. ASU 2014-09 applies to all contracts with customers except those that are within the scope of other topics in the FASB’s ASC. In August 2015, the FASB issued ASU 2015-14, “Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date” (“ASU 2015-14”), which delayed the effective date of ASU 2014-09 by one year making it effective for the first interim period within annual reporting periods beginning after December 15, 2017. Early adoption was permitted as of the original effective date. In May 2016, the FASB issued ASU No. 2016-12, “Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients” (“ASU 2016-12”). ASU 2016-12 is intended to clarify and provide practical expedients for certain aspects of ASU 2014-09 and notes that lease contracts with customers are a scope exception. ASU 2014-09 was effective for the Company for reporting periods beginning after December 15, 2017. The Company adopted ASU 2014-09 effective January 1, 2018 using the modified retrospective approach. The adoption of ASU 2014-09 did not have a material impact on the Company’s consolidated financial statements. The Company applied the guidance only to contracts that were not completed as of January 1, 2018. The Company does not have material contract assets and liabilities within the scope of ASC 606. The adoption of ASU 2014-09 resulted in a change to the timing pattern of revenue recognized, but not the total revenue recognized over time for certain of the Company’s development services contracts. As a result, the modified retrospective approach resulted in the Company recognizing on January 1, 2018 the cumulative effect of adopting ASU 2014-09 aggregating approximately $4.9 million to Dividends in Excess of Earnings of Boston Properties, Inc. and Partners’ Capital of Boston Properties Limited Partnership and approximately $0.6 million to Noncontrolling Interests - Common Units of Boston Properties, Inc. and Noncontrolling Interests - Redeemable Partnership Units of Boston Properties Limited Partnership on the corresponding Consolidated Balance Sheets. The Company disaggregates its revenue by source within its Consolidated Statements of Operations. As an owner and operator of real estate, the Company derives the majority of its revenue from leasing space to tenants at its properties. As a result, the majority of the Company’s revenue is accounted for pursuant to ASC 840 and is reflected within Base Rent in the Consolidated Statements of Operations. In addition, the Company earns revenue from recoveries from tenants, consisting of amounts due from tenants for common area maintenance, real estate taxes and other recoverable costs. Revenue from recoveries from tenants is recognized under the guidance within ASC 840 until the adoption of ASC 842 “Leases” in 2019 at which time it may fall within the guidance under ASC 606 (see New Accounting Pronouncements Issued but not yet Adopted “ Leases ”). The Company also earns revenue from the following sources; parking and other revenue, hotel revenue and development and management services revenue. Parking and other revenue is derived primarily from monthly and transient daily parking. In addition, the Company has certain lease arrangements for parking accounted for under the guidance in ASC 840. The monthly and transient daily parking revenue falls within the scope of ASC 606 and is accounted for at the point in time when control of the goods or services transfers to the customer and the Company’s performance obligation is satisfied, consistent with the Company’s previous accounting. Hotel revenue is derived from room rentals and other sources such as charges to guests for telephone service, movie and vending commissions, meeting and banquet room revenue and laundry services. Hotel revenue also falls within the scope of ASC 606 and is accounted for at the point in time when control of the goods or services transfers to the customer and the Company’s performance obligation is satisfied, consistent with the Company’s previous accounting. Development and management services revenue is earned from unconsolidated joint venture entities and third-party property owners. The Company determined that the performance obligations associated with its development services contracts are satisfied over time and that the Company would recognize its development services revenue under the output method evenly over time from the development commencement date through the substantial completion date of the development management services project due to the stand-ready nature of the contracts. Significant judgments impacting the amount and timing of revenue recognized from the Company's development services contracts include estimates of total development project costs from which the fees are typically derived and estimates of the period of time until substantial completion of the development project, the period of time over which the development services are required to be performed. As a result, the pattern of revenue recognized over time under ASC 606 differs from the Company’s previous accounting. The Company recognizes development fees earned from unconsolidated joint venture projects equal to its cost plus profit to the extent of the third party partners’ ownership interest. Property management fees are recorded and earned based on a percentage of collected rents at the properties under management, and not on a straight-line basis, because such fees are contingent upon the collection of rents. The revenue recognized under property management services contracts is recognized consistent with the Company's previous accounting. ASU 2014-09 also updates the principal versus agent considerations and, as a result, the Company determined that amounts reimbursed for payroll and related costs received from unconsolidated joint venture entities and third party property owners in connection with management services contracts should be reflected on a gross basis instead of on a net basis as the Company has determined that it is the principal under these arrangements. During the year ended December 31, 2018, the Company recognized approximately $9.6 million of expenses consisting of payroll and related costs from management services contracts and recognized corresponding revenue of approximately $9.6 million reflecting the direct reimbursements of such costs from the unconsolidated joint venture entities and third-party property owners. Financial Instruments In January 2016, the FASB issued ASU 2016-01, “Financial Instruments – Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities” (“ASU 2016-01”). ASU 2016-01 requires equity investments (except those accounted for under the equity method of accounting or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income, requires public business entities to use the exit price notion when measuring the fair value of financial instruments for disclosure purposes, requires separate presentation of financial assets and financial liabilities by measurement category and form of financial asset, and eliminates the requirement for public business entities to disclose the method(s) and significant assumptions used to estimate the fair value that is required to be disclosed for financial instruments measured at amortized cost. ASU 2016-01 is effective for the Company for reporting periods beginning after December 15, 2017, with early adoption permitted. The Company adopted ASU 2016-01 effective January 1, 2018. The adoption of ASU 2016-01 did not have a material impact on the Company’s consolidated financial statements. Statement of Cash Flows In August 2016, the FASB issued ASU No. 2016-15, “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments (a consensus of the FASB Emerging Issues Task Force)” (“ASU 2016-15”). ASU 2016-15 is intended to reduce diversity in practice in how certain transactions are classified in the statement of cash flows. The areas addressed in the new guidance related to debt prepayment costs, settlement of zero-coupon debt instruments, contingent consideration payments made after a business combination, proceeds from the settlement of insurance claims, proceeds from the settlement of corporate-owned and bank-owned life insurance policies, distributions received from equity method investments, beneficial interest in securitization transactions, and separately identifiable cash flows and application of the predominance principle. ASU 2016-15 was effective for the Company for reporting periods beginning after December 15, 2017, with early adoption permitted (provided that all of the amendments are adopted in the same period), and was required to be applied retrospectively to all periods presented. The Company adopted ASU 2016-15 effective January 1, 2018. The adoption of ASU 2016-15 resulted in the classification of debt prepayment and extinguishment costs totaling approximately $16.0 million as a component of financing activities instead of as a component of operating activities in the Company's Consolidated Statements of Cash Flows for the year ended December 31, 2018. The adoption of ASU 2016-15 resulted in the retrospective classification of debt prepayment and extinguishment costs totaling approximately $12.8 million as a component of financing activities instead of as a component of operating activities in the Company's Consolidated Statements of Cash Flows for the year ended December 31, 2017. In November 2016, the FASB issued ASU No. 2016-18, “Statement of Cash Flows (Topic 230): Restricted Cash (a consensus of the FASB Emerging Issues Task Force)” (“ASU 2016-18”). ASU 2016-18 requires companies to include restricted cash and restricted cash equivalents with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 also requires a disclosure of a reconciliation between the statement of financial position and the statement of cash flows when the statement of financial position includes more than one line item for cash, cash equivalents, restricted cash and restricted cash equivalents. Entities with material restricted cash and restricted cash equivalents balances are required to disclose the nature of the restrictions. ASU 2016-18 was effective for reporting periods beginning after December 15, 2017, with early adoption permitted, and is required to be applied retrospectively to all periods presented. The Company adopted ASU 2016-18 effective January 1, 2018. The retrospective adoption of ASU 2016-18 resulted in an increase to net cash provided by operating activities totaling approximately $4.5 million , a decrease to net cash used in investing activities totaling approximately $15.8 million , a decrease to net cash provided by financing activities totaling approximately $12.9 million , and a corresponding increase to the net increase in cash and cash equivalents and cash held in escrows totaling approximately $7.4 million from amounts previously reported for the year ended December 31, 2017. The retrospective adoption of ASU 2016-18 resulted in a decrease to net cash provided by operating activities totaling approximately $2.3 million , an increase to net cash used in investing activities totaling approximately $8.3 million , no change to net cash used in financing activities, and a corresponding increase to the net decrease in cash and cash equivalents and cash held in escrows totaling approximately $10.6 million from amounts previously reported for the year ended December 31, 2016. Cash held in escrows include amounts established pursuant to various agreements for security deposits, property taxes, insurance and other costs. Cash held in escrows also include cash held by qualified intermediaries for possible investments in like-kind exchanges in accordance with Section 1031 of the Internal Revenue Code of 1986, as amended, in connection with sales of the Company’s properties. Business Combinations In January 2017, the FASB issued ASU 2017-01, “Business Combinations (Topic 805): Clarifying the Definition of a Business” (“ASU 2017-01”). ASU 2017-01 clarifies the framework for determining whether an integrated set of assets and activities meets the definition of a business. The revised framework establishes a screen for determining whether an integrated set of assets and activities is a business and narrows the definition of a business, which is expected to result in fewer transactions being accounted for as business combinations. Acquisitions of integrated sets of assets and activities that do not meet the definition of a business are accounted for as asset acquisitions. This update is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2017, with early adoption permitted for transactions that have not been reported in previously issued (or available to be issued) financial statements and shall be applied on a prospective basis. The Company early adopted ASU 2017-01 during the first quarter of 2017. The Company expects that acquisitions of real estate or in-substance real estate will not meet the revised definition of a business because substantially all of the fair value is concentrated in a single identifiable asset or group of similar identifiable assets (i.e. land, buildings, and related intangible assets) or because the acquisition does not include a substantive process in the form of an acquired workforce or an acquired contract that cannot be replaced without significant cost, effort or delay. Sales of Real Estate In February 2017, the FASB issued ASU No. 2017-05, “Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets (Subtopic 610-20): Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets” (“ASU 2017-05”). ASU 2017-05 updates the definition of an “in substance nonfinancial asset” and clarifies the derecognition guidance for nonfinancial assets to conform with the new revenue recognition standard. The effective date and transition methods of ASU 2017-05 are aligned with ASU 2014-09 described above and were effective for the first interim period within annual reporting periods beginning after December 15, 2017. The Company adopted ASU 2017-05 effective January 1, 2018 using the modified retrospective approach. The adoption of ASU 2017-05 did not have a material impact on the Company's consolidated financial statements. See also Note 3. Stock Compensation In May 2017, the FASB issued ASU 2017-09, “Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting” (“ASU 2017-09”). ASU 2017-09 is intended to provide clarity and reduce (1) diversity in practice, (2) cost and (3) complexity when applying the guidance in Topic 718 to a change to the terms or conditions of a share-based payment award. ASU 2017-09 was effective for public entities for fiscal years and interim periods beginning after December 15, 2017. The Company adopted ASU 2017-09 effective January 1, 2018. The adoption of ASU 2017-09 did not have a material impact on the Company's consolidated financial statements. Derivatives and Hedging In August 2017, the FASB issued ASU 2017-12, “Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities” (“ASU 2017-12”). ASU 2017-12 was issued with the objective of improving the financial reporting of hedging relationships to better portray the economic results of an entity’s risk management activities in its financial statements. ASU 2017-12 also makes certain targeted improvements to simplify the application of the hedge accounting guidance. ASU 2017-12 is effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. Early adoption is permitted. The Company early adopted ASU 2017-12 effective January 1, 2018. The adoption of ASU 2017-12 did not have a material impact on the Company's consolidated financial statements. As of December 31, 2018, the Company does not have any outstanding hedges, but continues to reclassify into earnings as an increase primarily to interest expense approximately $1.7 million per quarter relating to previously settled interest rate contracts. New Accounting Pronouncements Issued but not yet Adopted Leases In February 2016, the FASB issued ASU 2016-02, “Leases (Topic 842)” (“ASU 2016-02”), which sets out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e., lessees and lessors). ASU 2016-02 requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase of the leased asset by the lessee. This classification will determine whether the lease expense is recognized based on an effective interest method or on a straight-line basis over the term of the lease. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less will be accounted for similar to existing guidance for operating leases today. The new standard requires lessors to account for leases using an approach that is substantially equivalent to existing guidance for sales-type leases, direct financing leases and operating leases. ASU 2016-02 supersedes previous leasing standards. On July 30, 2018, the FASB issued ASU 2018-11, “Leases (Topic 842): Targeted Improvements” (“ASU 2018-11”), that (1) simplifies transition requirements for both lessees and lessors by adding an option that permits an organization to apply the transition provisions of the new standard at its adoption date instead of at the earliest comparative period presented in its financial statements and (2) allows lessors to elect, as a practical expedient, by class of underlying asset, to not separate nonlease components from the associated lease component and, instead, to account for those components as a single component if the nonlease components otherwise would be accounted for under the new revenue guidance (ASC 606) and both of the following are met: (1) the timing and pattern of transfer of the nonlease component(s) and associated lease components are the same; and (2) the lease component, if accounted for separately, would be classified as an operating lease. If the nonlease component or components associated with the lease component are the predominant component of the combined component, an entity is required to account for the combined component in accordance with ASC 606. Certain disclosures are required if applying this practical expedient. ASU 2016-02 is effective for the Company for reporting periods beginning after December 15, 2018, with early adoption permitted. The Company adopted ASU 2016-02 and ASU 2018-11 effective January 1, 2019. For purposes of transition, the Company did not elect the hindsight practical expedient but did elect the practical expedient package, which has been applied consistently to all of its leases. The practical expedient package did not require the Company to reassess the following: (i) whether an expired or existing contract meets the definition of a lease; (ii) the lease classification at the adoption date for existing leases; and (iii) whether costs previously capitalized as initial direct costs would continue to be amortized. This allows the Company to continue to account for its ground leases as operating leases, however, any new or renewed ground leases may be classified as financing leases unless they meet certain conditions. The Company does expect to record an adjustment to the opening balance of retained earnings of approximately $4.0 million related to initial direct costs that, as of January 1, 2019, had not started to amortize and would no longer be allowed to be capitalized in accordance with ASC 842. Lessor perspective - ASU 2018-11 provides lessors a practical expedient to not separate nonlease components from the associated lease component if certain criteria stated above are met. The Company assessed these criteria and concluded that the timing and pattern of transfer for nonlease components and the associated lease component are the same. The Company determined that the predominate component was the lease component and as such the leases will continue to qualify as operating leases and the Company will account for and present the lease component and the nonlease component as a single component on its Consolidated Statements of Operations beginning with the Quarterly Report on Form 10-Q for the period ending March 31, 2019. In addition, under ASU 2016-02, lessors will only capitalize incremental direct leasing costs. As a result, the Company will no longer be able to capitalize non-incremental legal costs and internal leasing wages and instead will be required to expense these and other non-incremental costs as incurred. Lessee perspective - For leases in which the Company is the lessee, primarily consisting of ground leases, the Company will recognize a right-of-use asset and a lease liability equal to the present value of the minimum lease payments in accordance with the prior lease accounting guidance. From a lessee perspective, the adoption on January 1, 2019 will result in the recognition of a right-of-use (“ROU”) asset and lease liability for four leases of approximately $148.8 million and $199.7 million , respectively. A ROU asset and lease liability will be presented on the Company’s Consolidated Balance Sheets beginning with the Quarterly Report on Form 10-Q for the period ending March 31, 2019. The adoption of this standard will also result in additional quantitative and qualitative footnote disclosures beginning with the Quarterly Report on Form 10-Q for the period ending March 31, 2019. In January 2018, the FASB issued ASU 2018-01, “Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842” (“ASU 2018-01”), which provides an optional transition practical expedient to not evaluate under Topic 842 existing or expired land easements that were not previously accounted for as leases under the current leases guidance in Topic 840. An entity that elects this practical expedient should evaluate new or modified land easements under Topic 842 beginning at the date that the entity adopts Topic 842. An entity that does not elect this practical expedient should evaluate all existing or expired land easements in connection with the adoption of the new lease requirements in Topic 842 to assess whether they meet the definition of a lease. The effective date and transition requirements for ASU 2018-01 are the same as the effective date and transition requirements in ASU 2016-02. The Company adopted ASU 2018-01 on January 1, 2019. The Company elected to utilize the practical expedient and has created procedures and controls to monitor new or modified land easements. Financial Instruments - Credit Losses In June 2016, the FASB issued ASU 2016-13, “Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments” (“ASU 2016-13”). ASU 2016-13 is intended to provide financial statement users with more decision-useful information about the expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date. To achieve this objective, ASU 2016-13 replaces the current incurred loss impairment methodology with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. ASU 2016-13 is effective for the Company for reporting periods beginning after December 15, 2019, with early adoption permitted. The Company is assessing the potential impact that the adoption of ASU 2016-13 will have on its consolidated financial statements. In November 2018, the FASB issued ASU 2018-19, “Codification Improvements to Topic 326, Financial Instruments - Credit Losses” (“ASU 2018-19”). ASU 2018-19 clarifies that receivables arising from operating leases are not within the scope of ASC 326-20, “Financial Instruments - Credit Losses - Measured at Amortized Cost,” which includes financial assets measured at amortized cost basis, including net investments in leases arising from sales-type and direct financing leases. Instead, impairment of receivables arising from operating leases should be accounted for in accordance with ASC 842, “Leases.” ASU 2018-19 is effective for the Company for reporting periods beginning after December 15, 2019, with early adoption permitted. The Company is assessing the potential impact that the adoption of ASU 2018-19 will have on its consolidated financial statements. Fair Value Measurement In August 2018, the FASB issued ASU 2018-13, “Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement” (“ASU 2018-13”). ASU 2018-13 is intended to improve the effectiveness of disclosures required by entities regarding recurring and nonrecurring fair value measurements. ASU 2018-13 is effective for the Company for reporting periods beginning after December 15, 2019, with early adoption permitted. The adoption of ASU 2018-13 will not have a material impact on the Company's consolidated financial statements. Derivatives and Hedging In October 2018, the FASB issued ASU 2018-16, “Derivatives and Hedging (Topic 815): Inclusion of the Secured Overnight Financing Rate (SOFR) Overnight Index Swap (OIS) Rate as a Benchmark Interest Rate for Hedge Accounting Purposes” (“ASU 2018-16”). ASU 2018-16 permits the use of the overnight index swap rate based on the Secured Overnight Financing Rate (“SOFR”) to be used as a U.S. benchmark interest rate for purposes of applying hedge accounting under ASC 815. ASU 2018-16 is effective for the Company, which has already adopted ASU 2017-12, for reporting periods beginning after December 15, 2018 and is required to be adopted on a prospective basis for qualifying new or re-designated hedging relationships entered into on or after the date of adoption. The adoption of ASU 2018-16 will not have a material impact on the Company's consolidated financial statements. Consolidation In October 2018, the FASB issued ASU 2018-17, “Consolidation (Topic 810): Targeted Improvements to Related Party Guidance for Variable Interest Entities” (“ASU 2018-17”). ASU 2018-17 is intended to improve the accounting when considering indirect interests held through related parties under common control for determining whether fees paid to decision makers and service providers are variable interests. ASU 2018-17 is effective for the Company for reporting periods beginning after December 15, 2019, with early adoption permitted. The Company is assessing the potential impact that the adoption of ASU 2018-17 will have on its consolidated financial statements.
Equity Offering Costs	Equity Offering Costs Underwriting commissions and offering costs have been reflected as a reduction of additional paid-in capital.
Treasury Stock	Treasury Stock Boston Properties, Inc.’s share repurchases are reflected as treasury stock utilizing the cost method of accounting and are presented as a reduction to consolidated stockholders’ equity.
Dividends	Dividends Earnings and profits, which determine the taxability of dividends to stockholders, will differ from income reported for financial reporting purposes due to the differences for federal income tax purposes in the treatment of gains/losses on the sale of real property, revenue and expense recognition, compensation expense, and in the estimated useful lives and basis used to compute depreciation. The tax treatment of common dividends per share for federal income tax purposes is as follows: For the year ended December 31, 2018 2017 2016 Per Share % Per Share % Per Share % Ordinary income $ 2.79 78.17 % $ 2.86 98.29 % $ 2.76 90.51 % Capital gain income 0.78 21.83 % 0.05 1.71 % 0.29 9.49 % Total $ 3.57 (1) 100.00 % $ 2.91 (2) 100.00 % $ 3.05 (3) 100.00 % _____________ (1) The fourth quarter 2018 regular quarterly dividend was $0.95 per common share of which approximately $0.69 per common share was allocable to 2018 and approximately $0.26 per common share is allocable to 2019. (2) The fourth quarter 2017 regular quarterly dividend was $0.80 per common share of which approximately $0.47 per common share was allocable to 2017 and approximately $0.33 per common share is allocable to 2018. (3) The fourth quarter 2016 regular quarterly dividend was $0.75 per common share of which approximately $0.56 per common share was allocable to 2016 and approximately $0.19 per common share is allocable to 2017.
Income Taxes	Income Taxes Boston Properties, Inc. has elected to be treated as a REIT under Sections 856 through 860 of the Internal Revenue Code of 1986, as amended (the “Code”), commencing with its taxable year ended December 31, 1997. As a result, it generally will not be subject to federal corporate income tax on its taxable income that is distributed to its stockholders. A REIT is subject to a number of organizational and operational requirements, including a requirement that it currently distribute at least 90% of its annual taxable income (with certain adjustments). Boston Properties, Inc.’s policy is to distribute at least 100% of its taxable income. Accordingly, the only provision for federal income taxes in the accompanying consolidated financial statements relates to Boston Properties, Inc.’s consolidated taxable REIT subsidiaries. Boston Properties, Inc.’s taxable REIT subsidiaries did not have significant tax provisions or deferred income tax items. Boston Properties, Inc. has no uncertain tax positions recognized as of December 31, 2018 and 2017 . The Company owns a hotel property that it leases to one of its taxable REIT subsidiaries and that is managed by Marriott International, Inc. The hotel taxable REIT subsidiary, a wholly owned subsidiary of Boston Properties Limited Partnership, is the lessee pursuant to the lease for the hotel property. As lessor, Boston Properties Limited Partnership is entitled to a percentage of gross receipts from the hotel property. Marriott International, Inc. continues to manage the hotel property under the Marriott name and under terms of the existing management agreement. The hotel taxable REIT subsidiary is subject to tax at the federal and state level and, accordingly, Boston Properties, Inc. has recorded a tax provision in its Consolidated Statements of Operations for the years ended December 31, 2018 , 2017 and 2016 . Certain entities included in Boston Properties, Inc.’s consolidated financial statements are subject to certain state and local taxes. These taxes are recorded as operating expenses in the accompanying consolidated financial statements. Boston Properties Limited Partnership Income Taxes The partners are required to report their respective share of Boston Properties Limited Partnership’s taxable income or loss on their respective tax returns and are liable for any related taxes thereon. Accordingly, the only provision for federal income taxes in the accompanying consolidated financial statements relates to Boston Properties Limited Partnership’s consolidated taxable REIT subsidiaries. Boston Properties Limited Partnership’s taxable REIT subsidiaries did not have significant tax provisions or deferred income tax items. Boston Properties Limited Partnership has no uncertain tax positions recognized as of December 31, 2018 and 2017 . The Company owns a hotel property which is managed through a taxable REIT subsidiary. The hotel taxable REIT subsidiary, a wholly owned subsidiary Boston Properties Limited Partnership, is the lessee pursuant to the lease for the hotel property. As lessor, Boston Properties Limited Partnership is entitled to a percentage of gross receipts from the hotel property. Marriott International, Inc. continues to manage the hotel property under the Marriott name and under terms of the existing management agreement. The hotel taxable REIT subsidiary is subject to tax at the federal and state level and, accordingly, Boston Properties Limited Partnership has recorded a tax provision in its Consolidated Statements of Operations for the years ended December 31, 2018 , 2017 and 2016 . Certain entities included in Boston Properties Limited Partnership’s consolidated financial statements are subject to certain state and local taxes. These taxes are recorded as operating expenses in the accompanying consolidated financial statements.

Summary Of Significant Accoun_3

Summary Of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items]
Property, Plant and Equipment [Table Text Block]	Depreciation is computed on a straight-line basis over the estimated useful lives of the assets as follows: Land improvements 25 to 40 years Buildings and improvements 10 to 40 years Tenant improvements Shorter of useful life or terms of related lease Furniture, fixtures, and equipment 3 to 7 years
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]	The following table summarizes the scheduled amortization of the Company’s acquired “above-” and “below-market” lease intangibles for each of the five succeeding years (in thousands). Acquired Above-Market Lease Intangibles Acquired Below-Market Lease Intangibles 2019 $ 7,099 $ 27,327 2020 5,394 10,462 2021 2,988 6,348 2022 314 5,669 2023 168 5,558 The following table summarizes the scheduled amortization of the Company’s acquired in-place lease intangibles for each of the five succeeding years (in thousands). Acquired In-Place Lease Intangibles 2019 $ 25,690 2020 13,051 2021 8,610 2022 4,798 2023 4,107
Schedule Of Future Contractual Minimum Lease Payments Under Non-Cancelable Ground Leases [Table Text Block]	The future contractual minimum lease payments to be made by the Company as of December 31, 2018 , under non-cancelable ground leases which expire on various dates through 2114 , are as follows: Years Ending December 31, (in thousands) 2019 $ 11,425 2020 18,425 2021 25,310 2022 8,894 2023 9,084 Thereafter 567,232
Capital Leases in Financial Statements of Lessee Disclosure [Text Block]	Capital Leases The Company has four capital lease obligations with various initial term expiration dates through 2036. The following reflects the gross amount of assets recorded under capital leases by asset class at December 31, 2018 and December 31, 2017 (in thousands): December 31, 2018 2017 Land held for future development $ 12,397 $ — Buildings and improvements 23,636 23,636 Construction in progress 28,962 28,962 Total $ 64,995 $ 52,598 The future minimum lease payments, as of December 31, 2018, related to the four capital leases, through 2036 are as follows: Years Ending December 31, (in thousands) 2019 $ 1,441 2020 12,682 2021 2,123 2022 1,253 2023 944 Thereafter 73,241 Total expected minimum lease payments 91,684 Interest portion (27,497 ) Present value of expected net minimum lease payments $ 64,187
Fair Value, by Balance Sheet Grouping [Table Text Block]	The following table presents the aggregate carrying value of the Company’s related party note receivable, note receivable, mortgage notes payable, net, unsecured senior notes, net, unsecured line of credit and unsecured term loan, net and the Company’s corresponding estimate of fair value as of December 31, 2018 and December 31, 2017 (in thousands): December 31, 2018 December 31, 2017 Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Related party note receivable $ 80,000 $ 80,000 $ — $ — Note receivable 19,468 19,468 — — Total $ 99,468 $ 99,468 $ — $ — Mortgage notes payable, net $ 2,964,572 $ 2,903,925 $ 2,979,281 $ 3,042,920 Unsecured senior notes, net 7,544,697 7,469,338 7,247,330 7,461,615 Unsecured line of credit — — 45,000 45,000 Unsecured term loan, net 498,488 500,783 — — Total $ 11,007,757 $ 10,874,046 $ 10,271,611 $ 10,549,535
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes, Table [Table Text Block]	The tax treatment of common dividends per share for federal income tax purposes is as follows: For the year ended December 31, 2018 2017 2016 Per Share % Per Share % Per Share % Ordinary income $ 2.79 78.17 % $ 2.86 98.29 % $ 2.76 90.51 % Capital gain income 0.78 21.83 % 0.05 1.71 % 0.29 9.49 % Total $ 3.57 (1) 100.00 % $ 2.91 (2) 100.00 % $ 3.05 (3) 100.00 % _____________ (1) The fourth quarter 2018 regular quarterly dividend was $0.95 per common share of which approximately $0.69 per common share was allocable to 2018 and approximately $0.26 per common share is allocable to 2019. (2) The fourth quarter 2017 regular quarterly dividend was $0.80 per common share of which approximately $0.47 per common share was allocable to 2017 and approximately $0.33 per common share is allocable to 2018. (3) The fourth quarter 2016 regular quarterly dividend was $0.75 per common share of which approximately $0.56 per common share was allocable to 2016 and approximately $0.19 per common share is allocable to 2017.

Real Estate (Tables)

Real Estate (Tables)	12 Months Ended
	Dec. 31, 2018
Real Estate Properties [Line Items]
Schedule of Property Subject to or Available for Operating Lease	Boston Properties, Inc. Real estate consisted of the following at December 31, 2018 and December 31, 2017 (in thousands): 2018 2017 Land $ 5,072,568 $ 5,080,679 Land held for future development (1) 200,498 204,925 Buildings and improvements 13,356,751 12,284,164 Tenant improvements 2,396,932 2,219,608 Furniture, fixtures and equipment 44,351 37,928 Construction in progress 578,796 1,269,338 Total 21,649,896 21,096,642 Less: Accumulated depreciation (4,897,777 ) (4,589,634 ) $ 16,752,119 $ 16,507,008 _______________ (1) Includes pre-development costs. Boston Properties Limited Partnership Real estate consisted of the following at December 31, 2018 and December 31, 2017 (in thousands): 2018 2017 Land $ 4,971,475 $ 4,976,303 Land held for future development (1) 200,498 204,925 Buildings and improvements 13,059,488 11,977,062 Tenant improvements 2,396,932 2,219,608 Furniture, fixtures and equipment 44,351 37,928 Construction in progress 578,796 1,269,338 Total 21,251,540 20,685,164 Less: Accumulated depreciation (4,800,475 ) (4,496,959 ) $ 16,451,065 $ 16,188,205 _______________ (1) Includes pre-development costs.
Platform 16
Real Estate Properties [Line Items]
Schedule of Future Minimum Lease Payments for Capital Leases [Table Text Block]	As of November 29, 2018, future minimum lease payments related to the recognized portion of the capital lease are as follows (in thousands): Period from November 29, 2018 through December 31, 2018 $ 1,385 2019 427 2020 11,132 Total expected minimum lease payments 12,944 Interest portion (547 ) Present value of expected net minimum lease payments $ 12,397

Deferred Charges (Tables)

Deferred Charges (Tables)	12 Months Ended
	Dec. 31, 2018
Deferred Charges [Abstract]
Deferred Charges	Deferred charges consisted of the following at December 31, 2018 and December 31, 2017 (in thousands): 2018 2017 Leasing costs, including lease related intangibles $ 1,191,297 $ 1,147,181 Financing costs 12,796 14,991 1,204,093 1,162,172 Less: Accumulated amortization (525,369 ) (483,134 ) $ 678,724 $ 679,038
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]	The following table summarizes the scheduled amortization of the Company’s acquired “above-” and “below-market” lease intangibles for each of the five succeeding years (in thousands). Acquired Above-Market Lease Intangibles Acquired Below-Market Lease Intangibles 2019 $ 7,099 $ 27,327 2020 5,394 10,462 2021 2,988 6,348 2022 314 5,669 2023 168 5,558 The following table summarizes the scheduled amortization of the Company’s acquired in-place lease intangibles for each of the five succeeding years (in thousands). Acquired In-Place Lease Intangibles 2019 $ 25,690 2020 13,051 2021 8,610 2022 4,798 2023 4,107

Investments in Unconsolidated_2

Investments in Unconsolidated Joint Ventures (Tables)	12 Months Ended
	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Investments In Unconsolidated Joint Ventures	The investments in unconsolidated joint ventures consist of the following at December 31, 2018 and 2017 : Carrying Value of Investment (1) Entity Properties Nominal % Ownership December 31, December 31, (in thousands) Square 407 Limited Partnership Market Square North 50.0 % $ (6,424 ) $ (8,258 ) The Metropolitan Square Associates LLC Metropolitan Square 20.0 % 2,644 3,339 BP/CRF 901 New York Avenue LLC 901 New York Avenue 25.0 % (2) (13,640 ) (13,811 ) WP Project Developer LLC Wisconsin Place Land and Infrastructure 33.3 % (3) 38,214 39,710 Annapolis Junction NFM LLC Annapolis Junction 50.0 % (4) 25,268 18,381 540 Madison Venture LLC 540 Madison Avenue 60.0 % 66,391 66,179 500 North Capitol Venture LLC 500 North Capitol Street, NW 30.0 % (5,026 ) (3,876 ) 501 K Street LLC 1001 6th Street 50.0 % (5) 42,557 42,657 Podium Developer LLC The Hub on Causeway - Podium 50.0 % 69,302 67,120 Residential Tower Developer LLC The Hub on Causeway - Residential 50.0 % 47,505 28,212 Hotel Tower Developer LLC The Hub on Causeway - Hotel Air Rights 50.0 % 3,022 1,690 Office Tower Developer LLC 100 Causeway Street 50.0 % (6) 23,804 — 1265 Main Office JV LLC 1265 Main Street 50.0 % 3,918 4,641 BNY Tower Holdings LLC Dock 72 50.0 % 82,520 72,104 CA-Colorado Center Limited Partnership Colorado Center 50.0 % 253,495 254,440 7750 Wisconsin Avenue LLC 7750 Wisconsin Avenue 50.0 % (6) 69,724 21,452 BP-M 3HB Venture LLC 3 Hudson Boulevard 25.0 % 46,993 — SMBP Venture LP Santa Monica Business Park 55.0 % 180,952 — $ 931,219 $ 593,980 _______________ (1) Investments with deficit balances aggregating approximately $25.1 million and $25.9 million at December 31, 2018 and 2017 , respectively, are included within Other Liabilities in the Company’s Consolidated Balance Sheets. (2) The Company’s economic ownership has increased based on the achievement of certain return thresholds. (3) The Company’s wholly-owned subsidiary that owns Wisconsin Place Office also owns a 33.3% interest in the joint venture entity that owns the land, parking garage and infrastructure of the project. (4) The joint venture owns three in-service buildings and two undeveloped land parcels. (5) Under the joint venture agreement for this land parcel, the partner will be entitled to up to two additional payments from the venture based on increases in total entitled square footage of the project above 520,000 square feet and achieving certain project returns at stabilization. (6) This entity is a VIE (See Note 1 ).
Schedule Of Balance Sheets Of The Unconsolidated Joint Ventures [Text Block]	The combined summarized balance sheets of the Company’s unconsolidated joint ventures are as follows: December 31, December 31, (in thousands) ASSETS Real estate and development in process, net $ 3,545,906 $ 1,768,996 Other assets 543,512 367,743 Total assets $ 4,089,418 $ 2,136,739 LIABILITIES AND MEMBERS’/PARTNERS’ EQUITY Mortgage and notes payable, net $ 2,017,609 $ 1,437,440 Other liabilities 582,006 99,215 Members’/Partners’ equity 1,489,803 600,084 Total liabilities and members’/partners’ equity $ 4,089,418 $ 2,136,739 Company’s share of equity $ 622,498 $ 286,495 Basis differentials (1) 308,721 307,485 Carrying value of the Company’s investments in unconsolidated joint ventures (2) $ 931,219 $ 593,980 _______________ (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 result from impairments of investments, acquisitions through joint ventures with no change in control 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. At December 31, 2018 and 2017 , there was an aggregate basis differential of approximately $316.7 million and $322.5 million , respectively, between the carrying value of the Company’s investment in the joint venture that owns Colorado Center and the joint venture’s basis in the assets and liabilities, which differential (excluding land) shall be amortized over the remaining lives of the related assets and liabilities. (2) Investments with deficit balances aggregating approximately $25.1 million and $25.9 million at December 31, 2018 and 2017 , respectively, have been reflected within Other Liabilities in the Company’s Consolidated Balance Sheets.
Statements Of Operations Of The Joint Ventures	The combined summarized statements of operations of the Company’s unconsolidated joint ventures are as follows: For the year ended December 31, 2018 2017 2016 (in thousands) Total revenue (1) $ 271,951 $ 222,517 $ 177,182 Expenses Operating 106,610 90,542 76,741 Depreciation and amortization (2) 103,079 57,079 44,989 Total expenses 209,689 147,621 121,730 Other income (expense) Interest expense (71,308 ) (46,371 ) (34,016 ) Gain on sale of real estate 16,951 — — Net income $ 7,905 $ 28,525 $ 21,436 Company’s share of net income $ 8,084 $ 18,439 $ 9,873 Basis differential (3) (5,862 ) (7,207 ) (1,799 ) Income from unconsolidated joint ventures $ 2,222 $ 11,232 $ 8,074 Gain on sale of investment in unconsolidated joint venture $ — $ — $ 59,370 _______________ (1) Includes straight-line rent adjustments of approximately $15.9 million , $21.7 million and $18.1 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. (2) During the year ended December 31, 2018, the joint venture that owns Metropolitan Square in Washington, DC, commenced a renovation project and recorded accelerated depreciation expense of approximately $22.4 million related to the remaining book value of the assets to be replaced. The Company's share of the accelerated depreciation expense totaled approximately $4.5 million . (3) Includes straight-line rent adjustments of approximately $2.4 million , $1.9 million and $1.4 million for the years ended December 31, 2018, 2017 and 2016, respectively. Also includes net above-/below-market rent adjustments of approximately $1.6 million , $2.9 million and $0.9 million for the years ended December 31, 2018, 2017 and 2016, respectively.
Santa Monica Business Park [Member]
Schedule of Equity Method Investments [Line Items]
Schedule of Asset Acquistion [Table Text Block]	The following table summarizes the allocation of the joint venture's aggregate purchase price for Santa Monica Business Park at the date of acquisition (in thousands). Land and improvements $ 100,453 Leasehold interest in land 248,944 Site improvements 13,379 Building and improvements 593,669 Tenant improvements 31,329 In-place lease intangibles 47,955 Above-market lease intangible 4,495 Below-market lease intangible (17,503 ) Capital lease obligation (396,008 ) Net assets acquired $ 626,713

Mortgage Notes Payable, Net Sch

Mortgage Notes Payable, Net Schedule of Aggregate Principal Payments On Mortgage Notes (Tables)	12 Months Ended
	Dec. 31, 2018
Mortgage Notes Payable [Abstract]
Schedule of Aggregate Principal Payments On Mortgage Notes [Table Text Block]	Contractual aggregate principal payments of mortgage notes payable at December 31, 2018 are as follows (in thousands): Principal Payments 2019 $ 19,670 2020 20,766 2021 40,182 2022 614,710 2023 — Thereafter 2,300,000 Total aggregate principal payments 2,995,328 Deferred financing costs, net (30,756 ) Total carrying value of mortgage notes payable, net $ 2,964,572

Unsecured Senior Notes (Tables)

Unsecured Senior Notes (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of Senior Notes	The following summarizes the unsecured senior notes outstanding as of December 31, 2018 (dollars in thousands): Coupon/ Stated Rate Effective Rate(1) Principal Amount Maturity Date(2) 10 Year Unsecured Senior Notes 5.625 % 5.708 % $ 700,000 November 15, 2020 10 Year Unsecured Senior Notes 4.125 % 4.289 % 850,000 May 15, 2021 11 Year Unsecured Senior Notes 3.850 % 3.954 % 1,000,000 February 1, 2023 10.5 Year Unsecured Senior Notes 3.125 % 3.279 % 500,000 September 1, 2023 10.5 Year Unsecured Senior Notes 3.800 % 3.916 % 700,000 February 1, 2024 7 Year Unsecured Senior Notes 3.200 % 3.350 % 850,000 January 15, 2025 10 Year Unsecured Senior Notes 3.650 % 3.766 % 1,000,000 February 1, 2026 10 Year Unsecured Senior Notes 2.750 % 3.495 % 1,000,000 October 1, 2026 10 Year Unsecured Senior Notes 4.500 % 4.628 % 1,000,000 December 1, 2028 Total principal 7,600,000 Net unamortized discount (18,722 ) Deferred financing costs, net (36,581 ) Total $ 7,544,697 _______________ (1) Yield on issuance date including the effects of discounts on the notes, settlements of interest rate contracts and the amortization of financing costs. (2) No principal amounts are due prior to maturity.

