Boston Properties (BXP) 10-Q7 Aug 182018 Q2 Quarterly reportFinancial data

Company Profile

Document And Entity Information

Document And Entity Information - shares	6 Months Ended
Document And Entity Information - shares	Jun. 30, 2018	Aug. 02, 2018
Entity Information [Line Items]
Document Type	10-Q
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q2
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		154,419,806
Boston Properties Limited Partnership
Entity Information [Line Items]
Document Type	10-Q
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q2
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

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
ASSETS
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $7,358,363 and $7,172,718 at June 30, 2018 and December 31, 2017, respectively)	$ 21,526,520	$ 21,096,642
Less: accumulated depreciation (amounts related to VIEs of $(910,381) and $(854,172) at June 30, 2018 and December 31, 2017, respectively)	(4,745,590)	(4,589,634)
Total real estate	16,780,930	16,507,008
Cash and cash equivalents (amounts related to VIEs of $277,252 and $304,955 at June 30, 2018 and December 31, 2017, respectively)	472,555	434,767
Cash held in escrows (amounts related to VIEs of $6,099 and $6,135 at June 30, 2018 and December 31, 2017, respectively)	254,505	70,602
Investments in securities	30,063	29,161
Tenant and other receivables (amounts related to VIEs of $17,130 and $27,057 at June 30, 2018 and December 31, 2017, respectively)	63,660	92,186
Accrued rental income (amounts related to VIEs of $268,120 and $242,589 at June 30, 2018 and December 31, 2017, respectively)	912,652	861,575
Deferred charges, net (amounts related to VIEs of $264,973 and $281,678 at June 30, 2018 and December 31, 2017, respectively)	678,319	679,038
Prepaid expenses and other assets (amounts related to VIEs of $34,853 and $33,666 at June 30, 2018 and December 31, 2017, respectively)	85,972	77,971
Investments in unconsolidated joint ventures	682,507	619,925
Total assets	19,961,163	19,372,233
Liabilities:
Mortgage notes payable, net (amounts related to VIEs of $2,934,336 and $2,939,183 at June 30, 2018 and December 31, 2017, respectively)	2,972,052	2,979,281
Unsecured senior notes, net	7,251,578	7,247,330
Unsecured line of credit	0	45,000
Unsecured term loan, net	498,248	0
Accounts payable and accrued expenses (amounts related to VIEs of $80,098 and $106,683 at June 30, 2018 and December 31, 2017, respectively)	327,067	331,500
Dividends and distributions payable	139,263	139,040
Accrued interest payable (amounts related to VIEs of $6,669 and $6,907 at June 30, 2018 and December 31, 2017, respectively)	96,844	83,646
Other liabilities (amounts related to VIEs of $183,114 and $164,806 at June 30, 2018 and December 31, 2017, respectively)	462,869	443,980
Total liabilities	11,747,921	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, $.01 par value, 50,000,000 shares authorized
5.25% Series B cumulative redeemable preferred stock/unit, liquidation preference $2,500 per share/unit, 92,000 shares authorized, 80,000 shares/units issued and outstanding at June 30, 2018 and December 31, 2016	200,000	200,000
Common stock, $0.01 par value, 250,000,000 shares authorized, 154,490,429 and 154,404,186 issued and 154,411,529 and 154,325,286 outstanding at June 30, 2018 and December 31, 2017, respectively	1,544	1,543
Additional paid-in capital	6,391,460	6,377,908
Dividends in excess of earnings	(649,747)	(712,343)
Treasury common stock at cost, 78,900 shares at June 30, 2018 and December 31, 2017	(2,722)	(2,722)
Accumulated other comprehensive loss	(47,695)	(50,429)
Total stockholders’ equity attributable to Boston Properties, Inc.	5,892,840	5,813,957
Noncontrolling interests:
Common units of Boston Properties Limited Partnership	621,221	604,739
Property partnerships	1,699,181	1,683,760
Total equity / capital	8,213,242	8,102,456
Total liabilities and equity / capital	19,961,163	19,372,233
Boston Properties Limited Partnership
ASSETS
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $7,358,363 and $7,172,718 at June 30, 2018 and December 31, 2017, respectively)	21,118,909	20,685,164
Less: accumulated depreciation (amounts related to VIEs of $(910,381) and $(854,172) at June 30, 2018 and December 31, 2017, respectively)	(4,649,907)	(4,496,959)
Total real estate	16,469,002	16,188,205
Cash and cash equivalents (amounts related to VIEs of $277,252 and $304,955 at June 30, 2018 and December 31, 2017, respectively)	472,555	434,767
Cash held in escrows (amounts related to VIEs of $6,099 and $6,135 at June 30, 2018 and December 31, 2017, respectively)	254,505	70,602
Investments in securities	30,063	29,161
Tenant and other receivables (amounts related to VIEs of $17,130 and $27,057 at June 30, 2018 and December 31, 2017, respectively)	63,660	92,186
Accrued rental income (amounts related to VIEs of $268,120 and $242,589 at June 30, 2018 and December 31, 2017, respectively)	912,652	861,575
Deferred charges, net (amounts related to VIEs of $264,973 and $281,678 at June 30, 2018 and December 31, 2017, respectively)	678,319	679,038
Prepaid expenses and other assets (amounts related to VIEs of $34,853 and $33,666 at June 30, 2018 and December 31, 2017, respectively)	85,972	77,971
Investments in unconsolidated joint ventures	682,507	619,925
Total assets	19,649,235	19,053,430
Liabilities:
Mortgage notes payable, net (amounts related to VIEs of $2,934,336 and $2,939,183 at June 30, 2018 and December 31, 2017, respectively)	2,972,052	2,979,281
Unsecured senior notes, net	7,251,578	7,247,330
Unsecured line of credit	0	45,000
Unsecured term loan, net	498,248	0
Accounts payable and accrued expenses (amounts related to VIEs of $80,098 and $106,683 at June 30, 2018 and December 31, 2017, respectively)	327,067	331,500
Dividends and distributions payable	139,263	139,040
Accrued interest payable (amounts related to VIEs of $6,669 and $6,907 at June 30, 2018 and December 31, 2017, respectively)	96,844	83,646
Other liabilities (amounts related to VIEs of $183,114 and $164,806 at June 30, 2018 and December 31, 2017, respectively)	462,869	443,980
Total liabilities	11,747,921	11,269,777
Commitments and contingencies	0	0
Noncontrolling interest:
Redeemable partnership units—16,831,182 and 16,810,378 common units and 992,387 and 818,343 long term incentive units outstanding at redemption value at June 30, 2018 and December 31, 2017, respectively	2,235,432	2,292,263
Preferred stock, $.01 par value, 50,000,000 shares authorized
5.25% Series B cumulative redeemable preferred stock/unit, liquidation preference $2,500 per share/unit, 92,000 shares authorized, 80,000 shares/units issued and outstanding at June 30, 2018 and December 31, 2016	193,623	193,623
Noncontrolling interests:
Boston Properties Limited Partnership partners’ capital—1,722,351 and 1,719,540 general partner units and 152,689,178 and 152,605,746 limited partner units outstanding at June 30, 2018 and December 31, 2017, respectively	3,773,078	3,614,007
Noncontrolling interests in property partnerships	1,699,181	1,683,760
Total equity / capital	5,665,882	5,491,390
Total liabilities and equity / capital	$ 19,649,235	$ 19,053,430

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
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	154,490,429	154,404,186
Common stock, shares outstanding	154,411,529	154,325,286
Treasury common stock at cost, shares	78,900	78,900
General Partners' Capital Account, Units Outstanding	1,722,351
Limited Partners' Capital Account, Units Outstanding	152,689,178
Real Estate Investment Property, at Cost	$ 21,526,520	$ 21,096,642
Accumulated depreciation	(4,745,590)	(4,589,634)
Cash and Cash Equivalents	472,555	434,767
Cash held in escrow	254,505	70,602
Tenant and other receivables	63,660	92,186
Accrued rental income	912,652	861,575
Deferred Charges, net	678,319	679,038
Prepaid expense and other assets	85,972	77,971
Mortgage notes payable, net	2,972,052	2,979,281
Accounts payable and accrued expenses	327,067	331,500
Accrued interest payable	96,844	83,646
Other Liabilities	$ 462,869	$ 443,980
Series B Cumulative Redeemable Preferred Stock [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%
Series B, Liquidation Preference Per Share (dollars per share)	$ 2,500	$ 2,500
Series B, shares issued	80,000	80,000
Series B, Shares Outstanding (in shares)	80,000	80,000
Boston Properties Limited Partnership
NonControlling Interest Redeemable Partnership Units Common Units Shares Outstanding	16,831,182	16,810,378
NonControlling Interest Redeemable Partnership Units Common Units Long Term Incentive Units At Redemption Value Shares Outstanding	992,387	818,343
General Partners' Capital Account, Units Outstanding	1,722,351	1,719,540
Limited Partners' Capital Account, Units Outstanding	152,689,178	152,605,746
Real Estate Investment Property, at Cost	$ 21,118,909	$ 20,685,164
Accumulated depreciation	(4,649,907)	(4,496,959)
Cash and Cash Equivalents	472,555	434,767
Cash held in escrow	254,505	70,602
Tenant and other receivables	63,660	92,186
Accrued rental income	912,652	861,575
Deferred Charges, net	678,319	679,038
Prepaid expense and other assets	85,972	77,971
Mortgage notes payable, net	2,972,052	2,979,281
Accounts payable and accrued expenses	327,067	331,500
Accrued interest payable	96,844	83,646
Other Liabilities	$ 462,869	$ 443,980
Boston Properties Limited Partnership \| Series B Cumulative Redeemable Preferred Stock [Member]
Series B Dividend Rate Percentage	5.25%	5.25%
Series B, Liquidation Preference Per Share (dollars per share)	$ 2,500	$ 2,500
Series B, shares issued	80,000	80,000
Series B, Shares Outstanding (in shares)	80,000	80,000
VIE
Real Estate Investment Property, at Cost	$ 7,358,363	$ 7,172,718
Accumulated depreciation	(910,381)	(854,172)
Cash and Cash Equivalents	277,252	304,955
Cash held in escrow	6,099	6,135
Tenant and other receivables	17,130	27,057
Accrued rental income	268,120	242,589
Deferred Charges, net	264,973	281,678
Prepaid expense and other assets	34,853	33,666
Mortgage notes payable, net	2,934,336	2,939,183
Accounts payable and accrued expenses	80,098	106,683
Accrued interest payable	6,669	6,907
Other Liabilities	183,114	164,806
VIE \| Boston Properties Limited Partnership
Real Estate Investment Property, at Cost	7,358,363	7,172,718
Accumulated depreciation	(910,381)	(854,172)
Cash and Cash Equivalents	277,252	304,955
Cash held in escrow	6,099	6,135
Tenant and other receivables	17,130	27,057
Accrued rental income	268,120	242,589
Deferred Charges, net	264,973	281,678
Prepaid expense and other assets	34,853	33,666
Mortgage notes payable, net	2,934,336	2,939,183
Accounts payable and accrued expenses	80,098	106,683
Accrued interest payable	6,669	6,907
Other Liabilities	$ 183,114	$ 164,806

Consolidated Statements Of Oper

Consolidated Statements Of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue
Base rent	$ 516,439	$ 520,542	$ 1,035,946	$ 1,024,104
Recoveries from tenants	95,259	89,163	190,377	178,327
Parking and other	26,904	26,462	53,038	52,072
Total rental revenue	638,602	636,167	1,279,361	1,254,503
Hotel revenue	14,607	13,375	23,709	20,795
Development and management services	9,305	7,365	17,710	13,837
Direct reimbursements of payroll and related costs from management services contracts	1,970	0	4,855	0
Total revenue	664,484	656,907	1,325,635	1,289,135
Expenses
Rental	237,790	230,454	478,119	458,741
Hotel	8,741	8,404	16,814	15,495
General and administrative	28,468	27,141	64,362	58,527
Payroll and related costs from management services contracts	1,970	0	4,855	0
Transaction costs	474	299	495	333
Depreciation and amortization	156,417	151,919	322,214	311,124
Total expenses	433,860	418,217	886,859	844,220
Operating income	230,624	238,690	438,776	444,915
Other income (expense)
Income from unconsolidated joint ventures	769	3,108	1,230	6,192
Interest and other income	2,579	1,504	4,227	2,118
Gains from investments in securities	505	730	379	1,772
Gains from early extinguishments of debt	0	14,354	0	14,354
Interest expense	(92,204)	(95,143)	(182,424)	(190,677)
Income before gains on sales of real estate	142,273	163,243	262,188	278,674
Gains on sales of real estate	18,292	3,767	114,689	3,900
Net income	160,565	167,010	376,877	282,574
Net income attributable to noncontrolling interests
Noncontrolling interests in property partnerships	(14,400)	(15,203)	(31,634)	(19,627)
Noncontrolling interest—common units of Boston Properties Limited Partnership	(14,859)	(15,473)	(35,311)	(26,933)
Net income attributable to the Company	131,306	136,334	309,932	236,014
Preferred dividends / distributions	(2,625)	(2,625)	(5,250)	(5,250)
Net income attributable to the Company's common shareholders / unitholders	$ 128,681	$ 133,709	$ 304,682	$ 230,764
Basic earnings per common share / unit attributable to the Company's common shareholders / unitholders
Net income (in dollars per share / unit)	$ 0.83	$ 0.87	$ 1.97	$ 1.50
Weighted average number of common shares / units outstanding	154,415	154,177	154,400	154,019
Diluted earnings per common share / unit attributable to the Company's common shareholders / unitholders
Diluted Earnings: Net income, Per Share Amount (in dollars per share / unit)	$ 0.83	$ 0.87	$ 1.97	$ 1.50
Weighted average number of common and common equivalent shares / units outstanding (in shares / units)	154,571	154,331	154,638	154,273
Dividends / Distributions, Per Share / Unit, Declared	$ 0.80	$ 0.75	$ 1.60	$ 1.50
Boston Properties Limited Partnership
Revenue
Base rent	$ 516,439	$ 520,542	$ 1,035,946	$ 1,024,104
Recoveries from tenants	95,259	89,163	190,377	178,327
Parking and other	26,904	26,462	53,038	52,072
Total rental revenue	638,602	636,167	1,279,361	1,254,503
Hotel revenue	14,607	13,375	23,709	20,795
Development and management services	9,305	7,365	17,710	13,837
Direct reimbursements of payroll and related costs from management services contracts	1,970	0	4,855	0
Total revenue	664,484	656,907	1,325,635	1,289,135
Expenses
Rental	237,790	230,454	478,119	458,741
Hotel	8,741	8,404	16,814	15,495
General and administrative	28,468	27,141	64,362	58,527
Payroll and related costs from management services contracts	1,970	0	4,855	0
Transaction costs	474	299	495	333
Depreciation and amortization	154,474	149,834	318,327	306,892
Total expenses	431,917	416,132	882,972	839,988
Operating income	232,567	240,775	442,663	449,147
Other income (expense)
Income from unconsolidated joint ventures	769	3,108	1,230	6,192
Interest and other income	2,579	1,504	4,227	2,118
Gains from investments in securities	505	730	379	1,772
Gains from early extinguishments of debt	0	14,354	0	14,354
Interest expense	(92,204)	(95,143)	(182,424)	(190,677)
Income before gains on sales of real estate	144,216	165,328	266,075	282,906
Gains on sales of real estate	18,770	4,344	117,677	4,477
Net income	162,986	169,672	383,752	287,383
Net income attributable to noncontrolling interests
Noncontrolling interests in property partnerships	(14,400)	(15,203)	(31,634)	(19,627)
Net income attributable to the Company	148,586	154,469	352,118	267,756
Preferred dividends / distributions	(2,625)	(2,625)	(5,250)	(5,250)
Net income attributable to the Company's common shareholders / unitholders	$ 145,961	$ 151,844	$ 346,868	$ 262,506
Basic earnings per common share / unit attributable to the Company's common shareholders / unitholders
Net income (in dollars per share / unit)	$ 0.85	$ 0.88	$ 2.02	$ 1.53
Weighted average number of common shares / units outstanding	171,916	171,675	171,892	171,628
Diluted earnings per common share / unit attributable to the Company's common shareholders / unitholders
Diluted Earnings: Net income, Per Share Amount (in dollars per share / unit)	$ 0.85	$ 0.88	$ 2.01	$ 1.53
Weighted average number of common and common equivalent shares / units outstanding (in shares / units)	172,072	171,829	172,130	171,882
Dividends / Distributions, Per Share / Unit, Declared	$ 0.80	$ 0.75	$ 1.60	$ 1.50

Consolidated Statements Of Comp

Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net income		$ 160,565	$ 167,010	$ 376,877	$ 282,574
Other comprehensive income (loss):
Effective portion of interest rate contracts		0	(6,313)	0	(6,133)
Amortization of interest rate contracts	[1]	1,666	1,397	3,332	2,703
Other comprehensive income (loss)		1,666	(4,916)	3,332	(3,430)
Comprehensive income		162,231	162,094	380,209	279,144
Comprehensive income attributable to noncontrolling interests		(29,259)	(30,676)	(66,945)	(46,560)
Other comprehensive (income) loss attributable to noncontrolling interests		(299)	2,738	(598)	2,520
Comprehensive income attributable to the Company		132,673	134,156	312,666	235,104
Boston Properties Limited Partnership
Net income		162,986	169,672	383,752	287,383
Other comprehensive income (loss):
Effective portion of interest rate contracts		0	(6,313)	0	(6,133)
Amortization of interest rate contracts	[2]	1,666	1,397	3,332	2,703
Other comprehensive income (loss)		1,666	(4,916)	3,332	(3,430)
Comprehensive income		164,652	164,756	387,084	283,953
Comprehensive income attributable to noncontrolling interests		(14,544)	(12,715)	(31,922)	(17,211)
Comprehensive income attributable to the Company		$ 150,108	$ 152,041	$ 355,162	$ 266,742