Noncontrolling Interests (Table

Noncontrolling Interests (Tables)	12 Months Ended
	Dec. 31, 2018
Entity Information [Line Items]
Dividends Declared [Table Text Block]	The following table presents Boston Properties, Inc.’s dividends per share and Boston Properties Limited Partnership’s distributions per OP Unit and LTIP Unit paid or payable in 2018 : Record Date Payment Date Dividend (Per Share) Distribution (Per Unit) December 31, 2018 January 30, 2019 $0.95 $0.95 September 28, 2018 October 31, 2018 $0.95 $0.95 June 29, 2018 July 31, 2018 $0.80 $0.80 March 29, 2018 April 30, 2018 $0.80 $0.80 December 29, 2017 January 30, 2018 $0.80 $0.80
Schedule Of Noncontrolling Interest Property Partnerships [Table Text Block]	The following table reflects the activity of the noncontrolling interests—property partnerships for the years ended December 31, 2018 , 2017 and 2016 (in thousands): Balance at December 31, 2015 $ 1,574,400 Capital contributions 10,756 Net loss (2,068 ) Accumulated other comprehensive loss (877 ) Distributions (51,564 ) Balance at December 31, 2016 1,530,647 Capital contributions (1) 161,585 Net income 47,832 Accumulated other comprehensive loss (2,128 ) Distributions (54,176 ) Balance at December 31, 2017 1,683,760 Capital contributions 46,701 Net income 62,909 Accumulated other comprehensive income 576 Distributions (82,501 ) Balance at December 31, 2018 $ 1,711,445
Boston Properties Limited Partnership
Entity Information [Line Items]
Schedule Of Noncontrolling Interest Common Units [Table Text Block]	The following table reflects the activity of noncontrolling interests—redeemable common units of Boston Properties Limited Partnership for the years ended December 31, 2018 , 2017 and 2016 (in thousands): Balance at December 31, 2015 $ 2,286,689 Contributions 31,395 Net income 59,260 Distributions (49,087 ) Conversion of redeemable partnership units (6,461 ) Unearned compensation (3,464 ) Other comprehensive loss (4,379 ) Adjustment to reflect redeemable partnership units at redemption value (51,913 ) Balance at December 31, 2016 2,262,040 Contributions 31,743 Net income 52,210 Distributions (54,494 ) Conversion of redeemable partnership units (16,916 ) Unearned compensation 1,650 Cumulative effect of a change in accounting principle (1,763 ) Other comprehensive income 206 Adjustment to reflect redeemable partnership units at redemption value 17,587 Balance at December 31, 2017 2,292,263 Contributions 34,680 Net income 66,807 Distributions (62,731 ) Conversion of redeemable partnership units (2,880 ) Unearned compensation 2,181 Cumulative effect of a change in accounting principle 563 Other comprehensive income 304 Adjustment to reflect redeemable partnership units at redemption value (330,596 ) Balance at December 31, 2018 $ 2,000,591
Noncontrolling Interests [Member]
Entity Information [Line Items]
Dividends Declared [Table Text Block]	The following table presents Boston Properties Limited Partnership’s distributions on the OP Units and LTIP Units (including the 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units and, after the February 4, 2018 measurement date, the 2015 MYLTIP Units) and its distributions on the 2015 MYLTIP Units (prior to the February 4, 2018 measurement date), 2016 MYLTIP Units, 2017 MYLTIP Units and 2018 MYLTIP Units (after the February 5, 2018 issuance date) paid in 2018: Record Date Payment Date Distributions per OP Unit and LTIP Unit Distributions per MYLTIP Unit December 31, 2018 January 30, 2019 $0.95 $0.095 September 28, 2018 October 31, 2018 $0.95 $0.095 June 29, 2018 July 31, 2018 $0.80 $0.080 March 29, 2018 April 30, 2018 $0.80 $0.080 December 29, 2017 January 30, 2018 $0.80 $0.080

Stockholders' Equity _ Partne_2

Stockholders' Equity / Partners' Capital (Tables)	12 Months Ended
	Dec. 31, 2018
Class of Stock [Line Items]
Dividends Declared [Table Text Block]	The following table presents Boston Properties, Inc.’s dividends per share and Boston Properties Limited Partnership’s distributions per OP Unit and LTIP Unit paid or payable in 2018 : Record Date Payment Date Dividend (Per Share) Distribution (Per Unit) December 31, 2018 January 30, 2019 $0.95 $0.95 September 28, 2018 October 31, 2018 $0.95 $0.95 June 29, 2018 July 31, 2018 $0.80 $0.80 March 29, 2018 April 30, 2018 $0.80 $0.80 December 29, 2017 January 30, 2018 $0.80 $0.80
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Dividends Declared [Table Text Block]	The following table presents Boston Properties Inc.’s dividends per share on its outstanding Series B Preferred Stock paid or payable in 2018 : Record Date Payment Date Dividend (Per Share) February 4, 2019 February 15, 2019 $32.8125 November 2, 2018 November 15, 2018 $32.8125 August 3, 2018 August 15, 2018 $32.8125 May 4, 2018 May 15, 2018 $32.8125 February 2, 2018 February 15, 2018 $32.8125
Boston Properties Limited Partnership
Class of Stock [Line Items]
Schedule Of Changes In Partners Capital Unit [Table Text Block]	The following table presents the changes in the issued and outstanding partners’ capital units since January 1, 2016 : General Partner Units Limited Partner Units Total Partners’ Outstanding at December 31, 2015 1,715,092 151,864,874 153,579,966 Units issued to Boston Properties, Inc. related to Common Stock issued under the Employee Stock Purchase Plan 72 5,623 5,695 Units issued to Boston Properties, Inc. related to Common Stock issued under the Stock Option and Incentive Plan, net 172 13,485 13,657 Units issued to Boston Properties, Inc. related to Common Stock issued in exchange for OP Units 2,407 188,450 190,857 Outstanding at December 31, 2016 1,717,743 152,072,432 153,790,175 Units issued to Boston Properties, Inc. related to Common Stock issued under the Employee Stock Purchase Plan 21 6,296 6,317 Units issued to Boston Properties, Inc. related to Common Stock issued under the Stock Option and Incentive Plan, net 111 33,046 33,157 Units issued to Boston Properties, Inc. related to Common Stock issued in exchange for OP Units 1,665 493,972 495,637 Outstanding at December 31, 2017 1,719,540 152,605,746 154,325,286 Units issued to Boston Properties, Inc. related to Common Stock issued under the Employee Stock Purchase Plan 132 6,136 6,268 Units issued to Boston Properties, Inc. related to Common Stock issued under the Stock Option and Incentive Plan, net 919 42,869 43,788 Units issued to Boston Properties, Inc. related to Common Stock issued in exchange for OP Units 1,745 81,391 83,136 Outstanding at December 31, 2018 1,722,336 152,736,142 154,458,478
Schedule of Changes in Series B Preferred Units [Table Text Block]	The following table reflects the activity of the Series B Preferred Units for the years ended December 31, 2018 , 2017 and 2016 (in thousands), which activity is included within Boston Properties Limited Partnership’s Consolidated Statements of Partners’ Capital: Balance at December 31, 2015 $ 193,623 Net income 10,500 Distributions (10,500 ) Balance at December 31, 2016 193,623 Net income 10,500 Distributions (10,500 ) Balance at December 31, 2017 193,623 Net income 10,500 Distributions (10,500 ) Balance at December 31, 2018 $ 193,623

Future Minimum Rents (Tables)

Future Minimum Rents (Tables)	12 Months Ended
	Dec. 31, 2018
Future Minimum Rents [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]	The future contractual minimum lease payments to be received (excluding operating expense reimbursements) by the Company as of December 31, 2018 , under non-cancelable operating leases which expire on various dates through 2049 , are as follows: Years Ending December 31, (in thousands) 2019 $ 2,088,171 2020 2,106,963 2021 2,015,031 2022 1,838,699 2023 1,736,636 Thereafter 12,295,464

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Schedule Of Reconciliation Of Net Operating Income To Net Income	Boston Properties, Inc. Year ended December 31, 2018 2017 2016 (in thousands) Net income attributable to Boston Properties, Inc. common shareholders $ 572,347 $ 451,939 $ 502,285 Add: Preferred dividends 10,500 10,500 10,500 Noncontrolling interest—common units of the Operating Partnership 66,807 52,210 59,260 Noncontrolling interests in property partnerships 62,909 47,832 (2,068 ) Losses from interest rate contracts — — 140 Interest expense 378,168 374,481 412,849 Impairment losses 11,812 — 1,783 Depreciation and amortization expense 645,649 617,547 694,403 Transaction costs 1,604 668 2,387 Payroll and related costs from management services contracts 9,590 — — General and administrative expense 121,722 113,715 105,229 Less: Gains (losses) from early extinguishments of debt (16,490 ) 496 (371 ) Gains (losses) from investments in securities (1,865 ) 3,678 2,273 Interest and other income 10,823 5,783 7,230 Gains on sales of real estate 182,356 7,663 80,606 Gain on sale of investment in unconsolidated joint venture — — 59,370 Income from unconsolidated joint ventures 2,222 11,232 8,074 Direct reimbursements of payroll and related costs from management services contracts 9,590 — — Development and management services revenue 45,158 34,605 28,284 Net Operating Income $ 1,649,314 $ 1,605,435 $ 1,601,302 Boston Properties Limited Partnership Year ended December 31, 2018 2017 2016 (in thousands) Net income attributable to Boston Properties Limited Partnership common unitholders $ 656,903 $ 512,866 $ 575,341 Add: Preferred distributions 10,500 10,500 10,500 Noncontrolling interests in property partnerships 62,909 47,832 (2,068 ) Losses from interest rate contracts — — 140 Interest expense 378,168 374,481 412,849 Impairment losses 10,181 — 1,783 Depreciation and amortization expense 637,891 609,407 682,776 Transaction costs 1,604 668 2,387 Payroll and related costs from management services contracts 9,590 — — General and administrative expense 121,722 113,715 105,229 Less: Gains (losses) from early extinguishments of debt (16,490 ) 496 (371 ) Gains (losses) from investments in securities (1,865 ) 3,678 2,273 Interest and other income 10,823 5,783 7,230 Gains on sales of real estate 190,716 8,240 82,775 Gain on sale of investment in unconsolidated joint venture — — 59,370 Income from unconsolidated joint ventures 2,222 11,232 8,074 Direct reimbursements of payroll and related costs from management services contracts 9,590 — — Development and management services revenue 45,158 34,605 28,284 Net Operating Income $ 1,649,314 $ 1,605,435 $ 1,601,302
Schedule Of Segment Information By Geographic Area And Property Type	Information by geographic area and property type (dollars in thousands): For the year ended December 31, 2018 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 838,341 $ 959,050 $ 397,180 $ 396,088 $ 2,590,659 Residential 6,694 — — 15,857 22,551 Hotel 49,118 — — — 49,118 Total 894,153 959,050 397,180 411,945 2,662,328 % of Grand Totals 33.59 % 36.02 % 14.92 % 15.47 % 100.00 % Rental Expenses: Office 315,653 377,992 130,016 142,886 966,547 Residential 3,632 — — 8,972 12,604 Hotel 33,863 — — — 33,863 Total 353,148 377,992 130,016 151,858 1,013,014 % of Grand Totals 34.86 % 37.32 % 12.83 % 14.99 % 100.00 % Net operating income $ 541,005 $ 581,058 $ 267,164 $ 260,087 $ 1,649,314 % of Grand Totals 32.80 % 35.23 % 16.20 % 15.77 % 100.00 % For the year ended December 31, 2017 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 776,279 $ 969,371 $ 345,519 $ 414,103 $ 2,505,272 Residential 4,745 — — 11,851 16,596 Hotel 45,603 — — — 45,603 Total 826,627 969,371 345,519 425,954 2,567,471 % of Grand Totals 32.20 % 37.75 % 13.46 % 16.59 % 100.00 % Rental Expenses: Office 301,097 372,810 105,253 144,515 923,675 Residential 2,044 — — 4,258 6,302 Hotel 32,059 — — — 32,059 Total 335,200 372,810 105,253 148,773 962,036 % of Grand Totals 34.84 % 38.76 % 10.94 % 15.46 % 100.00 % Net operating income $ 491,427 $ 596,561 $ 240,266 $ 277,181 $ 1,605,435 % of Grand Totals 30.61 % 37.15 % 14.97 % 17.27 % 100.00 % For the year ended December 31, 2016 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 727,265 $ 1,012,518 $ 318,609 $ 402,561 $ 2,460,953 Residential 4,812 — — 11,887 16,699 Hotel 44,884 — — — 44,884 Total 776,961 1,012,518 318,609 414,448 2,522,536 % of Grand Totals 30.80 % 40.14 % 12.63 % 16.43 % 100.00 % Rental Expenses: Office 282,827 363,188 100,787 135,890 882,692 Residential 2,708 — — 4,368 7,076 Hotel 31,466 — — — 31,466 Total 317,001 363,188 100,787 140,258 921,234 % of Grand Totals 34.41 % 39.42 % 10.94 % 15.23 % 100.00 % Net operating income $ 459,960 $ 649,330 $ 217,822 $ 274,190 $ 1,601,302 % of Grand Totals 28.73 % 40.55 % 13.60 % 17.12 % 100.00 %

Earnings Per Share _ Common U_2

Earnings Per Share / Common Unit (Tables)	12 Months Ended
	Dec. 31, 2018
Entity Information [Line Items]
Computation Of Basic And Diluted Earnings Per Share / Unit	For the Year Ended December 31, 2018 Income (Numerator) Shares (Denominator) Per Share Amount (in thousands, except for per share amounts) Basic Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 572,347 154,427 $ 3.71 Allocation of undistributed earnings to participating securities (101 ) — — Net income attributable to Boston Properties, Inc. common shareholders $ 572,246 154,427 $ 3.71 Effect of Dilutive Securities: Stock Based Compensation — 255 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 572,246 154,682 $ 3.70 For the Year Ended December 31, 2017 Income (Numerator) Shares (Denominator) Per Share Amount (in thousands, except for per share amounts) Basic Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 451,939 154,190 $ 2.93 Effect of Dilutive Securities: Stock Based Compensation — 200 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 451,939 154,390 $ 2.93 For the Year Ended December 31, 2016 Income (Numerator) Shares (Denominator) Per Share Amount (in thousands, except for per share amounts) Basic Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 502,285 153,715 $ 3.27 Allocation of undistributed earnings to participating securities (283 ) — — Net income attributable to Boston Properties, Inc. common shareholders $ 502,002 153,715 $ 3.27 Effect of Dilutive Securities: Stock Based Compensation — 262 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 502,002 153,977 $ 3.26
Boston Properties Limited Partnership
Entity Information [Line Items]
Computation Of Basic And Diluted Earnings Per Share / Unit	Included in the number of units (the denominator) below are approximately 17,485,000 , 17,471,000 and 17,646,000 redeemable common units for the years ended December 31, 2018 , 2017 and 2016 , respectively. For the Year Ended December 31, 2018 Income (Numerator) Units (Denominator) Per Unit Amount (in thousands, except for per unit amounts) Basic Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 656,903 171,912 $ 3.82 Allocation of undistributed earnings to participating securities (113 ) — — Net income attributable to Boston Properties Limited Partnership common unitholders $ 656,790 171,912 $ 3.82 Effect of Dilutive Securities: Stock Based Compensation — 255 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 656,790 172,167 $ 3.81 For the Year Ended December 31, 2017 Income (Numerator) Units (Denominator) Per Unit Amount (in thousands, except for per unit amounts) Basic Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 512,866 171,661 $ 2.99 Effect of Dilutive Securities: Stock Based Compensation — 200 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 512,866 171,861 $ 2.98 For the Year Ended December 31, 2016 Income (Numerator) Units (Denominator) Per Unit Amount (in thousands, except for per unit amounts) Basic Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 575,341 171,361 $ 3.36 Allocation of undistributed earnings to participating securities (316 ) — — Net income attributable to Boston Properties Limited Partnership common unitholders $ 575,025 171,361 $ 3.36 Effect of Dilutive Securities: Stock Based Compensation — 262 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 575,025 171,623 $ 3.35

Stock Option and Incentive Pl_2

Stock Option and Incentive Plan (Tables)	12 Months Ended
	Dec. 31, 2018
Stock Option and Incentive Plan and Stock Purchase Plan [Abstract]
Share-based Compensation, Stock Options, Activity [Table Text Block]	A summary of the status of Boston Properties, Inc.’s stock options as of December 31, 2018 , 2017 and 2016 and changes during the years then ended are presented below: Shares Weighted-Average Exercise Price Outstanding at December 31, 2015 547,129 $ 96.38 Exercised — $ — Outstanding at December 31, 2016 547,129 $ 96.38 Exercised (6,688 ) $ 99.15 Outstanding at December 31, 2017 540,441 $ 96.35 Exercised — $ — Outstanding at December 31, 2018 540,441 $ 96.35
Schedule of Stock Options Outstanding [Table Text Block]	The following table summarizes information about Boston Properties, Inc.’s stock options outstanding at December 31, 2018 : Options Outstanding Options Exercisable Number Outstanding at 12/31/18 Weighted-Average Remaining Contractual Life Exercise Price Number Exercisable at 12/31/18 Exercise Price 118,502 2.1 years $ 86.86 118,502 $ 86.86 54,282 4.3 years $ 95.69 54,282 $ 95.69 202,030 4.1 years $ 98.46 202,030 $ 98.46 165,627 3.1 years $ 100.77 165,627 $ 100.77

Selected Interim Financial In_2

Selected Interim Financial Information (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information [Table Text Block]	Boston Properties, Inc. The tables below reflect Boston Properties, Inc.’s selected quarterly information for the years ended December 31, 2018 and 2017 . 2018 Quarter Ended March 31, June 30, September 30, December 31, (in thousands, except for per share amounts) Total revenue $ 661,151 $ 664,484 $ 686,284 $ 705,157 Net income $ 216,312 $ 160,565 $ 150,445 $ 185,241 Net income attributable to Boston Properties, Inc. common shareholders $ 176,021 $ 128,681 $ 119,118 $ 148,529 Income attributable to Boston Properties, Inc. per share—basic $ 1.14 $ 0.83 $ 0.77 $ 0.96 Income attributable to Boston Properties, Inc. per share—diluted $ 1.14 $ 0.83 $ 0.77 $ 0.96 2017 Quarter Ended March 31, June 30, September 30, December 31, (in thousands, except for per share amounts) Total revenue $ 632,228 $ 656,907 $ 657,712 $ 655,229 Net income $ 115,564 $ 167,010 $ 147,704 $ 132,203 Net income attributable to Boston Properties, Inc. common shareholders $ 97,083 $ 133,709 $ 117,337 $ 103,829 Income attributable to Boston Properties, Inc. per share—basic $ 0.63 $ 0.87 $ 0.76 $ 0.67 Income attributable to Boston Properties, Inc. per share—diluted $ 0.63 $ 0.87 $ 0.76 $ 0.67 Boston Properties Limited Partnership The tables below reflect Boston Properties Limited Partnership’s selected quarterly information for the years ended December 31, 2018 and 2017 . 2018 Quarter Ended March 31, June 30, September 30, December 31, (in thousands, except for per unit amounts) Total revenue $ 661,151 $ 664,484 $ 686,284 $ 705,157 Net income $ 220,766 $ 162,986 $ 153,676 $ 192,884 Net income attributable to Boston Properties Limited Partnership common unitholders $ 200,907 $ 145,961 $ 136,201 $ 173,834 Income attributable to Boston Properties Limited Partnership per unit—basic $ 1.17 $ 0.85 $ 0.79 $ 1.01 Income attributable to Boston Properties Limited Partnership per unit—diluted $ 1.17 $ 0.85 $ 0.79 $ 1.01 2017 Quarter Ended March 31, June 30, September 30, December 31, (in thousands, except for per unit amounts) Total revenue $ 632,228 $ 656,907 $ 657,712 $ 655,229 Net income $ 117,711 $ 169,672 $ 149,658 $ 134,157 Net income attributable to Boston Properties Limited Partnership common unitholders $ 110,662 $ 151,844 $ 132,693 $ 117,667 Income attributable to Boston Properties Limited Partnership per unit—basic $ 0.64 $ 0.88 $ 0.77 $ 0.69 Income attributable to Boston Properties Limited Partnership per unit—diluted $ 0.64 $ 0.88 $ 0.77 $ 0.68

Real Estate and Accumulated D_3

Real Estate and Accumulated Depreciation Real Estate and Accumulated Depreciation (Tables)	12 Months Ended
	Dec. 31, 2018
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate and Accumulated Depreciation, By Property [Table Text Block]	Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2018 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building 767 Fifth Avenue (the General Motors Building) Office New York, NY $ 2,270,534 $ 1,796,252 $ 1,532,654 $ 189,657 $ 1,796,252 $ 1,722,311 $ — $ — $ 3,518,563 $ 271,534 1968 2013 (1) Prudential Center Office Boston, MA — 92,077 948,357 532,802 115,638 1,457,494 104 — 1,573,236 550,109 1965/1993/2002/2016-2017 1998/1999/2000 (1) Embarcadero Center Office San Francisco, CA — 179,697 847,410 368,967 195,987 1,200,087 — — 1,396,074 612,981 1970/1989 1998-1999 (1) 399 Park Avenue Office New York, NY — 339,200 700,358 247,092 354,107 932,543 — — 1,286,650 332,911 1961/2018 2002 (1) Salesforce Tower Office San Francisco, CA — 200,349 919,565 — 200,349 919,565 — — 1,119,914 9,509 2018 2013 (1) 601 Lexington Avenue Office New York, NY 658,792 241,600 494,782 361,985 289,639 637,044 — 171,684 1,098,367 272,936 1977/1997 2001 (1) 200 Clarendon Street and Garage Office Boston, MA — 219,543 667,884 164,073 219,616 822,218 9,666 — 1,051,500 192,137 1976 2010 (1) 250 West 55th Street Office New York, NY — 285,263 603,167 48,642 285,263 651,809 — — 937,072 94,434 2014 2007 (1) 100 Federal Street Office Boston, MA — 131,067 435,954 99,702 131,067 535,656 — — 666,723 105,536 1971-1975/2017 2012 (1) Carnegie Center Office Princeton, NJ — 107,997 389,359 158,752 108,948 543,974 3,186 — 656,108 241,570 1983-2016 1998/1999/2000/2007/2014/2017 (1) Times Square Tower Office New York, NY — 165,413 380,438 94,451 169,193 471,109 — — 640,302 206,067 2004 2000 (1) Atlantic Wharf Office Boston, MA — 63,988 454,537 17,184 63,988 471,721 — — 535,709 116,238 2011 2007 (1) 510 Madison Avenue Office New York, NY — 103,000 253,665 24,992 103,000 278,657 — — 381,657 62,507 2012 2010 (1) Fountain Square Office Reston, VA — 56,853 306,298 3,170 56,853 309,468 — — 366,321 68,390 1986-1990 2012 (1) 599 Lexington Avenue Office New York, NY — 81,040 100,507 174,213 87,852 267,908 — — 355,760 170,678 1986 1997 (1) 680 Folsom Street Office San Francisco, CA — 72,545 219,766 7,829 72,545 227,595 — — 300,140 38,230 2014 2012 (1) 601 Massachusetts Avenue Office Washington, DC — 95,310 165,173 3,900 95,322 169,061 — — 264,383 18,263 2016 2008 (1) South of Market and Democracy Tower Office Reston, VA — 13,603 237,479 12,428 13,687 249,823 — — 263,510 91,072 2008-2009 2003 (1) Bay Colony Corporate Center Office Waltham, MA — 18,789 148,451 77,133 18,789 225,584 — — 244,373 68,903 1985-1989 2011 (1) Gateway Center Office San Francisco, CA — 28,255 139,245 64,831 30,627 201,704 — — 232,331 107,640 1984/1986/2002 1999 (1) 535 Mission Street Office San Francisco, CA — 40,933 148,378 3,259 40,933 151,637 — — 192,570 20,576 2015 2013 (1) 2200 Pennsylvania Avenue Office Washington, DC — — 183,541 4,535 — 188,076 — — 188,076 52,280 2011 2008 (1) Mountain View Research Park Office Mountain View, CA — 95,066 68,373 9,988 95,066 78,361 — — 173,427 17,866 1977-1981/2007-2013 2013 (1) Reservoir Place Office Waltham, MA — 18,605 104,124 45,144 20,108 147,765 — — 167,873 64,683 1955/1987/2017 1997/1998 (1) 1330 Connecticut Avenue Office Washington, DC — 25,982 82,311 36,089 27,135 117,247 — — 144,382 27,535 1984/2018 2004 (1) Kingstowne Towne Center Office Alexandria, VA — 18,021 109,038 2,098 18,062 111,095 — — 129,157 41,469 2003-2006 2007 (1) Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2018 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building One Freedom Square Office Reston, VA — 9,929 84,504 32,256 11,293 115,396 — — 126,689 54,652 2000 2003 (1) Capital Gallery Office Washington, DC — 4,725 29,565 87,231 8,662 112,859 — — 121,521 67,759 1981/2006 2007 (1) Weston Corporate Center Office Weston, MA — 25,753 92,312 (123 ) 25,854 92,088 — — 117,942 26,176 2010 2001 (1) Two Freedom Square Office Reston, VA — 13,930 77,739 23,427 15,420 99,676 — — 115,096 51,291 2001 2003 (1) One and Two Reston Overlook Office Reston, VA — 16,456 66,192 24,181 16,179 90,650 — — 106,829 47,668 1999 2000 (1) 140 Kendrick Street Office Needham, MA — 18,095 66,905 17,553 19,092 83,461 — — 102,553 32,360 2000 2004 (1) Discovery Square Office Reston, VA — 11,198 71,782 17,753 12,533 88,200 — — 100,733 39,574 2001 2003 (1) 355 Main Street Office Cambridge, MA — 18,863 53,346 23,701 21,173 74,737 — — 95,910 23,691 1981/1996/2013 2006 (1) 10 CityPoint Office Waltham, MA — 1,953 85,752 4,515 2,116 90,104 — — 92,220 7,772 2016 1997 (1) 90 Broadway Office Cambridge, MA — 19,104 52,078 18,363 20,785 68,760 — — 89,545 21,302 1983/1998/2013 2006 (1) 230 CityPoint Office Waltham, MA — 13,189 49,823 21,914 13,593 71,333 — — 84,926 26,357 1992 2005 (1) Waltham Weston Corporate Center Office Waltham, MA — 10,385 60,694 11,449 11,097 71,431 — — 82,528 32,739 2003 1999 (1) 77 CityPoint Office Waltham, MA — 13,847 60,383 5,858 13,873 66,215 — — 80,088 25,107 2008 2001 (1) 3625-3635 Peterson Way Office Santa Clara, CA — 63,206 14,879 673 63,206 14,879 673 — 78,758 8,146 1979 2016 (1) 2440 West El Camino Real Office Mountain View, CA — 16,741 51,285 3,411 16,741 54,696 — — 71,437 12,562 1987/2003 2011 (1) 300 Binney Street Office Cambridge, MA — 18,080 51,262 140 18,080 51,402 — — 69,482 9,450 2013 2009 (1) 191 Spring Street Office Lexington, MA — 2,850 59,751 6,235 3,151 65,685 — — 68,836 19,543 1971/1995/2018 1997 (1) Wisconsin Place Office Chevy Chase, MD — — 53,349 14,889 — 68,238 — — 68,238 22,936 2009 2004 (1) Reston Corporate Center Office Reston, VA — 9,135 50,857 6,236 10,148 56,080 — — 66,228 28,315 1984 1998 (1) New Dominion Technology Park, Bldg. Two Office Herndon, VA — 5,584 51,868 4,157 6,510 55,099 — — 61,609 25,421 2004 1998 (1) 255 Main Street Office Cambridge, MA — 134 25,110 29,672 548 54,368 — — 54,916 30,180 1987 1997 (1) 200 West Street Office Waltham, MA — 16,148 24,983 11,120 16,813 35,438 — — 52,251 22,544 1999 1997 (1) New Dominion Technology Park, Bldg. One Office Herndon, VA 29,675 3,880 43,227 3,927 4,583 46,451 — — 51,034 27,542 2001 1998 (1) Sumner Square Office Washington, DC — 624 28,745 19,054 1,478 46,945 — — 48,423 25,384 1985 1999 (1) University Place Office Cambridge, MA 5,571 — 37,091 9,001 390 45,702 — — 46,092 27,871 1985 1998 (1) 2600 Tower Oaks Boulevard Office Rockville, MD — 4,243 31,125 6,517 4,244 37,641 — — 41,885 21,426 2001 1998 (1) North First Business Park Office San Jose, CA — 23,398 13,069 4,613 23,377 17,703 — — 41,080 16,076 1981 2007 (1) 150 Broadway Office Cambridge, MA — 850 25,042 8,540 1,323 33,109 — — 34,432 18,404 1999 1997 (1) 325 Main Street Office Cambridge, MA — 174 12,200 16,437 965 23,319 4,527 — 28,811 13,676 1987/2013 1997 (1) 105 Broadway Office Cambridge, MA — 1,299 12,943 9,401 2,395 21,248 — — 23,643 13,950 1990 1997 (1) Lexington Office Park Office Lexington, MA — 998 1,426 18,700 1,264 19,860 — — 21,124 13,614 1982 1997 (1) 201 Spring Street Office Lexington, MA — 2,849 15,303 1,390 3,124 16,418 — — 19,542 8,344 1997 1997 (1) The Point Office Waltham, MA — 6,395 10,040 431 6,480 10,386 — — 16,866 1,031 2015 2007 (1) 690 Folsom Street Office San Francisco, CA — 3,219 11,038 1,157 3,219 12,195 — — 15,414 1,790 2015 2012 (1) 92-100 Hayden Avenue Office Lexington, MA — 594 6,748 7,255 802 13,795 — — 14,597 11,809 1985 1997 (1) Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2018 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building 181 Spring Street Office Lexington, MA — 1,066 9,520 2,230 1,160 11,656 — — 12,816 5,424 1999 1997 (1) 195 West Street Office Waltham, MA — 1,611 6,652 4,270 1,858 10,675 — — 12,533 8,330 1990 1997 (1) 33 Hayden Avenue Office Lexington, MA — 266 3,234 8,223 425 11,298 — — 11,723 9,033 1979 1997 (1) 7501 Boston Boulevard, Building Seven Office Springfield, VA — 665 9,273 819 791 9,966 — — 10,757 5,121 1997 1997 (1) 7450 Boston Boulevard, Building Three Office Springfield, VA — 1,165 4,681 3,278 1,430 7,694 — — 9,124 3,733 1987 1998 (1) 7435 Boston Boulevard, Building One Office Springfield, VA — 392 3,822 4,737 659 8,292 — — 8,951 5,917 1982 1997 (1) 250 Binney Street Office Cambridge, MA — 110 4,483 3,593 273 7,913 — — 8,186 5,448 1983 1997 (1) 8000 Grainger Court, Building Five Office Springfield, VA — 366 4,282 3,536 601 7,583 — — 8,184 5,864 1984 1997 (1) 453 Ravendale Drive Office Mountain View, CA — 5,477 1,090 676 5,477 1,766 — — 7,243 558 1977 2012 (1) 7300 Boston Boulevard, Building Thirteen Office Springfield, VA — 608 4,773 1,438 661 6,158 — — 6,819 3,011 2002 1997 (1) 7601 Boston Boulevard, Building Eight Office Springfield, VA — 200 878 5,373 551 5,900 — — 6,451 4,487 1986 1997 (1) 17 Hartwell Avenue Office Lexington, MA — 26 150 6,064 65 6,175 — — 6,240 1,445 1968 1997 (1) 7500 Boston Boulevard, Building Six Office Springfield, VA — 138 3,749 1,673 406 5,154 — — 5,560 4,121 1985 1997 (1) 8000 Corporate Court, Building Eleven Office Springfield, VA — 136 3,071 1,596 774 4,029 — — 4,803 3,051 1989 1997 (1) 7375 Boston Boulevard, Building Ten Office Springfield, VA — 23 2,685 992 93 3,607 — — 3,700 2,593 1988 1997 (1) 7374 Boston Boulevard, Building Four Office Springfield, VA — 241 1,605 1,828 398 3,276 — — 3,674 2,685 1984 1997 (1) 7451 Boston Boulevard, Building Two Office Springfield, VA — 249 1,542 1,659 613 2,837 — — 3,450 2,527 1982 1997 (1) 32 Hartwell Avenue Office Lexington, MA — 168 1,943 817 314 2,614 — — 2,928 1,821 1968/1979/1987 1997 (1) 164 Lexington Road Office Billerica, MA — 592 1,370 319 643 1,638 — — 2,281 906 1982 1997 (1) Signature at Reston Residential Reston, VA — 27,076 190,580 — 27,076 190,580 — — 217,656 3,938 2018 2013 (1) Proto Kendall Square Residential Cambridge, MA — 9,243 127,248 — 9,243 127,248 — — 136,491 1,324 2018 2015 (1) The Avant at Reston Town Center Residential Reston, VA — 20,350 91,995 830 20,350 92,825 — — 113,175 12,254 2014 2010 (1) The Lofts at Atlantic Wharf Residential Boston, MA — 3,529 54,891 1,768 3,529 56,659 — — 60,188 11,131 2011 2007 (1) Boston Marriott Cambridge Hotel Cambridge, MA — 478 37,918 36,697 1,201 73,892 — — 75,093 46,576 1986/2017 1997 (1) Kendall Center Green Garage Garage Cambridge, MA — — 35,035 7,448 103 42,380 — — 42,483 12,208 1984 2006 (1) Kendall Center Yellow Garage Garage Cambridge, MA — 1,256 15,697 1,621 1,434 17,140 — — 18,574 5,643 2006 2004 (1) Kendall Center Blue Garage Garage Cambridge, MA — 1,163 11,633 2,145 1,579 13,362 — — 14,941 9,437 1990 1997 (1) 145 Broadway Development Cambridge, MA — 121 — 223,845 324 — — 223,642 223,966 — N/A 1997 N/A MacArthur Station Residences Development Oakland, CA — — — 87,159 — — — 87,159 87,159 — N/A N/A N/A 20 CityPoint Development Waltham, MA — — 6,287 46,024 — 6,287 — 46,024 52,311 — N/A 2007 N/A Boston Properties, Inc. Schedule 3 - Real Estate and Accumulated Depreciation December 31, 2018 (dollars in thousands) Property Name Type Location Encumbrances Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Land Building Reston Gateway Development Reston, VA — — — 25,167 — — — 25,167 25,167 — N/A 1998 N/A 17Fifty Presidents Street Development Reston, VA — — — 25,120 — — — 25,120 25,120 — N/A 2013 N/A North First Master Plan Land San Jose, CA — 35,004 — 3,932 — — 38,936 — 38,936 — N/A 2007 N/A Plaza at Almaden Land San Jose, CA — — — 29,928 — — 29,928 — 29,928 — N/A 2006 N/A Springfield Metro Center Land Springfield, VA — — — 19,823 — — 19,823 — 19,823 — N/A 2007 N/A 214 Third Avenue Land Waltham, MA — — — 15,233 — — 15,233 — 15,233 — N/A 2006 N/A Platform 16 Land San Jose, CA — — — 12,962 — — 12,962 — 12,962 — N/A 2018 N/A 103 Fourth Avenue Land Waltham, MA — — — 12,208 — — 12,208 — 12,208 — N/A 2007 N/A Reston Gateway Master Plan Land Reston, VA — — — 11,014 — — 11,014 — 11,014 — N/A 1998 N/A Fourth and Harrison Land San Francisco, CA — — — 10,350 — — 10,350 — 10,350 — N/A N/A N/A 2100 Pennsylvania Avenue Land Washington, DC — — — 9,700 — — 9,700 — 9,700 — N/A N/A N/A Crane Meadow Land Marlborough, MA — — — 8,852 — — 8,852 — 8,852 — N/A 2000 N/A Washingtonian North Land Gaithersburg, MD — — — 7,473 — — 7,473 — 7,473 — N/A 1998 N/A Broad Run Business Park Land Loudoun County, VA — — — 2,388 — — 2,388 — 2,388 — N/A 1998 N/A Kendall Center Master Plan Land Cambridge, MA — — — 2,199 — — 2,199 — 2,199 — N/A 1997 N/A Weston Quarry Land Weston, MA — — — 1,237 — — 1,237 — 1,237 — N/A 2001 N/A Reston Overlook Master Plan Land Reston, VA — — — 39 — — 39 — 39 — N/A 2000 N/A $ 2,964,572 (2 ) $ 4,959,995 $ 12,763,317 $ 3,882,233 $ 5,072,568 $ 15,753,683 $ 200,498 (3 ) $ 578,796 $ 21,605,545 $ 4,871,102 Note: Total Real Estate does not include Furniture, Fixtures and Equipment totaling approximately $44,351 . Accumulated Depreciation does not include approximately $26,675 of accumulated depreciation related to Furniture, Fixtures and Equipment. The aggregate cost and accumulated depreciation for tax purposes was approximately $17.9 billion and $3.9 billion , respectively. (1) Depreciation of the buildings and improvements are calculated over lives ranging from the life of the lease to 40 years. (2) Includes unamortized deferred financing costs totaling approximately $(30.8) million . (3) Includes pre-development costs.
Activity of Real Estate and Accumulated Depreciation [Table Text Block]	A summary of activity for real estate and accumulated depreciation is as follows: 2018 2017 2016 Real Estate: Balance at the beginning of the year $ 21,058,714 $ 20,114,576 $ 19,451,683 Additions to/improvements of real estate 1,043,379 1,099,286 977,287 Assets sold/written-off (496,548 ) (155,148 ) (314,394 ) Balance at the end of the year $ 21,605,545 $ 21,058,714 $ 20,114,576 Accumulated Depreciation: Balance at the beginning of the year $ 4,566,570 $ 4,201,891 $ 3,905,940 Depreciation expense 533,342 497,059 560,024 Assets sold/written-off (228,810 ) (132,380 ) (264,073 ) Balance at the end of the year $ 4,871,102 $ 4,566,570 $ 4,201,891 Note: Real Estate and Accumulated Depreciation amounts do not include Furniture, Fixtures and Equipment.
Boston Properties Limited Partnership
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate and Accumulated Depreciation, By Property [Table Text Block]	Boston Properties Limited Partnership Schedule 3—Real Estate and Accumulated Depreciation December 31, 2018 (dollars in thousands) Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Property Name Type Location Encumbrances Land Building 767 Fifth Avenue (the General Motors Building) Office New York, NY $ 2,270,534 $ 1,796,252 $ 1,532,654 $ 189,657 $ 1,796,252 $ 1,722,311 $ — $ — $ 3,518,563 $ 271,534 1968 2013 (1) Prudential Center Office Boston, MA — 92,077 948,357 472,432 100,540 1,412,222 104 — 1,512,866 535,305 1965/1993/2002/2016-2017 1998/1999/2000 (1) Embarcadero Center Office San Francisco, CA — 179,697 847,410 306,586 180,420 1,153,273 — — 1,333,693 597,613 1970/1989 1998-1999 (1) 399 Park Avenue Office New York, NY — 339,200 700,358 187,484 339,200 887,842 — — 1,227,042 318,267 1961/2018 2002 (1) Salesforce Tower Office San Francisco, CA — 200,349 919,565 — 200,349 919,565 — — 1,119,914 9,509 2018 2013 (1) 601 Lexington Avenue Office New York, NY 658,792 241,600 494,782 324,899 279,281 610,316 — 171,684 1,061,281 264,150 1977/1997 2001 (1) 200 Clarendon Street and Garage Office Boston, MA — 219,543 667,884 164,073 219,616 822,218 9,666 — 1,051,500 192,137 1976 2010 (1) 250 West 55th Street Office New York, NY — 285,263 603,167 48,642 285,263 651,809 — — 937,072 94,434 2014 2007 (1) 100 Federal Street Office Boston, MA — 131,067 435,954 99,702 131,067 535,656 — — 666,723 105,536 1971-1975/2017 2012 (1) Carnegie Center Office Princeton, NJ — 107,997 389,359 141,434 104,617 530,987 3,186 — 638,790 237,322 1983-2016 1998/1999/2000/2007/2014/2017 (1) Times Square Tower Office New York, NY — 165,413 380,438 56,472 159,694 442,629 — — 602,323 196,753 2004 2000 (1) Atlantic Wharf Office Boston, MA — 63,988 454,537 17,184 63,988 471,721 — — 535,709 116,238 2011 2007 (1) 510 Madison Avenue Office New York, NY — 103,000 253,665 24,992 103,000 278,657 — — 381,657 62,507 2012 2010 (1) Fountain Square Office Reston, VA — 56,853 306,298 3,170 56,853 309,468 — — 366,321 68,390 1986-1990 2012 (1) 599 Lexington Avenue Office New York, NY — 81,040 100,507 146,971 81,040 247,478 — — 328,518 164,002 1986 1997 (1) 680 Folsom Street Office San Francisco, CA — 72,545 219,766 7,829 72,545 227,595 — — 300,140 38,230 2014 2012 (1) 601 Massachusetts Avenue Office Washington, DC — 95,310 165,173 3,888 95,310 169,061 — — 264,371 18,263 2016 2008 (1) South of Market and Democracy Tower Office Reston, VA — 13,603 237,479 12,092 13,603 249,571 — — 263,174 91,006 2008-2009 2003 (1) Bay Colony Corporate Center Office Waltham, MA — 18,789 148,451 77,133 18,789 225,584 — — 244,373 68,903 1985-1989 2011 (1) Gateway Center Office San Francisco, CA — 28,255 139,245 58,442 29,029 196,913 — — 225,942 106,074 1984/1986/2002 1999 (1) 535 Mission Street Office San Francisco, CA — 40,933 148,378 3,259 40,933 151,637 — — 192,570 20,576 2015 2013 (1) 2200 Pennsylvania Avenue Office Washington, DC — — 183,541 4,535 — 188,076 — — 188,076 52,280 2011 2008 (1) Mountain View Research Park Office Mountain View, CA — 95,066 68,373 9,988 95,066 78,361 — — 173,427 17,866 1977-1981/2007-2013 2013 (1) Reservoir Place Office Waltham, MA — 18,605 104,124 41,069 19,089 144,709 — — 163,798 63,684 1955/1987/2017 1997/1998 (1) 1330 Connecticut Avenue Office Washington, DC — 25,982 82,311 31,476 25,982 113,787 — — 139,769 26,400 1984/2018 2004 (1) Kingstowne Towne Center Office Alexandria, VA — 18,021 109,038 1,934 18,021 110,972 — — 128,993 41,436 2003-2006 2007 (1) One Freedom Square Office Reston, VA — 9,929 84,504 26,619 9,883 111,169 — — 121,052 53,268 2000 2003 (1) Weston Corporate Center Office Weston, MA — 25,753 92,312 (123 ) 25,854 92,088 — — 117,942 26,176 2010 2001 (1) Capital Gallery Office Washington, DC — 4,725 29,565 77,100 6,128 105,262 — — 111,390 65,272 1981/2006 2007 (1) Two Freedom Square Office Reston, VA — 13,930 77,739 17,215 13,866 95,018 — — 108,884 49,768 2001 2003 (1) One and Two Reston Overlook Office Reston, VA — 16,456 66,192 19,763 15,074 87,337 — — 102,411 46,584 1999 2000 (1) Boston Properties Limited Partnership Schedule 3—Real Estate and Accumulated Depreciation December 31, 2018 (dollars in thousands) Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Property Name Type Location Encumbrances Land Building 140 Kendrick Street Office Needham, MA — 18,095 66,905 13,563 18,095 80,468 — — 98,563 31,381 2000 2004 (1) 355 Main Street Office Cambridge, MA — 18,863 53,346 23,403 21,098 74,514 — — 95,612 23,620 1981/1996/2013 2006 (1) Discovery Square Office Reston, VA — 11,198 71,782 12,208 11,146 84,042 — — 95,188 38,212 2001 2003 (1) 10 CityPoint Office Waltham, MA — 1,953 85,752 4,352 1,953 90,104 — — 92,057 7,772 2016 1997 (1) 90 Broadway Office Cambridge, MA — 19,104 52,078 18,184 20,741 68,625 — — 89,366 21,265 1983/1998/2013 2006 (1) 230 CityPoint Office Waltham, MA — 13,189 49,823 20,297 13,189 70,120 — — 83,309 25,964 1992 2005 (1) 77 CityPoint Office Waltham, MA — 13,847 60,383 5,753 13,847 66,136 — — 79,983 25,085 2008 2001 (1) Waltham Weston Corporate Center Office Waltham, MA — 10,385 60,694 8,462 10,350 69,191 — — 79,541 32,005 2003 1999 (1) 3625-3635 Peterson Way Office Santa Clara, CA — 63,206 14,879 673 63,206 14,879 673 — 78,758 8,146 1979 2016 (1) 2440 West El Camino Real Office Mountain View, CA — 16,741 51,285 3,411 16,741 54,696 — — 71,437 12,562 1987/2003 2011 (1) 300 Binney Street Office Cambridge, MA — 18,080 51,262 140 18,080 51,402 — — 69,482 9,450 2013 2009 (1) Wisconsin Place Office Chevy Chase, MD — — 53,349 14,889 — 68,238 — — 68,238 22,936 2009 2004 (1) 191 Spring Street Office Lexington, MA — 2,850 59,751 5,603 2,850 65,354 — — 68,204 19,435 1971/1995/2018 1997 (1) Reston Corporate Center Office Reston, VA — 9,135 50,857 3,625 9,496 54,121 — — 63,617 27,674 1984 1998 (1) New Dominion Technology Park, Bldg. Two Office Herndon, VA — 5,584 51,868 412 5,574 52,290 — — 57,864 24,498 2004 1998 (1) 255 Main Street Office Cambridge, MA — 134 25,110 28,016 134 53,126 — — 53,260 29,776 1987 1997 (1) 200 West Street Office Waltham, MA — 16,148 24,983 8,459 16,148 33,442 — — 49,590 21,891 1999 1997 (1) New Dominion Technology Park, Bldg. One Office Herndon, VA 29,675 3,880 43,227 1,117 3,880 44,344 — — 48,224 26,852 2001 1998 (1) Sumner Square Office Washington, DC — 624 28,745 16,974 958 45,385 — — 46,343 24,877 1985 1999 (1) University Place Office Cambridge, MA 5,571 — 37,091 7,551 27 44,615 — — 44,642 27,519 1985 1998 (1) 2600 Tower Oaks Boulevard Office Rockville, MD — 4,243 31,125 6,517 4,244 37,641 — — 41,885 21,426 2001 1998 (1) North First Business Park Office San Jose, CA — 23,398 13,069 4,590 23,371 17,686 — — 41,057 16,076 1981 2007 (1) 150 Broadway Office Cambridge, MA — 850 25,042 6,535 822 31,605 — — 32,427 17,909 1999 1997 (1) 325 Main Street Office Cambridge, MA — 174 12,200 15,666 772 22,741 4,527 — 28,040 13,484 1987/2013 1997 (1) 105 Broadway Office Cambridge, MA — 1,299 12,943 7,295 1,868 19,669 — — 21,537 13,432 1990 1997 (1) Lexington Office Park Office Lexington, MA — 998 1,426 17,936 1,073 19,287 — — 20,360 13,430 1982 1997 (1) 201 Spring Street Office Lexington, MA — 2,849 15,303 291 2,849 15,594 — — 18,443 8,073 1997 1997 (1) The Point Office Waltham, MA — 6,395 10,040 431 6,480 10,386 — — 16,866 1,031 2015 2007 (1) 690 Folsom Street Office San Francisco, CA — 3,219 11,038 1,157 3,219 12,195 — — 15,414 1,790 2015 2012 (1) 92-100 Hayden Avenue Office Lexington, MA — 594 6,748 6,526 619 13,249 — — 13,868 11,629 1985 1997 (1) 181 Spring Street Office Lexington, MA — 1,066 9,520 1,853 1,066 11,373 — — 12,439 5,332 1999 1997 (1) 195 West Street Office Waltham, MA — 1,611 6,652 3,281 1,611 9,933 — — 11,544 8,084 1990 1997 (1) 33 Hayden Avenue Office Lexington, MA — 266 3,234 7,586 266 10,820 — — 11,086 8,877 1979 1997 (1) 7501 Boston Boulevard, Building Seven Office Springfield, VA — 665 9,273 314 665 9,587 — — 10,252 4,995 1997 1997 (1) Boston Properties Limited Partnership Schedule 3—Real Estate and Accumulated Depreciation December 31, 2018 (dollars in thousands) Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Property Name Type Location Encumbrances Land Building 7450 Boston Boulevard, Building Three Office Springfield, VA — 1,165 4,681 2,864 1,327 7,383 — — 8,710 3,628 1987 1998 (1) 7435 Boston Boulevard, Building One Office Springfield, VA — 392 3,822 4,044 486 7,772 — — 8,258 5,748 1982 1997 (1) 8000 Grainger Court, Building Five Office Springfield, VA — 366 4,282 2,942 453 7,137 — — 7,590 5,720 1984 1997 (1) 250 Binney Street Office Cambridge, MA — 110 4,483 2,939 110 7,422 — — 7,532 5,291 1983 1997 (1) 453 Ravendale Drive Office Mountain View, CA — 5,477 1,090 676 5,477 1,766 — — 7,243 558 1977 2012 (1) 7300 Boston Boulevard, Building Thirteen Office Springfield, VA — 608 4,773 1,226 608 5,999 — — 6,607 2,959 2002 1997 (1) 17 Hartwell Avenue Office Lexington, MA — 26 150 5,907 26 6,057 — — 6,083 1,406 1968 1997 (1) 7601 Boston Boulevard, Building Eight Office Springfield, VA — 200 878 4,680 378 5,380 — — 5,758 4,318 1986 1997 (1) 7500 Boston Boulevard, Building Six Office Springfield, VA — 138 3,749 1,140 273 4,754 — — 5,027 3,991 1985 1997 (1) 8000 Corporate Court, Building Eleven Office Springfield, VA — 136 3,071 1,245 686 3,766 — — 4,452 2,961 1989 1997 (1) 7375 Boston Boulevard, Building Ten Office Springfield, VA — 23 2,685 811 47 3,472 — — 3,519 2,552 1988 1997 (1) 7374 Boston Boulevard, Building Four Office Springfield, VA — 241 1,605 1,445 303 2,988 — — 3,291 2,594 1984 1997 (1) 7451 Boston Boulevard, Building Two Office Springfield, VA — 249 1,542 1,346 535 2,602 — — 3,137 2,449 1982 1997 (1) 32 Hartwell Avenue Office Lexington, MA — 168 1,943 231 168 2,174 — — 2,342 1,676 1968/1979/1987 1997 (1) 164 Lexington Road Office Billerica, MA — 592 1,370 117 592 1,487 — — 2,079 853 1982 1997 (1) Signature at Reston Residential Reston, VA — 27,076 190,580 — 27,076 190,580 — — 217,656 3,938 2018 2013 (1) Proto Kendall Square Residential Cambridge, MA — 9,243 127,248 — 9,243 127,248 — — 136,491 1,324 2018 2015 (1) The Avant at Reston Town Center Residential Reston, VA — 20,350 91,995 830 20,350 92,825 — — 113,175 12,254 2014 2010 (1) The Lofts at Atlantic Wharf Residential Boston, MA — 3,529 54,891 1,768 3,529 56,659 — — 60,188 11,131 2011 2007 (1) Boston Marriott Cambridge Hotel Cambridge, MA — 478 37,918 33,806 478 71,724 — — 72,202 45,868 1986/2017 1997 (1) Kendall Center Green Garage Garage Cambridge, MA — — 35,035 7,034 — 42,069 — — 42,069 12,108 1984 2006 (1) Kendall Center Yellow Garage Garage Cambridge, MA — 1,256 15,697 909 1,256 16,606 — — 17,862 5,472 2006 2004 (1) Kendall Center Blue Garage Garage Cambridge, MA — 1,163 11,633 480 1,163 12,113 — — 13,276 9,030 1990 1997 (1) 145 Broadway Development Cambridge, MA — 121 — 223,642 121 — — 223,642 223,763 — N/A 1997 N/A MacArthur Station Residences Development Oakland, CA — — — 87,159 — — — 87,159 87,159 — N/A N/A N/A 20 CityPoint Development Waltham, MA — — 6,287 46,024 — 6,287 — 46,024 52,311 — N/A 2007 N/A Reston Gateway Development Reston, VA — — — 25,167 — — — 25,167 25,167 — N/A 1998 N/A 17Fifty Presidents Street Development Reston, VA — — — 25,120 — — — 25,120 25,120 — N/A 2013 N/A North First Master Plan Land San Jose, CA — 35,004 — 3,932 — — 38,936 — 38,936 — N/A 2007 N/A Plaza at Almaden Land San Jose, CA — — — 29,928 — — 29,928 — 29,928 — N/A 2006 N/A Boston Properties Limited Partnership Schedule 3—Real Estate and Accumulated Depreciation December 31, 2018 (dollars in thousands) Original Costs Capitalized Subsequent to Acquisition Land and Improvements Building and Improvements Land Held for Development Development and Construction in Progress Total Accumulated Depreciation Year(s) Built/ Renovated Year(s) Acquired Depreciable Lives (Years) Property Name Type Location Encumbrances Land Building Springfield Metro Center Land Springfield, VA — — — 19,823 — — 19,823 — 19,823 — N/A 2007 N/A 214 Third Avenue Land Waltham, MA — — — 15,233 — — 15,233 — 15,233 — N/A 2006 N/A Platform 16 Land San Jose, CA — — — 12,962 — — 12,962 — 12,962 — N/A 2018 N/A 103 Fourth Avenue Land Waltham, MA — — — 12,208 — — 12,208 — 12,208 — N/A 2007 N/A Reston Gateway Master Plan Land Reston, VA — — — 11,014 — — 11,014 — 11,014 — N/A 1998 N/A Fourth and Harrison Land San Francisco, CA — — — 10,350 — — 10,350 — 10,350 — N/A N/A N/A 2100 Pennsylvania Avenue Land Washington, DC — — — 9,700 — — 9,700 — 9,700 — N/A N/A N/A Crane Meadow Land Marlborough, MA — — — 8,852 — — 8,852 — 8,852 — N/A 2000 N/A Washingtonian North Land Gaithersburg, MD — — — 7,473 — — 7,473 — 7,473 — N/A 1998 N/A Broad Run Business Park Land Loudoun County, VA — — — 2,388 — — 2,388 — 2,388 — N/A 1998 N/A Kendall Center Master Plan Land Cambridge, MA — — — 2,199 — — 2,199 — 2,199 — N/A 1997 N/A Weston Quarry Land Weston, MA — — — 1,237 — — 1,237 — 1,237 — N/A 2001 N/A Reston Overlook Master Plan Land Reston, VA — — — 39 — — 39 — 39 — N/A 2000 N/A $ 2,964,572 (2 ) $ 4,959,995 $ 12,763,317 $ 3,483,877 $ 4,971,475 $ 15,456,420 $ 200,498 (3 ) $ 578,796 $ 21,207,189 $ 4,773,800 Note: Total Real Estate does not include Furniture, Fixtures and Equipment totaling approximately $44,351 . Accumulated Depreciation does not include approximately $26,675 of accumulated depreciation related to Furniture, Fixtures and Equipment. The aggregate cost and accumulated depreciation for tax purposes was approximately $19.9 billion and $4.3 billion , respectively. (1) Depreciation of the buildings and improvements are calculated over lives ranging from the life of the lease to 40 years. (2) Includes unamortized deferred financing costs totaling approximately $(30.8) million . (3) Includes pre-development costs.
Activity of Real Estate and Accumulated Depreciation [Table Text Block]	A summary of activity for real estate and accumulated depreciation is as follows: 2018 2017 2016 Real Estate: Balance at the beginning of the year $ 20,647,236 $ 19,701,185 $ 19,031,289 Additions to/improvements of real estate 1,043,379 1,099,286 977,287 Assets sold/written-off (483,426 ) (153,235 ) (307,391 ) Balance at the end of the year $ 21,207,189 $ 20,647,236 $ 19,701,185 Accumulated Depreciation: Balance at the beginning of the year $ 4,473,895 $ 4,116,020 $ 3,826,862 Depreciation expense 525,584 488,919 548,397 Assets sold/written-off (225,679 ) (131,044 ) (259,239 ) Balance at the end of the year $ 4,773,800 $ 4,473,895 $ 4,116,020 Note: Real Estate and Accumulated Depreciation amounts do not include Furniture, Fixtures and Equipment.