[1]	Amounts reclassified from comprehensive income primarily to interest expense within the Boston Properties, Inc.’s Consolidated Statements of Operations.
[2]	Amounts reclassified from comprehensive income primarily to interest expense within the 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 (Income) Loss [Member]	Noncontrolling Interests [Member]
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]
Conversion of operating partnership units to Common Stock, shares		481,000
Conversion of operating partnership units to Common Stock, value	0	$ 5		16,417				(16,422)
Allocated net income for the year	282,574				236,014			46,560
Dividends/distributions declared	(263,345)				(236,368)			(26,977)
Shares issued pursuant to stock purchase plan, shares		3,000
Shares issued pursuant to stock purchase plan, value	373			373
Net activity from stock option and incentive plan, shares		34,000
Net activity from stock option and incentive plan, value	21,168	$ 0		1,980				19,188
Cumulative effect of a change in accounting principle	(2,035)				(272)			(1,763)
Contributions from noncontrolling interests in property partnerships	133,072							133,072
Distributions to noncontrolling interests in property partnerships	(26,949)							(26,949)
Effective portion of interest rate contracts	(6,133)						(3,301)	(2,832)
Amortization of interest rate contracts	2,703						2,391	312
Reallocation of noncontrolling interest	0			10,840				(10,840)
Equity, value at Jun. 30, 2017	8,073,352	$ 1,543	200,000	6,363,034	(694,320)	(2,722)	(53,161)	2,258,978
Equity, shares at Jun. 30, 2017		154,308,000
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]
Conversion of operating partnership units to Common Stock, shares		35,000
Conversion of operating partnership units to Common Stock, value		$ 1		1,195				(1,196)
Allocated net income for the year	$ 376,877				309,932			66,945
Dividends/distributions declared	(280,977)				(252,269)			(28,708)
Shares issued pursuant to stock purchase plan, shares		3,000
Shares issued pursuant to stock purchase plan, value	429			429
Net activity from stock option and incentive plan, shares		49,000
Net activity from stock option and incentive plan, value	22,130			600				21,530
Cumulative effect of a change in accounting principle	5,496				4,933			563
Contributions from noncontrolling interests in property partnerships	27,532							27,532
Distributions to noncontrolling interests in property partnerships	(44,033)							(44,033)
Amortization of interest rate contracts	3,332						2,734	598
Reallocation of noncontrolling interest				11,328				(11,328)
Equity, value at Jun. 30, 2018	$ 8,213,242	$ 1,544	$ 200,000	$ 6,391,460	$ (649,747)	$ (2,722)	$ (47,695)	$ 2,320,402
Equity, shares at Jun. 30, 2018	154,411,529	154,412,000

Consolidated Statement of Partn

Consolidated Statement of Partners' Capital Statement - USD ($) $ in Thousands	Total	Boston Properties Limited Partnership
Beginning Balance at Dec. 31, 2016		$ 3,811,717
Contributions		4,682
Net income allocable to general and limited partner units		240,823
Distributions		(236,368)
Other comprehensive income (loss)		(910)
Cumulative effect of a change in accounting principle	$ (2,035)	(272)
Unearned compensation		(2,329)
Conversion of redeemable partnership units		16,422
Adjustment to reflect redeemable partnership units at redemption value		92,740
Ending Balance at Jun. 30, 2017		3,926,505
Beginning Balance at Dec. 31, 2017		3,807,630
Contributions		1,685
Net income allocable to general and limited partner units		316,807
Distributions		(252,269)
Other comprehensive income (loss)		2,734
Cumulative effect of a change in accounting principle	$ 5,496	4,933
Unearned compensation		(656)
Conversion of redeemable partnership units		1,196
Adjustment to reflect redeemable partnership units at redemption value		84,641
Ending Balance at Jun. 30, 2018		$ 3,966,701

Consolidated Statements Of Cash

Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities:
Net income	$ 376,877	$ 282,574
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	322,214	311,124
Non-cash compensation expense	23,243	19,237
Income from unconsolidated joint ventures	(1,230)	(6,192)
Distributions of net cash flow from operations of unconsolidated joint ventures	1,663	2,905
Gains from investments in securities	(379)	(1,772)
Gains from early extinguishments of debt	0	(14,354)
Non-cash portion of interest expense	10,607	(11,979)
Gains on sales of real estate	(114,689)	(3,900)
Change in assets and liabilities:
Tenant and other receivables, net	33,012	2,033
Accrued rental income, net	(45,759)	(19,348)
Prepaid expenses and other assets	(4,641)	36,223
Accounts payable and accrued expenses	(9,899)	(2,608)
Accrued interest payable	12,999	(158,761)
Other liabilities	11,571	(33,121)
Tenant leasing costs	(54,743)	(37,252)
Total adjustments	183,969	82,235
Net cash provided by operating activities	560,846	364,809
Cash flows from investing activities:
Acquisitions of real estate	0	(15,953)
Construction in progress	(380,565)	(297,747)
Building and other capital improvements	(96,730)	(100,808)
Tenant improvements	(83,982)	(107,533)
Proceeds from sales of real estate	141,249	17,049
Capital contributions to unconsolidated joint ventures	(65,250)	(41,491)
Investments in securities, net	(523)	(1,195)
Net cash used in investing activities	(485,801)	(547,678)
Cash flows from financing activities:
Proceeds from mortgage notes payable	0	2,300,000
Repayments of mortgage notes payable	(9,192)	(1,308,708)
Borrowings on unsecured line of credit	345,000	430,000
Repayments of unsecured line of credit	(390,000)	(430,000)
Proceeds from unsecured term loan	500,000	0
Repayments of mezzanine notes payable	0	(306,000)
Repayments of outside members’ notes payable	0	(70,424)
Payments on capital lease obligations	0	(548)
Payments on real estate financing transactions	(960)	(1,013)
Deposit on mortgage note payable interest rate lock	0	(23,200)
Return of deposit on mortgage note payable interest rate lock	0	23,200
Deferred financing costs	(263)	(43,635)
Debt prepayment and extinguishment costs	0	(90)
Net proceeds from equity transactions	(684)	(181)
Dividends and distributions	(280,754)	(263,221)
Contributions from noncontrolling interests in property partnerships	27,532	23,496
Distributions to noncontrolling interests in property partnerships	(44,033)	(27,115)
Net cash provided by financing activities	146,646	302,561
Net increase in cash and cash equivalents and cash held in escrows	221,691	119,692
Cash and cash equivalents and cash held in escrows, beginning of period	505,369	420,088
Cash and cash equivalents and cash held in escrows, end of period	727,060	539,780
Reconciliation of cash and cash equivalents and cash held in escrows:
Cash and cash equivalents, beginning of period	434,767	356,914
Cash held in escrows, beginning of period	70,602	63,174
Cash and Cash Equivalents, end of period	472,555	492,435
Cash held in escrows, end of period	254,505	47,345
Supplemental disclosures:
Cash paid for interest	192,898	388,045
Interest capitalized	34,999	26,628
Non-cash investing and financing activities:
Write-off of fully depreciated real estate	(78,900)	(86,135)
Additions to real estate included in accounts payable and accrued expenses	326	22,994
Real estate acquired through capital lease	0	28,962
Outside members’ notes payable contributed to noncontrolling interests in property partnerships	0	109,576
Dividends and distributions declared but not paid	139,263	130,432
Conversions of noncontrolling interests to stockholders’ equity / partners' capital	1,196	16,422
Issuance of restricted securities to employees	37,342	35,945
Boston Properties Limited Partnership
Cash flows from operating activities:
Net income	383,752	287,383
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	318,327	306,892
Non-cash compensation expense	23,243	19,237
Income from unconsolidated joint ventures	(1,230)	(6,192)
Distributions of net cash flow from operations of unconsolidated joint ventures	1,663	2,905
Gains from investments in securities	(379)	(1,772)
Gains from early extinguishments of debt	0	(14,354)
Non-cash portion of interest expense	10,607	(11,979)
Gains on sales of real estate	(117,677)	(4,477)
Change in assets and liabilities:
Tenant and other receivables, net	33,012	2,033
Accrued rental income, net	(45,759)	(19,348)
Prepaid expenses and other assets	(4,641)	36,223
Accounts payable and accrued expenses	(9,899)	(2,608)
Accrued interest payable	12,999	(158,761)
Other liabilities	11,571	(33,121)
Tenant leasing costs	(54,743)	(37,252)
Total adjustments	177,094	77,426
Net cash provided by operating activities	560,846	364,809
Cash flows from investing activities:
Acquisitions of real estate	0	(15,953)
Construction in progress	(380,565)	(297,747)
Building and other capital improvements	(96,730)	(100,808)
Tenant improvements	(83,982)	(107,533)
Proceeds from sales of real estate	141,249	17,049
Capital contributions to unconsolidated joint ventures	(65,250)	(41,491)
Investments in securities, net	(523)	(1,195)
Net cash used in investing activities	(485,801)	(547,678)
Cash flows from financing activities:
Proceeds from mortgage notes payable	0	2,300,000
Repayments of mortgage notes payable	(9,192)	(1,308,708)
Borrowings on unsecured line of credit	345,000	430,000
Repayments of unsecured line of credit	(390,000)	(430,000)
Proceeds from unsecured term loan	500,000	0
Repayments of mezzanine notes payable	0	(306,000)
Repayments of outside members’ notes payable	0	(70,424)
Payments on capital lease obligations	0	(548)
Payments on real estate financing transactions	(960)	(1,013)
Deposit on mortgage note payable interest rate lock	0	(23,200)
Return of deposit on mortgage note payable interest rate lock	0	23,200
Deferred financing costs	(263)	(43,635)
Debt prepayment and extinguishment costs	0	(90)
Net proceeds from equity transactions	(684)	(181)
Dividends and distributions	(280,754)	(263,221)
Contributions from noncontrolling interests in property partnerships	27,532	23,496
Distributions to noncontrolling interests in property partnerships	(44,033)	(27,115)
Net cash provided by financing activities	146,646	302,561
Net increase in cash and cash equivalents and cash held in escrows	221,691	119,692
Cash and cash equivalents and cash held in escrows, beginning of period	505,369	420,088
Cash and cash equivalents and cash held in escrows, end of period	727,060	539,780
Reconciliation of cash and cash equivalents and cash held in escrows:
Cash and cash equivalents, beginning of period	434,767	356,914
Cash held in escrows, beginning of period	70,602	63,174
Cash and Cash Equivalents, end of period	472,555	492,435
Cash held in escrows, end of period	254,505	47,345
Supplemental disclosures:
Cash paid for interest	192,898	388,045
Interest capitalized	34,999	26,628
Non-cash investing and financing activities:
Write-off of fully depreciated real estate	(78,900)	(85,525)
Additions to real estate included in accounts payable and accrued expenses	326	22,994
Real estate acquired through capital lease	0	28,962
Outside members’ notes payable contributed to noncontrolling interests in property partnerships	0	109,576
Dividends and distributions declared but not paid	139,263	130,432
Conversions of noncontrolling interests to stockholders’ equity / partners' capital	1,196	16,422
Issuance of restricted securities to employees	$ 37,342	$ 35,945

Organization

Organization	6 Months Ended
Organization	Jun. 30, 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 June 30, 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 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 7 , 8 and 10 ). At June 30, 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 8 ). Properties At June 30, 2018 , the Company owned or had interests in a portfolio of 178 commercial real estate properties (the “Properties”) aggregating approximately 50.2 million net rentable square feet of primarily Class A office properties, including twelve properties under construction/redevelopment totaling approximately 6.0 million net rentable square feet. At June 30, 2018 , the Properties consisted of: • 166 office properties (including nine properties under construction/redevelopment); • six residential properties (including three properties under construction); • five retail properties; 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 And Summa

Basis Of Presentation And Summary Of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Basis Of Presentation And Summary Of Significant Accounting Policies	2. Basis of Presentation and Summary of Significant Accounting Policies Boston Properties, Inc. does not have any other significant assets, liabilities or operations, other than its investment in 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. The accompanying interim financial statements are unaudited; however, the financial statements have been prepared in accordance with generally accepted accounting principles (“GAAP”) for interim financial information and in conjunction with the rules and regulations of the Securities and Exchange Commission. Accordingly, they do not include all of the disclosures required by GAAP for complete financial statements. In the opinion of management, all adjustments (consisting solely of normal recurring matters) necessary for a fair statement of the financial statements for these interim periods have been included. The results of operations for the interim periods are not necessarily indicative of the results to be obtained for other interim periods or for the full fiscal year. The year-end consolidated balance sheet data was derived from audited financial statements, but does not include all disclosure required by GAAP. These financial statements should be read in conjunction with the Company’s financial statements and notes thereto contained in the Company’s Annual Report in the Company’s Form 10-K for its fiscal year ended December 31, 2017 . Fair Value of Financial 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 Accounting Standards Codification ("ASC") 820 "Fair Value Measurements and Disclosures," the accounting standards for Fair Value Measurements and Disclosures) 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 the accounting standards for Fair Value Measurements and Disclosures) if trading volumes are low. The Company determines the fair value of its mortgage notes payable using discounted cash flow analysis by discounting the spread between the future contractual interest payments and hypothetical future interest payments on 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 mortgage notes payable are categorized at a Level 3 basis (as defined in the accounting standards for Fair Value Measurements and Disclosures) 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 mortgage notes payable, net, unsecured line of credit, unsecured term loan, net and unsecured senior notes, net and the Company’s corresponding estimate of fair value as of June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Mortgage notes payable, net $ 2,972,052 $ 2,938,167 $ 2,979,281 $ 3,042,920 Unsecured senior notes, net 7,251,578 7,188,261 7,247,330 7,461,615 Unsecured line of credit — — 45,000 45,000 Unsecured term loan, net 498,248 500,181 — — Total $ 10,721,878 $ 10,626,609 $ 10,271,611 $ 10,549,535 Variable Interest Entities (VIEs) 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 nine entities that are VIEs. Consolidated Variable Interest Entities As of June 30, 2018 , Boston Properties, Inc. has identified seven consolidated VIEs, including Boston Properties Limited Partnership. The VIEs own (1) the following five in-service properties: 767 Fifth Avenue (the General Motors Building), Times Square Tower, 601 Lexington Avenue, Atlantic Wharf Office Building and 100 Federal Street and (2) Salesforce Tower, which was partially placed in-service on December 1, 2017. The Company consolidates these VIEs because it is the primary beneficiary. The third parties’ interests in these consolidated entities, with the exception of Boston Properties Limited Partnership, are reflected as noncontrolling interest in property partnerships in the accompanying Consolidated Financial Statements (See Note 7 ). 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 Residential Tower Developer LLC joint ventures, which own 7750 Wisconsin Avenue and The Hub on Causeway - Residential, respectively, are VIEs. 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. New 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 “Leases” (“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 three and six months ended June 30, 2018, the Company recognized approximately $2.0 million and $4.9 million , respectively, of expenses consisting of payroll and related costs from management services contracts and recognized corresponding revenue of approximately $2.0 million and $4.9 million , respectively, reflecting the direct reimbursements of such costs from the unconsolidated joint venture entities and third party property owners. 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 did not have a material impact on the Company’s consolidated financial statements. The adoption of ASU 2016-15 will result in the retrospective classification of debt prepayment costs as a component of financing activities instead of as a component of operating activities in the Company's Consolidated Statements of Cash Flows. 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 adoption of ASU 2016-18 did not have a material impact on the Company’s consolidated financial statements. The retrospective adoption of ASU 2016-18 resulted in a decrease to net cash provided by operating activities totaling approximately $7.5 million , an increase to net cash used in investing activities totaling approximately $8.2 million , a decrease to net cash provided by financing activities totaling approximately $0.1 million , and a corresponding decrease to the net increase in cash and cash equivalents and cash held in escrows totaling approximately $15.8 million from amounts previously reported for the six months ended June 30, 2017 . 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. 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 June 30, 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. ASU 2016-02 is effective for the Company for reporting periods beginning after December 15, 2018, with early adoption permitted. The Company will adopt ASU 2016-02 effective January 1, 2019 using the modified retrospective approach. The Company is in the pro cess of evaluating whether it will elect to apply the practical expedients. The Company is in the process of adopting ASU 2016-02 and its project team has compiled an inventory of its leases that will be impacted by the adoption of ASU 2016-02. The Company continues to assess the impact of adopting ASU 2016-02. However, the Company will account for operating leases under which it is the lessor on its balance sheet in a manner similar to its current accounting with t he underlying leased asset recognized as real estate. On July 30, 2018, the FASB issued ASU 2018-11, “Leases (Topic 842): Targeted Improvements” (“ASU 2018-11”), that 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. 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. The Company’s project team is evaluating this recently issued ASU 2018-11. 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 with rental payments being applied to the lease liability and to interest expense and the right-of-use asset being amortized to expense over the term of the lease. 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 legal costs and internal leasing wages and instead will be required to expense these and other non-incremental costs as incurred. 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 plans to elect this practical expedient and has gathered its inventory and is in the process of drafting procedures and controls.