Organization (Details)

Organization (Details) ft² in Millions	12 Months Ended
	Dec. 31, 2018ft²Real_Estate_Propertiesyrshares	Dec. 31, 2017shares
Real Estate Properties [Line Items]
General and limited partnership interest in the operating partnership (percent)	89.70%	89.70%
Restriction on redemption of OP units from date of issuance (years) | yr	1
One OP unit is equivalent to one share of Common Stock (in shares) | shares	1
OP unit conversion rate (in shares) | shares	1
Number Of series Of preferred units outstanding	1
Commercial Real Estate Properties [Member]
Real Estate Properties [Line Items]
Number of real estate properties	197
Net Rentable Area | ft²	51.6
Total Properties Under Construction [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	11
Net Rentable Area | ft²	5.3
Total Office Properties [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	178
Office Properties Under Construction [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	9
Retail Properties [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	12
Residential Properties [Member]
Real Estate Properties [Line Items]
Number of real estate properties	6
Residential Properties Under Construction [Member]
Real Estate Properties [Line Items]
Number of real estate properties	2
Hotel Property [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	1
Series B Cumulative Redeemable Preferred Stock / Unit [Member]
Real Estate Properties [Line Items]
Preferred stock / units, shares / units outstanding (in shares / units) | shares	80,000	80,000
Preferred Stock, Dividend Rate, Percentage	5.25%
Depositary shares of Series B Cumulative Redeemable Preferred [Member]
Real Estate Properties [Line Items]
Preferred stock / units, shares / units outstanding (in shares / units) | shares	8,000,000
Series B Preferred Units [Member]
Real Estate Properties [Line Items]
Preferred stock / units, shares / units outstanding (in shares / units) | shares	80,000

Summary Of Significant Accoun_4

Summary Of Significant Accounting Policies (Narrative) (Details)	Jan. 01, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Dec. 31, 2018USD ($)yr	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Entity Information [Line Items]
Maximum Period After Construction The Company Considers A Construction Project As Substantially Completed (In Years) | yr				1
Interest costs capitalized				$ 65,766,000	$ 61,070,000	$ 39,200,000
Salaries And Related Costs Capitalized				12,500,000	13,200,000	11,100,000
Cash FDIC Insured Limit		$ 250,000		250,000
Separate Unrestricted Cash For Deferred Compensation Plan.		28,200,000		28,200,000	29,200,000
Gains (losses) from investments in securities				(1,865,000)	3,678,000	2,273,000
Internal Leasing Salaries And Related Costs Capitalized				5,400,000	5,000,000	7,200,000
Straight-line rent adjustments				(51,900,000)	(54,800,000)	(31,700,000)
Above and below market rent adjustments, net				$ 23,800,000	23,500,000	30,200,000
Ground Lease Expiration Date, Maximum				2,114
REIT Annual Taxable Income Distribution Requirement Percentage, Minimum				90.00%
Company Annual Taxable Income Distribution Percentage				100.00%
Debt Issuance Costs, Net		30,756,000		$ 30,756,000
Cumulative effect of a change in accounting principle				(5,496,000)	2,035,000
Payroll and related costs from management services contracts				9,590,000	0	0
Direct reimbursements of payroll and related costs from management services contracts				9,590,000	0	0
Net Cash Provided by (Used in) Operating Activities				1,150,245,000	911,979,000	1,034,548,000
Net Cash Provided by (Used in) Investing Activities				1,098,876,000	882,044,000	1,337,347,000
Net Cash Provided by (Used in) Financing Activities				82,453,000	55,346,000	(74,621,000)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents		639,191,000		639,191,000	505,369,000	420,088,000	$ 797,508,000
Interest Expense				378,168,000	374,481,000	412,849,000
Boston Properties Limited Partnership
Entity Information [Line Items]
Interest costs capitalized				65,766,000	61,070,000	39,237,000
Gains (losses) from investments in securities				(1,865,000)	3,678,000	2,273,000
Debt Issuance Costs, Net		30,800,000		30,800,000
Cumulative effect of a change in accounting principle				(4,933,000)	272,000
Payroll and related costs from management services contracts				9,590,000	0	0
Direct reimbursements of payroll and related costs from management services contracts				9,590,000	0	0
Net Cash Provided by (Used in) Operating Activities				1,150,245,000	911,979,000	1,034,548,000
Net Cash Provided by (Used in) Investing Activities				1,098,876,000	882,044,000	1,337,347,000
Net Cash Provided by (Used in) Financing Activities				82,453,000	55,346,000	(74,621,000)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents		639,191,000		639,191,000	505,369,000	420,088,000	$ 797,508,000
Interest Expense				378,168,000	374,481,000	412,849,000
Dividends In Excess Of Earnings [Member]
Entity Information [Line Items]
Cumulative effect of a change in accounting principle				(4,933,000)	272,000
Noncontrolling Interests [Member]
Entity Information [Line Items]
Cumulative effect of a change in accounting principle				(563,000)	1,763,000
Noncontrolling Interests [Member] | Boston Properties Limited Partnership
Entity Information [Line Items]
Cumulative effect of a change in accounting principle				(563,000)	1,763,000
Accounting Standards Update 2014-09 [Member]
Entity Information [Line Items]
Cumulative effect of a change in accounting principle			$ (4,900,000)
Accounting Standards Update 2014-09 [Member] | Noncontrolling Interests [Member]
Entity Information [Line Items]
Cumulative effect of a change in accounting principle			$ (600,000)
Accounting Standards Update 2016-15 [Member]
Entity Information [Line Items]
Non Cash Portion Of Loss From Early Extinguishment Of Debt				$ 16,000,000	12,800,000
Accounting Standards Update 2016-18 [Member]
Entity Information [Line Items]
Net Cash Provided by (Used in) Operating Activities					4,500,000	(2,300,000)
Net Cash Provided by (Used in) Investing Activities					(15,800,000)	8,300,000
Net Cash Provided by (Used in) Financing Activities					(12,900,000)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents					$ 7,400,000	$ 10,600,000
Accounting Standards Update 2017-12 [Member]
Entity Information [Line Items]
Interest Expense		$ 1,700,000
Subsequent Event [Member] | Accounting Standards Update 2016-02 [Member]
Entity Information [Line Items]
Cumulative effect of a change in accounting principle	$ (4,000,000)
Operating Lease, Right-of-Use Asset	148,800,000
Operating Lease, Liability	$ 199,700,000

Summary Of Significant Accoun_5

Summary Of Significant Accounting Policies Schedule of Estimated Useful Lives (Details)	12 Months Ended
	Dec. 31, 2018
Land Improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (years)	25 years
Land Improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (years)	40 years
Building and Building Improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (years)	10 years
Building and Building Improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (years)	40 years
Tenant Improvement [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life, description	Shorter of useful life or terms of related lease
Furniture, fixtures and equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (years)	3 years
Furniture, fixtures and equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (years)	7 years

Summary Of Significant Accoun_6

Summary Of Significant Accounting Policies Schedule of Finite Lived Intangible Assets Future Amortization Expense (Details) $ in Thousands	Dec. 31, 2018USD ($)
Finite-Lived Intangible Assets [Line Items]
2,019	$ 25,690
2,020	13,051
2,021	8,610
2,022	4,798
2,023	4,107
Acquired Above-Market Lease Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
2,019	7,099
2,020	5,394
2,021	2,988
2,022	314
2,023	168
Acquired Below-Market Lease Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
2,019	27,327
2,020	10,462
2,021	6,348
2,022	5,669
2,023	$ 5,558

Summary Of Significant Accoun_7

Summary Of Significant Accounting Policies Schedule Of Future Contractual Minimum Lease Payments Under Non-Cancelable Ground Leases (Details) $ in Thousands	Dec. 31, 2018USD ($)
Summary of Significant Accounting Policies [Abstract]
2,019	$ 11,425
2,020	18,425
2,021	25,310
2,022	8,894
2,023	9,084
Thereafter	$ 567,232

Summary Of Significant Accoun_8

Summary Of Significant Accounting Policies Capital Leases Disclosures (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Capital Leased Assets [Line Items]
Land held for future development	[1]	$ 200,498	$ 204,925
Buildings and improvements		13,356,751	12,284,164
Construction in progress		578,796	1,269,338
2,019		1,441
2,020		12,682
2,021		2,123
2,022		1,253
2,023		944
Thereafter		73,241
Total expected minimum lease payments		91,684
Interest portion		(27,497)
Present value of expected net minimum lease payments		64,187
Capital Lease Obligations [Member]
Capital Leased Assets [Line Items]
Land held for future development		12,397	0
Buildings and improvements		23,636	23,636
Construction in progress		28,962	28,962
Total		$ 64,995	$ 52,598
[1]	Includes pre-development costs.

Summary Of Significant Accoun_9

Summary Of Significant Accounting Policies (Carrying Value Of Indebtedness And Corresponding Estimate Of Fair Value) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Summary Of Significant Accounting Policies [Line Items]
Related party note receivable	$ 80,000	$ 0
Mortgage notes payable, net	2,964,572	2,979,281
Unsecured senior notes, net	7,544,697	7,247,330
Unsecured line of credit	0	45,000
Unsecured term loan, net	498,488	0
Total	2,995,328
Carrying Amount [Member]
Summary Of Significant Accounting Policies [Line Items]
Related party note receivable	80,000	0
Note receivable	19,468	0
Total	99,468	0
Mortgage notes payable, net	2,964,572	2,979,281
Unsecured senior notes, net	7,544,697	7,247,330
Unsecured line of credit	0	45,000
Unsecured term loan, net	498,488	0
Total	11,007,757	10,271,611
Estimated Fair Value [Member]
Summary Of Significant Accounting Policies [Line Items]
Related party note receivable	80,000	0
Note receivable	19,468	0
Total	99,468	0
Mortgage notes payable, net	2,903,925	3,042,920
Unsecured senior notes, net	7,469,338	7,461,615
Unsecured line of credit	0	45,000
Unsecured term loan, net	500,783	0
Total	$ 10,874,046	$ 10,549,535

Summary Of Significant Accou_10

Summary Of Significant Accounting Policies Schedule of Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016		Dec. 17, 2018
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Dividends Treatment For Federal Tax Purposes, Percentage	100.00%		100.00%		100.00%
Dividends treatment for federal tax purposes.	$ 3.57	[1]	$ 2.91	[2]	$ 3.05	[3]
Dividends Payable, Amount Per Share							$ 0.95
Dividend Declared
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Dividends Payable, Amount Per Share	0.95		0.80		0.75
Allocated to fiscal 2016
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Special dividend / distribution (per share / common unit amount)					0.56
Allocated to fiscal 2017
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Special dividend / distribution (per share / common unit amount)			0.47
Dividends Payable, Amount Per Share					$ 0.19
Allocated to fiscal 2019 [Domain]
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Dividends Payable, Amount Per Share	0.26
Allocated to fiscal 2018 [Member]
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Special dividend / distribution (per share / common unit amount)	$ 0.69
Dividends Payable, Amount Per Share			$ 0.33
Capital Gains Income
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Dividends Treatment For Federal Tax Purposes, Percentage	21.83%		1.71%		9.49%
Dividends treatment for federal tax purposes.	$ 0.78		$ 0.05		$ 0.29
Ordinary Income
Tax Treatment Of Common Dividends Per Share For Federal Tax Purposes [Line Items]
Dividends Treatment For Federal Tax Purposes, Percentage	78.17%		98.29%		90.51%
Dividends treatment for federal tax purposes.	$ 2.79		$ 2.86		$ 2.76
[1]	The fourth quarter 2018 regular quarterly dividend was $0.95 per common share of which approximately $0.69 per common share was allocable to 2018 and approximately $0.26 per common share is allocable to 2019
[2]	The fourth quarter 2017 regular quarterly dividend was $0.80 per common share of which approximately $0.47 per common share was allocable to 2017 and approximately $0.33 per common share is allocable to 2018.
[3]	The fourth quarter 2016 regular quarterly dividend was $0.75 per common share of which approximately $0.56 per common share was allocable to 2016 and approximately $0.19 per common share is allocable to 2017.

Real Estate Schedule of Real Es

Real Estate Schedule of Real Estate Properties (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Real Estate Properties [Line Items]
Land		$ 5,072,568	$ 5,080,679
Land held for future development	[1]	200,498	204,925
Buildings and improvements		13,356,751	12,284,164
Tenant improvements		2,396,932	2,219,608
Furniture, fixtures and equipment		44,351	37,928
Construction in progress		578,796	1,269,338
Total		21,649,896	21,096,642
Less: accumulated depreciation		(4,897,777)	(4,589,634)
Total real estate		16,752,119	16,507,008
Boston Properties Limited Partnership
Real Estate Properties [Line Items]
Land		4,971,475	4,976,303
Land held for future development	[1]	200,498	204,925
Buildings and improvements		13,059,488	11,977,062
Tenant improvements		2,396,932	2,219,608
Furniture, fixtures and equipment		44,351	37,928
Construction in progress		578,796	1,269,338
Total		21,251,540	20,685,164
Less: accumulated depreciation		(4,800,475)	(4,496,959)
Total real estate		$ 16,451,065	$ 16,188,205
[1]	Includes pre-development costs.

Real Estate (Narrative) (Detail

Real Estate (Narrative) (Details) $ in Thousands	Dec. 20, 2018USD ($)a	Dec. 13, 2018USD ($)ft²	Nov. 30, 2018USD ($)ft²	Nov. 29, 2018USD ($)ft²ayr	Sep. 27, 2018USD ($)ft²	May 24, 2018USD ($)ft²	Feb. 23, 2018ft²Buildings	Jan. 09, 2018USD ($)ft²	Jan. 08, 2018USD ($)	Dec. 31, 2018USD ($)ft²	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	May 23, 2018USD ($)	Sep. 26, 2018USD ($)	Nov. 30, 2018USD ($)ft²	Dec. 31, 2018USD ($)ft²	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 01, 2018ft²	Nov. 09, 2018ft²	Sep. 01, 2018ft²apartments	Aug. 07, 2018ft²	Jun. 07, 2018ft²apartments	Jan. 24, 2018ft²	Dec. 31, 2015USD ($)
Real Estate Properties [Line Items]
Cash held in escrows										$ 95,832				$ 70,602	$ 70,602						$ 95,832	$ 70,602	$ 63,174							$ 73,790
Revenues										705,157	$ 686,284	$ 664,484	$ 661,151	655,229	657,712	$ 656,907	$ 632,228				2,717,076	2,602,076	2,550,820
Proceeds from sales of real estate																					455,409	29,810	122,750
Impairment losses																					11,812	0	1,783
Gains on sales of real estate																					182,356	7,663	80,606
Note receivable										19,468				0							19,468	0
Present value of expected net minimum lease payments										$ 64,187											$ 64,187
500 E Street
Real Estate Properties [Line Items]
Net Contractual Sales Price								$ 118,600
Net Rentable Area | ft²								262,000
Operating Income (Loss)									$ 100													6,500	7,600
Proceeds from sales of real estate								$ 116,100
Gains on sales of real estate								96,400
91 Hartwell Avenue [Member]
Real Estate Properties [Line Items]
Net Rentable Area | ft²						119,000
Operating Income (Loss)																		$ 300				500	400
Contractual Sales Price						$ 22,200
Proceeds from sales of real estate						21,700
Gains on sales of real estate						15,500
Quorum Office Park
Real Estate Properties [Line Items]
Net Rentable Area | ft²					268,000
Operating Income (Loss)																			$ 700			900	900
Contractual Sales Price					$ 35,300
Proceeds from sales of real estate					34,300
Gains on sales of real estate					7,900
6595 Springfield Center Drive [Member]
Real Estate Properties [Line Items]
Net Rentable Area | ft²		634,000
Contractual Sales Price		$ 98,100
Proceeds from sales of real estate		97,100
Impairment losses		$ 8,700
1333 New Hampshire Avenue [Member]
Real Estate Properties [Line Items]
Net Rentable Area | ft²			315,000																	315,000
Operating Income (Loss)																				$ 6,700		7,400	6,100
Contractual Sales Price			$ 142,000																	142,000
Future payment by an anchor tenant			5,500																	$ 5,500
Proceeds from sales of real estate			133,700
Gains on sales of real estate			44,400
Tower Oaks Land [Member]
Real Estate Properties [Line Items]
Loans Receivable with Fixed Rates of Interest	0.0192
Contractual Sales Price	$ 46,000
Proceeds from sales of real estate	25,900
Gains on sales of real estate	15,700
Note receivable	$ 21,000
Area of Land | a	41
17Fifty Presidents Street
Real Estate Properties [Line Items]
Net Rentable Area | ft²																													276,000
191 Spring Street
Real Estate Properties [Line Items]
Net Rentable Area | ft²																									171,000
Salesforce Tower
Real Estate Properties [Line Items]
Net Rentable Area | ft²																								1,421,000
Ownership Percentage by Parent																								95.00%
Signature at Reston
Real Estate Properties [Line Items]
Net Rentable Area | ft²																												518,000
Number of apartment units | apartments																												508
Reston Gateway Master Plan
Real Estate Properties [Line Items]
Net Rentable Area | ft²							1,100,000
Square Footage Of Signed Lease | ft²							850,000
Number of real estate properties | Buildings							2
Proto Kendall Square
Real Estate Properties [Line Items]
Net Rentable Area | ft²																										167,000
Number of apartment units | apartments																										280
343 Madison Avenue [Member]
Real Estate Properties [Line Items]
Net Rentable Area | ft²																											850,000
Ownership Percentage by Parent																											55.00%
Platform 16
Real Estate Properties [Line Items]
Net Rentable Area | ft²				1,100,000
Capital Lease - fixed purchase price				$ 134,800
Cash held in escrows				$ 15,000
Ground Lease Term (in years) | yr				65
Area of Land | a				5.6
Present value of expected net minimum lease payments				$ 12,397
2600 Tower Oaks Boulevard
Real Estate Properties [Line Items]
Net Rentable Area | ft²										179,000											179,000
Impairment losses										$ 3,100
Boston Properties Limited Partnership
Real Estate Properties [Line Items]
Cash held in escrows										95,832				70,602							$ 95,832	70,602	63,174							$ 73,790
Revenues										705,157	$ 686,284	$ 664,484	$ 661,151	655,229	$ 657,712	$ 656,907	$ 632,228				2,717,076	2,602,076	2,550,820
Proceeds from sales of real estate																					455,409	29,810	122,750
Impairment losses																					10,181	0	1,783
Gains on sales of real estate																					190,716	8,240	$ 82,775
Note receivable										19,468				$ 0							$ 19,468	$ 0
Boston Properties Limited Partnership | 500 E Street
Real Estate Properties [Line Items]
Gains on sales of real estate								$ 98,900
Boston Properties Limited Partnership | 91 Hartwell Avenue [Member]
Real Estate Properties [Line Items]
Gains on sales of real estate						$ 15,900
Boston Properties Limited Partnership | Quorum Office Park
Real Estate Properties [Line Items]
Gains on sales of real estate					$ 9,200
Boston Properties Limited Partnership | 1333 New Hampshire Avenue [Member]
Real Estate Properties [Line Items]
Gains on sales of real estate			$ 48,400
Boston Properties Limited Partnership | 2600 Tower Oaks Boulevard
Real Estate Properties [Line Items]
Impairment losses										$ 1,500

Real Estate Future minimum paym

Real Estate Future minimum payments for Platform 16 capital lease (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Nov. 29, 2018
Capital Leased Assets [Line Items]
2,019	$ 1,441
2,020	12,682
Total expected minimum lease payments	91,684
Interest portion	27,497
Present value of expected net minimum lease payments	$ 64,187
Platform 16
Capital Leased Assets [Line Items]
Period from November 29, 2018 through December 31, 2018		$ 1,385
2,019		427
2,020		11,132
Total expected minimum lease payments		12,944
Interest portion		547
Present value of expected net minimum lease payments		$ 12,397

Deferred Charges (Details)

Deferred Charges (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred Charges [Abstract]
Leasing costs, including lease related intangibles	$ 1,191,297	$ 1,147,181
Financing costs	12,796	14,991
Deferred charges, gross	1,204,093	1,162,172
Less: Accumulated amortization	(525,369)	(483,134)
Deferred charges, total	$ 678,724	$ 679,038

Deferred Charges Schedule of Ac

Deferred Charges Schedule of Acquired In-Place Lease Intangibles (Details) $ in Thousands	Dec. 31, 2018USD ($)
Deferred Charges [Abstract]
2,019	$ 25,690
2,020	13,051
2,021	8,610
2,022	4,798
2,023	$ 4,107

Investments in Unconsolidated_3

Investments in Unconsolidated Joint Ventures (Investments in Unconsolidated Joint Ventures) (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2018USD ($)ft²Land_ParcelsBuildingspayments		Jul. 27, 2018	Jul. 13, 2018	Dec. 31, 2017USD ($)
Schedule of Equity Method Investments [Line Items]
Other Liabilities		$ 503,726				$ 443,980
Investments in unconsolidated joint ventures		956,309				619,925
Investments In Affiliates Subsidiaries Associates And Joint Ventures net	[1]	931,219				593,980
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Other Liabilities		$ 25,100				25,900
Square 407 Limited Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Market Square North
Ownership Percentage		50.00%
Other Liabilities	[1]	$ 6,424				8,258
The Metropolitan Square Associates LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Metropolitan Square
Ownership Percentage		20.00%
Investments in unconsolidated joint ventures	[1]	$ 2,644				3,339
BP/CRF 901 New York Avenue LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		901 New York Avenue
Ownership Percentage	[2]	25.00%
Other Liabilities	[1]	$ 13,640				13,811
WP Project Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Wisconsin Place Land and Infrastructure
Ownership Percentage	[3]	33.30%
Investments in unconsolidated joint ventures	[1]	$ 38,214				39,710
Annapolis Junction NFM, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Annapolis Junction
Ownership Percentage	[4]	50.00%
Investments in unconsolidated joint ventures	[1]	$ 25,268				18,381
Number of real estate properties | Buildings		3
Parcels of undeveloped land | Land_Parcels		2
540 Madison Venture LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		540 Madison Avenue
Ownership Percentage		60.00%
Investments in unconsolidated joint ventures	[1]	$ 66,391				66,179
500 North Capitol Venture LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		500 North Capitol Street, NW
Ownership Percentage		30.00%
Other Liabilities	[1]	$ 5,026				3,876
501 K Street LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		1001 6th Street
Ownership Percentage	[5]	50.00%
Investments in unconsolidated joint ventures	[1]	$ 42,557				42,657
Potential additonal payments to joint venture partner | payments		2
Minimum square footage to make a potential additional payment to joint venture partner (in sqft) | ft²		520,000
Podium Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		The Hub on Causeway - Podium
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 69,302				67,120
Residential Tower Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		The Hub on Causeway - Residential
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 47,505				28,212
Hotel Tower Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		The Hub on Causeway - Hotel Air Rights
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 3,022				1,690
100 Causeway Street [Member]
Schedule of Equity Method Investments [Line Items]
Properties	[6]	100 Causeway Street
Ownership Percentage		50.00%	[6]	50.00%
Investments in unconsolidated joint ventures	[1]	$ 23,804				0
Entity Owning Land And Infrastructure Of Project [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		33.30%
1265 Main Office JV LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		1265 Main Street
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 3,918				4,641
BNY Tower Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Dock 72
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 82,520				72,104
CA-Colorado Center Limited Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Colorado Center
Ownership Percentage		50.00%
Investments in unconsolidated joint ventures	[1]	$ 253,495				254,440
7750 Wisconsin Avenue LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		7750 Wisconsin Avenue
Ownership Percentage	[6]	50.00%
Investments in unconsolidated joint ventures	[1]	$ 69,724				21,452
BP-M 3HB Venture LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		3 Hudson Boulevard
Ownership Percentage		25.00%			25.00%
Investments in unconsolidated joint ventures	[1]	$ 46,993				0
SMBP Venture LP [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Santa Monica Business Park
Ownership Percentage		55.00%
Investments in unconsolidated joint ventures	[1]	$ 180,952				$ 0
[1]	Investments with deficit balances aggregating approximately $25.1 million and $25.9 million at December 31, 2018 and 2017, respectively, are included within Other Liabilities in the Company’s Consolidated Balance Sheets.
[2]	The Company’s economic ownership has increased based on the achievement of certain return thresholds.
[3]	The Company’s wholly-owned subsidiary that owns Wisconsin Place Office also owns a 33.3% interest in the joint venture entity that owns the land, parking garage and infrastructure of the project.
[4]	The joint venture owns three in-service buildings and two undeveloped land parcels.
[5]	Under the joint venture agreement for this land parcel, the partner will be entitled to up to two additional payments from the venture based on increases in total entitled square footage of the project above 520,000 square feet and achieving certain project returns at stabilization.
[6]	This entity is a VIE (See Note 1).