Real Estate

Real Estate	6 Months Ended
Real Estate	Jun. 30, 2018
Real Estate [Abstract]
Real Estate	3. Real Estate Boston Properties, Inc. Real estate consisted of the following at June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Land $ 5,108,880 $ 5,080,679 Land held for future development (1) 210,902 204,925 Buildings and improvements 12,720,779 12,284,164 Tenant improvements 2,278,755 2,219,608 Furniture, fixtures and equipment 44,164 37,928 Construction in progress 1,163,040 1,269,338 Total 21,526,520 21,096,642 Less: Accumulated depreciation (4,745,590 ) (4,589,634 ) $ 16,780,930 $ 16,507,008 _______________ (1) Includes pre-development costs. Boston Properties Limited Partnership Real estate consisted of the following at June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Land $ 5,005,471 $ 4,976,303 Land held for future development (1) 210,902 204,925 Buildings and improvements 12,416,577 11,977,062 Tenant improvements 2,278,755 2,219,608 Furniture, fixtures and equipment 44,164 37,928 Construction in progress 1,163,040 1,269,338 Total 21,118,909 20,685,164 Less: Accumulated depreciation (4,649,907 ) (4,496,959 ) $ 16,469,002 $ 16,188,205 _______________ (1) Includes pre-development costs. Development On January 24, 2018, the Company entered into a lease agreement with Leidos 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 approximately 1.1 million net rentable square feet. The Company expects to begin construction in the second half of 2018 upon receipt of all necessary approvals. 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. 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 $1.6 million and $3.2 million of net income to the Company for the three and six months ended June 30, 2017 , 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 $0.1 million and $0.3 million of net income to the Company for the period from April 1, 2018 through May 23, 2018 and the period from January 1, 2018 through May 23, 2018, respectively, and contributed approximately $0.1 million and $0.3 million of net income to the Company for the three and six months ended June 30, 2017 , respectively.

Investments in Unconsolidated J

Investments in Unconsolidated Joint Ventures	6 Months Ended
Investments in Unconsolidated Joint Ventures	Jun. 30, 2018
Investments In Unconsolidated Joint Ventures [Abstract]
Investments In Unconsolidated Joint Ventures	4. Investments in Unconsolidated Joint Ventures The investments in unconsolidated joint ventures consist of the following at June 30, 2018 and December 31, 2017 : Nominal % Ownership Carrying Value of Investment (1) Entity Properties June 30, 2018 December 31, 2017 (in thousands) Square 407 Limited Partnership Market Square North 50.0 % $ (7,371 ) $ (8,258 ) The Metropolitan Square Associates LLC Metropolitan Square 20.0 % 4,628 3,339 BP/CRF 901 New York Avenue LLC 901 New York Avenue 25.0 % (2) (12,824 ) (13,811 ) WP Project Developer LLC Wisconsin Place Land and Infrastructure 33.3 % (3) 39,015 39,710 Annapolis Junction NFM, LLC Annapolis Junction 50.0 % (4) 17,597 18,381 540 Madison Venture LLC 540 Madison Avenue 60.0 % 66,385 66,179 500 North Capitol Venture LLC 500 North Capitol Street, NW 30.0 % (4,416 ) (3,876 ) 501 K Street LLC 1001 6th Street 50.0 % (5) 42,646 42,657 Podium Developer LLC The Hub on Causeway 50.0 % 72,900 67,120 Residential Tower Developer LLC The Hub on Causeway - Residential 50.0 % (6) 38,958 28,212 Hotel Tower Developer LLC The Hub on Causeway - Hotel Air Rights 50.0 % 2,046 1,690 1265 Main Office JV LLC 1265 Main Street 50.0 % 4,413 4,641 BNY Tower Holdings LLC Dock 72 at the Brooklyn Navy Yard 50.0 % 71,651 72,104 CA-Colorado Center Limited Partnership Colorado Center 50.0 % 253,864 254,440 7750 Wisconsin Avenue LLC 7750 Wisconsin Avenue 50.0 % (6) 68,404 21,452 $ 657,896 $ 593,980 _______________ (1) Investments with deficit balances aggregating approximately $24.6 million and $25.9 million at June 30, 2018 and December 31, 2017 , respectively, have been reflected 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 four 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 2 ). 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: June 30, 2018 December 31, 2017 (in thousands) ASSETS Real estate and development in process, net $ 1,938,438 $ 1,768,996 Other assets 397,442 367,743 Total assets $ 2,335,880 $ 2,136,739 LIABILITIES AND MEMBERS’/PARTNERS’ EQUITY Mortgage and notes payable, net $ 1,524,951 $ 1,437,440 Other liabilities 126,179 99,215 Members’/Partners’ equity 684,750 600,084 Total liabilities and members’/partners’ equity $ 2,335,880 $ 2,136,739 Company’s share of equity $ 349,576 $ 286,495 Basis differentials (1) 308,320 307,485 Carrying value of the Company’s investments in unconsolidated joint ventures (2) $ 657,896 $ 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 June 30, 2018 and December 31, 2017 , there was an aggregate basis differential of approximately $319.7 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 $24.6 million and $25.9 million at June 30, 2018 and December 31, 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: Three months ended June 30, Six months ended June 30, 2018 2017 2018 2017 (in thousands) Total revenue (1) $ 57,096 $ 55,862 $ 113,582 $ 110,623 Expenses Operating 22,868 22,103 45,717 44,182 Depreciation and amortization 14,527 14,224 29,252 28,533 Total expenses 37,395 36,327 74,969 72,715 Operating income 19,701 19,535 38,613 37,908 Other expense Interest expense 14,708 9,427 29,132 18,727 Net income $ 4,993 $ 10,108 $ 9,481 $ 19,181 Company’s share of net income $ 2,105 $ 4,344 $ 3,931 $ 8,667 Basis differential (2) (1,336 ) (1,236 ) (2,701 ) (2,475 ) Income from unconsolidated joint ventures $ 769 $ 3,108 $ 1,230 $ 6,192 _______________ (1) Includes straight-line rent adjustments of approximately $3.2 million and $4.3 million for the three months ended June 30, 2018 and 2017 , respectively, and $5.0 million and $11.3 million for the six months ended June 30, 2018 and 2017 , respectively. (2) Includes straight-line rent adjustments of approximately $0.7 million and $0.8 million for the three months ended June 30, 2018 and 2017 , respectively, and $1.4 million and $1.5 million for the six months ended June 30, 2018 and 2017 , respectively. Also includes net above-/below-market rent adjustments of approximately $0.4 million and $0.4 million for the three months ended June 30, 2018 and 2017 , respectively, and $0.8 million and $0.9 million for the six months ended June 30, 2018 and 2017 , 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. The joint venture has not yet drawn any funds 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.

Debt

Debt	6 Months Ended
Debt	Jun. 30, 2018
Debt [Abstract]
Debt Disclosure [Text Block]	5. Debt 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 permits Boston Properties Limited Partnership to draw until the first anniversary of the closing date. Based on Boston Properties Limited Partnership’s current 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, and (2) the facility fee on the Revolving Facility commitment is 0.125% per annum. 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. As of June 30, 2018 , Boston Properties Limited Partnership had $500.0 million of borrowings outstanding under its Delayed Draw Facility, no borrowings outstanding under its Revolving Facility and outstanding letters of credit totaling approximately $1.6 million , with the ability to borrow approximately $1.5 billion .

Commitments And Contingencies

Commitments And Contingencies	6 Months Ended
Commitments And Contingencies	Jun. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments And Contingencies	6. 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 $9.3 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 7 . 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 June 30, 2018 , the maximum funding obligation under the guarantee was approximately $144.7 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 June 30, 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, a fee mortgage on the hotel property, or both. As of June 30, 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 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 and 2016, the Company received distributions of approximately $7.7 million , $8.1 million and $1.4 million , respectively. On May 19, 2017, the Company received a fifth interim distribution totaling approximately $0.4 million , leaving a remaining claim of approximately $27.6 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 June 30, 2018 . 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 is $160 million and the coinsurance is 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.

Noncontrolling Interests

Noncontrolling Interests	6 Months Ended
Noncontrolling Interests	Jun. 30, 2018
Noncontrolling Interest [Abstract]
Noncontrolling Interests	7. 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 June 30, 2018 , the noncontrolling interests in Boston Properties Limited Partnership consisted of 16,831,182 OP Units, 992,387 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 six months ended June 30, 2018 , 34,741 OP Units were presented by the holders for redemption (including 31,741 OP Units 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. At June 30, 2018 , Boston Properties Limited Partnership had outstanding 471,579 2016 MYLTIP Units, 398,871 2017 MYLTIP Units and 341,366 2018 MYLTIP Units. Prior to the applicable measurement date (February 9, 2019 for 2016 MYLTIP Units, February 6, 2020 for 2017 MYLTIP Units and February 5, 2021 for the 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, 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 and 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 6, 2018 issuance date) paid in 2018 : Record Date Payment Date Distributions per OP Unit and LTIP Unit Distributions per MYLTIP Unit 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 June 30, 2018 was approximately $2.2 billion based on the last reported price of a share of Common Stock on the New York Stock Exchange of $125.42 per share on June 29, 2018. Boston Properties Limited Partnership The following table reflects the activity of noncontrolling interests—redeemable partnership units of Boston Properties Limited Partnership for the six months ended June 30, 2018 and 2017 (in thousands): Balance at December 31, 2017 $ 2,292,263 Contributions 34,973 Net income 35,311 Distributions (28,708 ) Conversion of redeemable partnership units (1,196 ) Unearned compensation (13,443 ) Cumulative effect of a change in accounting principle 563 Other comprehensive income 310 Adjustment to reflect redeemable partnership units at redemption value (84,641 ) Balance at June 30, 2018 $ 2,235,432 Balance at December 31, 2016 $ 2,262,040 Contributions 31,532 Net income 26,933 Distributions (26,977 ) Conversion of redeemable partnership units (16,422 ) Unearned compensation (12,344 ) Cumulative effect of a change in accounting principle (1,763 ) Other comprehensive loss (104 ) Adjustment to reflect redeemable partnership units at redemption value (92,740 ) Balance at June 30, 2017 $ 2,170,155 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 June 30, 2018 and December 31, 2017 , are included in Noncontrolling Interests—Property Partnerships in 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 June 30, 2018 , the Company had contributed an aggregate of approximately $20.7 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. 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. The stabilization date is expected to occur in the second half of 2018. The following table reflects the activity of the noncontrolling interests — property partnerships for the six months ended June 30, 2018 and 2017 (in thousands): Balance at December 31, 2017 $ 1,683,760 Capital contributions 27,532 Net income 31,634 Accumulated other comprehensive income 288 Distributions (44,033 ) Balance at June 30, 2018 $ 1,699,181 Balance at December 31, 2016 $ 1,530,647 Capital contributions 133,072 Net income 19,627 Accumulated other comprehensive loss (2,416 ) Distributions (26,949 ) Balance at June 30, 2017 $ 1,653,981

Stockholders' Equity _ Partners

Stockholders' Equity / Partners' Capital	6 Months Ended
Stockholders' Equity / Partners' Capital	Jun. 30, 2018
Equity [Abstract]
Stockholders' Equity / Partners' Capital	8. Stockholders’ Equity / Partners’ Capital As of June 30, 2018 , Boston Properties, Inc. had 154,411,529 shares of Common Stock outstanding. As of June 30, 2018 , Boston Properties, Inc. owned 1,722,351 general partnership units and 152,689,178 limited partnership units of Boston Properties Limited Partnership. 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 six months ended June 30, 2018 , Boston Properties, Inc. issued 34,741 shares of Common Stock 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 in 2018 : Record Date Payment Date Dividend (Per Share) Distribution (Per Unit) 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 June 30, 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 have the right to 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 during 2018 : Record Date Payment Date Dividend (Per Share) August 3, 2018 August 15, 2018 $32.8125 May 4, 2018 May 15, 2018 $32.8125 February 2, 2018 February 15, 2018 $32.8125

Earnings Per Share _ Common Uni

Earnings Per Share / Common Unit	6 Months Ended
Earnings Per Share / Common Unit	Jun. 30, 2018
Earnings Per Share [Abstract]
Earnings Per Share / Common Unit	9. 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. Three months ended June 30, 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 $ 128,681 154,415 $ 0.83 Allocation of undistributed earnings to participating securities (16 ) — — Net income attributable to Boston Properties, Inc. common shareholders $ 128,665 154,415 $ 0.83 Effect of Dilutive Securities: Stock Based Compensation — 156 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 128,665 154,571 $ 0.83 Three months ended June 30, 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 $ 133,709 154,177 $ 0.87 Allocation of undistributed earnings to participating securities (43 ) — — Net income attributable to Boston Properties, Inc. common shareholders $ 133,666 154,177 $ 0.87 Effect of Dilutive Securities: Stock Based Compensation — 154 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 133,666 154,331 $ 0.87 Six months ended June 30, 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 $ 304,682 154,400 $ 1.97 Allocation of undistributed earnings to participating securities (142 ) — — Net income attributable to Boston Properties, Inc. common shareholders $ 304,540 154,400 $ 1.97 Effect of Dilutive Securities: Stock Based Compensation — 238 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 304,540 154,638 $ 1.97 Six months ended June 30, 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 $ 230,764 154,019 $ 1.50 Allocation of undistributed earnings to participating securities (9 ) — — Net income attributable to Boston Properties, Inc. common shareholders $ 230,755 154,019 $ 1.50 Effect of Dilutive Securities: Stock Based Compensation — 254 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 230,755 154,273 $ 1.50 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 17,501,000 and 17,498,000 redeemable common units for the three months ended June 30, 2018 and 2017 , respectively, and 17,492,000 and 17,609,000 redeemable common units for the six months ended June 30, 2018 and 2017 , respectively. Three months ended June 30, 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 $ 145,961 171,916 $ 0.85 Allocation of undistributed earnings to participating securities (18 ) — — Net income attributable to Boston Properties Limited Partnership common unitholders $ 145,943 171,916 $ 0.85 Effect of Dilutive Securities: Stock Based Compensation — 156 — Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 145,943 172,072 $ 0.85 Three months ended June 30, 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 $ 151,844 171,675 $ 0.88 Allocation of undistributed earnings to participating securities (48 ) — — Net income attributable to Boston Properties Limited Partnership common unitholders $ 151,796 171,675 $ 0.88 Effect of Dilutive Securities: Stock Based Compensation — 154 — Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 151,796 171,829 $ 0.88 Six months ended June 30, 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 $ 346,868 171,892 $ 2.02 Allocation of undistributed earnings to participating securities (158 ) — — Net income attributable to Boston Properties Limited Partnership common unitholders $ 346,710 171,892 $ 2.02 Effect of Dilutive Securities: Stock Based Compensation — 238 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 346,710 172,130 $ 2.01 Six months ended June 30, 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 $ 262,506 171,628 $ 1.53 Allocation of undistributed earnings to participating securities (10 ) — — Net income attributable to Boston Properties Limited Partnership common unitholders $ 262,496 171,628 $ 1.53 Effect of Dilutive Securities: Stock Based Compensation — 254 — Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 262,496 171,882 $ 1.53

Stock Option and Incentive Plan

Stock Option and Incentive Plan	6 Months Ended
Stock Option and Incentive Plan	Jun. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Option and Incentive Plan	10. Stock Option and Incentive Plan 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 at least 1,000 basis points below the index, 100% of target if the Company's TSR equals the index return, 200% of target if the Company's TSR is equal to or greater than 1,000 basis points above the index to a maximum of 200% of target value, 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. During the six months ended June 30, 2018 , Boston Properties, Inc. issued 20,320 shares of restricted common stock and Boston Properties Limited Partnership issued 205,838 LTIP Units and 342,659 2018 MYLTIP Units to employees under the 2012 Plan. Employees paid $0.01 per share of restricted common stock and $0.25 per LTIP Unit and 2018 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. The shares of restricted stock granted during the six months ended June 30, 2018 were valued at approximately $2.4 million ( $119.27 per share weighted-average). The LTIP Units granted were valued at approximately $22.7 million (approximately $110.29 per unit weighted-average fair value) using a Monte Carlo simulation method model. The per unit fair values of the LTIP Units granted were estimated on the dates of grant and for a substantial majority of such units were valued using the following assumptions: an expected life of 5.7 years , a risk-free interest rate of 2.63% and an expected price volatility of 27.0% . Because the 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units, 2015 MYLTIP Units, 2016 MYLTIP Units, 2017 MYLTIP Units and 2018 MYLTIP Units are subject to both a service condition and a market condition, the Company recognizes the related compensation expense 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. 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 $7.9 million and $7.9 million for the three months ended June 30, 2018 and 2017 , respectively, and $22.1 million and $18.1 million for the six months ended June 30, 2018 and 2017 , respectively. At June 30, 2018 , there was (1) an aggregate of approximately $31.7 million of unrecognized compensation expense related to unvested restricted stock, LTIP Units and 2015 MYLTIP Units and (2) an aggregate of approximately $22.4 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 2.6 years.