Investments in Unconsolidated_4

Investments in Unconsolidated Joint Ventures (Balance Sheets of the Unconsolidated Joint Ventures) (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
ASSETS
Real estate and development in process, net		$ 16,752,119	$ 16,507,008
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Mortgage and notes payable, net		2,964,572	2,979,281
Other Liabilities		503,726	443,980
Total liabilities and equity / capital		20,256,477	19,372,233
Carying value of the Company's investment in unconsolidated joint ventures		956,309	619,925
Unconsolidated Joint Ventures [Member]
ASSETS
Real estate and development in process, net		3,545,906	1,768,996
Other assets		543,512	367,743
Total assets		4,089,418	2,136,739
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Mortgage and notes payable, net		2,017,609	1,437,440
Other Liabilities		582,006	99,215
Members'/Partners' equity		1,489,803	600,084
Total liabilities and equity / capital		4,089,418	2,136,739
Company's share of equity		622,498	286,495
Basis differentials	[1]	308,721	307,485
Carying value of the Company's investment in unconsolidated joint ventures	[2]	931,219	593,980
Colorado Center [Member]
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Basis differentials		316,700	322,500
Unconsolidated Joint Ventures [Member]
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Other Liabilities		$ 25,100	$ 25,900
[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 result from impairments of investments, acquisitions through joint ventures with no change in control 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. At December 31, 2018 and 2017, there was an aggregate basis differential of approximately $316.7 million and $322.5 million, respectively, between the carrying value of the Company’s investment in the joint venture that owns Colorado Center and the joint venture’s basis in the assets and liabilities, which differential (excluding land) shall be amortized over the remaining lives of the related assets and liabilities.
[2]	Investments with deficit balances aggregating approximately $25.1 million and $25.9 million at December 31, 2018 and 2017, respectively, have been reflected within Other Liabilities in the Company’s Consolidated Balance Sheets.

Investments in Unconsolidated_5

Investments in Unconsolidated Joint Ventures (Statements of Operations of the Joint Ventures) (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Total revenue		$ 705,157	$ 686,284	$ 664,484	$ 661,151	$ 655,229	$ 657,712	$ 656,907	$ 632,228	$ 2,717,076	$ 2,602,076	$ 2,550,820
Expenses
Depreciation and amortization										645,649	617,547	694,403
Total expenses										1,791,579	1,693,966	1,723,253
Other income (expense)
Interest expense										(378,168)	(374,481)	(412,849)
Gains on sales of real estate										182,356	7,663	80,606
Net income										712,563	562,481	569,977
Income from unconsolidated joint ventures										2,222	11,232	8,074
Gain on sale of investment in unconsolidated joint venture										0	0	59,370
Straight-line rent adjustments										51,900	54,800	31,700
Mortgage and notes payable, net		2,964,572				2,979,281				2,964,572	2,979,281
Above and below market rent adjustments, net										23,800	23,500	30,200
Gain on sale of investment in unconsolidated joint venture										0	0	55,707
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Total revenue	[1]									271,951	222,517	177,182
Expenses
Operating										106,610	90,542	76,741
Depreciation and amortization	[2]									103,079	57,079	44,989
Total expenses										209,689	147,621	121,730
Other income (expense)
Interest expense										(71,308)	(46,371)	(34,016)
Gains on sales of real estate										16,951	0	0
Net income										7,905	28,525	21,436
Company's share of net income										8,084	18,439	9,873
Basis differential	[3]									(5,862)	(7,207)	(1,799)
Income from unconsolidated joint ventures										2,222	11,232	8,074
Gain on sale of investment in unconsolidated joint venture										0	0	59,370
Straight-line rent adjustments										15,900	21,700	18,100
Mortgage and notes payable, net		$ 2,017,609				$ 1,437,440				2,017,609	1,437,440
The Metropolitan Square Associates LLC [Member]
Expenses
Depreciation and amortization										22,400
The Metropolitan Square Associates LLC [Member] | Boston Properties, Inc. [Member]
Expenses
Depreciation and amortization										4,500
Colorado Center [Member]
Other income (expense)
Straight-line rent adjustments										2,400	1,900	1,400
Above and below market rent adjustments, net										$ 1,600	$ 2,900	$ 900
[1]	Includes straight-line rent adjustments of approximately $15.9 million, $21.7 million and $18.1 million for the years ended December 31, 2018, 2017 and 2016, respectively.
[2]	During the year ended December 31, 2018, the joint venture that owns Metropolitan Square in Washington, DC, commenced a renovation project and recorded accelerated depreciation expense of approximately $22.4 million related to the remaining book value of the assets to be replaced. The Company's share of the accelerated depreciation expense totaled approximately $4.5 million.
[3]	Includes straight-line rent adjustments of approximately $2.4 million, $1.9 million and $1.4 million for the years ended December 31, 2018, 2017 and 2016, respectively. Also includes net above-/below-market rent adjustments of approximately $1.6 million, $2.9 million and $0.9 million for the years ended December 31, 2018, 2017 and 2016, respectively.

Investment in unconsolidated Jo

Investment in unconsolidated Joint Ventures (Narrative) (Details) $ in Thousands	Nov. 16, 2018USD ($)ft²yr	Jul. 27, 2018USD ($)ft²yr	Jul. 19, 2018USD ($)ft²ayrBuildings	Jul. 13, 2018USD ($)ft²	Apr. 27, 2018USD ($)ft²	Apr. 26, 2018	Apr. 19, 2018USD ($)ft²yrapartments	Dec. 31, 2018USD ($)ft²		Dec. 31, 2018USD ($)ft²		Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2017USD ($)	Dec. 31, 2015USD ($)
Schedule of Equity Method Investments [Line Items]
Gains on sales of real estate										$ 182,356		$ 7,663	$ 80,606
Proceeds from Issuance of Secured Debt										0		2,300,000	0
Payments to Acquire Equity Method Investments										345,717		109,015	575,795
Mortgage notes payable, net								$ 2,964,572		2,964,572		2,979,281
Capital distributions from unconsolidated joint ventures										0		251,000	20,440
Restricted Cash and Cash Equivalents, Current								95,832		95,832		70,602	$ 63,174	$ 70,602	$ 73,790
Accumulated Other Comprehensive Income (Loss), Net of Tax								$ (47,741)		$ (47,741)		$ (50,429)
Santa Monica Business Park [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage								55.00%		55.00%
100 Causeway Street [Member]
Schedule of Equity Method Investments [Line Items]
Net Rentable Area | ft²		627,000
Term of Lease Signed (in years) | yr		20
Ownership Percentage		50.00%						50.00%	[1]	50.00%	[1]
Payment for improvements for equity method investment		$ 3,900
Payments to Acquire Equity Method Investments		$ 37,400
Podium Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage								50.00%		50.00%
The Hub on Causeway - Residential [Member]
Schedule of Equity Method Investments [Line Items]
Construction Loan Facility Borrowing Capacity							$ 180,000
Debt Instrument, Basis Spread on Variable Rate							2.00%
Number of extensions							2
Extension Option (in years) | yr							1
Construction Loan								$ 40,500		$ 40,500
Net Rentable Area | ft²							320,000
Ownership Percentage							50.00%
Number of apartment units | apartments							440
540 Madison Avenue [Member]
Schedule of Equity Method Investments [Line Items]
Debt Instrument, Basis Spread on Variable Rate					1.10%	1.50%
Net Rentable Area | ft²					284,000
Ownership Percentage					60.00%
Mortgage notes payable, net					$ 120,000
3 Hudson Boulevard [Member]
Schedule of Equity Method Investments [Line Items]
Debt Instrument, Basis Spread on Variable Rate				3.50%
Net Rentable Area | ft²				2,000,000
Ownership Percentage				25.00%				25.00%		25.00%
Payments to Acquire Equity Method Investments				$ 45,600
Future payments to acquire equity method investments				62,200
Mortgage notes payable, net				$ 80,000
Annapolis Junction Building Six [Member]
Schedule of Equity Method Investments [Line Items]
Construction Loan Facility Borrowing Capacity	$ 14,300
Debt Instrument, Basis Spread on Variable Rate	2.00%
Number of extensions	1
Extension Option (in years) | yr	1
Construction Loan	$ 13,100
Net Rentable Area | ft²	119,000
Ownership Percentage	50.00%
Annapolis Junction Building One [Member]
Schedule of Equity Method Investments [Line Items]
Net Rentable Area | ft²								118,000		118,000
Ownership Percentage								50.00%		50.00%
Gains on sales of real estate								$ 8,300
Santa Monica Business Park [Member] | Santa Monica Business Park [Member]
Schedule of Equity Method Investments [Line Items]
Debt Instrument, Basis Spread on Variable Rate			1.28%
Net Rentable Area | ft²			1,200,000
rentable square feet subject to a ground lease (percetnage)			70.00%
Term of Lease Signed (in years) | yr			80
Payments to Acquire Equity Method Investments			$ 179,700
Mortgage notes payable, net			$ 300,000
number of buildings | Buildings			21
Area of Land | a			47
Aggregate purchase price			$ 626,700
seller funded leasing costs			11,500
Derivative, Notional Amount			$ 300,000
Derivative, Fixed Interest Rate			4.063%
Accumulated Other Comprehensive Income (Loss), Net of Tax								(5,600)		$ (5,600)
Joint venture partner [Member] | Santa Monica Business Park [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage			45.00%
Payments to Acquire Equity Method Investments			$ 147,000
Joint venture partner [Member] | 100 Causeway Street [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		50.00%
Payments to Acquire Equity Method Investments		$ 41,300
BXP [Member]
Schedule of Equity Method Investments [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax								$ (3,100)		$ (3,100)
[1]	This entity is a VIE (See Note 1).

Investments in Unconsolidated_6

Investments in Unconsolidated Joint Ventures Purchase price allocation table (Details) - Santa Monica Business Park [Member] $ in Thousands	Jul. 19, 2018USD ($)
Schedule of Asset Acquisition [Line Items]
Land and improvements	$ 100,453
Leasehold interest in land	248,944
Site improvements	13,379
Building and improvements	593,669
Tenant improvements	31,329
In-place lease intangibles	47,955
Above-market lease intangible	4,495
Below-market lease intangible	(17,503)
Capital lease obligation	(396,008)
Net assets acquired	$ 626,713

Mortgage Notes Payable, Net S_2

Mortgage Notes Payable, Net Schedule Of Aggregate Principal Payments On Mortgage Notes (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Mortgage Notes Payable [Abstract]
2,019	$ 19,670
2,020	20,766
2,021	40,182
2,022	614,710
2,023	0
Thereafter	2,300,000
Total	2,995,328
Deferred finance costs, net	(30,756)
Total carrying value of mortgage notes payable, net	$ 2,964,572	$ 2,979,281

Mortgage Notes Payable, Net (Na

Mortgage Notes Payable, Net (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Mortgage Notes Payable [Line Items]
Mortgage notes payable, net (amounts related to VIEs of $2,929,326 and $2,939,183 at December 31, 2018 and 2017, respectively)	$ 2,964,572	$ 2,979,281
Number Of Mortgage Loans Accounted For Fair Value	0	0
Interest Expense Decrease Due To Recording Mortgage Loans At Fair Value		$ 19,600	$ 46,400
Minimum [Member]
Mortgage Notes Payable [Line Items]
Coupon/Stated Rate	3.43%	3.43%
Number Real Estate Assets Used For Mortgage Loan Collateral	1
Maximum [Member]
Mortgage Notes Payable [Line Items]
Coupon/Stated Rate	7.69%	7.69%
Fixed Rate Mortgages [Member]
Mortgage Notes Payable [Line Items]
Mortgage notes payable, net (amounts related to VIEs of $2,929,326 and $2,939,183 at December 31, 2018 and 2017, respectively)	$ 3,000,000	$ 3,000,000
Debt, Weighted Average Interest Rate	3.77%	3.78%
Variable Rate Mortgages [Member]
Mortgage Notes Payable [Line Items]
Number of variable rate mortgage loans	0	0

Unsecured Senior Notes Schedule

Unsecured Senior Notes Schedule of Unsecured Senior Notes (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018		Nov. 28, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Deferred finance costs, net		$ (30,756)
Total		7,544,697			$ 7,247,330
Boston Properties Limited Partnership
Debt Instrument [Line Items]
Deferred finance costs, net		(30,800)
Total		7,544,697			$ 7,247,330
Boston Properties Limited Partnership | Senior Notes [Member]
Debt Instrument [Line Items]
Principal Amount		7,600,000
Net unamortized discount		(18,722)
Deferred finance costs, net		(36,581)
Total		$ 7,544,697
Boston Properties Limited Partnership | Senior Notes [Member] | Unsecured Senior Notes 5.708%
Debt Instrument [Line Items]
Coupon/Stated Rate		5.625%
Effective Rate	[1]	5.708%
Principal Amount		$ 700,000
Maturity date	[2]	Nov. 15, 2020
Boston Properties Limited Partnership | Senior Notes [Member] | Unsecured Senior Notes 4.289%
Debt Instrument [Line Items]
Coupon/Stated Rate		4.125%
Effective Rate	[1]	4.289%
Principal Amount		$ 850,000
Maturity date	[2]	May 15, 2021
Boston Properties Limited Partnership | Senior Notes [Member] | Unsecured Senior Notes 3.954%
Debt Instrument [Line Items]
Coupon/Stated Rate		3.85%
Effective Rate	[1]	3.954%
Principal Amount		$ 1,000,000
Maturity date	[2]	Feb. 1, 2023
Boston Properties Limited Partnership | Senior Notes [Member] | Unsecured Senior Notes 3.279%
Debt Instrument [Line Items]
Coupon/Stated Rate		3.125%
Effective Rate	[1]	3.279%
Principal Amount		$ 500,000
Maturity date	[2]	Sep. 1, 2023
Boston Properties Limited Partnership | Senior Notes [Member] | Unsecured Senior Notes 3.916%
Debt Instrument [Line Items]
Coupon/Stated Rate		3.80%
Effective Rate	[1]	3.916%
Principal Amount		$ 700,000
Maturity date	[2]	Feb. 1, 2024
Boston Properties Limited Partnership | Senior Notes [Member] | Unsecured Senior Notes 3.35%
Debt Instrument [Line Items]
Coupon/Stated Rate		3.20%
Effective Rate	[1]	3.35%
Principal Amount		$ 850,000
Maturity date	[2]	Jan. 15, 2025
Boston Properties Limited Partnership | Senior Notes [Member] | Unsecured Senior Note 3.766%
Debt Instrument [Line Items]
Coupon/Stated Rate		3.65%
Effective Rate	[1]	3.766%
Principal Amount		$ 1,000,000
Maturity date	[2]	Feb. 1, 2026
Boston Properties Limited Partnership | Senior Notes [Member] | Unsecured Senior Note 3.495%
Debt Instrument [Line Items]
Coupon/Stated Rate		2.75%
Effective Rate	[1]	3.495%
Principal Amount		$ 1,000,000
Maturity date	[2]	Oct. 1, 2026
Boston Properties Limited Partnership | Senior Notes [Member] | Unsecured Senior Notes 4.628%
Debt Instrument [Line Items]
Coupon/Stated Rate		4.50%		4.50%
Effective Rate		4.628%	[1]	4.628%
Principal Amount		$ 1,000,000
Maturity date	[2]	Dec. 1, 2028
[1]	Yield on issuance date including the effects of discounts on the notes, settlements of interest rate contracts and the amortization of financing costs.
[2]	principal amounts are due prior to maturity.

Unsecured Senior Notes Unsecure

Unsecured Senior Notes Unsecured Senior Notes (Narrative) (Details) - USD ($) $ in Thousands	Dec. 13, 2018	Nov. 28, 2018	Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Loss on Extinguishment of Debt			$ 16,490		$ (496)	$ 371
Repayments of Unsecured Debt			699,517		848,020	0
Proceeds from unsecured senior notes			$ 996,410		847,935	1,989,790
Senior Notes [Member]
Debt Instrument [Line Items]
Maximum Leverage Ratio			60.00%
Maximum Secured Debt Leverage Ratio			50.00%
Minimum Interest Coverage Ratio			1.50
Minimum Unencumbered Asset Value Percentage Of Unsecured Debt			150.00%
Boston Properties Limited Partnership
Debt Instrument [Line Items]
Loss on Extinguishment of Debt			$ 16,490		(496)	371
Repayments of Unsecured Debt			699,517		848,020	0
Proceeds from unsecured senior notes			$ 996,410		$ 847,935	$ 1,989,790
Boston Properties Limited Partnership | Senior Notes [Member] | Unsecured Senior Notes 4.628%
Debt Instrument [Line Items]
Coupon/Stated Rate		4.50%	4.50%
Senior Notes Pricing		99.641%
Effective Rate		4.628%	4.628%	[1]
Proceeds from unsecured senior notes		$ 988,100
Debt Instrument, Face Amount		$ 1,000,000
Boston Properties Limited Partnership | Senior Notes [Member] | Unsecured Senior Notes 5.967%
Debt Instrument [Line Items]
Debt Instrument, Increase, Accrued Interest	$ 6,600
Debt Instrument, Redemption Price, Percentage	102.28%
Loss on Extinguishment of Debt	$ 16,500
Redemption Premium	$ 16,000
Coupon/Stated Rate	5.875%
Repayments of Unsecured Debt	$ 722,600
Debt Instrument, Face Amount	$ 700,000
[1]	Yield on issuance date including the effects of discounts on the notes, settlements of interest rate contracts and the amortization of financing costs.

Unsecured Credit Facility (Deta

Unsecured Credit Facility (Details) $ in Thousands	Apr. 24, 2017USD ($)mo	Dec. 31, 2018USD ($)	Dec. 31, 2018USD ($)yr	Apr. 24, 2018USD ($)	Dec. 31, 2017USD ($)	Apr. 23, 2017USD ($)
Line of Credit Facility [Line Items]
Unsecured term loan, net		$ 498,488	$ 498,488		$ 0
Line of Credit Facility, Amount Outstanding		$ 0	$ 0		45,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 1,500,000					$ 1,000,000
Competitive bid quote	65.00%
Line of Credit Facility, Amount Outstanding					$ 45,000
Maximum Leverage Ratio		60.00%
Leverage Ratio Maximum Increasing Limit		65.00%
Leverage Ratio Reduction Limit		60.00%
Leverage Ratio Reduction Period, Years | yr			1
Maximum Secured Debt Leverage Ratio		55.00%
Fixed Charge Coverage Ratio Minimum.		1.40	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		1.75	1
Potential increase to line of credit				$ 500,000
Delayed Draw Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity						$ 500,000
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.15%
Unsecured term loan, net				$ 500,000
Line of Credit Facility, Amount Outstanding		$ 500,000	$ 500,000
Maximum [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.30%
Minimum [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.10%
Current credit rating [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.125%
Interest Rate Based on LIBOR or CDOR [Member] | Delayed Draw Facility [Member]
Line of Credit Facility [Line Items]
Margin added to Calculated Interest Rate				0.90%
Interest Rate Based on LIBOR or CDOR [Member] | Maximum [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Margin added to Calculated Interest Rate	1.55%
Interest Rate Based on LIBOR or CDOR [Member] | Maximum [Member] | Delayed Draw Facility [Member]
Line of Credit Facility [Line Items]
Margin added to Calculated Interest Rate	1.75%
Interest Rate Based on LIBOR or CDOR [Member] | Minimum [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Margin added to Calculated Interest Rate	0.775%
Interest Rate Based on LIBOR or CDOR [Member] | Minimum [Member] | Delayed Draw Facility [Member]
Line of Credit Facility [Line Items]
Margin added to Calculated Interest Rate	0.85%
Interest Rate Based on LIBOR or CDOR [Member] | Current credit rating [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Margin added to Calculated Interest Rate		0.825%	0.825%
Interest Rate Based on LIBOR or CDOR [Member] | Current credit rating [Member] | Delayed Draw Facility [Member]
Line of Credit Facility [Line Items]
Margin added to Calculated Interest Rate		0.90%	0.90%
Alternative Base Interest Rate Calculation [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Amount added to Federal Funds Rate to Calculate Interest Rate	0.50%
LIBOR Period Used to Calculate Interest Rate (in months) | mo	1
Amount added to LIBOR to Calculate Interest Rate	1.00%
Alternative Base Interest Rate Calculation [Member] | Maximum [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Margin added to Calculated Interest Rate	0.55%
Alternative Base Interest Rate Calculation [Member] | Maximum [Member] | Delayed Draw Facility [Member]
Line of Credit Facility [Line Items]
Margin added to Calculated Interest Rate	0.75%
Alternative Base Interest Rate Calculation [Member] | Minimum [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Margin added to Calculated Interest Rate	0.00%
Alternative Base Interest Rate Calculation [Member] | Minimum [Member] | Delayed Draw Facility [Member]
Line of Credit Facility [Line Items]
Margin added to Calculated Interest Rate	0.00%
Alternative Base Interest Rate Calculation [Member] | Current credit rating [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Margin added to Calculated Interest Rate		0.00%	0.00%
Alternative Base Interest Rate Calculation [Member] | Current credit rating [Member] | Delayed Draw Facility [Member]
Line of Credit Facility [Line Items]
Margin added to Calculated Interest Rate		0.00%	0.00%

Commitments And Contingencies (

Commitments And Contingencies (Details) - USD ($) $ in Millions	10 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2009	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 18, 2014	Jan. 10, 2014
Commitments And Contingencies [Line Items]
Letter of credit and performance obligations	$ 7.8	$ 7.8
Property insurance program per occurrence limits	1,000	1,000
Per occurrence limit for NBCR Coverage		1,000
Value of program trigger	160	$ 160
Coinsurance of program trigger		18.00%
Deductible in insurance as a percentage of the value of the affected property, San Francisco and Los Angeles		3.00%
Per occurrence limit of the earthquake insurance which covers San Francisco and Los Angeles regions	240
Annual aggregate limit of the earthquake insurance which covers San Francisco and Los Angeles regions	240
Amount of earthquake insurance provided by IXP, LLC as direct insurer San Francisco and Los Angeles		$ 20
767 Venture, LLC [Member]
Commitments And Contingencies [Line Items]
Maximum funding obligation	116.1	116.1
Property insurance program per occurrence limits	1,625	1,625
Lehman [Member]
Commitments And Contingencies [Line Items]
Bankruptcy claim, amount filed by general creditor			$ 45.3
Bankruptcy claim amount allowed by court to creditor								$ 45.2
Bankruptcy Claims, Amount of Claims Settled	0.3	0.3		$ 0.4	$ 1.4	$ 8.1	$ 7.7
Bankruptcy remaining claim amount allowed by court to creditor	27.2	27.2
601 Lexington Avenue
Commitments And Contingencies [Line Items]
Coverage For Acts Of Terrorism Under TRIA Covered in Excess of Amount Covered by IXP		250
Boston Properties Limited Partnership
Commitments And Contingencies [Line Items]
Operating partnership guarantee to cover liabilities of IXP	$ 20	$ 20

Noncontrolling Interests (Narra

Noncontrolling Interests (Narrative) (Details) - Boston Properties Limited Partnership	Dec. 31, 2018shares
Noncontrolling Interest [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Operating Partnership (OP) Units (in shares)	16,783,558
Long-Term Incentive Plan (LTIP) Units (in shares)	991,577
OPP Units 2012 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Outperformance awards in LTIP Units (in shares)	118,067
MYLTIP 2,013
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2013 MYLTIP	68,889
MYLTIP 2,014
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2014 MYLTIP	23,187
MYLTIP 2015 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2015 MYLTIP	28,724
MYLTIP 2016 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2016 MYLTIP	471,579
MYLTIP 2017 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2017 MYLTIP	398,871
MYLTIP 2,018
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2018 MYLTIP	341,366

(Common Units) (Narrative) (Det

(Common Units) (Narrative) (Details) $ / shares in Units, $ in Millions	Feb. 04, 2018USD ($)shares	Feb. 03, 2017USD ($)shares	Feb. 04, 2016USD ($)shares	Dec. 31, 2018USD ($)sharesyr$ / shares	Dec. 31, 2017shares	May 02, 2016shares
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Conversion of LTIP Units to OP Units (in units)						625,043
MYLTIP 2,014
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Final awards percentage of target		27.70%
Value of MYLTIP Awards | $		$ 3.5
MYLTIP Units forfeited		447,386
2012 OPP and 2013 MYLTIP [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Conversion of LTIP Units to OP Units (in units)						32,349
OP Units [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
OP Units for redemption (in shares)				83,136	495,637
Redemption of OP units issued on conversion of LTIP Units (in shares)				48,389	36,486
MYLTIP Units distribution as percentage of OP Unit distribution prior to measurement date				10.00%
Restriction on redemption of OP Unit to Common Stock (in years) | yr				1
Redemption of OP Unit equivalence to Common Stock (in shares)				1
Common units of operating partnership if converted value | $				$ 2,000
Closing price of common stock (in dollars per share) | $ / shares				$ 112.55
MYLTIP 2015 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Final awards percentage of target	22.00%
Value of MYLTIP Awards | $	$ 3.6
MYLTIP Units forfeited	337,847
MYLTIP 2,013
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Final awards percentage of target			109.50%
Value of MYLTIP Awards | $			$ 13.5
MYLTIP Units forfeited			205,762
Boston Properties Limited Partnership | MYLTIP 2014
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2014 MYLTIP				23,187
Boston Properties Limited Partnership | MYLTIP 2016 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2016 MYLTIP				471,579
Boston Properties Limited Partnership | MYLTIP 2017 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2017 MYLTIP				398,871
Boston Properties Limited Partnership | MYLTIP 2015 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2015 MYLTIP				28,724
Boston Properties Limited Partnership | MYLTIP 2018
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2018 MYLTIP				341,366

Noncontrolling Interests Common

Noncontrolling Interests Common Units Distributions (Details) - Boston Properties Limited Partnership - $ / shares	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Jan. 30, 2018	Dec. 17, 2018
Noncontrolling Interest [Line Items]
Distributions Declared To OP And LTIP Units Per Unit					$ 0.95
Distributions Declared To MYLTIP Units Per Unit					$ 0.095
Distributions made to OP and LTIP units per unit (in dollars per share)	$ 0.95	$ 0.80	$ 0.80	$ 0.80
Distributions Made To MYLTIP Units Per Unit	$ 0.095	$ 0.080	$ 0.080	$ 0.080

Noncontrolling Interests Redeem

Noncontrolling Interests Redeemable common units of Boston Properties Limited Partnership (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Conversion of redeemable partnership units	$ 0	$ 0	$ 0
Cumulative effect of a change in accounting principle	5,496	(2,035)
Boston Properties Limited Partnership
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Cumulative effect of a change in accounting principle	4,933	(272)
Noncontrolling Interest [Member]
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Conversion of redeemable partnership units	(24,311)	(22,879)	(15,374)
Cumulative effect of a change in accounting principle	563	(1,763)
Noncontrolling Interest [Member] | Boston Properties Limited Partnership
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning Balance	2,292,263	2,262,040	2,286,689
Contributions	34,680	31,743	31,395
Net income	(66,807)	52,210	59,260
Distributions	(62,731)	(54,494)	(49,087)
Conversion of redeemable partnership units	(2,880)	(16,916)	(6,461)
Unearned compensation	2,181	1,650	(3,464)
Cumulative effect of a change in accounting principle	563	(1,763)
Other Comprehensive Income (Loss)	304	206	(4,379)
Adjustment to reflect redeemable partnership units at redemption value	(330,596)	17,587	(51,913)
Ending Balance	$ 2,000,591	$ 2,292,263	$ 2,262,040

Noncontrolling Interests (Prope

Noncontrolling Interests (Property Partnerships) (Narrative) (Details) - USD ($) $ in Thousands	May 12, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 06, 2017
Noncontrolling Interest [Line Items]
Property partnerships		$ 1,711,445	$ 1,683,760
Proceeds from sales of real estate		455,409	29,810	$ 122,750
Gains on sales of real estate		182,356	7,663	80,606
Boston Properties Limited Partnership
Noncontrolling Interest [Line Items]
Proceeds from sales of real estate		455,409	29,810	122,750
Gains on sales of real estate		190,716	$ 8,240	$ 82,775
Salesforce Tower | Consolidated Properties [Member]
Noncontrolling Interest [Line Items]
Ownership Percentage	5.00%
Portion of project costs covered by a construction loan	50.00%
Portion of costs funded (in percentage)	50.00%
Debt Instrument, Basis Spread on Variable Rate	3.00%
Salesforce Tower | Boston Properties, Inc. [Member] | Consolidated Properties [Member]
Noncontrolling Interest [Line Items]
Costs funded (in percentage)	2.50%
Preferred equity funded		$ 22,600
767 Fifth Avenue (the general motors building) [Member] | Consolidated Properties [Member]
Noncontrolling Interest [Line Items]
Ownership Percentage by Parent					60.00%
Unpaid principal balance of the members' notes payable contributed to equity					$ 273,900
Property partnerships					109,600
Consolidation, Eliminations [Member] | 767 Fifth Avenue (the general motors building) [Member] | Consolidated Properties [Member]
Noncontrolling Interest [Line Items]
Unpaid principal balance of the members' notes payable contributed to equity					$ 164,400

Noncontrolling Interests Noncon

Noncontrolling Interests Noncontrolling Interests—Property Partnerships Table (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Noncontrolling Interest [Line Items]
Beginning Balance	$ 1,683,760,000
Capital contributions	46,701,000	$ 161,585,000		$ 11,951,000
Net income (loss)	62,909,000	47,832,000		(2,068,000)
Accumulated other comprehensive income (loss)	880,000	(1,922,000)		(5,256,000)
Ending Balance	1,711,445,000	1,683,760,000
Property Partnerships Member
Noncontrolling Interest [Line Items]
Beginning Balance	1,683,760,000	1,530,647,000		1,574,400,000
Capital contributions	46,701,000	161,585,000	[1]	10,756,000
Net income (loss)	62,909,000	47,832,000		(2,068,000)
Accumulated other comprehensive income (loss)	576,000	(2,128,000)		(877,000)
Distributions	(82,501,000)	54,176,000		51,564,000
Ending Balance	1,711,445,000	$ 1,683,760,000		$ 1,530,647,000
767 Fifth Avenue (the general motors building) [Member] | Property Partnerships Member
Noncontrolling Interest [Line Items]
Ending Balance	$ 109,576
[1]	Includes the contribution of the remaining unpaid principal balance of the members’ notes payable totaling $109,576 to equity in the consolidated entity that owns 767 Fifth Avenue (the General Motors Building).

Stockholders' Equity _ Partne_3

Stockholders' Equity / Partners' Capital (Details) $ / shares in Units, $ in Millions	Jun. 02, 2017USD ($)yr	Dec. 31, 2018$ / sharesshares	Dec. 31, 2017$ / sharesshares	Dec. 31, 2016shares	Mar. 27, 2018$ / shares	Jun. 03, 2014USD ($)
Class of Stock [Line Items]
General Partners' Capital Account, Units Outstanding (in units)		1,722,336
Limited Partners' Capital Account, Units Outstanding		152,736,142
Common stock, shares outstanding		154,458,478	154,325,286
Shares of Common Stock issued upon the exercise of options to purchase Common Stock by certain employees		0	6,688	0
Shares of its Common Stock issued in connection with the redemption of an equal number of OP Units		83,136	495,637
ATM Program [Member]
Class of Stock [Line Items]
At the market stock offering program, aggregate value of common stock | $	$ 600					$ 600
At Market Stock Offering Program Maximum Length Of Sale In Years | yr	3
Series B Cumulative Redeemable Preferred Stock / Unit [Member]
Class of Stock [Line Items]
Preferred stock, shares outstanding		80,000	80,000
Preferred Stock, Dividend Rate, Percentage		5.25%
Series B Liquidation Preference Per Share | $ / shares		$ 2,500	$ 2,500		$ 2,500
Depositary shares of Series B Cumulative Redeemable Preferred [Member]
Class of Stock [Line Items]
Preferred stock, shares outstanding		8,000,000
Series B Liquidation Preference Per Share | $ / shares		$ 25			$ 25
Boston Properties Limited Partnership
Class of Stock [Line Items]
General Partners' Capital Account, Units Outstanding (in units)		1,722,336	1,719,540
Limited Partners' Capital Account, Units Outstanding		152,736,142	152,605,746
Shares of its Common Stock issued in connection with the redemption of an equal number of OP Units		83,136	495,637	190,857
Boston Properties Limited Partnership | Series B Cumulative Redeemable Preferred Stock / Unit [Member]
Class of Stock [Line Items]
Preferred stock, shares outstanding		80,000	80,000
Series B Liquidation Preference Per Share | $ / shares		$ 2,500	$ 2,500

Stockholders' Equity _ Partne_4

Stockholders' Equity / Partners' Capital Dividends / Distributions (Details) - $ / shares	Nov. 15, 2018	Oct. 31, 2018	Aug. 15, 2018	Jul. 31, 2018	May 15, 2018	Apr. 30, 2018	Feb. 15, 2018	Jan. 30, 2018	Dec. 17, 2018
Dividends / Distributions [Line Items]
Common Stock / Unit, Dividends / Distributions, Per Share / Unit, Cash Paid		$ 0.95		$ 0.80		$ 0.80		$ 0.80
Dividends Payable, Amount Per Share / Unit									$ 0.95
Boston Properties Limited Partnership
Dividends / Distributions [Line Items]
Common Stock / Unit, Dividends / Distributions, Per Share / Unit, Cash Paid		$ 0.95		$ 0.80		$ 0.80		$ 0.80
Dividends Payable, Amount Per Share / Unit									0.95
Series B Cumulative Redeemable Preferred Stock / Unit [Member]
Dividends / Distributions [Line Items]
Common Stock / Unit, Dividends / Distributions, Per Share / Unit, Cash Paid	$ 32.8125		$ 32.8125		$ 32.8125		$ 32.8125
Dividends Payable, Amount Per Share / Unit									$ 32.8125

Stockholders' Equity _ Partne_5

Stockholders' Equity / Partners' Capital Partners' Capital Changes in Issued and Outstanding Partners' Capital Units (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Limited Partners' Capital Account [Line Items]
Units issued to Boston Properties, Inc. related to Common Stock issued in exchange for OP Units	83,136	495,637
Limited Partners' Ending Balance	152,736,142
General Partners' Ending Balance	1,722,336
Boston Properties Limited Partnership
Limited Partners' Capital Account [Line Items]
General Partners' Beginning Balance	1,719,540
Limited Partners Beginning Balance	152,605,746
Partners' Capital Beginning Balance	154,325,286	153,790,175	153,579,966
Units issued to Boston Properties, Inc. related to Common Stock issued under the Employee Stock Purchase Plan	6,268	6,317	5,695
Units issued to Boston Properties, Inc. related to Common Stock issued under the Stock Option and Incentive Plan, net	43,788	33,157	13,657
Units issued to Boston Properties, Inc. related to Common Stock issued in exchange for OP Units	83,136	495,637	190,857
Limited Partners' Ending Balance	152,736,142	152,605,746
Partners' Capital Ending Balance	154,458,478	154,325,286	153,790,175
General Partners' Ending Balance	1,722,336	1,719,540
Boston Properties Limited Partnership | General Partner [Member]
Limited Partners' Capital Account [Line Items]
General Partners' Beginning Balance	1,719,540	1,717,743	1,715,092
Units issued to Boston Properties, Inc. related to Common Stock issued under the Employee Stock Purchase Plan	132	21	72
Units issued to Boston Properties, Inc. related to Common Stock issued under the Stock Option and Incentive Plan, net	919	111	172
Units issued to Boston Properties, Inc. related to Common Stock issued in exchange for OP Units	1,745	1,665	2,407
General Partners' Ending Balance	1,722,336	1,719,540	1,717,743
Boston Properties Limited Partnership | Limited Partner [Member]
Limited Partners' Capital Account [Line Items]
Limited Partners Beginning Balance	152,605,746	152,072,432	151,864,874
Units issued to Boston Properties, Inc. related to Common Stock issued under the Employee Stock Purchase Plan	6,136	6,296	5,623
Units issued to Boston Properties, Inc. related to Common Stock issued under the Stock Option and Incentive Plan, net	42,869	33,046	13,485
Units issued to Boston Properties, Inc. related to Common Stock issued in exchange for OP Units	81,391	493,972	188,450
Limited Partners' Ending Balance	152,736,142	152,605,746	152,072,432

Stockholders' Equity _ Partne_6

Stockholders' Equity / Partners' Capital Partners' Capital Change in Series B Preferred Units (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Entity Information [Line Items]
Beginning Balance	$ 200,000
Ending Balance	200,000	$ 200,000
Boston Properties Limited Partnership
Entity Information [Line Items]
Beginning Balance	193,623	193,623	$ 193,623
Net Income	10,500	10,500	10,500
Distributions	(10,500)	(10,500)	(10,500)
Ending Balance	$ 193,623	$ 193,623	$ 193,623

Future Minimum Rents Narrative

Future Minimum Rents Narrative (Details) - tenants	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Future Minimum Rent [Line Items]
Number Of Tenants Above Concentration Amount.	0	0	0
Concentration Risk, Percentage	10.00%	10.00%	10.00%
Maximum [Member]
Future Minimum Rent [Line Items]
Initial Term Lease Expiration Date	2,049

Future Minimum Rents Future min

Future Minimum Rents Future minimum rent under non-cancelable operating leases (Details) $ in Thousands	Dec. 31, 2018USD ($)
Future minimum rent [Abstract]
2,019	$ 2,088,171
2,020	2,106,963
2,021	2,015,031
2,022	1,838,699
2,023	1,736,636
Thereafter	$ 12,295,464