Segment Information

Segment Information	6 Months Ended
Segment Information	Jun. 30, 2018
Segment Reporting [Abstract]
Segment Information	11. 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 three and six months ended June 30, 2018 and 2017 . Boston Properties, Inc. Three months ended June 30, Six months ended June 30, 2018 2017 2018 2017 (in thousands) Net income attributable to Boston Properties, Inc. common shareholders $ 128,681 $ 133,709 $ 304,682 $ 230,764 Add: Preferred dividends 2,625 2,625 5,250 5,250 Noncontrolling interest—common units of Boston Properties Limited Partnership 14,859 15,473 35,311 26,933 Noncontrolling interests in property partnerships 14,400 15,203 31,634 19,627 Interest expense 92,204 95,143 182,424 190,677 Depreciation and amortization expense 156,417 151,919 322,214 311,124 Transaction costs 474 299 495 333 Payroll and related costs from management services contracts 1,970 — 4,855 — General and administrative expense 28,468 27,141 64,362 58,527 Less: Gains on sales of real estate 18,292 3,767 114,689 3,900 Gains from early extinguishments of debt — 14,354 — 14,354 Gains from investments in securities 505 730 379 1,772 Interest and other income 2,579 1,504 4,227 2,118 Income from unconsolidated joint ventures 769 3,108 1,230 6,192 Direct reimbursements of payroll and related costs from management services contracts 1,970 — 4,855 — Development and management services revenue 9,305 7,365 17,710 13,837 Net Operating Income $ 406,678 $ 410,684 $ 808,137 $ 801,062 Boston Properties Limited Partnership Three months ended June 30, Six months ended June 30, 2018 2017 2018 2017 (in thousands) Net income attributable to Boston Properties Limited Partnership common unitholders $ 145,961 $ 151,844 $ 346,868 $ 262,506 Add: Preferred distributions 2,625 2,625 5,250 5,250 Noncontrolling interests in property partnerships 14,400 15,203 31,634 19,627 Interest expense 92,204 95,143 182,424 190,677 Depreciation and amortization expense 154,474 149,834 318,327 306,892 Transaction costs 474 299 495 333 Payroll and related costs from management services contracts 1,970 — 4,855 — General and administrative expense 28,468 27,141 64,362 58,527 Less: Gains on sales of real estate 18,770 4,344 117,677 4,477 Gains from early extinguishments of debt — 14,354 — 14,354 Gains from investments in securities 505 730 379 1,772 Interest and other income 2,579 1,504 4,227 2,118 Income from unconsolidated joint ventures 769 3,108 1,230 6,192 Direct reimbursements of payroll and related costs from management services contracts 1,970 — 4,855 — Development and management services revenue 9,305 7,365 17,710 13,837 Net Operating Income $ 406,678 $ 410,684 $ 808,137 $ 801,062 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, interest expense, depreciation and amortization expense, transaction costs, payroll and related costs from management services contracts and corporate general and administrative expense less (2) gains on sales of real estate, gains from early extinguishments of debt, gains from investments in securities, interest and other income, 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 the Company's 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 to noncontrolling interests, interest expense, depreciation and amortization expense, transaction costs, payroll and related costs from management services contracts, corporate general and administrative expense, gains on sales of real estate, gains from early extinguishments of debt, gains from investments in securities, interest and other income, 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 three months ended June 30, 2018 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 207,810 $ 234,006 $ 93,482 $ 98,505 $ 633,803 Residential 1,195 — — 3,604 4,799 Hotel 14,607 — — — 14,607 Total 223,612 234,006 93,482 102,109 653,209 % of Grand Totals 34.23 % 35.83 % 14.31 % 15.63 % 100.00 % Rental Expenses: Office 77,147 91,838 31,214 34,678 234,877 Residential 706 — — 2,207 2,913 Hotel 8,741 — — — 8,741 Total 86,594 91,838 31,214 36,885 246,531 % of Grand Totals 35.12 % 37.26 % 12.66 % 14.96 % 100.00 % Net operating income $ 137,018 $ 142,168 $ 62,268 $ 65,224 $ 406,678 % of Grand Totals 33.69 % 34.96 % 15.31 % 16.04 % 100.00 % For the three months ended June 30, 2017 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 191,760 $ 251,844 $ 85,483 $ 102,870 $ 631,957 Residential 1,153 — — 3,057 4,210 Hotel 13,375 — — — 13,375 Total 206,288 251,844 85,483 105,927 649,542 % of Grand Totals 31.76 % 38.77 % 13.16 % 16.31 % 100.00 % Rental Expenses: Office 74,160 93,110 25,938 35,611 228,819 Residential 545 — — 1,090 1,635 Hotel 8,404 — — — 8,404 Total 83,109 93,110 25,938 36,701 238,858 % of Grand Totals 34.79 % 38.98 % 10.86 % 15.37 % 100.00 % Net operating income $ 123,179 $ 158,734 $ 59,545 $ 69,226 $ 410,684 % of Grand Totals 29.99 % 38.65 % 14.50 % 16.86 % 100.00 % For the six months ended June 30, 2018 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 412,807 $ 476,404 $ 183,375 $ 197,817 $ 1,270,403 Residential 2,347 — — 6,611 8,958 Hotel 23,709 — — — 23,709 Total 438,863 476,404 183,375 204,428 1,303,070 % of Grand Totals 33.68 % 36.56 % 14.07 % 15.69 % 100.00 % Rental Expenses: Office 157,471 185,600 58,842 71,021 472,934 Residential 1,220 — — 3,965 5,185 Hotel 16,814 — — — 16,814 Total 175,505 185,600 58,842 74,986 494,933 % of Grand Totals 35.46 % 37.50 % 11.89 % 15.15 % 100.00 % Net operating income $ 263,358 $ 290,804 $ 124,533 $ 129,442 $ 808,137 % of Grand Totals 32.59 % 35.98 % 15.41 % 16.02 % 100.00 % For the six months ended June 30, 2017 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 377,196 $ 493,414 $ 170,124 $ 205,603 $ 1,246,337 Residential 2,292 — — 5,874 8,166 Hotel 20,795 — — — 20,795 Total 400,283 493,414 170,124 211,477 1,275,298 % of Grand Totals 31.39 % 38.69 % 13.34 % 16.58 % 100.00 % Rental Expenses: Office 149,416 184,794 50,412 70,933 455,555 Residential 1,040 — — 2,146 3,186 Hotel 15,495 — — — 15,495 Total 165,951 184,794 50,412 73,079 474,236 % of Grand Totals 34.99 % 38.97 % 10.63 % 15.41 % 100.00 % Net operating income $ 234,332 $ 308,620 $ 119,712 $ 138,398 $ 801,062 % of Grand Totals 29.25 % 38.53 % 14.94 % 17.28 % 100.00 %

Subsequent Events

Subsequent Events	6 Months Ended
Subsequent Events	Jun. 30, 2018
Subsequent Events [Abstract]
Subsequent Events [Text Block]	12. Subsequent Events 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 will be 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 in the future approximately $62.2 million 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 has provided $80.0 million of mortgage financing to the joint venture which 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. On July 19, 2018, the Company completed the acquisition of Santa Monica Business Park in the Ocean Park neighborhood of Santa Monica, California for a purchase price of approximately $627.5 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 Company with the right to purchase the land underlying the properties in 2028 with subsequent purchase rights every 15 years. The acquisition was completed in a joint venture with Canada Pension Plan Investment Board, which invested approximately $147.4 million for a 45% ownership interest in the joint venture. The Company will provide customary operating, property management and leasing services to, and invested approximately $180.1 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. 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. 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 will serve as 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 August 7, 2018, the Company entered into an agreement with a third party to (1) agree to share certain pre-development costs during the pre-lease period and (2) to agree to form a joint venture to thereafter own and develop a leasehold interest in 343 Madison Avenue located in New York City. 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. The site will support a Class A office tower with approximately 900,000 net rentable square feet. There can be no assurances that the transaction will be completed on the terms currently contemplated, or at all.