Segment Information (Schedule O

Segment Information (Schedule Of Reconciliation Of Net Operating Income To Net Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net income attributable to the Company's common shareholders / unitholders	$ 572,347	$ 451,939	$ 502,285
Preferred dividends / distributions	(10,500)	(10,500)	(10,500)
Noncontrolling interest-common units of the Operating Partnership	(66,807)	(52,210)	(59,260)
Noncontrolling interest in property partnerships	(62,909)	(47,832)	2,068
Losses from interest rate contracts	0	0	(140)
Interest expense	(378,168)	(374,481)	(412,849)
Impairment losses	(11,812)	0	(1,783)
Depreciation and amortization expense	(645,649)	(617,547)	(694,403)
Transaction costs	(1,604)	(668)	(2,387)
Payroll and related costs from management services contracts	(9,590)	0	0
General and administrative expense	(121,722)	(113,715)	(105,229)
Gains (losses) from early extinguishments of debt	16,490	(496)	371
Gains (losses) from investments in securities	1,865	(3,678)	(2,273)
Interest and other income	(10,823)	(5,783)	(7,230)
Gain on sale of investment in unconsolidated joint venture	0	0	(59,370)
Income from unconsolidated joint ventures	(2,222)	(11,232)	(8,074)
Direct reimbursements of payroll and related costs from management services contracts	(9,590)	0	0
Development and management services revenue	(45,158)	(34,605)	(28,284)
Business Intersegment, Eliminations [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net income attributable to the Company's common shareholders / unitholders	572,347	451,939	502,285
Preferred dividends / distributions	10,500	10,500	10,500
Noncontrolling interest-common units of the Operating Partnership	66,807	52,210	59,260
Noncontrolling interest in property partnerships	62,909	47,832	(2,068)
Losses from interest rate contracts	0	0	140
Interest expense	378,168	374,481	412,849
Impairment losses	11,812	0	1,783
Depreciation and amortization expense	645,649	617,547	694,403
Transaction costs	1,604	668	2,387
Payroll and related costs from management services contracts	9,590	0	0
General and administrative expense	121,722	113,715	105,229
Gains (losses) from early extinguishments of debt	(16,490)	496	(371)
Gains (losses) from investments in securities	(1,865)	3,678	2,273
Interest and other income	10,823	5,783	7,230
Gains on sales of real estate	182,356	7,663	80,606
Gain on sale of investment in unconsolidated joint venture	0	0	59,370
Income from unconsolidated joint ventures	2,222	11,232	8,074
Direct reimbursements of payroll and related costs from management services contracts	9,590	0	0
Development and management services revenue	45,158	34,605	28,284
Net Operating Income	1,649,314	1,605,435	1,601,302
Boston Properties Limited Partnership
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net income attributable to the Company's common shareholders / unitholders	656,903	512,866	575,341
Preferred dividends / distributions	(10,500)	(10,500)	(10,500)
Noncontrolling interest in property partnerships	(62,909)	(47,832)	2,068
Losses from interest rate contracts	0	0	(140)
Interest expense	(378,168)	(374,481)	(412,849)
Impairment losses	(10,181)	0	(1,783)
Depreciation and amortization expense	(637,891)	(609,407)
Transaction costs	(1,604)	(668)	(2,387)
Payroll and related costs from management services contracts	(9,590)	0	0
General and administrative expense	(121,722)	(113,715)	(105,229)
Gains (losses) from early extinguishments of debt	16,490	(496)	371
Gains (losses) from investments in securities	1,865	(3,678)	(2,273)
Interest and other income	(10,823)	(5,783)	(7,230)
Gain on sale of investment in unconsolidated joint venture	0	0	(59,370)
Income from unconsolidated joint ventures	(2,222)	(11,232)	(8,074)
Direct reimbursements of payroll and related costs from management services contracts	(9,590)	0	0
Development and management services revenue	(45,158)	(34,605)	(28,284)
Boston Properties Limited Partnership | Business Intersegment, Eliminations [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net income attributable to the Company's common shareholders / unitholders	656,903	512,866	575,341
Preferred dividends / distributions	10,500	10,500	10,500
Noncontrolling interest in property partnerships	62,909	47,832	(2,068)
Losses from interest rate contracts	0	0	140
Interest expense	378,168	374,481	412,849
Impairment losses	10,181	0	1,783
Depreciation and amortization expense	637,891	609,407	682,776
Transaction costs	1,604	668	2,387
Payroll and related costs from management services contracts	9,590	0	0
General and administrative expense	121,722	113,715	105,229
Gains (losses) from early extinguishments of debt	(16,490)	496	(371)
Gains (losses) from investments in securities	(1,865)	3,678	2,273
Interest and other income	10,823	5,783	7,230
Gains on sales of real estate	190,716	8,240	82,775
Gain on sale of investment in unconsolidated joint venture	0	0	59,370
Income from unconsolidated joint ventures	2,222	11,232	8,074
Direct reimbursements of payroll and related costs from management services contracts	9,590	0	0
Development and management services revenue	45,158	34,605	28,284
Net Operating Income	$ 1,649,314	$ 1,605,435	$ 1,601,302

Segment Information (Schedule_2

Segment Information (Schedule Of Segment Reporting By Geographic Area And Property Type) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 2,590,659	$ 2,505,272	$ 2,460,953
Rental Revenue: Residential	22,551	16,596	16,699
Rental Revenue: Hotel	49,118	45,603	44,884
Rental Revenue Total	$ 2,662,328	$ 2,567,471	$ 2,522,536
Rental Revenue: % of Grand Totals	100.00%	100.00%	100.00%
Rental Expenses: Class A Office	$ 966,547	$ 923,675	$ 882,692
Rental Expenses: Residential	12,604	6,302	7,076
Rental Expenses: Hotel	33,863	32,059	31,466
Rental Expenses: Total	$ 1,013,014	$ 962,036	$ 921,234
Rental Expenses: % Of Grand Totals	100.00%	100.00%	100.00%
Net Operating Income	$ 1,649,314	$ 1,605,435	$ 1,601,302
Net Operating Income: % of Grand Totals	100.00%	100.00%	100.00%
Boston [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 838,341	$ 776,279	$ 727,265
Rental Revenue: Residential	6,694	4,745	4,812
Rental Revenue: Hotel	49,118	45,603	44,884
Rental Revenue Total	$ 894,153	$ 826,627	$ 776,961
Rental Revenue: % of Grand Totals	33.59%	32.20%	30.80%
Rental Expenses: Class A Office	$ 315,653	$ 301,097	$ 282,827
Rental Expenses: Residential	3,632	2,044	2,708
Rental Expenses: Hotel	33,863	32,059	31,466
Rental Expenses: Total	$ 353,148	$ 335,200	$ 317,001
Rental Expenses: % Of Grand Totals	34.86%	34.84%	34.41%
Net Operating Income	$ 541,005	$ 491,427	$ 459,960
Net Operating Income: % of Grand Totals	32.80%	30.61%	28.73%
New York [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 959,050	$ 969,371	$ 1,012,518
Rental Revenue: Residential	0	0	0
Rental Revenue: Hotel	0	0	0
Rental Revenue Total	$ 959,050	$ 969,371	$ 1,012,518
Rental Revenue: % of Grand Totals	36.02%	37.75%	40.14%
Rental Expenses: Class A Office	$ 377,992	$ 372,810	$ 363,188
Rental Expenses: Residential	0	0	0
Rental Expenses: Hotel	0	0	0
Rental Expenses: Total	$ 377,992	$ 372,810	$ 363,188
Rental Expenses: % Of Grand Totals	37.32%	38.76%	39.42%
Net Operating Income	$ 581,058	$ 596,561	$ 649,330
Net Operating Income: % of Grand Totals	35.23%	37.15%	40.55%
San Francisco [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 397,180	$ 345,519	$ 318,609
Rental Revenue: Residential	0	0	0
Rental Revenue: Hotel	0	0	0
Rental Revenue Total	$ 397,180	$ 345,519	$ 318,609
Rental Revenue: % of Grand Totals	14.92%	13.46%	12.63%
Rental Expenses: Class A Office	$ 130,016	$ 105,253	$ 100,787
Rental Expenses: Residential	0	0	0
Rental Expenses: Hotel	0	0	0
Rental Expenses: Total	$ 130,016	$ 105,253	$ 100,787
Rental Expenses: % Of Grand Totals	12.83%	10.94%	10.94%
Net Operating Income	$ 267,164	$ 240,266	$ 217,822
Net Operating Income: % of Grand Totals	16.20%	14.97%	13.60%
Washington, DC [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 396,088	$ 414,103	$ 402,561
Rental Revenue: Residential	15,857	11,851	11,887
Rental Revenue: Hotel	0	0	0
Rental Revenue Total	$ 411,945	$ 425,954	$ 414,448
Rental Revenue: % of Grand Totals	15.47%	16.59%	16.43%
Rental Expenses: Class A Office	$ 142,886	$ 144,515	$ 135,890
Rental Expenses: Residential	8,972	4,258	4,368
Rental Expenses: Hotel	0	0	0
Rental Expenses: Total	$ 151,858	$ 148,773	$ 140,258
Rental Expenses: % Of Grand Totals	14.99%	15.46%	15.23%
Net Operating Income	$ 260,087	$ 277,181	$ 274,190
Net Operating Income: % of Grand Totals	15.77%	17.27%	17.12%

Earnings Per Share _ Common U_3

Earnings Per Share / Common Unit (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Basic Earnings:
Net income attributable to the Company's shareholders/unitholders (Numerator)									$ 572,347	$ 451,939	$ 502,285
Net income attributable to the Company in Shares / Units (Denominator)									154,427,000	154,190,000	153,715,000
Earnings Per Share, Basic	$ 0.96	$ 0.77	$ 0.83	$ 1.14	$ 0.67	$ 0.76	$ 0.87	$ 0.63	$ 3.71	$ 2.93	$ 3.27
Net income attributable to the Company's shareholders/unitholders (in dollars per share / unit)									$ 3.71	$ 2.93	$ 3.27
Allocation of undistributed earnings to participating securities (Numerator)									$ (101)		$ (283)
Allocation of undistributed earnings to participating securities (in shares) (Denominator)									0		0
Allocation of undistributed earnings to participating securities (in dollars per share / unit)									$ 0		$ 0
Net Income Available To Common Stockholders After Allocation of Undistributed Earnings to Participating Securities Basic									$ 572,246		$ 502,002
Weighted Average Number Of Shares Outstanding After Allocation of Undistributed Earnings to Participating Securities Basic (in shares)									154,427,000		153,715,000
Earnings Per Share After Allccation of Undistributed Earnings to Particiapting Securities Basic (dollars per share)									$ 3.71		$ 3.27
Effect of Dilutive Securities:
Stock Based Compensation (Numerator)									$ 0	$ 0	$ 0
Stock Based Compensation, Shares / Units (Denominator)									255,000	200,000	262,000
Stock Based Compensation Per Share / Unit Amount									$ (0.01)	$ 0	$ (0.01)
Diluted Earnings:
Diluted Earnings: Net income attributable to the Company's shareholders/unitholdersIncome (Numerator)									$ 572,246	$ 451,939	$ 502,002
Diluted Earnings Net income attributable to the Company's shareholders/unitholders Shares / Units (Denominator)									154,682,000	154,390,000	153,977,000
Diluted Earnings: Net income, Per Share / Unit Amount (in dollars per share / unit)	0.96	0.77	0.83	1.14	0.67	0.76	0.87	0.63	$ 3.70	$ 2.93	$ 3.26
Boston Properties Limited Partnership
Redeemable Common Units									17,485,000	17,471,000	17,646,000
Basic Earnings:
Net income attributable to the Company's shareholders/unitholders (Numerator)									$ 656,903	$ 512,866	$ 575,341
Net income attributable to the Company in Shares / Units (Denominator)									171,912,000	171,661,000	171,361,000
Earnings Per Share, Basic	1.01	0.79	0.85	1.17	0.69	0.77	0.88	0.64	$ 3.82	$ 2.99	$ 3.36
Net income attributable to the Company's shareholders/unitholders (in dollars per share / unit)											$ 3.36
Allocation of undistributed earnings to participating securities (Numerator)									$ (113)		$ (316)
Allocation of undistributed earnings to participating securities (in shares) (Denominator)									0		0
Allocation of undistributed earnings to participating securities (in dollars per share / unit)									$ 0		$ 0
Net Income Available To Common Stockholders After Allocation of Undistributed Earnings to Participating Securities Basic									$ 656,790		$ 575,025
Weighted Average Number Of Shares Outstanding After Allocation of Undistributed Earnings to Participating Securities Basic (in shares)									171,912,000		171,361,000
Earnings Per Share After Allccation of Undistributed Earnings to Particiapting Securities Basic (dollars per share)									$ 3.82		$ 3.36
Effect of Dilutive Securities:
Stock Based Compensation (Numerator)									$ 0	$ 0	$ 0
Stock Based Compensation, Shares / Units (Denominator)									255,000	200,000	262,000
Stock Based Compensation Per Share / Unit Amount									$ (0.01)	$ (0.01)	$ (0.01)
Diluted Earnings:
Diluted Earnings: Net income attributable to the Company's shareholders/unitholdersIncome (Numerator)									$ 656,790	$ 512,866	$ 575,025
Diluted Earnings Net income attributable to the Company's shareholders/unitholders Shares / Units (Denominator)									172,167,000	171,861,000	171,623,000
Diluted Earnings: Net income, Per Share / Unit Amount (in dollars per share / unit)	$ 1.01	$ 0.79	$ 0.85	$ 1.17	$ 0.68	$ 0.77	$ 0.88	$ 0.64	$ 3.81	$ 2.98	$ 3.35

Employee Benefit Plans (Details

Employee Benefit Plans (Details)	12 Months Ended			216 Months Ended	228 Months Ended
	Dec. 31, 2018USD ($)mo	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2018USD ($)yrage	Dec. 31, 2018USD ($)
Employee Benefit Plans [Abstract]
Eligibility Period For 401K Savings Plan In Months | mo	3
Employer Matching Contribution, Percent of Match	200.00%
Employer Matching Contribution, Percent of Employees' Gross Pay					3.00%
Maximum Eligible Earnings As Established By IRS For Matching Contributions	$ 275,000	$ 270,000	$ 265,000
Employer Contribution Amount	4,100,000	4,100,000	4,000,000
Years Of Service For Supplemental Retirement Contribution | yr				10
Age Of Employee For Supplemental Retirement Contribution | age				40
Annual Supplemental Retirement Contribution And Credit Total.	18,000	18,000	$ 21,000
Separate Unrestricted Cash For Deferred Compensation Plan.	28,200,000	29,200,000		$ 28,200,000	$ 28,200,000
Deferred Compensation Liability	$ 28,200,000	$ 29,200,000		$ 28,200,000	$ 28,200,000

Stock Option and Incentive Pl_3

Stock Option and Incentive Plan (Narrative) (Details) $ in Millions	Feb. 06, 2018USD ($)yr	Feb. 04, 2018USD ($)shares	Feb. 03, 2017USD ($)shares	Feb. 04, 2016USD ($)shares	May 15, 2012yrshares
MYLTIP 2,013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value of MYLTIP Awards | $				$ 13.5
MYLTIP Units forfeited | shares				205,762
Final awards percentage of target				109.50%
2012 Stock Option and Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Additional Shares Authorized | shares					13,000,000
Other Than Stock Options Awards Conversion Ratio					2.32
Stock Option Awards Conversion Ratio					1
Stock Option and Incentive Plan Term Period | yr					10
MYLTIP 2,018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
TSR measurement (in years) | yr	3
Distributions percent before measurement date	10.00%
Percentage of annualized TSR for Reduction of Earned Awards	0.00%
Percentage to Cause Some Awards to be Earned Even if on a Relative Basis it Would Not Result in any Earned Awards	12.00%
Value of MYLTIP Awards | $	$ 13.3
MYLTIP Value Amortized Into Earnings, Years | yr	4
MYLTIP 2,014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value of MYLTIP Awards | $			$ 3.5
MYLTIP Units forfeited | shares			447,386
Final awards percentage of target			27.70%
MYLTIP 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value of MYLTIP Awards | $		$ 3.6
MYLTIP Units forfeited | shares		337,847
Final awards percentage of target		22.00%
Cohen & Steers Realty Majors Portfolio Index [Member] | MYLTIP 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Percentage of Index Used to Compare to TSR	50.00%
NAREIT Office Index adjusted [Member] | MYLTIP 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Percentage of Index Used to Compare to TSR	50.00%
MYLTIP vesting 2021 | MYLTIP 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Percentage	50.00%
MYLTIP vesting 2022 | MYLTIP 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Percentage	50.00%

Stock Option and Incentive Pl_4

Stock Option and Incentive Plan (Restricted Stock) (Narrative) (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)VestingInstallmentsd$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	May 23, 2018shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued	154,537,378	154,404,186		36,836
Stock-based compensation associated with restricted stock, non-qualified options, LTIP Units, OPP and MYLTIP Units | $	$ 38,000	$ 33,200	$ 30,600
Value of shares of common stock | $	1,545	$ 1,543
Exercisable, Weighted Average Exercise Price | $ / shares		$ 96.35	$ 96.32
Total intrinsic value of the outstanding and exercisable stock options | $	$ 8,800
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued	20,320	37,414	22,067
Employee and director payment per share (in dollars per share) | $ / shares	$ 0.01
Value of shares of common stock | $	$ 2,400	$ 4,900	$ 2,500
Employee's weighted average cost per share (in dollars per share) | $ / shares	$ 119.27	$ 130.32	$ 113.51
LTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value of LTIP units issued | $	$ 22,700	$ 13,600	$ 15,400
Per unit fair value weighted-average (in dollars per share) | $ / shares	$ 110.29	$ 119.41	$ 103.83
Expected life assumed to calculate per unit fair value per LTIP unit (years)	5 years 8 months 12 days	5 years 8 months 12 days	5 years 8 months 12 days
Risk-free rate	2.63%	2.14%	1.61%
Expected price volatility	27.00%	28.00%	33.00%
Unvested Restricted stock, LTIP and 2013 - 2015 MYLTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expenses | $	$ 22,700
LTIPs And Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting annual installments | VestingInstallments	4
Unvested 2016 - 2018 MYLTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expenses | $	$ 15,200
Weighted-average period (years)	2 years 3 months 18 days
Unvested
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average period (years)	2 years 4 months 24 days
LTIPs, OPP and MYLTIP Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee and director payment per share (in dollars per share) | $ / shares	$ 0.25
Non-Qualified Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Common Stock available for issuance	250,000
Employee Common Stock options, percent of average closing price	85.00%
Number Of Days Used In Calculation, Average Closing Prices Of Common Stock | d	10
Shares issued	6,268	6,317	5,695
Shares issued, weighted-average purchase price per share | $ / shares	$ 107.20	$ 105.97	$ 109.27
Boston Properties Limited Partnership | MYLTIP 2016 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
MYLTIP units issued			475,004
Boston Properties Limited Partnership | LTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
LTIP units issued (in shares)	205,838	113,918	147,872
Boston Properties Limited Partnership | MYLTIP 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
MYLTIP units issued	342,659
Boston Properties Limited Partnership | MYLTIP 2017 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
MYLTIP units issued		400,000

Stock Option and Incentive Pl_5

Stock Option and Incentive Plan Schedule of Stock Options Status (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning Outstanding, Shares	540,441	547,129	547,129
Beginning Oustanding, Weighted Average Exercise Price	$ 96.35	$ 96.38	$ 96.38
Exercised, Shares	0	(6,688)	0
Exercised, Weighted Averge Exercise Price	$ 0	$ 99.15	$ 0
Ending Outstanding, Shares	540,441	540,441	547,129
Ending Oustanding, Weighted Average Exercise Pric	$ 96.35	$ 96.35	$ 96.38

Stock Option and Incentive Pl_6

Stock Option and Incentive Plan Schedule of Stock Options Outstanding (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number Outstanding at period end	540,441	540,441	547,129	547,129
Outstanding, Weighted Average Exercise Price	$ 96.35	$ 96.35	$ 96.38	$ 96.38
Number Exercisable		540,441	514,360
Exercisable, Weighted Average Exercise Price		$ 96.35	$ 96.32
Exercise Price of $86.86 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Weighted Average Remaining Contractual Life (Years)	2 years 1 month 6 days
Number Outstanding at period end	118,502
Outstanding, Weighted Average Exercise Price	$ 86.86
Number Exercisable	118,502
Exercisable, Weighted Average Exercise Price	$ 86.86
Exercise Price of $95.69 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Weighted Average Remaining Contractual Life (Years)	4 years 3 months 18 days
Number Outstanding at period end	54,282
Outstanding, Weighted Average Exercise Price	$ 95.69
Number Exercisable	54,282
Exercisable, Weighted Average Exercise Price	$ 95.69
Exercise Price of $98.46 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Weighted Average Remaining Contractual Life (Years)	4 years 1 month 6 days
Number Outstanding at period end	202,030
Outstanding, Weighted Average Exercise Price	$ 98.46
Number Exercisable	202,030
Exercisable, Weighted Average Exercise Price	$ 98.46
Exercise Price of $100.77 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Weighted Average Remaining Contractual Life (Years)	3 years 1 month 6 days
Number Outstanding at period end	165,627
Outstanding, Weighted Average Exercise Price	$ 100.77
Number Exercisable	165,627
Exercisable, Weighted Average Exercise Price	$ 100.77
Unvested 2016 - 2018 MYLTIP Units [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Weighted-average period (years)	2 years 3 months 18 days

Related Party Transactions (Det

Related Party Transactions (Details)	12 Months Ended
	Dec. 31, 2018USD ($)nonemployeedirectorsshares	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)	May 23, 2018shares
Related Party Transaction [Line Items]
Number Of Non Employee Directors Electing To Receive Deferred Stock Units | nonemployeedirectors	4
Shares issued | shares	154,537,378	154,404,186		36,836
Deferred Stock Units Outstanding	74,966	105,479
Brother of Senior Executive Vice President [Member]
Related Party Transaction [Line Items]
Aggregate leasing commissions paid to related parties | $	$ 921,000	$ 368,000	$ 374,000

Selected Interim Financial In_3

Selected Interim Financial Information (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Total revenue	$ 705,157	$ 686,284	$ 664,484	$ 661,151	$ 655,229	$ 657,712	$ 656,907	$ 632,228	$ 2,717,076	$ 2,602,076	$ 2,550,820
Net income	185,241	150,445	160,565	216,312	132,203	147,704	167,010	115,564
Net income attributable to the Company	$ 148,529	$ 119,118	$ 128,681	$ 176,021	$ 103,829	$ 117,337	$ 133,709	$ 97,083	$ 582,847	$ 462,439	$ 512,785
Income attributable to the Company (in dollars per share / unit) - Basic	$ 0.96	$ 0.77	$ 0.83	$ 1.14	$ 0.67	$ 0.76	$ 0.87	$ 0.63	$ 3.71	$ 2.93	$ 3.27
Income attributable to the Company (in dollars per share / unit) - Diluted	$ 0.96	$ 0.77	$ 0.83	$ 1.14	$ 0.67	$ 0.76	$ 0.87	$ 0.63	$ 3.70	$ 2.93	$ 3.26
Boston Properties Limited Partnership
Total revenue	$ 705,157	$ 686,284	$ 664,484	$ 661,151	$ 655,229	$ 657,712	$ 656,907	$ 632,228	$ 2,717,076	$ 2,602,076	$ 2,550,820
Net income	192,884	153,676	162,986	220,766	134,157	149,658	169,672	117,711
Net income attributable to the Company	$ 173,834	$ 136,201	$ 145,961	$ 200,907	$ 117,667	$ 132,693	$ 151,844	$ 110,662	$ 667,403	$ 523,366	$ 585,841
Income attributable to the Company (in dollars per share / unit) - Basic	$ 1.01	$ 0.79	$ 0.85	$ 1.17	$ 0.69	$ 0.77	$ 0.88	$ 0.64	$ 3.82	$ 2.99	$ 3.36
Income attributable to the Company (in dollars per share / unit) - Diluted	$ 1.01	$ 0.79	$ 0.85	$ 1.17	$ 0.68	$ 0.77	$ 0.88	$ 0.64	$ 3.81	$ 2.98	$ 3.35

Subsequent Events (Details)

Subsequent Events (Details) $ in Thousands

Apr. 01, 2019USD ($)

Feb. 14, 2019ft²yr

Feb. 09, 2019USD ($)shares

Feb. 05, 2019USD ($)shares

Jan. 24, 2019USD ($)ft²ayr

Nov. 29, 2018ft²ayr

Nov. 16, 2018USD ($)ft²yr

Dec. 31, 2018USD ($)shares

Dec. 31, 2017USD ($)shares

Dec. 31, 2016USD ($)

Feb. 01, 2019shares

Jan. 10, 2019USD ($)ft²

Dec. 01, 2018ft²

May 23, 2018shares

Subsequent Event [Line Items]

Payments to Noncontrolling Interests

$ 82,501

$ 54,342

$ 55,474

Common stock, shares issued | shares

154,537,378

154,404,186

36,836

Subsequent Event [Member] | MYLTIPS 2019 [Member]

Subsequent Event [Line Items]

Value of MYLTIP Awards

$ 13,500

Subsequent Event [Member] | MYLTIPS 2019 [Member] | NAREIT Office Index adjusted [Member]

Subsequent Event [Line Items]

Target Tier | shares

110,367

Subsequent Event [Member] | MYLTIP 2016 [Member]

Subsequent Event [Line Items]

Value of MYLTIP Awards

$ 13,600

Final awards percentage of target

69.50%

MYLTIP Units forfeited | shares

364,980

Subsequent Event [Member] | Minimum [Member] | MYLTIPS 2019 [Member] | NAREIT Office Index adjusted [Member]

Subsequent Event [Line Items]

Minimum earned awards | shares

0

Subsequent Event [Member] | Maximum [Member] | MYLTIPS 2019 [Member] | NAREIT Office Index adjusted [Member]

Subsequent Event [Line Items]

maximum earned awards | shares

220,734

Subsequent Event [Member] | Restricted Stock [Member]

Subsequent Event [Line Items]

Common stock, shares issued | shares

23,083

Subsequent Event [Member] | LTIP Units [Member]

Subsequent Event [Line Items]

LTIP units issued (in shares) | shares

172,166

Boston Properties Limited Partnership

Subsequent Event [Line Items]

Payments to Noncontrolling Interests

$ 82,501

$ 54,342

$ 55,474

Salesforce Tower

Subsequent Event [Line Items]

Net Rentable Area | ft²

1,421,000

Salesforce Tower | Salesforce Tower | Subsequent Event [Member]

Subsequent Event [Line Items]

Ownership Percentage

5.00%

Payments to Noncontrolling Interests

$ 210,900

Repayment preferred equity

$ 24,100

Platform 16

Subsequent Event [Line Items]

Net Rentable Area | ft²

1,100,000

Ground Lease Term (in years) | yr

65

Area of Land | a

5.6

Platform 16 | Subsequent Event [Member]

Subsequent Event [Line Items]

Ground Lease Term (in years) | yr

65

Area of Land | a

5.6

325 Main Street | Subsequent Event [Member]

Subsequent Event [Line Items]

Net Rentable Area | ft²

115,000

Term of Lease Signed (in years) | yr

15

Square Footage Of Signed Lease | ft²

362,000

Future office building [Member] | 325 Main Street | Subsequent Event [Member]

Subsequent Event [Line Items]

Net Rentable Area | ft²

400,000

Future retail building [Member] | 325 Main Street | Subsequent Event [Member]

Subsequent Event [Line Items]

Net Rentable Area | ft²

38,000

2600 Tower Oaks Boulevard | Subsequent Event [Member]

Subsequent Event [Line Items]

Contractual Sales Price

$ 22,700

Net Rentable Area | ft²

179,000

Annapolis Junction Building Six [Member]

Subsequent Event [Line Items]

Net Rentable Area | ft²

119,000

Ownership Percentage

50.00%

Construction Loan

$ 13,100

Number of extensions

1

Extension Option (in years) | yr

1

Construction Loan Facility Borrowing Capacity

$ 14,300

Debt Instrument, Basis Spread on Variable Rate

2.00%

Annapolis Junction Building Six [Member] | Subsequent Event [Member]

Subsequent Event [Line Items]

Net Rentable Area | ft²

119,000

Ownership Percentage

50.00%

Construction Loan

$ 13,000

Number of extensions

1

Extension Option (in years) | yr

1

Construction Loan Facility Borrowing Capacity

$ 14,300

Debt Instrument, Basis Spread on Variable Rate

2.00%

Carnegie Center | Subsequent Event [Member]

Subsequent Event [Line Items]

Aggregate purchase price

$ 42,900

Deferred purchase price

$ 8,600

Net Rentable Area | ft²

1,700,000

Real Estate and Accumulated D_4

Real Estate and Accumulated Depreciation Schedule of Real Estate and Accumulated Depreciation (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	[1]	$ 2,964,572
Original Land		4,959,995
Original Building		12,763,317
Costs Capitalized Subsequent to Acquisition		3,882,233
Land and improvements		5,072,568
Buildings and Improvements		15,753,683
Land Held for Development	[2]	200,498
Development and Construction in Progress		578,796
Total		21,605,545
Accumulated Depreciation		4,871,102
Furniture, fixtures and equipment		44,351	$ 37,928
Furniture, fixtures and equipment accumulated depreciation		26,675
Real Estate Aggregate Cost For Tax Purposes		17,900,000
Real Estate Aggregate Accumulated Depreciation For Tax Purposes		$ 3,900,000
Real Estate and Accumulated Depreciation, Life Used for Depreciation		40 years
Unamortized deferred finance costs		$ (30,756)
767 Fifth Avenue (the General Motors Building)
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		767 Fifth Avenue (the General Motors Building)
Type		Office
Location		New York, NY
Encumbrances		$ 2,270,534
Original Land		1,796,252
Original Building		1,532,654
Costs Capitalized Subsequent to Acquisition		189,657
Land and improvements		1,796,252
Buildings and Improvements		1,722,311
Land Held for Development		0
Development and Construction in Progress		0
Total		3,518,563
Accumulated Depreciation		$ 271,534
Year(s) Built / Renovated		1,968
Year(s) Acquired		2,013
Depreciable Lives (Years)	[3]	(1)
Prudential Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Prudential Center
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		92,077
Original Building		948,357
Costs Capitalized Subsequent to Acquisition		532,802
Land and improvements		115,638
Buildings and Improvements		1,457,494
Land Held for Development		104
Development and Construction in Progress		0
Total		1,573,236
Accumulated Depreciation		$ 550,109
Year(s) Built / Renovated		1965/1993/2002/2016-2017
Year(s) Acquired		1998/1999/2000
Depreciable Lives (Years)	[3]	(1)
Embarcadero Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Embarcadero Center
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		179,697
Original Building		847,410
Costs Capitalized Subsequent to Acquisition		368,967
Land and improvements		195,987
Buildings and Improvements		1,200,087
Land Held for Development		0
Development and Construction in Progress		0
Total		1,396,074
Accumulated Depreciation		$ 612,981
Year(s) Built / Renovated		1970/1989
Year(s) Acquired		1998-1999
Depreciable Lives (Years)	[3]	(1)
399 Park Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		399 Park Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		339,200
Original Building		700,358
Costs Capitalized Subsequent to Acquisition		247,092
Land and improvements		354,107
Buildings and Improvements		932,543
Land Held for Development		0
Development and Construction in Progress		0
Total		1,286,650
Accumulated Depreciation		$ 332,911
Year(s) Built / Renovated		1961/2018
Year(s) Acquired		2,002
Depreciable Lives (Years)	[3]	(1)
Salesforce Tower
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Salesforce Tower
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		200,349
Original Building		919,565
Costs Capitalized Subsequent to Acquisition		0
Land and improvements		200,349
Buildings and Improvements		919,565
Land Held for Development		0
Development and Construction in Progress		0
Total		1,119,914
Accumulated Depreciation		$ 9,509
Year(s) Built / Renovated		2,018
Year(s) Acquired		2,013
Depreciable Lives (Years)	[3]	(1)
601 Lexington Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		601 Lexington Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 658,792
Original Land		241,600
Original Building		494,782
Costs Capitalized Subsequent to Acquisition		361,985
Land and improvements		289,639
Buildings and Improvements		637,044
Land Held for Development		0
Development and Construction in Progress		171,684
Total		1,098,367
Accumulated Depreciation		$ 272,936
Year(s) Built / Renovated		1977/1997
Year(s) Acquired		2,001
Depreciable Lives (Years)	[3]	(1)
200 Clarendon Street and Garage
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		200 Clarendon Street and Garage
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		219,543
Original Building		667,884
Costs Capitalized Subsequent to Acquisition		164,073
Land and improvements		219,616
Buildings and Improvements		822,218
Land Held for Development		9,666
Development and Construction in Progress		0
Total		1,051,500
Accumulated Depreciation		$ 192,137
Year(s) Built / Renovated		1,976
Year(s) Acquired		2,010
Depreciable Lives (Years)	[3]	(1)
250 West 55th Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		250 West 55th Street
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		285,263
Original Building		603,167
Costs Capitalized Subsequent to Acquisition		48,642
Land and improvements		285,263
Buildings and Improvements		651,809
Land Held for Development		0
Development and Construction in Progress		0
Total		937,072
Accumulated Depreciation		$ 94,434
Year(s) Built / Renovated		2,014
Year(s) Acquired		2,007
Depreciable Lives (Years)	[3]	(1)
100 Federal Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		100 Federal Street
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		131,067
Original Building		435,954
Costs Capitalized Subsequent to Acquisition		99,702
Land and improvements		131,067
Buildings and Improvements		535,656
Land Held for Development		0
Development and Construction in Progress		0
Total		666,723
Accumulated Depreciation		$ 105,536
Year(s) Built / Renovated		1971-1975/2017
Year(s) Acquired		2,012
Depreciable Lives (Years)	[3]	(1)
Carnegie Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Carnegie Center
Type		Office
Location		Princeton, NJ
Encumbrances		$ 0
Original Land		107,997
Original Building		389,359
Costs Capitalized Subsequent to Acquisition		158,752
Land and improvements		108,948
Buildings and Improvements		543,974
Land Held for Development		3,186
Development and Construction in Progress		0
Total		656,108
Accumulated Depreciation		$ 241,570
Year(s) Built / Renovated		1983-2016
Year(s) Acquired		1998/1999/2000/2007/2014/2017
Depreciable Lives (Years)	[3]	(1)
Times Square Tower
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Times Square Tower
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		165,413
Original Building		380,438
Costs Capitalized Subsequent to Acquisition		94,451
Land and improvements		169,193
Buildings and Improvements		471,109
Land Held for Development		0
Development and Construction in Progress		0
Total		640,302
Accumulated Depreciation		$ 206,067
Year(s) Built / Renovated		2,004
Year(s) Acquired		2,000
Depreciable Lives (Years)	[3]	(1)
Atlantic Wharf
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Atlantic Wharf
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		63,988
Original Building		454,537
Costs Capitalized Subsequent to Acquisition		17,184
Land and improvements		63,988
Buildings and Improvements		471,721
Land Held for Development		0
Development and Construction in Progress		0
Total		535,709
Accumulated Depreciation		$ 116,238
Year(s) Built / Renovated		2,011
Year(s) Acquired		2,007
Depreciable Lives (Years)	[3]	(1)
510 Madison Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		510 Madison Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		103,000
Original Building		253,665
Costs Capitalized Subsequent to Acquisition		24,992
Land and improvements		103,000
Buildings and Improvements		278,657
Land Held for Development		0
Development and Construction in Progress		0
Total		381,657
Accumulated Depreciation		$ 62,507
Year(s) Built / Renovated		2,012
Year(s) Acquired		2,010
Depreciable Lives (Years)	[3]	(1)
Fountain Square
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Fountain Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		56,853
Original Building		306,298
Costs Capitalized Subsequent to Acquisition		3,170
Land and improvements		56,853
Buildings and Improvements		309,468
Land Held for Development		0
Development and Construction in Progress		0
Total		366,321
Accumulated Depreciation		$ 68,390
Year(s) Built / Renovated		1986-1990
Year(s) Acquired		2,012
Depreciable Lives (Years)	[3]	(1)
599 Lexington Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		599 Lexington Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		81,040
Original Building		100,507
Costs Capitalized Subsequent to Acquisition		174,213
Land and improvements		87,852
Buildings and Improvements		267,908
Land Held for Development		0
Development and Construction in Progress		0
Total		355,760
Accumulated Depreciation		$ 170,678
Year(s) Built / Renovated		1,986
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
680 Folsom Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		680 Folsom Street
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		72,545
Original Building		219,766
Costs Capitalized Subsequent to Acquisition		7,829
Land and improvements		72,545
Buildings and Improvements		227,595
Land Held for Development		0
Development and Construction in Progress		0
Total		300,140
Accumulated Depreciation		$ 38,230
Year(s) Built / Renovated		2,014
Year(s) Acquired		2,012
Depreciable Lives (Years)	[3]	(1)
601 Massachusetts Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		601 Massachusetts Avenue
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		95,310
Original Building		165,173
Costs Capitalized Subsequent to Acquisition		3,900
Land and improvements		95,322
Buildings and Improvements		169,061
Land Held for Development		0
Development and Construction in Progress		0
Total		264,383
Accumulated Depreciation		$ 18,263
Year(s) Built / Renovated		2,016
Year(s) Acquired		2,008
Depreciable Lives (Years)	[3]	(1)
South of Market and Democracy Tower
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		South of Market and Democracy Tower
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		13,603
Original Building		237,479
Costs Capitalized Subsequent to Acquisition		12,428
Land and improvements		13,687
Buildings and Improvements		249,823
Land Held for Development		0
Development and Construction in Progress		0
Total		263,510
Accumulated Depreciation		$ 91,072
Year(s) Built / Renovated		2008-2009
Year(s) Acquired		2,003
Depreciable Lives (Years)	[3]	(1)
Bay Colony Corporate Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Bay Colony Corporate Center
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		18,789
Original Building		148,451
Costs Capitalized Subsequent to Acquisition		77,133
Land and improvements		18,789
Buildings and Improvements		225,584
Land Held for Development		0
Development and Construction in Progress		0
Total		244,373
Accumulated Depreciation		$ 68,903
Year(s) Built / Renovated		1985-1989
Year(s) Acquired		2,011
Depreciable Lives (Years)	[3]	(1)
Gateway Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Gateway Center
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		28,255
Original Building		139,245
Costs Capitalized Subsequent to Acquisition		64,831
Land and improvements		30,627
Buildings and Improvements		201,704
Land Held for Development		0
Development and Construction in Progress		0
Total		232,331
Accumulated Depreciation		$ 107,640
Year(s) Built / Renovated		1984/1986/2002
Year(s) Acquired		1,999
Depreciable Lives (Years)	[3]	(1)
535 Mission Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		535 Mission Street
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		40,933
Original Building		148,378
Costs Capitalized Subsequent to Acquisition		3,259
Land and improvements		40,933
Buildings and Improvements		151,637
Land Held for Development		0
Development and Construction in Progress		0
Total		192,570
Accumulated Depreciation		$ 20,576
Year(s) Built / Renovated		2,015
Year(s) Acquired		2,013
Depreciable Lives (Years)	[3]	(1)
2200 Pennsylvania Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		2200 Pennsylvania Avenue
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		0
Original Building		183,541
Costs Capitalized Subsequent to Acquisition		4,535
Land and improvements		0
Buildings and Improvements		188,076
Land Held for Development		0
Development and Construction in Progress		0
Total		188,076
Accumulated Depreciation		$ 52,280
Year(s) Built / Renovated		2,011
Year(s) Acquired		2,008
Depreciable Lives (Years)	[3]	(1)
Mountain View Research Park
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Mountain View Research Park
Type		Office
Location		Mountain View, CA
Encumbrances		$ 0
Original Land		95,066
Original Building		68,373
Costs Capitalized Subsequent to Acquisition		9,988
Land and improvements		95,066
Buildings and Improvements		78,361
Land Held for Development		0
Development and Construction in Progress		0
Total		173,427
Accumulated Depreciation		$ 17,866
Year(s) Built / Renovated		1977-1981/2007-2013
Year(s) Acquired		2,013
Depreciable Lives (Years)	[3]	(1)
Reservoir Place
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reservoir Place
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		18,605
Original Building		104,124
Costs Capitalized Subsequent to Acquisition		45,144
Land and improvements		20,108
Buildings and Improvements		147,765
Land Held for Development		0
Development and Construction in Progress		0
Total		167,873
Accumulated Depreciation		$ 64,683
Year(s) Built / Renovated		1955/1987/2017
Year(s) Acquired		1997/1998
Depreciable Lives (Years)	[3]	(1)
1330 Connecticut Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		1330 Connecticut Avenue
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		25,982
Original Building		82,311
Costs Capitalized Subsequent to Acquisition		36,089
Land and improvements		27,135
Buildings and Improvements		117,247
Land Held for Development		0
Development and Construction in Progress		0
Total		144,382
Accumulated Depreciation		$ 27,535
Year(s) Built / Renovated		1984/2018
Year(s) Acquired		2,004
Depreciable Lives (Years)	[3]	(1)
Kingstowne Towne Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kingstowne Towne Center
Type		Office
Location		Alexandria, VA
Encumbrances		$ 0
Original Land		18,021
Original Building		109,038
Costs Capitalized Subsequent to Acquisition		2,098
Land and improvements		18,062
Buildings and Improvements		111,095
Land Held for Development		0
Development and Construction in Progress		0
Total		129,157
Accumulated Depreciation		$ 41,469
Year(s) Built / Renovated		2003-2006
Year(s) Acquired		2,007
Depreciable Lives (Years)	[3]	(1)
One Freedom Square
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		One Freedom Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		9,929
Original Building		84,504
Costs Capitalized Subsequent to Acquisition		32,256
Land and improvements		11,293
Buildings and Improvements		115,396
Land Held for Development		0
Development and Construction in Progress		0
Total		126,689
Accumulated Depreciation		$ 54,652
Year(s) Built / Renovated		2,000
Year(s) Acquired		2,003
Depreciable Lives (Years)	[3]	(1)
Capital Gallery
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Capital Gallery
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		4,725
Original Building		29,565
Costs Capitalized Subsequent to Acquisition		87,231
Land and improvements		8,662
Buildings and Improvements		112,859
Land Held for Development		0
Development and Construction in Progress		0
Total		121,521
Accumulated Depreciation		$ 67,759
Year(s) Built / Renovated		1981/2006
Year(s) Acquired		2,007
Depreciable Lives (Years)	[3]	(1)
Weston Corporate Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Weston Corporate Center
Type		Office
Location		Weston, MA
Encumbrances		$ 0
Original Land		25,753
Original Building		92,312
Costs Capitalized Subsequent to Acquisition		(123)
Land and improvements		25,854
Buildings and Improvements		92,088
Land Held for Development		0
Development and Construction in Progress		0
Total		117,942
Accumulated Depreciation		$ 26,176
Year(s) Built / Renovated		2,010
Year(s) Acquired		2,001
Depreciable Lives (Years)	[3]	(1)
Two Freedom Square
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Two Freedom Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		13,930
Original Building		77,739
Costs Capitalized Subsequent to Acquisition		23,427
Land and improvements		15,420
Buildings and Improvements		99,676
Land Held for Development		0
Development and Construction in Progress		0
Total		115,096
Accumulated Depreciation		$ 51,291
Year(s) Built / Renovated		2,001
Year(s) Acquired		2,003
Depreciable Lives (Years)	[3]	(1)
One and Two Reston Overlook
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		One and Two Reston Overlook
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		16,456
Original Building		66,192
Costs Capitalized Subsequent to Acquisition		24,181
Land and improvements		16,179
Buildings and Improvements		90,650
Land Held for Development		0
Development and Construction in Progress		0
Total		106,829
Accumulated Depreciation		$ 47,668
Year(s) Built / Renovated		1,999
Year(s) Acquired		2,000
Depreciable Lives (Years)	[3]	(1)
140 Kendrick Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		140 Kendrick Street
Type		Office
Location		Needham, MA
Encumbrances		$ 0
Original Land		18,095
Original Building		66,905
Costs Capitalized Subsequent to Acquisition		17,553
Land and improvements		19,092
Buildings and Improvements		83,461
Land Held for Development		0
Development and Construction in Progress		0
Total		102,553
Accumulated Depreciation		$ 32,360
Year(s) Built / Renovated		2,000
Year(s) Acquired		2,004
Depreciable Lives (Years)	[3]	(1)
Discovery Square
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Discovery Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		11,198
Original Building		71,782
Costs Capitalized Subsequent to Acquisition		17,753
Land and improvements		12,533
Buildings and Improvements		88,200
Land Held for Development		0
Development and Construction in Progress		0
Total		100,733
Accumulated Depreciation		$ 39,574
Year(s) Built / Renovated		2,001
Year(s) Acquired		2,003
Depreciable Lives (Years)	[3]	(1)
355 Main Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		355 Main Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		18,863
Original Building		53,346
Costs Capitalized Subsequent to Acquisition		23,701
Land and improvements		21,173
Buildings and Improvements		74,737
Land Held for Development		0
Development and Construction in Progress		0
Total		95,910
Accumulated Depreciation		$ 23,691
Year(s) Built / Renovated		1981/1996/2013
Year(s) Acquired		2,006
Depreciable Lives (Years)	[3]	(1)
10 CityPoint
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		10 CityPoint
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		1,953
Original Building		85,752
Costs Capitalized Subsequent to Acquisition		4,515
Land and improvements		2,116
Buildings and Improvements		90,104
Land Held for Development		0
Development and Construction in Progress		0
Total		92,220
Accumulated Depreciation		$ 7,772
Year(s) Built / Renovated		2,016
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
90 Broadway
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		90 Broadway
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		19,104
Original Building		52,078
Costs Capitalized Subsequent to Acquisition		18,363
Land and improvements		20,785
Buildings and Improvements		68,760
Land Held for Development		0
Development and Construction in Progress		0
Total		89,545
Accumulated Depreciation		$ 21,302
Year(s) Built / Renovated		1983/1998/2013
Year(s) Acquired		2,006
Depreciable Lives (Years)	[3]	(1)
230 CityPoint
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		230 CityPoint
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		13,189
Original Building		49,823
Costs Capitalized Subsequent to Acquisition		21,914
Land and improvements		13,593
Buildings and Improvements		71,333
Land Held for Development		0
Development and Construction in Progress		0
Total		84,926
Accumulated Depreciation		$ 26,357
Year(s) Built / Renovated		1,992
Year(s) Acquired		2,005
Depreciable Lives (Years)	[3]	(1)
Waltham Weston Corporate Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Waltham Weston Corporate Center
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		10,385
Original Building		60,694
Costs Capitalized Subsequent to Acquisition		11,449
Land and improvements		11,097
Buildings and Improvements		71,431
Land Held for Development		0
Development and Construction in Progress		0
Total		82,528
Accumulated Depreciation		$ 32,739
Year(s) Built / Renovated		2,003
Year(s) Acquired		1,999
Depreciable Lives (Years)	[3]	(1)
77 CityPoint
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		77 CityPoint
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		13,847
Original Building		60,383
Costs Capitalized Subsequent to Acquisition		5,858
Land and improvements		13,873
Buildings and Improvements		66,215
Land Held for Development		0
Development and Construction in Progress		0
Total		80,088
Accumulated Depreciation		$ 25,107
Year(s) Built / Renovated		2,008
Year(s) Acquired		2,001
Depreciable Lives (Years)	[3]	(1)
3625-3635 Peterson Way
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		3625-3635 Peterson Way
Type		Office
Location		Santa Clara, CA
Encumbrances		$ 0
Original Land		63,206
Original Building		14,879
Costs Capitalized Subsequent to Acquisition		673
Land and improvements		63,206
Buildings and Improvements		14,879
Land Held for Development		673
Development and Construction in Progress		0
Total		78,758
Accumulated Depreciation		$ 8,146
Year(s) Built / Renovated		1,979
Year(s) Acquired		2,016
Depreciable Lives (Years)	[3]	(1)
2440 West El Camino Real
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		2440 West El Camino Real
Type		Office
Location		Mountain View, CA
Encumbrances		$ 0
Original Land		16,741
Original Building		51,285
Costs Capitalized Subsequent to Acquisition		3,411
Land and improvements		16,741
Buildings and Improvements		54,696
Land Held for Development		0
Development and Construction in Progress		0
Total		71,437
Accumulated Depreciation		$ 12,562
Year(s) Built / Renovated		1987/2003
Year(s) Acquired		2,011
Depreciable Lives (Years)	[3]	(1)
300 Binney Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		300 Binney Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		18,080
Original Building		51,262
Costs Capitalized Subsequent to Acquisition		140
Land and improvements		18,080
Buildings and Improvements		51,402
Land Held for Development		0
Development and Construction in Progress		0
Total		69,482
Accumulated Depreciation		$ 9,450
Year(s) Built / Renovated		2,013
Year(s) Acquired		2,009
Depreciable Lives (Years)	[3]	(1)
191 Spring Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		191 Spring Street
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		2,850
Original Building		59,751
Costs Capitalized Subsequent to Acquisition		6,235
Land and improvements		3,151
Buildings and Improvements		65,685
Land Held for Development		0
Development and Construction in Progress		0
Total		68,836
Accumulated Depreciation		$ 19,543
Year(s) Built / Renovated		1971/1995/2018
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
Wisconsin Place
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Wisconsin Place
Type		Office
Location		Chevy Chase, MD
Encumbrances		$ 0
Original Land		0
Original Building		53,349
Costs Capitalized Subsequent to Acquisition		14,889
Land and improvements		0
Buildings and Improvements		68,238
Land Held for Development		0
Development and Construction in Progress		0
Total		68,238
Accumulated Depreciation		$ 22,936
Year(s) Built / Renovated		2,009
Year(s) Acquired		2,004
Depreciable Lives (Years)	[3]	(1)
Reston Corporate Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Corporate Center
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		9,135
Original Building		50,857
Costs Capitalized Subsequent to Acquisition		6,236
Land and improvements		10,148
Buildings and Improvements		56,080
Land Held for Development		0
Development and Construction in Progress		0
Total		66,228
Accumulated Depreciation		$ 28,315
Year(s) Built / Renovated		1,984
Year(s) Acquired		1,998
Depreciable Lives (Years)	[3]	(1)
New Dominion Technology Park, Bldg. Two
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		New Dominion Technology Park, Bldg. Two
Type		Office
Location		Herndon, VA
Encumbrances		$ 0
Original Land		5,584
Original Building		51,868
Costs Capitalized Subsequent to Acquisition		4,157
Land and improvements		6,510
Buildings and Improvements		55,099
Land Held for Development		0
Development and Construction in Progress		0
Total		61,609
Accumulated Depreciation		$ 25,421
Year(s) Built / Renovated		2,004
Year(s) Acquired		1,998
Depreciable Lives (Years)	[3]	(1)
255 Main Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		255 Main Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		134
Original Building		25,110
Costs Capitalized Subsequent to Acquisition		29,672
Land and improvements		548
Buildings and Improvements		54,368
Land Held for Development		0
Development and Construction in Progress		0
Total		54,916
Accumulated Depreciation		$ 30,180
Year(s) Built / Renovated		1,987
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
200 West Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		200 West Street
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		16,148
Original Building		24,983
Costs Capitalized Subsequent to Acquisition		11,120
Land and improvements		16,813
Buildings and Improvements		35,438
Land Held for Development		0
Development and Construction in Progress		0
Total		52,251
Accumulated Depreciation		$ 22,544
Year(s) Built / Renovated		1,999
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
New Dominion Technology Park, Bldg. One
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		New Dominion Technology Park, Bldg. One
Type		Office
Location		Herndon, VA
Encumbrances		$ 29,675
Original Land		3,880
Original Building		43,227
Costs Capitalized Subsequent to Acquisition		3,927
Land and improvements		4,583
Buildings and Improvements		46,451
Land Held for Development		0
Development and Construction in Progress		0
Total		51,034
Accumulated Depreciation		$ 27,542
Year(s) Built / Renovated		2,001
Year(s) Acquired		1,998
Depreciable Lives (Years)	[3]	(1)
Sumner Square
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Sumner Square
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		624
Original Building		28,745
Costs Capitalized Subsequent to Acquisition		19,054
Land and improvements		1,478
Buildings and Improvements		46,945
Land Held for Development		0
Development and Construction in Progress		0
Total		48,423
Accumulated Depreciation		$ 25,384
Year(s) Built / Renovated		1,985
Year(s) Acquired		1,999
Depreciable Lives (Years)	[3]	(1)
University Place
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		University Place
Type		Office
Location		Cambridge, MA
Encumbrances		$ 5,571
Original Land		0
Original Building		37,091
Costs Capitalized Subsequent to Acquisition		9,001
Land and improvements		390
Buildings and Improvements		45,702
Land Held for Development		0
Development and Construction in Progress		0
Total		46,092
Accumulated Depreciation		$ 27,871
Year(s) Built / Renovated		1,985
Year(s) Acquired		1,998
Depreciable Lives (Years)	[3]	(1)
2600 Tower Oaks Boulevard
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		2600 Tower Oaks Boulevard
Type		Office
Location		Rockville, MD
Encumbrances		$ 0
Original Land		4,243
Original Building		31,125
Costs Capitalized Subsequent to Acquisition		6,517
Land and improvements		4,244
Buildings and Improvements		37,641
Land Held for Development		0
Development and Construction in Progress		0
Total		41,885
Accumulated Depreciation		$ 21,426
Year(s) Built / Renovated		2,001
Year(s) Acquired		1,998
Depreciable Lives (Years)	[3]	(1)
North First Business Park
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		North First Business Park
Type		Office
Location		San Jose, CA
Encumbrances		$ 0
Original Land		23,398
Original Building		13,069
Costs Capitalized Subsequent to Acquisition		4,613
Land and improvements		23,377
Buildings and Improvements		17,703
Land Held for Development		0
Development and Construction in Progress		0
Total		41,080
Accumulated Depreciation		$ 16,076
Year(s) Built / Renovated		1,981
Year(s) Acquired		2,007
Depreciable Lives (Years)	[3]	(1)
150 Broadway
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		150 Broadway
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		850
Original Building		25,042
Costs Capitalized Subsequent to Acquisition		8,540
Land and improvements		1,323
Buildings and Improvements		33,109
Land Held for Development		0
Development and Construction in Progress		0
Total		34,432
Accumulated Depreciation		$ 18,404
Year(s) Built / Renovated		1,999
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
325 Main Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		325 Main Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		174
Original Building		12,200
Costs Capitalized Subsequent to Acquisition		16,437
Land and improvements		965
Buildings and Improvements		23,319
Land Held for Development		4,527
Development and Construction in Progress		0
Total		28,811
Accumulated Depreciation		$ 13,676
Year(s) Built / Renovated		1987/2013
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
105 Broadway
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		105 Broadway
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		1,299
Original Building		12,943
Costs Capitalized Subsequent to Acquisition		9,401
Land and improvements		2,395
Buildings and Improvements		21,248
Land Held for Development		0
Development and Construction in Progress		0
Total		23,643
Accumulated Depreciation		$ 13,950
Year(s) Built / Renovated		1,990
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
Lexington Office Park
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Lexington Office Park
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		998
Original Building		1,426
Costs Capitalized Subsequent to Acquisition		18,700
Land and improvements		1,264
Buildings and Improvements		19,860
Land Held for Development		0
Development and Construction in Progress		0
Total		21,124
Accumulated Depreciation		$ 13,614
Year(s) Built / Renovated		1,982
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
201 Spring Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		201 Spring Street
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		2,849
Original Building		15,303
Costs Capitalized Subsequent to Acquisition		1,390
Land and improvements		3,124
Buildings and Improvements		16,418
Land Held for Development		0
Development and Construction in Progress		0
Total		19,542
Accumulated Depreciation		$ 8,344
Year(s) Built / Renovated		1,997
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
The Point
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		The Point
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		6,395
Original Building		10,040
Costs Capitalized Subsequent to Acquisition		431
Land and improvements		6,480
Buildings and Improvements		10,386
Land Held for Development		0
Development and Construction in Progress		0
Total		16,866
Accumulated Depreciation		$ 1,031
Year(s) Built / Renovated		2,015
Year(s) Acquired		2,007
Depreciable Lives (Years)	[3]	(1)
690 Folsom Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		690 Folsom Street
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		3,219
Original Building		11,038
Costs Capitalized Subsequent to Acquisition		1,157
Land and improvements		3,219
Buildings and Improvements		12,195
Land Held for Development		0
Development and Construction in Progress		0
Total		15,414
Accumulated Depreciation		$ 1,790
Year(s) Built / Renovated		2,015
Year(s) Acquired		2,012
Depreciable Lives (Years)	[3]	(1)
92-100 Hayden Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		92-100 Hayden Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		594
Original Building		6,748
Costs Capitalized Subsequent to Acquisition		7,255
Land and improvements		802
Buildings and Improvements		13,795
Land Held for Development		0
Development and Construction in Progress		0
Total		14,597
Accumulated Depreciation		$ 11,809
Year(s) Built / Renovated		1,985
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
181 Spring Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		181 Spring Street
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		1,066
Original Building		9,520
Costs Capitalized Subsequent to Acquisition		2,230
Land and improvements		1,160
Buildings and Improvements		11,656
Land Held for Development		0
Development and Construction in Progress		0
Total		12,816
Accumulated Depreciation		$ 5,424
Year(s) Built / Renovated		1,999
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
195 West Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		195 West Street
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		1,611
Original Building		6,652
Costs Capitalized Subsequent to Acquisition		4,270
Land and improvements		1,858
Buildings and Improvements		10,675
Land Held for Development		0
Development and Construction in Progress		0
Total		12,533
Accumulated Depreciation		$ 8,330
Year(s) Built / Renovated		1,990
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
33 Hayden Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		33 Hayden Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		266
Original Building		3,234
Costs Capitalized Subsequent to Acquisition		8,223
Land and improvements		425
Buildings and Improvements		11,298
Land Held for Development		0
Development and Construction in Progress		0
Total		11,723
Accumulated Depreciation		$ 9,033
Year(s) Built / Renovated		1,979
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
7501 Boston Boulevard, Building Seven
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7501 Boston Boulevard, Building Seven
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		665
Original Building		9,273
Costs Capitalized Subsequent to Acquisition		819
Land and improvements		791
Buildings and Improvements		9,966
Land Held for Development		0
Development and Construction in Progress		0
Total		10,757
Accumulated Depreciation		$ 5,121
Year(s) Built / Renovated		1,997
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
7450 Boston Boulevard, Building Three
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7450 Boston Boulevard, Building Three
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		1,165
Original Building		4,681
Costs Capitalized Subsequent to Acquisition		3,278
Land and improvements		1,430
Buildings and Improvements		7,694
Land Held for Development		0
Development and Construction in Progress		0
Total		9,124
Accumulated Depreciation		$ 3,733
Year(s) Built / Renovated		1,987
Year(s) Acquired		1,998
Depreciable Lives (Years)	[3]	(1)
7435 Boston Boulevard, Building One
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7435 Boston Boulevard, Building One
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		392
Original Building		3,822
Costs Capitalized Subsequent to Acquisition		4,737
Land and improvements		659
Buildings and Improvements		8,292
Land Held for Development		0
Development and Construction in Progress		0
Total		8,951
Accumulated Depreciation		$ 5,917
Year(s) Built / Renovated		1,982
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
250 Binney Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		250 Binney Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		110
Original Building		4,483
Costs Capitalized Subsequent to Acquisition		3,593
Land and improvements		273
Buildings and Improvements		7,913
Land Held for Development		0
Development and Construction in Progress		0
Total		8,186
Accumulated Depreciation		$ 5,448
Year(s) Built / Renovated		1,983
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
8000 Grainger Court, Building Five
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		8000 Grainger Court, Building Five
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		366
Original Building		4,282
Costs Capitalized Subsequent to Acquisition		3,536
Land and improvements		601
Buildings and Improvements		7,583
Land Held for Development		0
Development and Construction in Progress		0
Total		8,184
Accumulated Depreciation		$ 5,864
Year(s) Built / Renovated		1,984
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
453 Ravendale Drive
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		453 Ravendale Drive
Type		Office
Location		Mountain View, CA
Encumbrances		$ 0
Original Land		5,477
Original Building		1,090
Costs Capitalized Subsequent to Acquisition		676
Land and improvements		5,477
Buildings and Improvements		1,766
Land Held for Development		0
Development and Construction in Progress		0
Total		7,243
Accumulated Depreciation		$ 558
Year(s) Built / Renovated		1,977
Year(s) Acquired		2,012
Depreciable Lives (Years)	[3]	(1)
7300 Boston Boulevard, Building Thirteen
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7300 Boston Boulevard, Building Thirteen
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		608
Original Building		4,773
Costs Capitalized Subsequent to Acquisition		1,438
Land and improvements		661
Buildings and Improvements		6,158
Land Held for Development		0
Development and Construction in Progress		0
Total		6,819
Accumulated Depreciation		$ 3,011
Year(s) Built / Renovated		2,002
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
7601 Boston Boulevard, Building Eight
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7601 Boston Boulevard, Building Eight
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		200
Original Building		878
Costs Capitalized Subsequent to Acquisition		5,373
Land and improvements		551
Buildings and Improvements		5,900
Land Held for Development		0
Development and Construction in Progress		0
Total		6,451
Accumulated Depreciation		$ 4,487
Year(s) Built / Renovated		1,986
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
17 Hartwell Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		17 Hartwell Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		26
Original Building		150
Costs Capitalized Subsequent to Acquisition		6,064
Land and improvements		65
Buildings and Improvements		6,175
Land Held for Development		0
Development and Construction in Progress		0
Total		6,240
Accumulated Depreciation		$ 1,445
Year(s) Built / Renovated		1,968
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
7500 Boston Boulevard, Building Six
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7500 Boston Boulevard, Building Six
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		138
Original Building		3,749
Costs Capitalized Subsequent to Acquisition		1,673
Land and improvements		406
Buildings and Improvements		5,154
Land Held for Development		0
Development and Construction in Progress		0
Total		5,560
Accumulated Depreciation		$ 4,121
Year(s) Built / Renovated		1,985
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
8000 Corporate Court, Building Eleven
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		8000 Corporate Court, Building Eleven
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		136
Original Building		3,071
Costs Capitalized Subsequent to Acquisition		1,596
Land and improvements		774
Buildings and Improvements		4,029
Land Held for Development		0
Development and Construction in Progress		0
Total		4,803
Accumulated Depreciation		$ 3,051
Year(s) Built / Renovated		1,989
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
7375 Boston Boulevard, Building Ten
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7375 Boston Boulevard, Building Ten
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		23
Original Building		2,685
Costs Capitalized Subsequent to Acquisition		992
Land and improvements		93
Buildings and Improvements		3,607
Land Held for Development		0
Development and Construction in Progress		0
Total		3,700
Accumulated Depreciation		$ 2,593
Year(s) Built / Renovated		1,988
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
7374 Boston Boulevard, Building Four
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7374 Boston Boulevard, Building Four
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		241
Original Building		1,605
Costs Capitalized Subsequent to Acquisition		1,828
Land and improvements		398
Buildings and Improvements		3,276
Land Held for Development		0
Development and Construction in Progress		0
Total		3,674
Accumulated Depreciation		$ 2,685
Year(s) Built / Renovated		1,984
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
7451 Boston Boulevard, Building Two
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7451 Boston Boulevard, Building Two
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		249
Original Building		1,542
Costs Capitalized Subsequent to Acquisition		1,659
Land and improvements		613
Buildings and Improvements		2,837
Land Held for Development		0
Development and Construction in Progress		0
Total		3,450
Accumulated Depreciation		$ 2,527
Year(s) Built / Renovated		1,982
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
32 Hartwell Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		32 Hartwell Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		168
Original Building		1,943
Costs Capitalized Subsequent to Acquisition		817
Land and improvements		314
Buildings and Improvements		2,614
Land Held for Development		0
Development and Construction in Progress		0
Total		2,928
Accumulated Depreciation		$ 1,821
Year(s) Built / Renovated		1968/1979/1987
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
164 Lexington Road
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		164 Lexington Road
Type		Office
Location		Billerica, MA
Encumbrances		$ 0
Original Land		592
Original Building		1,370
Costs Capitalized Subsequent to Acquisition		319
Land and improvements		643
Buildings and Improvements		1,638
Land Held for Development		0
Development and Construction in Progress		0
Total		2,281
Accumulated Depreciation		$ 906
Year(s) Built / Renovated		1,982
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
Signature at Reston
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Signature at Reston
Type		Residential
Location		Reston, VA
Encumbrances		$ 0
Original Land		27,076
Original Building		190,580
Costs Capitalized Subsequent to Acquisition		0
Land and improvements		27,076
Buildings and Improvements		190,580
Land Held for Development		0
Development and Construction in Progress		0
Total		217,656
Accumulated Depreciation		$ 3,938
Year(s) Built / Renovated		2,018
Year(s) Acquired		2,013
Depreciable Lives (Years)	[3]	(1)
Proto Kendall Square
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Proto Kendall Square
Type		Residential
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		9,243
Original Building		127,248
Costs Capitalized Subsequent to Acquisition		0
Land and improvements		9,243
Buildings and Improvements		127,248
Land Held for Development		0
Development and Construction in Progress		0
Total		136,491
Accumulated Depreciation		$ 1,324
Year(s) Built / Renovated		2,018
Year(s) Acquired		2,015
Depreciable Lives (Years)	[3]	(1)
The Avant at Reston Town Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		The Avant at Reston Town Center
Type		Residential
Location		Reston, VA
Encumbrances		$ 0
Original Land		20,350
Original Building		91,995
Costs Capitalized Subsequent to Acquisition		830
Land and improvements		20,350
Buildings and Improvements		92,825
Land Held for Development		0
Development and Construction in Progress		0
Total		113,175
Accumulated Depreciation		$ 12,254
Year(s) Built / Renovated		2,014
Year(s) Acquired		2,010
Depreciable Lives (Years)	[3]	(1)
The Lofts at Atlantic Wharf
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		The Lofts at Atlantic Wharf
Type		Residential
Location		Boston, MA
Encumbrances		$ 0
Original Land		3,529
Original Building		54,891
Costs Capitalized Subsequent to Acquisition		1,768
Land and improvements		3,529
Buildings and Improvements		56,659
Land Held for Development		0
Development and Construction in Progress		0
Total		60,188
Accumulated Depreciation		$ 11,131
Year(s) Built / Renovated		2,011
Year(s) Acquired		2,007
Depreciable Lives (Years)	[3]	(1)
Boston Marriott Cambridge
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Boston Marriott Cambridge
Type		Hotel
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		478
Original Building		37,918
Costs Capitalized Subsequent to Acquisition		36,697
Land and improvements		1,201
Buildings and Improvements		73,892
Land Held for Development		0
Development and Construction in Progress		0
Total		75,093
Accumulated Depreciation		$ 46,576
Year(s) Built / Renovated		1986/2017
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
Kendall Center Green Garage
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Green Garage
Type		Garage
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		0
Original Building		35,035
Costs Capitalized Subsequent to Acquisition		7,448
Land and improvements		103
Buildings and Improvements		42,380
Land Held for Development		0
Development and Construction in Progress		0
Total		42,483
Accumulated Depreciation		$ 12,208
Year(s) Built / Renovated		1,984
Year(s) Acquired		2,006
Depreciable Lives (Years)	[3]	(1)
Kendall Center Yellow Garage
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Yellow Garage
Type		Garage
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		1,256
Original Building		15,697
Costs Capitalized Subsequent to Acquisition		1,621
Land and improvements		1,434
Buildings and Improvements		17,140
Land Held for Development		0
Development and Construction in Progress		0
Total		18,574
Accumulated Depreciation		$ 5,643
Year(s) Built / Renovated		2,006
Year(s) Acquired		2,004
Depreciable Lives (Years)	[3]	(1)
Kendall Center Blue Garage
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Blue Garage
Type		Garage
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		1,163
Original Building		11,633
Costs Capitalized Subsequent to Acquisition		2,145
Land and improvements		1,579
Buildings and Improvements		13,362
Land Held for Development		0
Development and Construction in Progress		0
Total		14,941
Accumulated Depreciation		$ 9,437
Year(s) Built / Renovated		1,990
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
145 Broadway
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		145 Broadway
Type		Development
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		121
Original Building		0
Costs Capitalized Subsequent to Acquisition		223,845
Land and improvements		324
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		223,642
Total		223,966
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1,997
Depreciable Lives (Years)		N/A
MacArthur Station Residences
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		MacArthur Station Residences
Type		Development
Location		Oakland, CA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		87,159
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		87,159
Total		87,159
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		N/A
Depreciable Lives (Years)		N/A
20 CityPoint
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		20 CityPoint
Type		Development
Location		Waltham, MA
Encumbrances		$ 0
Original Land		0
Original Building		6,287
Costs Capitalized Subsequent to Acquisition		46,024
Land and improvements		0
Buildings and Improvements		6,287
Land Held for Development		0
Development and Construction in Progress		46,024
Total		52,311
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,007
Depreciable Lives (Years)		N/A
Reston Gateway
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Gateway
Type		Development
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		25,167
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		25,167
Total		25,167
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1,998
Depreciable Lives (Years)		N/A
17Fifty Presidents Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		17Fifty Presidents Street
Type		Development
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		25,120
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		25,120
Total		25,120
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,013
Depreciable Lives (Years)		N/A
North First Master Plan
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		North First Master Plan
Type		Land
Location		San Jose, CA
Encumbrances		$ 0
Original Land		35,004
Original Building		0
Costs Capitalized Subsequent to Acquisition		3,932
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		38,936
Development and Construction in Progress		0
Total		38,936
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,007
Depreciable Lives (Years)		N/A
Plaza at Almaden
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Plaza at Almaden
Type		Land
Location		San Jose, CA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		29,928
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		29,928
Development and Construction in Progress		0
Total		29,928
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,006
Depreciable Lives (Years)		N/A
Springfield Metro Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Springfield Metro Center
Type		Land
Location		Springfield, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		19,823
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		19,823
Development and Construction in Progress		0
Total		19,823
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,007
Depreciable Lives (Years)		N/A
214 Third Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		214 Third Avenue
Type		Land
Location		Waltham, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		15,233
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		15,233
Development and Construction in Progress		0
Total		15,233
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,006
Depreciable Lives (Years)		N/A
Platform 16
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Platform 16
Type		Land
Location		San Jose, CA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		12,962
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		12,962
Development and Construction in Progress		0
Total		12,962
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,018
Depreciable Lives (Years)		N/A
103 Fourth Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		103 Fourth Avenue
Type		Land
Location		Waltham, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		12,208
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		12,208
Development and Construction in Progress		0
Total		12,208
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,007
Depreciable Lives (Years)		N/A
Reston Gateway Master Plan
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Gateway Master Plan
Type		Land
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		11,014
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		11,014
Development and Construction in Progress		0
Total		11,014
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1,998
Depreciable Lives (Years)		N/A
Fourth and Harrison
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Fourth and Harrison
Type		Land
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		10,350
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		10,350
Development and Construction in Progress		0
Total		10,350
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		N/A
Depreciable Lives (Years)		N/A
2100 Pennsylvania Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		2100 Pennsylvania Avenue
Type		Land
Location		Washington, DC
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		9,700
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		9,700
Development and Construction in Progress		0
Total		9,700
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		N/A
Depreciable Lives (Years)		N/A
Crane Meadow
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Crane Meadow
Type		Land
Location		Marlborough, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		8,852
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		8,852
Development and Construction in Progress		0
Total		8,852
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,000
Depreciable Lives (Years)		N/A
Washingtonian North
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Washingtonian North
Type		Land
Location		Gaithersburg, MD
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		7,473
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		7,473
Development and Construction in Progress		0
Total		7,473
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1,998
Depreciable Lives (Years)		N/A
Broad Run Business Park
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Broad Run Business Park
Type		Land
Location		Loudoun County, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		2,388
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		2,388
Development and Construction in Progress		0
Total		2,388
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1,998
Depreciable Lives (Years)		N/A
Kendall Center Master Plan
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Master Plan
Type		Land
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		2,199
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		2,199
Development and Construction in Progress		0
Total		2,199
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1,997
Depreciable Lives (Years)		N/A
Weston Quarry
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Weston Quarry
Type		Land
Location		Weston, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		1,237
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		1,237
Development and Construction in Progress		0
Total		1,237
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,001
Depreciable Lives (Years)		N/A
Reston Overlook Master Plan
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Overlook Master Plan
Type		Land
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		39
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		39
Development and Construction in Progress		0
Total		39
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,000
Depreciable Lives (Years)		N/A
Minimum [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Life Used for Depreciation		life of the lease
[1]	Includes unamortized deferred financing costs totaling approximately $(30.8) million.
[2]	Includes pre-development costs.
[3]	Depreciation of the buildings and improvements are calculated over lives ranging from the life of the lease to 40 years.

Real Estate and Accumulated D_5

Real Estate and Accumulated Depreciation Activity of Real Estate and Accumulated Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Real Estate, Balance at the beginning of the year	$ 21,058,714	$ 20,114,576	$ 19,451,683
Real Estate, Additions to / improvements of real estate	1,043,379	1,099,286	977,287
Real Estate, Assets sold / written off	(496,548)	(155,148)	(314,394)
Real Estate, Balance at the end of the year	21,605,545	21,058,714	20,114,576
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Accumulated depreciation, Balance at beginning of the year	4,566,570	4,201,891	3,905,940
Accumulated depreciation, Depreciation expense	533,342	497,059	560,024
Accumulated depreciation, Assets sold / written off	(228,810)	(132,380)	(264,073)
Accumulated depreciation, Balance at end of the year	$ 4,871,102	$ 4,566,570	$ 4,201,891

Real Estate and Accumulated D_6

Real Estate and Accumulated Depreciation Schedule of Real Estate and Accumulated Depreciation (BPLP) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	[1]	$ 2,964,572
Original Land		4,959,995
Original Building		12,763,317
Costs Capitalized Subsequent to Acquisition		3,882,233
Land and improvements		5,072,568
Buildings and Improvements		15,753,683
Land Held for Development	[2]	200,498
Development and Construction in Progress		578,796
Total		21,605,545
Accumulated Depreciation		4,871,102
Furniture, fixtures and equipment		44,351	$ 37,928
Furniture, fixtures and equipment accumulated depreciation		26,675
Real Estate Aggregate Cost For Tax Purposes		17,900,000
Real Estate Aggregate Accumulated Depreciation For Tax Purposes		$ 3,900,000
Real Estate and Accumulated Depreciation, Life Used for Depreciation		40 years
Unamortized deferred finance costs		$ (30,756)
767 Fifth Avenue (the General Motors Building)
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		767 Fifth Avenue (the General Motors Building)
Type		Office
Location		New York, NY
Encumbrances		$ 2,270,534
Original Land		1,796,252
Original Building		1,532,654
Costs Capitalized Subsequent to Acquisition		189,657
Land and improvements		1,796,252
Buildings and Improvements		1,722,311
Land Held for Development		0
Development and Construction in Progress		0
Total		3,518,563
Accumulated Depreciation		$ 271,534
Year(s) Built / Renovated		1,968
Year(s) Acquired		2,013
Depreciable Lives (Years)	[3]	(1)
Prudential Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Prudential Center
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		92,077
Original Building		948,357
Costs Capitalized Subsequent to Acquisition		532,802
Land and improvements		115,638
Buildings and Improvements		1,457,494
Land Held for Development		104
Development and Construction in Progress		0
Total		1,573,236
Accumulated Depreciation		$ 550,109
Year(s) Built / Renovated		1965/1993/2002/2016-2017
Year(s) Acquired		1998/1999/2000
Depreciable Lives (Years)	[3]	(1)
Embarcadero Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Embarcadero Center
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		179,697
Original Building		847,410
Costs Capitalized Subsequent to Acquisition		368,967
Land and improvements		195,987
Buildings and Improvements		1,200,087
Land Held for Development		0
Development and Construction in Progress		0
Total		1,396,074
Accumulated Depreciation		$ 612,981
Year(s) Built / Renovated		1970/1989
Year(s) Acquired		1998-1999
Depreciable Lives (Years)	[3]	(1)
399 Park Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		399 Park Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		339,200
Original Building		700,358
Costs Capitalized Subsequent to Acquisition		247,092
Land and improvements		354,107
Buildings and Improvements		932,543
Land Held for Development		0
Development and Construction in Progress		0
Total		1,286,650
Accumulated Depreciation		$ 332,911
Year(s) Built / Renovated		1961/2018
Year(s) Acquired		2,002
Depreciable Lives (Years)	[3]	(1)
Salesforce Tower
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Salesforce Tower
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		200,349
Original Building		919,565
Costs Capitalized Subsequent to Acquisition		0
Land and improvements		200,349
Buildings and Improvements		919,565
Land Held for Development		0
Development and Construction in Progress		0
Total		1,119,914
Accumulated Depreciation		$ 9,509
Year(s) Built / Renovated		2,018
Year(s) Acquired		2,013
Depreciable Lives (Years)	[3]	(1)
601 Lexington Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		601 Lexington Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 658,792
Original Land		241,600
Original Building		494,782
Costs Capitalized Subsequent to Acquisition		361,985
Land and improvements		289,639
Buildings and Improvements		637,044
Land Held for Development		0
Development and Construction in Progress		171,684
Total		1,098,367
Accumulated Depreciation		$ 272,936
Year(s) Built / Renovated		1977/1997
Year(s) Acquired		2,001
Depreciable Lives (Years)	[3]	(1)
200 Clarendon Street and Garage
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		200 Clarendon Street and Garage
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		219,543
Original Building		667,884
Costs Capitalized Subsequent to Acquisition		164,073
Land and improvements		219,616
Buildings and Improvements		822,218
Land Held for Development		9,666
Development and Construction in Progress		0
Total		1,051,500
Accumulated Depreciation		$ 192,137
Year(s) Built / Renovated		1,976
Year(s) Acquired		2,010
Depreciable Lives (Years)	[3]	(1)
250 West 55th Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		250 West 55th Street
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		285,263
Original Building		603,167
Costs Capitalized Subsequent to Acquisition		48,642
Land and improvements		285,263
Buildings and Improvements		651,809
Land Held for Development		0
Development and Construction in Progress		0
Total		937,072
Accumulated Depreciation		$ 94,434
Year(s) Built / Renovated		2,014
Year(s) Acquired		2,007
Depreciable Lives (Years)	[3]	(1)
100 Federal Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		100 Federal Street
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		131,067
Original Building		435,954
Costs Capitalized Subsequent to Acquisition		99,702
Land and improvements		131,067
Buildings and Improvements		535,656
Land Held for Development		0
Development and Construction in Progress		0
Total		666,723
Accumulated Depreciation		$ 105,536
Year(s) Built / Renovated		1971-1975/2017
Year(s) Acquired		2,012
Depreciable Lives (Years)	[3]	(1)
Carnegie Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Carnegie Center
Type		Office
Location		Princeton, NJ
Encumbrances		$ 0
Original Land		107,997
Original Building		389,359
Costs Capitalized Subsequent to Acquisition		158,752
Land and improvements		108,948
Buildings and Improvements		543,974
Land Held for Development		3,186
Development and Construction in Progress		0
Total		656,108
Accumulated Depreciation		$ 241,570
Year(s) Built / Renovated		1983-2016
Year(s) Acquired		1998/1999/2000/2007/2014/2017
Depreciable Lives (Years)	[3]	(1)
Times Square Tower
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Times Square Tower
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		165,413
Original Building		380,438
Costs Capitalized Subsequent to Acquisition		94,451
Land and improvements		169,193
Buildings and Improvements		471,109
Land Held for Development		0
Development and Construction in Progress		0
Total		640,302
Accumulated Depreciation		$ 206,067
Year(s) Built / Renovated		2,004
Year(s) Acquired		2,000
Depreciable Lives (Years)	[3]	(1)
Atlantic Wharf
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Atlantic Wharf
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		63,988
Original Building		454,537
Costs Capitalized Subsequent to Acquisition		17,184
Land and improvements		63,988
Buildings and Improvements		471,721
Land Held for Development		0
Development and Construction in Progress		0
Total		535,709
Accumulated Depreciation		$ 116,238
Year(s) Built / Renovated		2,011
Year(s) Acquired		2,007
Depreciable Lives (Years)	[3]	(1)
510 Madison Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		510 Madison Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		103,000
Original Building		253,665
Costs Capitalized Subsequent to Acquisition		24,992
Land and improvements		103,000
Buildings and Improvements		278,657
Land Held for Development		0
Development and Construction in Progress		0
Total		381,657
Accumulated Depreciation		$ 62,507
Year(s) Built / Renovated		2,012
Year(s) Acquired		2,010
Depreciable Lives (Years)	[3]	(1)
Fountain Square
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Fountain Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		56,853
Original Building		306,298
Costs Capitalized Subsequent to Acquisition		3,170
Land and improvements		56,853
Buildings and Improvements		309,468
Land Held for Development		0
Development and Construction in Progress		0
Total		366,321
Accumulated Depreciation		$ 68,390
Year(s) Built / Renovated		1986-1990
Year(s) Acquired		2,012
Depreciable Lives (Years)	[3]	(1)
599 Lexington Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		599 Lexington Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		81,040
Original Building		100,507
Costs Capitalized Subsequent to Acquisition		174,213
Land and improvements		87,852
Buildings and Improvements		267,908
Land Held for Development		0
Development and Construction in Progress		0
Total		355,760
Accumulated Depreciation		$ 170,678
Year(s) Built / Renovated		1,986
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
680 Folsom Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		680 Folsom Street
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		72,545
Original Building		219,766
Costs Capitalized Subsequent to Acquisition		7,829
Land and improvements		72,545
Buildings and Improvements		227,595
Land Held for Development		0
Development and Construction in Progress		0
Total		300,140
Accumulated Depreciation		$ 38,230
Year(s) Built / Renovated		2,014
Year(s) Acquired		2,012
Depreciable Lives (Years)	[3]	(1)
601 Massachusetts Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		601 Massachusetts Avenue
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		95,310
Original Building		165,173
Costs Capitalized Subsequent to Acquisition		3,900
Land and improvements		95,322
Buildings and Improvements		169,061
Land Held for Development		0
Development and Construction in Progress		0
Total		264,383
Accumulated Depreciation		$ 18,263
Year(s) Built / Renovated		2,016
Year(s) Acquired		2,008
Depreciable Lives (Years)	[3]	(1)
South of Market and Democracy Tower
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		South of Market and Democracy Tower
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		13,603
Original Building		237,479
Costs Capitalized Subsequent to Acquisition		12,428
Land and improvements		13,687
Buildings and Improvements		249,823
Land Held for Development		0
Development and Construction in Progress		0
Total		263,510
Accumulated Depreciation		$ 91,072
Year(s) Built / Renovated		2008-2009
Year(s) Acquired		2,003
Depreciable Lives (Years)	[3]	(1)
Bay Colony Corporate Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Bay Colony Corporate Center
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		18,789
Original Building		148,451
Costs Capitalized Subsequent to Acquisition		77,133
Land and improvements		18,789
Buildings and Improvements		225,584
Land Held for Development		0
Development and Construction in Progress		0
Total		244,373
Accumulated Depreciation		$ 68,903
Year(s) Built / Renovated		1985-1989
Year(s) Acquired		2,011
Depreciable Lives (Years)	[3]	(1)
Gateway Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Gateway Center
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		28,255
Original Building		139,245
Costs Capitalized Subsequent to Acquisition		64,831
Land and improvements		30,627
Buildings and Improvements		201,704
Land Held for Development		0
Development and Construction in Progress		0
Total		232,331
Accumulated Depreciation		$ 107,640
Year(s) Built / Renovated		1984/1986/2002
Year(s) Acquired		1,999
Depreciable Lives (Years)	[3]	(1)
535 Mission Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		535 Mission Street
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		40,933
Original Building		148,378
Costs Capitalized Subsequent to Acquisition		3,259
Land and improvements		40,933
Buildings and Improvements		151,637
Land Held for Development		0
Development and Construction in Progress		0
Total		192,570
Accumulated Depreciation		$ 20,576
Year(s) Built / Renovated		2,015
Year(s) Acquired		2,013
Depreciable Lives (Years)	[3]	(1)
2200 Pennsylvania Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		2200 Pennsylvania Avenue
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		0
Original Building		183,541
Costs Capitalized Subsequent to Acquisition		4,535
Land and improvements		0
Buildings and Improvements		188,076
Land Held for Development		0
Development and Construction in Progress		0
Total		188,076
Accumulated Depreciation		$ 52,280
Year(s) Built / Renovated		2,011
Year(s) Acquired		2,008
Depreciable Lives (Years)	[3]	(1)
Mountain View Research Park
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Mountain View Research Park
Type		Office
Location		Mountain View, CA
Encumbrances		$ 0
Original Land		95,066
Original Building		68,373
Costs Capitalized Subsequent to Acquisition		9,988
Land and improvements		95,066
Buildings and Improvements		78,361
Land Held for Development		0
Development and Construction in Progress		0
Total		173,427
Accumulated Depreciation		$ 17,866
Year(s) Built / Renovated		1977-1981/2007-2013
Year(s) Acquired		2,013
Depreciable Lives (Years)	[3]	(1)
Reservoir Place
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reservoir Place
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		18,605
Original Building		104,124
Costs Capitalized Subsequent to Acquisition		45,144
Land and improvements		20,108
Buildings and Improvements		147,765
Land Held for Development		0
Development and Construction in Progress		0
Total		167,873
Accumulated Depreciation		$ 64,683
Year(s) Built / Renovated		1955/1987/2017
Year(s) Acquired		1997/1998
Depreciable Lives (Years)	[3]	(1)
1330 Connecticut Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		1330 Connecticut Avenue
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		25,982
Original Building		82,311
Costs Capitalized Subsequent to Acquisition		36,089
Land and improvements		27,135
Buildings and Improvements		117,247
Land Held for Development		0
Development and Construction in Progress		0
Total		144,382
Accumulated Depreciation		$ 27,535
Year(s) Built / Renovated		1984/2018
Year(s) Acquired		2,004
Depreciable Lives (Years)	[3]	(1)
Kingstowne Towne Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kingstowne Towne Center
Type		Office
Location		Alexandria, VA
Encumbrances		$ 0
Original Land		18,021
Original Building		109,038
Costs Capitalized Subsequent to Acquisition		2,098
Land and improvements		18,062
Buildings and Improvements		111,095
Land Held for Development		0
Development and Construction in Progress		0
Total		129,157
Accumulated Depreciation		$ 41,469
Year(s) Built / Renovated		2003-2006
Year(s) Acquired		2,007
Depreciable Lives (Years)	[3]	(1)
One Freedom Square
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		One Freedom Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		9,929
Original Building		84,504
Costs Capitalized Subsequent to Acquisition		32,256
Land and improvements		11,293
Buildings and Improvements		115,396
Land Held for Development		0
Development and Construction in Progress		0
Total		126,689
Accumulated Depreciation		$ 54,652
Year(s) Built / Renovated		2,000
Year(s) Acquired		2,003
Depreciable Lives (Years)	[3]	(1)
Weston Corporate Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Weston Corporate Center
Type		Office
Location		Weston, MA
Encumbrances		$ 0
Original Land		25,753
Original Building		92,312
Costs Capitalized Subsequent to Acquisition		(123)
Land and improvements		25,854
Buildings and Improvements		92,088
Land Held for Development		0
Development and Construction in Progress		0
Total		117,942
Accumulated Depreciation		$ 26,176
Year(s) Built / Renovated		2,010
Year(s) Acquired		2,001
Depreciable Lives (Years)	[3]	(1)
Capital Gallery
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Capital Gallery
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		4,725
Original Building		29,565
Costs Capitalized Subsequent to Acquisition		87,231
Land and improvements		8,662
Buildings and Improvements		112,859
Land Held for Development		0
Development and Construction in Progress		0
Total		121,521
Accumulated Depreciation		$ 67,759
Year(s) Built / Renovated		1981/2006
Year(s) Acquired		2,007
Depreciable Lives (Years)	[3]	(1)
Two Freedom Square
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Two Freedom Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		13,930
Original Building		77,739
Costs Capitalized Subsequent to Acquisition		23,427
Land and improvements		15,420
Buildings and Improvements		99,676
Land Held for Development		0
Development and Construction in Progress		0
Total		115,096
Accumulated Depreciation		$ 51,291
Year(s) Built / Renovated		2,001
Year(s) Acquired		2,003
Depreciable Lives (Years)	[3]	(1)
One and Two Reston Overlook
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		One and Two Reston Overlook
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		16,456
Original Building		66,192
Costs Capitalized Subsequent to Acquisition		24,181
Land and improvements		16,179
Buildings and Improvements		90,650
Land Held for Development		0
Development and Construction in Progress		0
Total		106,829
Accumulated Depreciation		$ 47,668
Year(s) Built / Renovated		1,999
Year(s) Acquired		2,000
Depreciable Lives (Years)	[3]	(1)
140 Kendrick Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		140 Kendrick Street
Type		Office
Location		Needham, MA
Encumbrances		$ 0
Original Land		18,095
Original Building		66,905
Costs Capitalized Subsequent to Acquisition		17,553
Land and improvements		19,092
Buildings and Improvements		83,461
Land Held for Development		0
Development and Construction in Progress		0
Total		102,553
Accumulated Depreciation		$ 32,360
Year(s) Built / Renovated		2,000
Year(s) Acquired		2,004
Depreciable Lives (Years)	[3]	(1)
355 Main Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		355 Main Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		18,863
Original Building		53,346
Costs Capitalized Subsequent to Acquisition		23,701
Land and improvements		21,173
Buildings and Improvements		74,737
Land Held for Development		0
Development and Construction in Progress		0
Total		95,910
Accumulated Depreciation		$ 23,691
Year(s) Built / Renovated		1981/1996/2013
Year(s) Acquired		2,006
Depreciable Lives (Years)	[3]	(1)
Discovery Square
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Discovery Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		11,198
Original Building		71,782
Costs Capitalized Subsequent to Acquisition		17,753
Land and improvements		12,533
Buildings and Improvements		88,200
Land Held for Development		0
Development and Construction in Progress		0
Total		100,733
Accumulated Depreciation		$ 39,574
Year(s) Built / Renovated		2,001
Year(s) Acquired		2,003
Depreciable Lives (Years)	[3]	(1)
10 CityPoint
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		10 CityPoint
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		1,953
Original Building		85,752
Costs Capitalized Subsequent to Acquisition		4,515
Land and improvements		2,116
Buildings and Improvements		90,104
Land Held for Development		0
Development and Construction in Progress		0
Total		92,220
Accumulated Depreciation		$ 7,772
Year(s) Built / Renovated		2,016
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
90 Broadway
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		90 Broadway
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		19,104
Original Building		52,078
Costs Capitalized Subsequent to Acquisition		18,363
Land and improvements		20,785
Buildings and Improvements		68,760
Land Held for Development		0
Development and Construction in Progress		0
Total		89,545
Accumulated Depreciation		$ 21,302
Year(s) Built / Renovated		1983/1998/2013
Year(s) Acquired		2,006
Depreciable Lives (Years)	[3]	(1)
230 CityPoint
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		230 CityPoint
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		13,189
Original Building		49,823
Costs Capitalized Subsequent to Acquisition		21,914
Land and improvements		13,593
Buildings and Improvements		71,333
Land Held for Development		0
Development and Construction in Progress		0
Total		84,926
Accumulated Depreciation		$ 26,357
Year(s) Built / Renovated		1,992
Year(s) Acquired		2,005
Depreciable Lives (Years)	[3]	(1)
77 CityPoint
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		77 CityPoint
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		13,847
Original Building		60,383
Costs Capitalized Subsequent to Acquisition		5,858
Land and improvements		13,873
Buildings and Improvements		66,215
Land Held for Development		0
Development and Construction in Progress		0
Total		80,088
Accumulated Depreciation		$ 25,107
Year(s) Built / Renovated		2,008
Year(s) Acquired		2,001
Depreciable Lives (Years)	[3]	(1)
Waltham Weston Corporate Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Waltham Weston Corporate Center
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		10,385
Original Building		60,694
Costs Capitalized Subsequent to Acquisition		11,449
Land and improvements		11,097
Buildings and Improvements		71,431
Land Held for Development		0
Development and Construction in Progress		0
Total		82,528
Accumulated Depreciation		$ 32,739
Year(s) Built / Renovated		2,003
Year(s) Acquired		1,999
Depreciable Lives (Years)	[3]	(1)
3625-3635 Peterson Way
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		3625-3635 Peterson Way
Type		Office
Location		Santa Clara, CA
Encumbrances		$ 0
Original Land		63,206
Original Building		14,879
Costs Capitalized Subsequent to Acquisition		673
Land and improvements		63,206
Buildings and Improvements		14,879
Land Held for Development		673
Development and Construction in Progress		0
Total		78,758
Accumulated Depreciation		$ 8,146
Year(s) Built / Renovated		1,979
Year(s) Acquired		2,016
Depreciable Lives (Years)	[3]	(1)
2440 West El Camino Real
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		2440 West El Camino Real
Type		Office
Location		Mountain View, CA
Encumbrances		$ 0
Original Land		16,741
Original Building		51,285
Costs Capitalized Subsequent to Acquisition		3,411
Land and improvements		16,741
Buildings and Improvements		54,696
Land Held for Development		0
Development and Construction in Progress		0
Total		71,437
Accumulated Depreciation		$ 12,562
Year(s) Built / Renovated		1987/2003
Year(s) Acquired		2,011
Depreciable Lives (Years)	[3]	(1)
300 Binney Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		300 Binney Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		18,080
Original Building		51,262
Costs Capitalized Subsequent to Acquisition		140
Land and improvements		18,080
Buildings and Improvements		51,402
Land Held for Development		0
Development and Construction in Progress		0
Total		69,482
Accumulated Depreciation		$ 9,450
Year(s) Built / Renovated		2,013
Year(s) Acquired		2,009
Depreciable Lives (Years)	[3]	(1)
Wisconsin Place
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Wisconsin Place
Type		Office
Location		Chevy Chase, MD
Encumbrances		$ 0
Original Land		0
Original Building		53,349
Costs Capitalized Subsequent to Acquisition		14,889
Land and improvements		0
Buildings and Improvements		68,238
Land Held for Development		0
Development and Construction in Progress		0
Total		68,238
Accumulated Depreciation		$ 22,936
Year(s) Built / Renovated		2,009
Year(s) Acquired		2,004
Depreciable Lives (Years)	[3]	(1)
191 Spring Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		191 Spring Street
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		2,850
Original Building		59,751
Costs Capitalized Subsequent to Acquisition		6,235
Land and improvements		3,151
Buildings and Improvements		65,685
Land Held for Development		0
Development and Construction in Progress		0
Total		68,836
Accumulated Depreciation		$ 19,543
Year(s) Built / Renovated		1971/1995/2018
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
Reston Corporate Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Corporate Center
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		9,135
Original Building		50,857
Costs Capitalized Subsequent to Acquisition		6,236
Land and improvements		10,148
Buildings and Improvements		56,080
Land Held for Development		0
Development and Construction in Progress		0
Total		66,228
Accumulated Depreciation		$ 28,315
Year(s) Built / Renovated		1,984
Year(s) Acquired		1,998
Depreciable Lives (Years)	[3]	(1)
New Dominion Technology Park, Bldg. Two
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		New Dominion Technology Park, Bldg. Two
Type		Office
Location		Herndon, VA
Encumbrances		$ 0
Original Land		5,584
Original Building		51,868
Costs Capitalized Subsequent to Acquisition		4,157
Land and improvements		6,510
Buildings and Improvements		55,099
Land Held for Development		0
Development and Construction in Progress		0
Total		61,609
Accumulated Depreciation		$ 25,421
Year(s) Built / Renovated		2,004
Year(s) Acquired		1,998
Depreciable Lives (Years)	[3]	(1)
255 Main Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		255 Main Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		134
Original Building		25,110
Costs Capitalized Subsequent to Acquisition		29,672
Land and improvements		548
Buildings and Improvements		54,368
Land Held for Development		0
Development and Construction in Progress		0
Total		54,916
Accumulated Depreciation		$ 30,180
Year(s) Built / Renovated		1,987
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
200 West Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		200 West Street
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		16,148
Original Building		24,983
Costs Capitalized Subsequent to Acquisition		11,120
Land and improvements		16,813
Buildings and Improvements		35,438
Land Held for Development		0
Development and Construction in Progress		0
Total		52,251
Accumulated Depreciation		$ 22,544
Year(s) Built / Renovated		1,999
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
New Dominion Technology Park, Bldg. One
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		New Dominion Technology Park, Bldg. One
Type		Office
Location		Herndon, VA
Encumbrances		$ 29,675
Original Land		3,880
Original Building		43,227
Costs Capitalized Subsequent to Acquisition		3,927
Land and improvements		4,583
Buildings and Improvements		46,451
Land Held for Development		0
Development and Construction in Progress		0
Total		51,034
Accumulated Depreciation		$ 27,542
Year(s) Built / Renovated		2,001
Year(s) Acquired		1,998
Depreciable Lives (Years)	[3]	(1)
Sumner Square
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Sumner Square
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		624
Original Building		28,745
Costs Capitalized Subsequent to Acquisition		19,054
Land and improvements		1,478
Buildings and Improvements		46,945
Land Held for Development		0
Development and Construction in Progress		0
Total		48,423
Accumulated Depreciation		$ 25,384
Year(s) Built / Renovated		1,985
Year(s) Acquired		1,999
Depreciable Lives (Years)	[3]	(1)
University Place
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		University Place
Type		Office
Location		Cambridge, MA
Encumbrances		$ 5,571
Original Land		0
Original Building		37,091
Costs Capitalized Subsequent to Acquisition		9,001
Land and improvements		390
Buildings and Improvements		45,702
Land Held for Development		0
Development and Construction in Progress		0
Total		46,092
Accumulated Depreciation		$ 27,871
Year(s) Built / Renovated		1,985
Year(s) Acquired		1,998
Depreciable Lives (Years)	[3]	(1)
2600 Tower Oaks Boulevard
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		2600 Tower Oaks Boulevard
Type		Office
Location		Rockville, MD
Encumbrances		$ 0
Original Land		4,243
Original Building		31,125
Costs Capitalized Subsequent to Acquisition		6,517
Land and improvements		4,244
Buildings and Improvements		37,641
Land Held for Development		0
Development and Construction in Progress		0
Total		41,885
Accumulated Depreciation		$ 21,426
Year(s) Built / Renovated		2,001
Year(s) Acquired		1,998
Depreciable Lives (Years)	[3]	(1)
North First Business Park
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		North First Business Park
Type		Office
Location		San Jose, CA
Encumbrances		$ 0
Original Land		23,398
Original Building		13,069
Costs Capitalized Subsequent to Acquisition		4,613
Land and improvements		23,377
Buildings and Improvements		17,703
Land Held for Development		0
Development and Construction in Progress		0
Total		41,080
Accumulated Depreciation		$ 16,076
Year(s) Built / Renovated		1,981
Year(s) Acquired		2,007
Depreciable Lives (Years)	[3]	(1)
150 Broadway
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		150 Broadway
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		850
Original Building		25,042
Costs Capitalized Subsequent to Acquisition		8,540
Land and improvements		1,323
Buildings and Improvements		33,109
Land Held for Development		0
Development and Construction in Progress		0
Total		34,432
Accumulated Depreciation		$ 18,404
Year(s) Built / Renovated		1,999
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
325 Main Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		325 Main Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		174
Original Building		12,200
Costs Capitalized Subsequent to Acquisition		16,437
Land and improvements		965
Buildings and Improvements		23,319
Land Held for Development		4,527
Development and Construction in Progress		0
Total		28,811
Accumulated Depreciation		$ 13,676
Year(s) Built / Renovated		1987/2013
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
105 Broadway
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		105 Broadway
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		1,299
Original Building		12,943
Costs Capitalized Subsequent to Acquisition		9,401
Land and improvements		2,395
Buildings and Improvements		21,248
Land Held for Development		0
Development and Construction in Progress		0
Total		23,643
Accumulated Depreciation		$ 13,950
Year(s) Built / Renovated		1,990
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
Lexington Office Park
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Lexington Office Park
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		998
Original Building		1,426
Costs Capitalized Subsequent to Acquisition		18,700
Land and improvements		1,264
Buildings and Improvements		19,860
Land Held for Development		0
Development and Construction in Progress		0
Total		21,124
Accumulated Depreciation		$ 13,614
Year(s) Built / Renovated		1,982
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
201 Spring Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		201 Spring Street
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		2,849
Original Building		15,303
Costs Capitalized Subsequent to Acquisition		1,390
Land and improvements		3,124
Buildings and Improvements		16,418
Land Held for Development		0
Development and Construction in Progress		0
Total		19,542
Accumulated Depreciation		$ 8,344
Year(s) Built / Renovated		1,997
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
The Point
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		The Point
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		6,395
Original Building		10,040
Costs Capitalized Subsequent to Acquisition		431
Land and improvements		6,480
Buildings and Improvements		10,386
Land Held for Development		0
Development and Construction in Progress		0
Total		16,866
Accumulated Depreciation		$ 1,031
Year(s) Built / Renovated		2,015
Year(s) Acquired		2,007
Depreciable Lives (Years)	[3]	(1)
690 Folsom Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		690 Folsom Street
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		3,219
Original Building		11,038
Costs Capitalized Subsequent to Acquisition		1,157
Land and improvements		3,219
Buildings and Improvements		12,195
Land Held for Development		0
Development and Construction in Progress		0
Total		15,414
Accumulated Depreciation		$ 1,790
Year(s) Built / Renovated		2,015
Year(s) Acquired		2,012
Depreciable Lives (Years)	[3]	(1)
92-100 Hayden Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		92-100 Hayden Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		594
Original Building		6,748
Costs Capitalized Subsequent to Acquisition		7,255
Land and improvements		802
Buildings and Improvements		13,795
Land Held for Development		0
Development and Construction in Progress		0
Total		14,597
Accumulated Depreciation		$ 11,809
Year(s) Built / Renovated		1,985
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
181 Spring Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		181 Spring Street
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		1,066
Original Building		9,520
Costs Capitalized Subsequent to Acquisition		2,230
Land and improvements		1,160
Buildings and Improvements		11,656
Land Held for Development		0
Development and Construction in Progress		0
Total		12,816
Accumulated Depreciation		$ 5,424
Year(s) Built / Renovated		1,999
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
195 West Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		195 West Street
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		1,611
Original Building		6,652
Costs Capitalized Subsequent to Acquisition		4,270
Land and improvements		1,858
Buildings and Improvements		10,675
Land Held for Development		0
Development and Construction in Progress		0
Total		12,533
Accumulated Depreciation		$ 8,330
Year(s) Built / Renovated		1,990
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
33 Hayden Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		33 Hayden Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		266
Original Building		3,234
Costs Capitalized Subsequent to Acquisition		8,223
Land and improvements		425
Buildings and Improvements		11,298
Land Held for Development		0
Development and Construction in Progress		0
Total		11,723
Accumulated Depreciation		$ 9,033
Year(s) Built / Renovated		1,979
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
7501 Boston Boulevard, Building Seven
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7501 Boston Boulevard, Building Seven
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		665
Original Building		9,273
Costs Capitalized Subsequent to Acquisition		819
Land and improvements		791
Buildings and Improvements		9,966
Land Held for Development		0
Development and Construction in Progress		0
Total		10,757
Accumulated Depreciation		$ 5,121
Year(s) Built / Renovated		1,997
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
7450 Boston Boulevard, Building Three
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7450 Boston Boulevard, Building Three
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		1,165
Original Building		4,681
Costs Capitalized Subsequent to Acquisition		3,278
Land and improvements		1,430
Buildings and Improvements		7,694
Land Held for Development		0
Development and Construction in Progress		0
Total		9,124
Accumulated Depreciation		$ 3,733
Year(s) Built / Renovated		1,987
Year(s) Acquired		1,998
Depreciable Lives (Years)	[3]	(1)
7435 Boston Boulevard, Building One
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7435 Boston Boulevard, Building One
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		392
Original Building		3,822
Costs Capitalized Subsequent to Acquisition		4,737
Land and improvements		659
Buildings and Improvements		8,292
Land Held for Development		0
Development and Construction in Progress		0
Total		8,951
Accumulated Depreciation		$ 5,917
Year(s) Built / Renovated		1,982
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
8000 Grainger Court, Building Five
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		8000 Grainger Court, Building Five
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		366
Original Building		4,282
Costs Capitalized Subsequent to Acquisition		3,536
Land and improvements		601
Buildings and Improvements		7,583
Land Held for Development		0
Development and Construction in Progress		0
Total		8,184
Accumulated Depreciation		$ 5,864
Year(s) Built / Renovated		1,984
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
250 Binney Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		250 Binney Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		110
Original Building		4,483
Costs Capitalized Subsequent to Acquisition		3,593
Land and improvements		273
Buildings and Improvements		7,913
Land Held for Development		0
Development and Construction in Progress		0
Total		8,186
Accumulated Depreciation		$ 5,448
Year(s) Built / Renovated		1,983
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
453 Ravendale Drive
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		453 Ravendale Drive
Type		Office
Location		Mountain View, CA
Encumbrances		$ 0
Original Land		5,477
Original Building		1,090
Costs Capitalized Subsequent to Acquisition		676
Land and improvements		5,477
Buildings and Improvements		1,766
Land Held for Development		0
Development and Construction in Progress		0
Total		7,243
Accumulated Depreciation		$ 558
Year(s) Built / Renovated		1,977
Year(s) Acquired		2,012
Depreciable Lives (Years)	[3]	(1)
7300 Boston Boulevard, Building Thirteen
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7300 Boston Boulevard, Building Thirteen
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		608
Original Building		4,773
Costs Capitalized Subsequent to Acquisition		1,438
Land and improvements		661
Buildings and Improvements		6,158
Land Held for Development		0
Development and Construction in Progress		0
Total		6,819
Accumulated Depreciation		$ 3,011
Year(s) Built / Renovated		2,002
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
17 Hartwell Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		17 Hartwell Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		26
Original Building		150
Costs Capitalized Subsequent to Acquisition		6,064
Land and improvements		65
Buildings and Improvements		6,175
Land Held for Development		0
Development and Construction in Progress		0
Total		6,240
Accumulated Depreciation		$ 1,445
Year(s) Built / Renovated		1,968
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
7601 Boston Boulevard, Building Eight
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7601 Boston Boulevard, Building Eight
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		200
Original Building		878
Costs Capitalized Subsequent to Acquisition		5,373
Land and improvements		551
Buildings and Improvements		5,900
Land Held for Development		0
Development and Construction in Progress		0
Total		6,451
Accumulated Depreciation		$ 4,487
Year(s) Built / Renovated		1,986
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
7500 Boston Boulevard, Building Six
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7500 Boston Boulevard, Building Six
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		138
Original Building		3,749
Costs Capitalized Subsequent to Acquisition		1,673
Land and improvements		406
Buildings and Improvements		5,154
Land Held for Development		0
Development and Construction in Progress		0
Total		5,560
Accumulated Depreciation		$ 4,121
Year(s) Built / Renovated		1,985
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
8000 Corporate Court, Building Eleven
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		8000 Corporate Court, Building Eleven
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		136
Original Building		3,071
Costs Capitalized Subsequent to Acquisition		1,596
Land and improvements		774
Buildings and Improvements		4,029
Land Held for Development		0
Development and Construction in Progress		0
Total		4,803
Accumulated Depreciation		$ 3,051
Year(s) Built / Renovated		1,989
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
7375 Boston Boulevard, Building Ten
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7375 Boston Boulevard, Building Ten
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		23
Original Building		2,685
Costs Capitalized Subsequent to Acquisition		992
Land and improvements		93
Buildings and Improvements		3,607
Land Held for Development		0
Development and Construction in Progress		0
Total		3,700
Accumulated Depreciation		$ 2,593
Year(s) Built / Renovated		1,988
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
7374 Boston Boulevard, Building Four
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7374 Boston Boulevard, Building Four
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		241
Original Building		1,605
Costs Capitalized Subsequent to Acquisition		1,828
Land and improvements		398
Buildings and Improvements		3,276
Land Held for Development		0
Development and Construction in Progress		0
Total		3,674
Accumulated Depreciation		$ 2,685
Year(s) Built / Renovated		1,984
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
7451 Boston Boulevard, Building Two
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7451 Boston Boulevard, Building Two
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		249
Original Building		1,542
Costs Capitalized Subsequent to Acquisition		1,659
Land and improvements		613
Buildings and Improvements		2,837
Land Held for Development		0
Development and Construction in Progress		0
Total		3,450
Accumulated Depreciation		$ 2,527
Year(s) Built / Renovated		1,982
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
32 Hartwell Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		32 Hartwell Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		168
Original Building		1,943
Costs Capitalized Subsequent to Acquisition		817
Land and improvements		314
Buildings and Improvements		2,614
Land Held for Development		0
Development and Construction in Progress		0
Total		2,928
Accumulated Depreciation		$ 1,821
Year(s) Built / Renovated		1968/1979/1987
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
164 Lexington Road
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		164 Lexington Road
Type		Office
Location		Billerica, MA
Encumbrances		$ 0
Original Land		592
Original Building		1,370
Costs Capitalized Subsequent to Acquisition		319
Land and improvements		643
Buildings and Improvements		1,638
Land Held for Development		0
Development and Construction in Progress		0
Total		2,281
Accumulated Depreciation		$ 906
Year(s) Built / Renovated		1,982
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
Signature at Reston
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Signature at Reston
Type		Residential
Location		Reston, VA
Encumbrances		$ 0
Original Land		27,076
Original Building		190,580
Costs Capitalized Subsequent to Acquisition		0
Land and improvements		27,076
Buildings and Improvements		190,580
Land Held for Development		0
Development and Construction in Progress		0
Total		217,656
Accumulated Depreciation		$ 3,938
Year(s) Built / Renovated		2,018
Year(s) Acquired		2,013
Depreciable Lives (Years)	[3]	(1)
Proto Kendall Square
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Proto Kendall Square
Type		Residential
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		9,243
Original Building		127,248
Costs Capitalized Subsequent to Acquisition		0
Land and improvements		9,243
Buildings and Improvements		127,248
Land Held for Development		0
Development and Construction in Progress		0
Total		136,491
Accumulated Depreciation		$ 1,324
Year(s) Built / Renovated		2,018
Year(s) Acquired		2,015
Depreciable Lives (Years)	[3]	(1)
The Avant at Reston Town Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		The Avant at Reston Town Center
Type		Residential
Location		Reston, VA
Encumbrances		$ 0
Original Land		20,350
Original Building		91,995
Costs Capitalized Subsequent to Acquisition		830
Land and improvements		20,350
Buildings and Improvements		92,825
Land Held for Development		0
Development and Construction in Progress		0
Total		113,175
Accumulated Depreciation		$ 12,254
Year(s) Built / Renovated		2,014
Year(s) Acquired		2,010
Depreciable Lives (Years)	[3]	(1)
The Lofts at Atlantic Wharf
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		The Lofts at Atlantic Wharf
Type		Residential
Location		Boston, MA
Encumbrances		$ 0
Original Land		3,529
Original Building		54,891
Costs Capitalized Subsequent to Acquisition		1,768
Land and improvements		3,529
Buildings and Improvements		56,659
Land Held for Development		0
Development and Construction in Progress		0
Total		60,188
Accumulated Depreciation		$ 11,131
Year(s) Built / Renovated		2,011
Year(s) Acquired		2,007
Depreciable Lives (Years)	[3]	(1)
Boston Marriott Cambridge
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Boston Marriott Cambridge
Type		Hotel
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		478
Original Building		37,918
Costs Capitalized Subsequent to Acquisition		36,697
Land and improvements		1,201
Buildings and Improvements		73,892
Land Held for Development		0
Development and Construction in Progress		0
Total		75,093
Accumulated Depreciation		$ 46,576
Year(s) Built / Renovated		1986/2017
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
Kendall Center Green Garage
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Green Garage
Type		Garage
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		0
Original Building		35,035
Costs Capitalized Subsequent to Acquisition		7,448
Land and improvements		103
Buildings and Improvements		42,380
Land Held for Development		0
Development and Construction in Progress		0
Total		42,483
Accumulated Depreciation		$ 12,208
Year(s) Built / Renovated		1,984
Year(s) Acquired		2,006
Depreciable Lives (Years)	[3]	(1)
Kendall Center Yellow Garage
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Yellow Garage
Type		Garage
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		1,256
Original Building		15,697
Costs Capitalized Subsequent to Acquisition		1,621
Land and improvements		1,434
Buildings and Improvements		17,140
Land Held for Development		0
Development and Construction in Progress		0
Total		18,574
Accumulated Depreciation		$ 5,643
Year(s) Built / Renovated		2,006
Year(s) Acquired		2,004
Depreciable Lives (Years)	[3]	(1)
Kendall Center Blue Garage
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Blue Garage
Type		Garage
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		1,163
Original Building		11,633
Costs Capitalized Subsequent to Acquisition		2,145
Land and improvements		1,579
Buildings and Improvements		13,362
Land Held for Development		0
Development and Construction in Progress		0
Total		14,941
Accumulated Depreciation		$ 9,437
Year(s) Built / Renovated		1,990
Year(s) Acquired		1,997
Depreciable Lives (Years)	[3]	(1)
145 Broadway
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		145 Broadway
Type		Development
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		121
Original Building		0
Costs Capitalized Subsequent to Acquisition		223,845
Land and improvements		324
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		223,642
Total		223,966
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1,997
Depreciable Lives (Years)		N/A
MacArthur Station Residences
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		MacArthur Station Residences
Type		Development
Location		Oakland, CA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		87,159
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		87,159
Total		87,159
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		N/A
Depreciable Lives (Years)		N/A
20 CityPoint
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		20 CityPoint
Type		Development
Location		Waltham, MA
Encumbrances		$ 0
Original Land		0
Original Building		6,287
Costs Capitalized Subsequent to Acquisition		46,024
Land and improvements		0
Buildings and Improvements		6,287
Land Held for Development		0
Development and Construction in Progress		46,024
Total		52,311
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,007
Depreciable Lives (Years)		N/A
Reston Gateway
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Gateway
Type		Development
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		25,167
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		25,167
Total		25,167
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1,998
Depreciable Lives (Years)		N/A
17Fifty Presidents Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		17Fifty Presidents Street
Type		Development
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		25,120
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		25,120
Total		25,120
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,013
Depreciable Lives (Years)		N/A
North First Master Plan
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		North First Master Plan
Type		Land
Location		San Jose, CA
Encumbrances		$ 0
Original Land		35,004
Original Building		0
Costs Capitalized Subsequent to Acquisition		3,932
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		38,936
Development and Construction in Progress		0
Total		38,936
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,007
Depreciable Lives (Years)		N/A
Plaza at Almaden
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Plaza at Almaden
Type		Land
Location		San Jose, CA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		29,928
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		29,928
Development and Construction in Progress		0
Total		29,928
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,006
Depreciable Lives (Years)		N/A
Springfield Metro Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Springfield Metro Center
Type		Land
Location		Springfield, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		19,823
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		19,823
Development and Construction in Progress		0
Total		19,823
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,007
Depreciable Lives (Years)		N/A
214 Third Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		214 Third Avenue
Type		Land
Location		Waltham, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		15,233
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		15,233
Development and Construction in Progress		0
Total		15,233
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,006
Depreciable Lives (Years)		N/A
Platform 16
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Platform 16
Type		Land
Location		San Jose, CA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		12,962
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		12,962
Development and Construction in Progress		0
Total		12,962
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,018
Depreciable Lives (Years)		N/A
103 Fourth Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		103 Fourth Avenue
Type		Land
Location		Waltham, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		12,208
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		12,208
Development and Construction in Progress		0
Total		12,208
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,007
Depreciable Lives (Years)		N/A
Reston Gateway Master Plan
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Gateway Master Plan
Type		Land
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		11,014
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		11,014
Development and Construction in Progress		0
Total		11,014
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1,998
Depreciable Lives (Years)		N/A
Fourth and Harrison
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Fourth and Harrison
Type		Land
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		10,350
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		10,350
Development and Construction in Progress		0
Total		10,350
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		N/A
Depreciable Lives (Years)		N/A
2100 Pennsylvania Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		2100 Pennsylvania Avenue
Type		Land
Location		Washington, DC
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		9,700
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		9,700
Development and Construction in Progress		0
Total		9,700
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		N/A
Depreciable Lives (Years)		N/A
Crane Meadow
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Crane Meadow
Type		Land
Location		Marlborough, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		8,852
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		8,852
Development and Construction in Progress		0
Total		8,852
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,000
Depreciable Lives (Years)		N/A
Washingtonian North
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Washingtonian North
Type		Land
Location		Gaithersburg, MD
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		7,473
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		7,473
Development and Construction in Progress		0
Total		7,473
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1,998
Depreciable Lives (Years)		N/A
Broad Run Business Park
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Broad Run Business Park
Type		Land
Location		Loudoun County, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		2,388
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		2,388
Development and Construction in Progress		0
Total		2,388
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1,998
Depreciable Lives (Years)		N/A
Kendall Center Master Plan
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Master Plan
Type		Land
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		2,199
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		2,199
Development and Construction in Progress		0
Total		2,199
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1,997
Depreciable Lives (Years)		N/A
Weston Quarry
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Weston Quarry
Type		Land
Location		Weston, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		1,237
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		1,237
Development and Construction in Progress		0
Total		1,237
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,001
Depreciable Lives (Years)		N/A
Reston Overlook Master Plan
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Overlook Master Plan
Type		Land
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		39
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		39
Development and Construction in Progress		0
Total		39
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,000
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	[4]	$ 2,964,572
Original Land		4,959,995
Original Building		12,763,317
Costs Capitalized Subsequent to Acquisition		3,483,877
Land and improvements		4,971,475
Buildings and Improvements		15,456,420
Land Held for Development	[5]	200,498
Development and Construction in Progress		578,796
Total		21,207,189
Accumulated Depreciation		4,773,800
Furniture, fixtures and equipment		44,351	$ 37,928
Furniture, fixtures and equipment accumulated depreciation		26,675
Real Estate Aggregate Cost For Tax Purposes		19,900,000
Real Estate Aggregate Accumulated Depreciation For Tax Purposes		$ 4,300,000
Real Estate and Accumulated Depreciation, Life Used for Depreciation		40 years
Unamortized deferred finance costs		$ (30,800)
Boston Properties Limited Partnership | 767 Fifth Avenue (the General Motors Building)
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		767 Fifth Avenue (the General Motors Building)
Type		Office
Location		New York, NY
Encumbrances		$ 2,270,534
Original Land		1,796,252
Original Building		1,532,654
Costs Capitalized Subsequent to Acquisition		189,657
Land and improvements		1,796,252
Buildings and Improvements		1,722,311
Land Held for Development		0
Development and Construction in Progress		0
Total		3,518,563
Accumulated Depreciation		$ 271,534
Year(s) Built / Renovated		1,968
Year(s) Acquired		2,013
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Prudential Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Prudential Center
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		92,077
Original Building		948,357
Costs Capitalized Subsequent to Acquisition		472,432
Land and improvements		100,540
Buildings and Improvements		1,412,222
Land Held for Development		104
Development and Construction in Progress		0
Total		1,512,866
Accumulated Depreciation		$ 535,305
Year(s) Built / Renovated		1965/1993/2002/2016-2017
Year(s) Acquired		1998/1999/2000
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Embarcadero Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Embarcadero Center
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		179,697
Original Building		847,410
Costs Capitalized Subsequent to Acquisition		306,586
Land and improvements		180,420
Buildings and Improvements		1,153,273
Land Held for Development		0
Development and Construction in Progress		0
Total		1,333,693
Accumulated Depreciation		$ 597,613
Year(s) Built / Renovated		1970/1989
Year(s) Acquired		1998-1999
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 399 Park Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		399 Park Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		339,200
Original Building		700,358
Costs Capitalized Subsequent to Acquisition		187,484
Land and improvements		339,200
Buildings and Improvements		887,842
Land Held for Development		0
Development and Construction in Progress		0
Total		1,227,042
Accumulated Depreciation		$ 318,267
Year(s) Built / Renovated		1961/2018
Year(s) Acquired		2,002
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Salesforce Tower
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Salesforce Tower
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		200,349
Original Building		919,565
Costs Capitalized Subsequent to Acquisition		0
Land and improvements		200,349
Buildings and Improvements		919,565
Land Held for Development		0
Development and Construction in Progress		0
Total		1,119,914
Accumulated Depreciation		$ 9,509
Year(s) Built / Renovated		2,018
Year(s) Acquired		2,013
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 601 Lexington Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		601 Lexington Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 658,792
Original Land		241,600
Original Building		494,782
Costs Capitalized Subsequent to Acquisition		324,899
Land and improvements		279,281
Buildings and Improvements		610,316
Land Held for Development		0
Development and Construction in Progress		171,684
Total		1,061,281
Accumulated Depreciation		$ 264,150
Year(s) Built / Renovated		1977/1997
Year(s) Acquired		2,001
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 200 Clarendon Street and Garage
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		200 Clarendon Street and Garage
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		219,543
Original Building		667,884
Costs Capitalized Subsequent to Acquisition		164,073
Land and improvements		219,616
Buildings and Improvements		822,218
Land Held for Development		9,666
Development and Construction in Progress		0
Total		1,051,500
Accumulated Depreciation		$ 192,137
Year(s) Built / Renovated		1,976
Year(s) Acquired		2,010
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 250 West 55th Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		250 West 55th Street
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		285,263
Original Building		603,167
Costs Capitalized Subsequent to Acquisition		48,642
Land and improvements		285,263
Buildings and Improvements		651,809
Land Held for Development		0
Development and Construction in Progress		0
Total		937,072
Accumulated Depreciation		$ 94,434
Year(s) Built / Renovated		2,014
Year(s) Acquired		2,007
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 100 Federal Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		100 Federal Street
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		131,067
Original Building		435,954
Costs Capitalized Subsequent to Acquisition		99,702
Land and improvements		131,067
Buildings and Improvements		535,656
Land Held for Development		0
Development and Construction in Progress		0
Total		666,723
Accumulated Depreciation		$ 105,536
Year(s) Built / Renovated		1971-1975/2017
Year(s) Acquired		2,012
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Carnegie Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Carnegie Center
Type		Office
Location		Princeton, NJ
Encumbrances		$ 0
Original Land		107,997
Original Building		389,359
Costs Capitalized Subsequent to Acquisition		141,434
Land and improvements		104,617
Buildings and Improvements		530,987
Land Held for Development		3,186
Development and Construction in Progress		0
Total		638,790
Accumulated Depreciation		$ 237,322
Year(s) Built / Renovated		1983-2016
Year(s) Acquired		1998/1999/2000/2007/2014/2017
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Times Square Tower
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Times Square Tower
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		165,413
Original Building		380,438
Costs Capitalized Subsequent to Acquisition		56,472
Land and improvements		159,694
Buildings and Improvements		442,629
Land Held for Development		0
Development and Construction in Progress		0
Total		602,323
Accumulated Depreciation		$ 196,753
Year(s) Built / Renovated		2,004
Year(s) Acquired		2,000
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Atlantic Wharf
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Atlantic Wharf
Type		Office
Location		Boston, MA
Encumbrances		$ 0
Original Land		63,988
Original Building		454,537
Costs Capitalized Subsequent to Acquisition		17,184
Land and improvements		63,988
Buildings and Improvements		471,721
Land Held for Development		0
Development and Construction in Progress		0
Total		535,709
Accumulated Depreciation		$ 116,238
Year(s) Built / Renovated		2,011
Year(s) Acquired		2,007
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 510 Madison Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		510 Madison Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		103,000
Original Building		253,665
Costs Capitalized Subsequent to Acquisition		24,992
Land and improvements		103,000
Buildings and Improvements		278,657
Land Held for Development		0
Development and Construction in Progress		0
Total		381,657
Accumulated Depreciation		$ 62,507
Year(s) Built / Renovated		2,012
Year(s) Acquired		2,010
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Fountain Square
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Fountain Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		56,853
Original Building		306,298
Costs Capitalized Subsequent to Acquisition		3,170
Land and improvements		56,853
Buildings and Improvements		309,468
Land Held for Development		0
Development and Construction in Progress		0
Total		366,321
Accumulated Depreciation		$ 68,390
Year(s) Built / Renovated		1986-1990
Year(s) Acquired		2,012
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 599 Lexington Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		599 Lexington Avenue
Type		Office
Location		New York, NY
Encumbrances		$ 0
Original Land		81,040
Original Building		100,507
Costs Capitalized Subsequent to Acquisition		146,971
Land and improvements		81,040
Buildings and Improvements		247,478
Land Held for Development		0
Development and Construction in Progress		0
Total		328,518
Accumulated Depreciation		$ 164,002
Year(s) Built / Renovated		1,986
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 680 Folsom Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		680 Folsom Street
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		72,545
Original Building		219,766
Costs Capitalized Subsequent to Acquisition		7,829
Land and improvements		72,545
Buildings and Improvements		227,595
Land Held for Development		0
Development and Construction in Progress		0
Total		300,140
Accumulated Depreciation		$ 38,230
Year(s) Built / Renovated		2,014
Year(s) Acquired		2,012
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 601 Massachusetts Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		601 Massachusetts Avenue
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		95,310
Original Building		165,173
Costs Capitalized Subsequent to Acquisition		3,888
Land and improvements		95,310
Buildings and Improvements		169,061
Land Held for Development		0
Development and Construction in Progress		0
Total		264,371
Accumulated Depreciation		$ 18,263
Year(s) Built / Renovated		2,016
Year(s) Acquired		2,008
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | South of Market and Democracy Tower
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		South of Market and Democracy Tower
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		13,603
Original Building		237,479
Costs Capitalized Subsequent to Acquisition		12,092
Land and improvements		13,603
Buildings and Improvements		249,571
Land Held for Development		0
Development and Construction in Progress		0
Total		263,174
Accumulated Depreciation		$ 91,006
Year(s) Built / Renovated		2008-2009
Year(s) Acquired		2,003
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Bay Colony Corporate Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Bay Colony Corporate Center
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		18,789
Original Building		148,451
Costs Capitalized Subsequent to Acquisition		77,133
Land and improvements		18,789
Buildings and Improvements		225,584
Land Held for Development		0
Development and Construction in Progress		0
Total		244,373
Accumulated Depreciation		$ 68,903
Year(s) Built / Renovated		1985-1989
Year(s) Acquired		2,011
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Gateway Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Gateway Center
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		28,255
Original Building		139,245
Costs Capitalized Subsequent to Acquisition		58,442
Land and improvements		29,029
Buildings and Improvements		196,913
Land Held for Development		0
Development and Construction in Progress		0
Total		225,942
Accumulated Depreciation		$ 106,074
Year(s) Built / Renovated		1984/1986/2002
Year(s) Acquired		1,999
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 535 Mission Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		535 Mission Street
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		40,933
Original Building		148,378
Costs Capitalized Subsequent to Acquisition		3,259
Land and improvements		40,933
Buildings and Improvements		151,637
Land Held for Development		0
Development and Construction in Progress		0
Total		192,570
Accumulated Depreciation		$ 20,576
Year(s) Built / Renovated		2,015
Year(s) Acquired		2,013
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 2200 Pennsylvania Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		2200 Pennsylvania Avenue
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		0
Original Building		183,541
Costs Capitalized Subsequent to Acquisition		4,535
Land and improvements		0
Buildings and Improvements		188,076
Land Held for Development		0
Development and Construction in Progress		0
Total		188,076
Accumulated Depreciation		$ 52,280
Year(s) Built / Renovated		2,011
Year(s) Acquired		2,008
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Mountain View Research Park
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Mountain View Research Park
Type		Office
Location		Mountain View, CA
Encumbrances		$ 0
Original Land		95,066
Original Building		68,373
Costs Capitalized Subsequent to Acquisition		9,988
Land and improvements		95,066
Buildings and Improvements		78,361
Land Held for Development		0
Development and Construction in Progress		0
Total		173,427
Accumulated Depreciation		$ 17,866
Year(s) Built / Renovated		1977-1981/2007-2013
Year(s) Acquired		2,013
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Reservoir Place
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reservoir Place
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		18,605
Original Building		104,124
Costs Capitalized Subsequent to Acquisition		41,069
Land and improvements		19,089
Buildings and Improvements		144,709
Land Held for Development		0
Development and Construction in Progress		0
Total		163,798
Accumulated Depreciation		$ 63,684
Year(s) Built / Renovated		1955/1987/2017
Year(s) Acquired		1997/1998
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 1330 Connecticut Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		1330 Connecticut Avenue
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		25,982
Original Building		82,311
Costs Capitalized Subsequent to Acquisition		31,476
Land and improvements		25,982
Buildings and Improvements		113,787
Land Held for Development		0
Development and Construction in Progress		0
Total		139,769
Accumulated Depreciation		$ 26,400
Year(s) Built / Renovated		1984/2018
Year(s) Acquired		2,004
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Kingstowne Towne Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kingstowne Towne Center
Type		Office
Location		Alexandria, VA
Encumbrances		$ 0
Original Land		18,021
Original Building		109,038
Costs Capitalized Subsequent to Acquisition		1,934
Land and improvements		18,021
Buildings and Improvements		110,972
Land Held for Development		0
Development and Construction in Progress		0
Total		128,993
Accumulated Depreciation		$ 41,436
Year(s) Built / Renovated		2003-2006
Year(s) Acquired		2,007
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | One Freedom Square
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		One Freedom Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		9,929
Original Building		84,504
Costs Capitalized Subsequent to Acquisition		26,619
Land and improvements		9,883
Buildings and Improvements		111,169
Land Held for Development		0
Development and Construction in Progress		0
Total		121,052
Accumulated Depreciation		$ 53,268
Year(s) Built / Renovated		2,000
Year(s) Acquired		2,003
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Weston Corporate Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Weston Corporate Center
Type		Office
Location		Weston, MA
Encumbrances		$ 0
Original Land		25,753
Original Building		92,312
Costs Capitalized Subsequent to Acquisition		(123)
Land and improvements		25,854
Buildings and Improvements		92,088
Land Held for Development		0
Development and Construction in Progress		0
Total		117,942
Accumulated Depreciation		$ 26,176
Year(s) Built / Renovated		2,010
Year(s) Acquired		2,001
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Capital Gallery
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Capital Gallery
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		4,725
Original Building		29,565
Costs Capitalized Subsequent to Acquisition		77,100
Land and improvements		6,128
Buildings and Improvements		105,262
Land Held for Development		0
Development and Construction in Progress		0
Total		111,390
Accumulated Depreciation		$ 65,272
Year(s) Built / Renovated		1981/2006
Year(s) Acquired		2,007
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Two Freedom Square
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Two Freedom Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		13,930
Original Building		77,739
Costs Capitalized Subsequent to Acquisition		17,215
Land and improvements		13,866
Buildings and Improvements		95,018
Land Held for Development		0
Development and Construction in Progress		0
Total		108,884
Accumulated Depreciation		$ 49,768
Year(s) Built / Renovated		2,001
Year(s) Acquired		2,003
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | One and Two Reston Overlook
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		One and Two Reston Overlook
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		16,456
Original Building		66,192
Costs Capitalized Subsequent to Acquisition		19,763
Land and improvements		15,074
Buildings and Improvements		87,337
Land Held for Development		0
Development and Construction in Progress		0
Total		102,411
Accumulated Depreciation		$ 46,584
Year(s) Built / Renovated		1,999
Year(s) Acquired		2,000
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 140 Kendrick Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		140 Kendrick Street
Type		Office
Location		Needham, MA
Encumbrances		$ 0
Original Land		18,095
Original Building		66,905
Costs Capitalized Subsequent to Acquisition		13,563
Land and improvements		18,095
Buildings and Improvements		80,468
Land Held for Development		0
Development and Construction in Progress		0
Total		98,563
Accumulated Depreciation		$ 31,381
Year(s) Built / Renovated		2,000
Year(s) Acquired		2,004
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 355 Main Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		355 Main Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		18,863
Original Building		53,346
Costs Capitalized Subsequent to Acquisition		23,403
Land and improvements		21,098
Buildings and Improvements		74,514
Land Held for Development		0
Development and Construction in Progress		0
Total		95,612
Accumulated Depreciation		$ 23,620
Year(s) Built / Renovated		1981/1996/2013
Year(s) Acquired		2,006
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Discovery Square
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Discovery Square
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		11,198
Original Building		71,782
Costs Capitalized Subsequent to Acquisition		12,208
Land and improvements		11,146
Buildings and Improvements		84,042
Land Held for Development		0
Development and Construction in Progress		0
Total		95,188
Accumulated Depreciation		$ 38,212
Year(s) Built / Renovated		2,001
Year(s) Acquired		2,003
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 10 CityPoint
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		10 CityPoint
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		1,953
Original Building		85,752
Costs Capitalized Subsequent to Acquisition		4,352
Land and improvements		1,953
Buildings and Improvements		90,104
Land Held for Development		0
Development and Construction in Progress		0
Total		92,057
Accumulated Depreciation		$ 7,772
Year(s) Built / Renovated		2,016
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 90 Broadway
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		90 Broadway
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		19,104
Original Building		52,078
Costs Capitalized Subsequent to Acquisition		18,184
Land and improvements		20,741
Buildings and Improvements		68,625
Land Held for Development		0
Development and Construction in Progress		0
Total		89,366
Accumulated Depreciation		$ 21,265
Year(s) Built / Renovated		1983/1998/2013
Year(s) Acquired		2,006
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 230 CityPoint
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		230 CityPoint
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		13,189
Original Building		49,823
Costs Capitalized Subsequent to Acquisition		20,297
Land and improvements		13,189
Buildings and Improvements		70,120
Land Held for Development		0
Development and Construction in Progress		0
Total		83,309
Accumulated Depreciation		$ 25,964
Year(s) Built / Renovated		1,992
Year(s) Acquired		2,005
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 77 CityPoint
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		77 CityPoint
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		13,847
Original Building		60,383
Costs Capitalized Subsequent to Acquisition		5,753
Land and improvements		13,847
Buildings and Improvements		66,136
Land Held for Development		0
Development and Construction in Progress		0
Total		79,983
Accumulated Depreciation		$ 25,085
Year(s) Built / Renovated		2,008
Year(s) Acquired		2,001
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Waltham Weston Corporate Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Waltham Weston Corporate Center
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		10,385
Original Building		60,694
Costs Capitalized Subsequent to Acquisition		8,462
Land and improvements		10,350
Buildings and Improvements		69,191
Land Held for Development		0
Development and Construction in Progress		0
Total		79,541
Accumulated Depreciation		$ 32,005
Year(s) Built / Renovated		2,003
Year(s) Acquired		1,999
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 3625-3635 Peterson Way
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		3625-3635 Peterson Way
Type		Office
Location		Santa Clara, CA
Encumbrances		$ 0
Original Land		63,206
Original Building		14,879
Costs Capitalized Subsequent to Acquisition		673
Land and improvements		63,206
Buildings and Improvements		14,879
Land Held for Development		673
Development and Construction in Progress		0
Total		78,758
Accumulated Depreciation		$ 8,146
Year(s) Built / Renovated		1,979
Year(s) Acquired		2,016
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 2440 West El Camino Real
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		2440 West El Camino Real
Type		Office
Location		Mountain View, CA
Encumbrances		$ 0
Original Land		16,741
Original Building		51,285
Costs Capitalized Subsequent to Acquisition		3,411
Land and improvements		16,741
Buildings and Improvements		54,696
Land Held for Development		0
Development and Construction in Progress		0
Total		71,437
Accumulated Depreciation		$ 12,562
Year(s) Built / Renovated		1987/2003
Year(s) Acquired		2,011
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 300 Binney Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		300 Binney Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		18,080
Original Building		51,262
Costs Capitalized Subsequent to Acquisition		140
Land and improvements		18,080
Buildings and Improvements		51,402
Land Held for Development		0
Development and Construction in Progress		0
Total		69,482
Accumulated Depreciation		$ 9,450
Year(s) Built / Renovated		2,013
Year(s) Acquired		2,009
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Wisconsin Place
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Wisconsin Place
Type		Office
Location		Chevy Chase, MD
Encumbrances		$ 0
Original Land		0
Original Building		53,349
Costs Capitalized Subsequent to Acquisition		14,889
Land and improvements		0
Buildings and Improvements		68,238
Land Held for Development		0
Development and Construction in Progress		0
Total		68,238
Accumulated Depreciation		$ 22,936
Year(s) Built / Renovated		2,009
Year(s) Acquired		2,004
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 191 Spring Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		191 Spring Street
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		2,850
Original Building		59,751
Costs Capitalized Subsequent to Acquisition		5,603
Land and improvements		2,850
Buildings and Improvements		65,354
Land Held for Development		0
Development and Construction in Progress		0
Total		68,204
Accumulated Depreciation		$ 19,435
Year(s) Built / Renovated		1971/1995/2018
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Reston Corporate Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Corporate Center
Type		Office
Location		Reston, VA
Encumbrances		$ 0
Original Land		9,135
Original Building		50,857
Costs Capitalized Subsequent to Acquisition		3,625
Land and improvements		9,496
Buildings and Improvements		54,121
Land Held for Development		0
Development and Construction in Progress		0
Total		63,617
Accumulated Depreciation		$ 27,674
Year(s) Built / Renovated		1,984
Year(s) Acquired		1,998
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | New Dominion Technology Park, Bldg. Two
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		New Dominion Technology Park, Bldg. Two
Type		Office
Location		Herndon, VA
Encumbrances		$ 0
Original Land		5,584
Original Building		51,868
Costs Capitalized Subsequent to Acquisition		412
Land and improvements		5,574
Buildings and Improvements		52,290
Land Held for Development		0
Development and Construction in Progress		0
Total		57,864
Accumulated Depreciation		$ 24,498
Year(s) Built / Renovated		2,004
Year(s) Acquired		1,998
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 255 Main Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		255 Main Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		134
Original Building		25,110
Costs Capitalized Subsequent to Acquisition		28,016
Land and improvements		134
Buildings and Improvements		53,126
Land Held for Development		0
Development and Construction in Progress		0
Total		53,260
Accumulated Depreciation		$ 29,776
Year(s) Built / Renovated		1,987
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 200 West Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		200 West Street
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		16,148
Original Building		24,983
Costs Capitalized Subsequent to Acquisition		8,459
Land and improvements		16,148
Buildings and Improvements		33,442
Land Held for Development		0
Development and Construction in Progress		0
Total		49,590
Accumulated Depreciation		$ 21,891
Year(s) Built / Renovated		1,999
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | New Dominion Technology Park, Bldg. One
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		New Dominion Technology Park, Bldg. One
Type		Office
Location		Herndon, VA
Encumbrances		$ 29,675
Original Land		3,880
Original Building		43,227
Costs Capitalized Subsequent to Acquisition		1,117
Land and improvements		3,880
Buildings and Improvements		44,344
Land Held for Development		0
Development and Construction in Progress		0
Total		48,224
Accumulated Depreciation		$ 26,852
Year(s) Built / Renovated		2,001
Year(s) Acquired		1,998
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Sumner Square
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Sumner Square
Type		Office
Location		Washington, DC
Encumbrances		$ 0
Original Land		624
Original Building		28,745
Costs Capitalized Subsequent to Acquisition		16,974
Land and improvements		958
Buildings and Improvements		45,385
Land Held for Development		0
Development and Construction in Progress		0
Total		46,343
Accumulated Depreciation		$ 24,877
Year(s) Built / Renovated		1,985
Year(s) Acquired		1,999
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | University Place
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		University Place
Type		Office
Location		Cambridge, MA
Encumbrances		$ 5,571
Original Land		0
Original Building		37,091
Costs Capitalized Subsequent to Acquisition		7,551
Land and improvements		27
Buildings and Improvements		44,615
Land Held for Development		0
Development and Construction in Progress		0
Total		44,642
Accumulated Depreciation		$ 27,519
Year(s) Built / Renovated		1,985
Year(s) Acquired		1,998
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 2600 Tower Oaks Boulevard
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		2600 Tower Oaks Boulevard
Type		Office
Location		Rockville, MD
Encumbrances		$ 0
Original Land		4,243
Original Building		31,125
Costs Capitalized Subsequent to Acquisition		6,517
Land and improvements		4,244
Buildings and Improvements		37,641
Land Held for Development		0
Development and Construction in Progress		0
Total		41,885
Accumulated Depreciation		$ 21,426
Year(s) Built / Renovated		2,001
Year(s) Acquired		1,998
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | North First Business Park
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		North First Business Park
Type		Office
Location		San Jose, CA
Encumbrances		$ 0
Original Land		23,398
Original Building		13,069
Costs Capitalized Subsequent to Acquisition		4,590
Land and improvements		23,371
Buildings and Improvements		17,686
Land Held for Development		0
Development and Construction in Progress		0
Total		41,057
Accumulated Depreciation		$ 16,076
Year(s) Built / Renovated		1,981
Year(s) Acquired		2,007
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 150 Broadway
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		150 Broadway
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		850
Original Building		25,042
Costs Capitalized Subsequent to Acquisition		6,535
Land and improvements		822
Buildings and Improvements		31,605
Land Held for Development		0
Development and Construction in Progress		0
Total		32,427
Accumulated Depreciation		$ 17,909
Year(s) Built / Renovated		1,999
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 325 Main Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		325 Main Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		174
Original Building		12,200
Costs Capitalized Subsequent to Acquisition		15,666
Land and improvements		772
Buildings and Improvements		22,741
Land Held for Development		4,527
Development and Construction in Progress		0
Total		28,040
Accumulated Depreciation		$ 13,484
Year(s) Built / Renovated		1987/2013
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 105 Broadway
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		105 Broadway
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		1,299
Original Building		12,943
Costs Capitalized Subsequent to Acquisition		7,295
Land and improvements		1,868
Buildings and Improvements		19,669
Land Held for Development		0
Development and Construction in Progress		0
Total		21,537
Accumulated Depreciation		$ 13,432
Year(s) Built / Renovated		1,990
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Lexington Office Park
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Lexington Office Park
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		998
Original Building		1,426
Costs Capitalized Subsequent to Acquisition		17,936
Land and improvements		1,073
Buildings and Improvements		19,287
Land Held for Development		0
Development and Construction in Progress		0
Total		20,360
Accumulated Depreciation		$ 13,430
Year(s) Built / Renovated		1,982
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 201 Spring Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		201 Spring Street
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		2,849
Original Building		15,303
Costs Capitalized Subsequent to Acquisition		291
Land and improvements		2,849
Buildings and Improvements		15,594
Land Held for Development		0
Development and Construction in Progress		0
Total		18,443
Accumulated Depreciation		$ 8,073
Year(s) Built / Renovated		1,997
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | The Point
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		The Point
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		6,395
Original Building		10,040
Costs Capitalized Subsequent to Acquisition		431
Land and improvements		6,480
Buildings and Improvements		10,386
Land Held for Development		0
Development and Construction in Progress		0
Total		16,866
Accumulated Depreciation		$ 1,031
Year(s) Built / Renovated		2,015
Year(s) Acquired		2,007
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 690 Folsom Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		690 Folsom Street
Type		Office
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		3,219
Original Building		11,038
Costs Capitalized Subsequent to Acquisition		1,157
Land and improvements		3,219
Buildings and Improvements		12,195
Land Held for Development		0
Development and Construction in Progress		0
Total		15,414
Accumulated Depreciation		$ 1,790
Year(s) Built / Renovated		2,015
Year(s) Acquired		2,012
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 92-100 Hayden Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		92-100 Hayden Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		594
Original Building		6,748
Costs Capitalized Subsequent to Acquisition		6,526
Land and improvements		619
Buildings and Improvements		13,249
Land Held for Development		0
Development and Construction in Progress		0
Total		13,868
Accumulated Depreciation		$ 11,629
Year(s) Built / Renovated		1,985
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 181 Spring Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		181 Spring Street
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		1,066
Original Building		9,520
Costs Capitalized Subsequent to Acquisition		1,853
Land and improvements		1,066
Buildings and Improvements		11,373
Land Held for Development		0
Development and Construction in Progress		0
Total		12,439
Accumulated Depreciation		$ 5,332
Year(s) Built / Renovated		1,999
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 195 West Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		195 West Street
Type		Office
Location		Waltham, MA
Encumbrances		$ 0
Original Land		1,611
Original Building		6,652
Costs Capitalized Subsequent to Acquisition		3,281
Land and improvements		1,611
Buildings and Improvements		9,933
Land Held for Development		0
Development and Construction in Progress		0
Total		11,544
Accumulated Depreciation		$ 8,084
Year(s) Built / Renovated		1,990
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 33 Hayden Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		33 Hayden Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		266
Original Building		3,234
Costs Capitalized Subsequent to Acquisition		7,586
Land and improvements		266
Buildings and Improvements		10,820
Land Held for Development		0
Development and Construction in Progress		0
Total		11,086
Accumulated Depreciation		$ 8,877
Year(s) Built / Renovated		1,979
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 7501 Boston Boulevard, Building Seven
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7501 Boston Boulevard, Building Seven
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		665
Original Building		9,273
Costs Capitalized Subsequent to Acquisition		314
Land and improvements		665
Buildings and Improvements		9,587
Land Held for Development		0
Development and Construction in Progress		0
Total		10,252
Accumulated Depreciation		$ 4,995
Year(s) Built / Renovated		1,997
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 7450 Boston Boulevard, Building Three
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7450 Boston Boulevard, Building Three
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		1,165
Original Building		4,681
Costs Capitalized Subsequent to Acquisition		2,864
Land and improvements		1,327
Buildings and Improvements		7,383
Land Held for Development		0
Development and Construction in Progress		0
Total		8,710
Accumulated Depreciation		$ 3,628
Year(s) Built / Renovated		1,987
Year(s) Acquired		1,998
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 7435 Boston Boulevard, Building One
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7435 Boston Boulevard, Building One
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		392
Original Building		3,822
Costs Capitalized Subsequent to Acquisition		4,044
Land and improvements		486
Buildings and Improvements		7,772
Land Held for Development		0
Development and Construction in Progress		0
Total		8,258
Accumulated Depreciation		$ 5,748
Year(s) Built / Renovated		1,982
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 8000 Grainger Court, Building Five
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		8000 Grainger Court, Building Five
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		366
Original Building		4,282
Costs Capitalized Subsequent to Acquisition		2,942
Land and improvements		453
Buildings and Improvements		7,137
Land Held for Development		0
Development and Construction in Progress		0
Total		7,590
Accumulated Depreciation		$ 5,720
Year(s) Built / Renovated		1,984
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 250 Binney Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		250 Binney Street
Type		Office
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		110
Original Building		4,483
Costs Capitalized Subsequent to Acquisition		2,939
Land and improvements		110
Buildings and Improvements		7,422
Land Held for Development		0
Development and Construction in Progress		0
Total		7,532
Accumulated Depreciation		$ 5,291
Year(s) Built / Renovated		1,983
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 453 Ravendale Drive
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		453 Ravendale Drive
Type		Office
Location		Mountain View, CA
Encumbrances		$ 0
Original Land		5,477
Original Building		1,090
Costs Capitalized Subsequent to Acquisition		676
Land and improvements		5,477
Buildings and Improvements		1,766
Land Held for Development		0
Development and Construction in Progress		0
Total		7,243
Accumulated Depreciation		$ 558
Year(s) Built / Renovated		1,977
Year(s) Acquired		2,012
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 7300 Boston Boulevard, Building Thirteen
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7300 Boston Boulevard, Building Thirteen
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		608
Original Building		4,773
Costs Capitalized Subsequent to Acquisition		1,226
Land and improvements		608
Buildings and Improvements		5,999
Land Held for Development		0
Development and Construction in Progress		0
Total		6,607
Accumulated Depreciation		$ 2,959
Year(s) Built / Renovated		2,002
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 17 Hartwell Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		17 Hartwell Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		26
Original Building		150
Costs Capitalized Subsequent to Acquisition		5,907
Land and improvements		26
Buildings and Improvements		6,057
Land Held for Development		0
Development and Construction in Progress		0
Total		6,083
Accumulated Depreciation		$ 1,406
Year(s) Built / Renovated		1,968
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 7601 Boston Boulevard, Building Eight
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7601 Boston Boulevard, Building Eight
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		200
Original Building		878
Costs Capitalized Subsequent to Acquisition		4,680
Land and improvements		378
Buildings and Improvements		5,380
Land Held for Development		0
Development and Construction in Progress		0
Total		5,758
Accumulated Depreciation		$ 4,318
Year(s) Built / Renovated		1,986
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 7500 Boston Boulevard, Building Six
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7500 Boston Boulevard, Building Six
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		138
Original Building		3,749
Costs Capitalized Subsequent to Acquisition		1,140
Land and improvements		273
Buildings and Improvements		4,754
Land Held for Development		0
Development and Construction in Progress		0
Total		5,027
Accumulated Depreciation		$ 3,991
Year(s) Built / Renovated		1,985
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 8000 Corporate Court, Building Eleven
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		8000 Corporate Court, Building Eleven
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		136
Original Building		3,071
Costs Capitalized Subsequent to Acquisition		1,245
Land and improvements		686
Buildings and Improvements		3,766
Land Held for Development		0
Development and Construction in Progress		0
Total		4,452
Accumulated Depreciation		$ 2,961
Year(s) Built / Renovated		1,989
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 7375 Boston Boulevard, Building Ten
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7375 Boston Boulevard, Building Ten
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		23
Original Building		2,685
Costs Capitalized Subsequent to Acquisition		811
Land and improvements		47
Buildings and Improvements		3,472
Land Held for Development		0
Development and Construction in Progress		0
Total		3,519
Accumulated Depreciation		$ 2,552
Year(s) Built / Renovated		1,988
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 7374 Boston Boulevard, Building Four
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7374 Boston Boulevard, Building Four
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		241
Original Building		1,605
Costs Capitalized Subsequent to Acquisition		1,445
Land and improvements		303
Buildings and Improvements		2,988
Land Held for Development		0
Development and Construction in Progress		0
Total		3,291
Accumulated Depreciation		$ 2,594
Year(s) Built / Renovated		1,984
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 7451 Boston Boulevard, Building Two
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		7451 Boston Boulevard, Building Two
Type		Office
Location		Springfield, VA
Encumbrances		$ 0
Original Land		249
Original Building		1,542
Costs Capitalized Subsequent to Acquisition		1,346
Land and improvements		535
Buildings and Improvements		2,602
Land Held for Development		0
Development and Construction in Progress		0
Total		3,137
Accumulated Depreciation		$ 2,449
Year(s) Built / Renovated		1,982
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 32 Hartwell Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		32 Hartwell Avenue
Type		Office
Location		Lexington, MA
Encumbrances		$ 0
Original Land		168
Original Building		1,943
Costs Capitalized Subsequent to Acquisition		231
Land and improvements		168
Buildings and Improvements		2,174
Land Held for Development		0
Development and Construction in Progress		0
Total		2,342
Accumulated Depreciation		$ 1,676
Year(s) Built / Renovated		1968/1979/1987
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 164 Lexington Road
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		164 Lexington Road
Type		Office
Location		Billerica, MA
Encumbrances		$ 0
Original Land		592
Original Building		1,370
Costs Capitalized Subsequent to Acquisition		117
Land and improvements		592
Buildings and Improvements		1,487
Land Held for Development		0
Development and Construction in Progress		0
Total		2,079
Accumulated Depreciation		$ 853
Year(s) Built / Renovated		1,982
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Signature at Reston
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Signature at Reston
Type		Residential
Location		Reston, VA
Encumbrances		$ 0
Original Land		27,076
Original Building		190,580
Costs Capitalized Subsequent to Acquisition		0
Land and improvements		27,076
Buildings and Improvements		190,580
Land Held for Development		0
Development and Construction in Progress		0
Total		217,656
Accumulated Depreciation		$ 3,938
Year(s) Built / Renovated		2,018
Year(s) Acquired		2,013
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Proto Kendall Square
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Proto Kendall Square
Type		Residential
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		9,243
Original Building		127,248
Costs Capitalized Subsequent to Acquisition		0
Land and improvements		9,243
Buildings and Improvements		127,248
Land Held for Development		0
Development and Construction in Progress		0
Total		136,491
Accumulated Depreciation		$ 1,324
Year(s) Built / Renovated		2,018
Year(s) Acquired		2,015
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | The Avant at Reston Town Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		The Avant at Reston Town Center
Type		Residential
Location		Reston, VA
Encumbrances		$ 0
Original Land		20,350
Original Building		91,995
Costs Capitalized Subsequent to Acquisition		830
Land and improvements		20,350
Buildings and Improvements		92,825
Land Held for Development		0
Development and Construction in Progress		0
Total		113,175
Accumulated Depreciation		$ 12,254
Year(s) Built / Renovated		2,014
Year(s) Acquired		2,010
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | The Lofts at Atlantic Wharf
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		The Lofts at Atlantic Wharf
Type		Residential
Location		Boston, MA
Encumbrances		$ 0
Original Land		3,529
Original Building		54,891
Costs Capitalized Subsequent to Acquisition		1,768
Land and improvements		3,529
Buildings and Improvements		56,659
Land Held for Development		0
Development and Construction in Progress		0
Total		60,188
Accumulated Depreciation		$ 11,131
Year(s) Built / Renovated		2,011
Year(s) Acquired		2,007
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Boston Marriott Cambridge
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Boston Marriott Cambridge
Type		Hotel
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		478
Original Building		37,918
Costs Capitalized Subsequent to Acquisition		33,806
Land and improvements		478
Buildings and Improvements		71,724
Land Held for Development		0
Development and Construction in Progress		0
Total		72,202
Accumulated Depreciation		$ 45,868
Year(s) Built / Renovated		1986/2017
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Kendall Center Green Garage
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Green Garage
Type		Garage
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		0
Original Building		35,035
Costs Capitalized Subsequent to Acquisition		7,034
Land and improvements		0
Buildings and Improvements		42,069
Land Held for Development		0
Development and Construction in Progress		0
Total		42,069
Accumulated Depreciation		$ 12,108
Year(s) Built / Renovated		1,984
Year(s) Acquired		2,006
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Kendall Center Yellow Garage
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Yellow Garage
Type		Garage
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		1,256
Original Building		15,697
Costs Capitalized Subsequent to Acquisition		909
Land and improvements		1,256
Buildings and Improvements		16,606
Land Held for Development		0
Development and Construction in Progress		0
Total		17,862
Accumulated Depreciation		$ 5,472
Year(s) Built / Renovated		2,006
Year(s) Acquired		2,004
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | Kendall Center Blue Garage
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Blue Garage
Type		Garage
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		1,163
Original Building		11,633
Costs Capitalized Subsequent to Acquisition		480
Land and improvements		1,163
Buildings and Improvements		12,113
Land Held for Development		0
Development and Construction in Progress		0
Total		13,276
Accumulated Depreciation		$ 9,030
Year(s) Built / Renovated		1,990
Year(s) Acquired		1,997
Depreciable Lives (Years)	[6]	(1)
Boston Properties Limited Partnership | 145 Broadway
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		145 Broadway
Type		Development
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		121
Original Building		0
Costs Capitalized Subsequent to Acquisition		223,642
Land and improvements		121
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		223,642
Total		223,763
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1,997
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership | MacArthur Station Residences
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		MacArthur Station Residences
Type		Development
Location		Oakland, CA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		87,159
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		87,159
Total		87,159
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		N/A
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership | 20 CityPoint
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		20 CityPoint
Type		Development
Location		Waltham, MA
Encumbrances		$ 0
Original Land		0
Original Building		6,287
Costs Capitalized Subsequent to Acquisition		46,024
Land and improvements		0
Buildings and Improvements		6,287
Land Held for Development		0
Development and Construction in Progress		46,024
Total		52,311
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,007
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership | Reston Gateway
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Gateway
Type		Development
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		25,167
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		25,167
Total		25,167
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1,998
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership | 17Fifty Presidents Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		17Fifty Presidents Street
Type		Development
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		25,120
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		0
Development and Construction in Progress		25,120
Total		25,120
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,013
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership | North First Master Plan
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		North First Master Plan
Type		Land
Location		San Jose, CA
Encumbrances		$ 0
Original Land		35,004
Original Building		0
Costs Capitalized Subsequent to Acquisition		3,932
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		38,936
Development and Construction in Progress		0
Total		38,936
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,007
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership | Plaza at Almaden
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Plaza at Almaden
Type		Land
Location		San Jose, CA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		29,928
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		29,928
Development and Construction in Progress		0
Total		29,928
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,006
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership | Springfield Metro Center
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Springfield Metro Center
Type		Land
Location		Springfield, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		19,823
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		19,823
Development and Construction in Progress		0
Total		19,823
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,007
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership | 214 Third Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		214 Third Avenue
Type		Land
Location		Waltham, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		15,233
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		15,233
Development and Construction in Progress		0
Total		15,233
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,006
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership | Platform 16
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Platform 16
Type		Land
Location		San Jose, CA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		12,962
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		12,962
Development and Construction in Progress		0
Total		12,962
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,018
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership | 103 Fourth Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		103 Fourth Avenue
Type		Land
Location		Waltham, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		12,208
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		12,208
Development and Construction in Progress		0
Total		12,208
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,007
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership | Reston Gateway Master Plan
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Gateway Master Plan
Type		Land
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		11,014
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		11,014
Development and Construction in Progress		0
Total		11,014
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1,998
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership | Fourth and Harrison
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Fourth and Harrison
Type		Land
Location		San Francisco, CA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		10,350
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		10,350
Development and Construction in Progress		0
Total		10,350
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		N/A
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership | 2100 Pennsylvania Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		2100 Pennsylvania Avenue
Type		Land
Location		Washington, DC
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		9,700
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		9,700
Development and Construction in Progress		0
Total		9,700
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		N/A
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership | Crane Meadow
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Crane Meadow
Type		Land
Location		Marlborough, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		8,852
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		8,852
Development and Construction in Progress		0
Total		8,852
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,000
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership | Washingtonian North
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Washingtonian North
Type		Land
Location		Gaithersburg, MD
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		7,473
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		7,473
Development and Construction in Progress		0
Total		7,473
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1,998
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership | Broad Run Business Park
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Broad Run Business Park
Type		Land
Location		Loudoun County, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		2,388
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		2,388
Development and Construction in Progress		0
Total		2,388
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1,998
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership | Kendall Center Master Plan
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Kendall Center Master Plan
Type		Land
Location		Cambridge, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		2,199
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		2,199
Development and Construction in Progress		0
Total		2,199
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		1,997
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership | Weston Quarry
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Weston Quarry
Type		Land
Location		Weston, MA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		1,237
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		1,237
Development and Construction in Progress		0
Total		1,237
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,001
Depreciable Lives (Years)		N/A
Boston Properties Limited Partnership | Reston Overlook Master Plan
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Property Name		Reston Overlook Master Plan
Type		Land
Location		Reston, VA
Encumbrances		$ 0
Original Land		0
Original Building		0
Costs Capitalized Subsequent to Acquisition		39
Land and improvements		0
Buildings and Improvements		0
Land Held for Development		39
Development and Construction in Progress		0
Total		39
Accumulated Depreciation		$ 0
Year(s) Built / Renovated		N/A
Year(s) Acquired		2,000
Depreciable Lives (Years)		N/A
Minimum [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Life Used for Depreciation		life of the lease
Minimum [Member] | Boston Properties Limited Partnership
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Life Used for Depreciation		life of the lease
[1]	Includes unamortized deferred financing costs totaling approximately $(30.8) million.
[2]	Includes pre-development costs.
[3]	Depreciation of the buildings and improvements are calculated over lives ranging from the life of the lease to 40 years.
[4]	Includes unamortized deferred financing costs totaling approximately $(30.8) million.
[5]	Includes pre-development costs.
[6]	Depreciation of the buildings and improvements are calculated over lives ranging from the life of the lease to 40 years.

Real Estate and Accumulated D_7

Real Estate and Accumulated Depreciation Activity of Real Estate and Accumulated Depreciation (BPLP) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Real Estate, Balance at the beginning of the year	$ 21,058,714	$ 20,114,576	$ 19,451,683
Real Estate, Additions to / improvements of real estate	1,043,379	1,099,286	977,287
Real Estate, Assets sold / written off	(496,548)	(155,148)	(314,394)
Real Estate, Balance at the end of the year	21,605,545	21,058,714	20,114,576
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Accumulated depreciation, Balance at beginning of the year	4,566,570	4,201,891	3,905,940
Accumulated depreciation, Depreciation expense	533,342	497,059	560,024
Accumulated depreciation, Assets sold / written off	(228,810)	(132,380)	(264,073)
Accumulated depreciation, Balance at end of the year	4,871,102	4,566,570	4,201,891
Boston Properties Limited Partnership
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Real Estate, Balance at the beginning of the year	20,647,236	19,701,185	19,031,289
Real Estate, Additions to / improvements of real estate	1,043,379	1,099,286	977,287
Real Estate, Assets sold / written off	(483,426)	(153,235)	(307,391)
Real Estate, Balance at the end of the year	21,207,189	20,647,236	19,701,185
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Accumulated depreciation, Balance at beginning of the year	4,473,895	4,116,020	3,826,862
Accumulated depreciation, Depreciation expense	525,584	488,919	548,397
Accumulated depreciation, Assets sold / written off	(225,679)	(131,044)	(259,239)
Accumulated depreciation, Balance at end of the year	$ 4,773,800	$ 4,473,895	$ 4,116,020