Basis Of Presentation And Sum21

Basis Of Presentation And Summary Of Significant Accounting Policies Recent Accounting Pronouncements (Policies)	6 Months Ended
	Jun. 30, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Recent Accounting Pronouncement [Policy Text Block]	New 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 “Leases” (“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 three and six months ended June 30, 2018, the Company recognized approximately $2.0 million and $4.9 million , respectively, of expenses consisting of payroll and related costs from management services contracts and recognized corresponding revenue of approximately $2.0 million and $4.9 million , respectively, reflecting the direct reimbursements of such costs from the unconsolidated joint venture entities and third party property owners. 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 did not have a material impact on the Company’s consolidated financial statements. The adoption of ASU 2016-15 will result in the retrospective classification of debt prepayment costs as a component of financing activities instead of as a component of operating activities in the Company's Consolidated Statements of Cash Flows. 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 adoption of ASU 2016-18 did not have a material impact on the Company’s consolidated financial statements. The retrospective adoption of ASU 2016-18 resulted in a decrease to net cash provided by operating activities totaling approximately $7.5 million , an increase to net cash used in investing activities totaling approximately $8.2 million , a decrease to net cash provided by financing activities totaling approximately $0.1 million , and a corresponding decrease to the net increase in cash and cash equivalents and cash held in escrows totaling approximately $15.8 million from amounts previously reported for the six months ended June 30, 2017 . 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. 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 June 30, 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. ASU 2016-02 is effective for the Company for reporting periods beginning after December 15, 2018, with early adoption permitted. The Company will adopt ASU 2016-02 effective January 1, 2019 using the modified retrospective approach. The Company is in the pro cess of evaluating whether it will elect to apply the practical expedients. The Company is in the process of adopting ASU 2016-02 and its project team has compiled an inventory of its leases that will be impacted by the adoption of ASU 2016-02. The Company continues to assess the impact of adopting ASU 2016-02. However, the Company will account for operating leases under which it is the lessor on its balance sheet in a manner similar to its current accounting with t he underlying leased asset recognized as real estate. On July 30, 2018, the FASB issued ASU 2018-11, “Leases (Topic 842): Targeted Improvements” (“ASU 2018-11”), that 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. 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. The Company’s project team is evaluating this recently issued ASU 2018-11. 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 with rental payments being applied to the lease liability and to interest expense and the right-of-use asset being amortized to expense over the term of the lease. 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 legal costs and internal leasing wages and instead will be required to expense these and other non-incremental costs as incurred. 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 plans to elect this practical expedient and has gathered its inventory and is in the process of drafting procedures and controls.
Revenue Recognition, Policy [Policy Text Block]	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 “Leases” (“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 three and six months ended June 30, 2018, the Company recognized approximately $2.0 million and $4.9 million , respectively, of expenses consisting of payroll and related costs from management services contracts and recognized corresponding revenue of approximately $2.0 million and $4.9 million , respectively, reflecting the direct reimbursements of such costs from the unconsolidated joint venture entities and third party property owners.
Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block]	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 did not have a material impact on the Company’s consolidated financial statements. The adoption of ASU 2016-15 will result in the retrospective classification of debt prepayment costs as a component of financing activities instead of as a component of operating activities in the Company's Consolidated Statements of Cash Flows. 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 adoption of ASU 2016-18 did not have a material impact on the Company’s consolidated financial statements. The retrospective adoption of ASU 2016-18 resulted in a decrease to net cash provided by operating activities totaling approximately $7.5 million , an increase to net cash used in investing activities totaling approximately $8.2 million , a decrease to net cash provided by financing activities totaling approximately $0.1 million , and a corresponding decrease to the net increase in cash and cash equivalents and cash held in escrows totaling approximately $15.8 million from amounts previously reported for the six months ended June 30, 2017 . 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.
Stock Compensation [Policy Text Block]	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 [Policy Text Block]	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 June 30, 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.
Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue Recognition, Policy [Policy Text Block]	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 .

Basis Of Presentation And Sum22

Basis Of Presentation And Summary Of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Carrying Value Of Indebtedness And Corresponding Estimate Of Fair Value	The following table presents the aggregate carrying value of the Company’s mortgage notes payable, net, unsecured line of credit, unsecured term loan, net and unsecured senior notes, net and the Company’s corresponding estimate of fair value as of June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Mortgage notes payable, net $ 2,972,052 $ 2,938,167 $ 2,979,281 $ 3,042,920 Unsecured senior notes, net 7,251,578 7,188,261 7,247,330 7,461,615 Unsecured line of credit — — 45,000 45,000 Unsecured term loan, net 498,248 500,181 — — Total $ 10,721,878 $ 10,626,609 $ 10,271,611 $ 10,549,535

Real Estate (Tables)

Real Estate (Tables)	6 Months Ended
Real Estate (Tables)	Jun. 30, 2018
Entity Information [Line Items]
Schedule of Real Estate Properties [Table Text Block]	Boston Properties, Inc. Real estate consisted of the following at June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Land $ 5,108,880 $ 5,080,679 Land held for future development (1) 210,902 204,925 Buildings and improvements 12,720,779 12,284,164 Tenant improvements 2,278,755 2,219,608 Furniture, fixtures and equipment 44,164 37,928 Construction in progress 1,163,040 1,269,338 Total 21,526,520 21,096,642 Less: Accumulated depreciation (4,745,590 ) (4,589,634 ) $ 16,780,930 $ 16,507,008 _______________ (1) Includes pre-development costs.
Boston Properties Limited Partnership
Entity Information [Line Items]
Schedule of Real Estate Properties [Table Text Block]	Boston Properties Limited Partnership Real estate consisted of the following at June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Land $ 5,005,471 $ 4,976,303 Land held for future development (1) 210,902 204,925 Buildings and improvements 12,416,577 11,977,062 Tenant improvements 2,278,755 2,219,608 Furniture, fixtures and equipment 44,164 37,928 Construction in progress 1,163,040 1,269,338 Total 21,118,909 20,685,164 Less: Accumulated depreciation (4,649,907 ) (4,496,959 ) $ 16,469,002 $ 16,188,205 _______________ (1) Includes pre-development costs.

Investments in Unconsolidated24

Investments in Unconsolidated Joint Ventures (Tables)	6 Months Ended
Investments in Unconsolidated Joint Ventures (Tables)	Jun. 30, 2018
Investments In Unconsolidated Joint Ventures [Abstract]
Investments In Unconsolidated Joint Ventures	The investments in unconsolidated joint ventures consist of the following at June 30, 2018 and December 31, 2017 : Nominal % Ownership Carrying Value of Investment (1) Entity Properties June 30, 2018 December 31, 2017 (in thousands) Square 407 Limited Partnership Market Square North 50.0 % $ (7,371 ) $ (8,258 ) The Metropolitan Square Associates LLC Metropolitan Square 20.0 % 4,628 3,339 BP/CRF 901 New York Avenue LLC 901 New York Avenue 25.0 % (2) (12,824 ) (13,811 ) WP Project Developer LLC Wisconsin Place Land and Infrastructure 33.3 % (3) 39,015 39,710 Annapolis Junction NFM, LLC Annapolis Junction 50.0 % (4) 17,597 18,381 540 Madison Venture LLC 540 Madison Avenue 60.0 % 66,385 66,179 500 North Capitol Venture LLC 500 North Capitol Street, NW 30.0 % (4,416 ) (3,876 ) 501 K Street LLC 1001 6th Street 50.0 % (5) 42,646 42,657 Podium Developer LLC The Hub on Causeway 50.0 % 72,900 67,120 Residential Tower Developer LLC The Hub on Causeway - Residential 50.0 % (6) 38,958 28,212 Hotel Tower Developer LLC The Hub on Causeway - Hotel Air Rights 50.0 % 2,046 1,690 1265 Main Office JV LLC 1265 Main Street 50.0 % 4,413 4,641 BNY Tower Holdings LLC Dock 72 at the Brooklyn Navy Yard 50.0 % 71,651 72,104 CA-Colorado Center Limited Partnership Colorado Center 50.0 % 253,864 254,440 7750 Wisconsin Avenue LLC 7750 Wisconsin Avenue 50.0 % (6) 68,404 21,452 $ 657,896 $ 593,980 _______________ (1) Investments with deficit balances aggregating approximately $24.6 million and $25.9 million at June 30, 2018 and December 31, 2017 , respectively, have been reflected 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 four 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 2 ).
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: June 30, 2018 December 31, 2017 (in thousands) ASSETS Real estate and development in process, net $ 1,938,438 $ 1,768,996 Other assets 397,442 367,743 Total assets $ 2,335,880 $ 2,136,739 LIABILITIES AND MEMBERS’/PARTNERS’ EQUITY Mortgage and notes payable, net $ 1,524,951 $ 1,437,440 Other liabilities 126,179 99,215 Members’/Partners’ equity 684,750 600,084 Total liabilities and members’/partners’ equity $ 2,335,880 $ 2,136,739 Company’s share of equity $ 349,576 $ 286,495 Basis differentials (1) 308,320 307,485 Carrying value of the Company’s investments in unconsolidated joint ventures (2) $ 657,896 $ 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 June 30, 2018 and December 31, 2017 , there was an aggregate basis differential of approximately $319.7 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 $24.6 million and $25.9 million at June 30, 2018 and December 31, 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: Three months ended June 30, Six months ended June 30, 2018 2017 2018 2017 (in thousands) Total revenue (1) $ 57,096 $ 55,862 $ 113,582 $ 110,623 Expenses Operating 22,868 22,103 45,717 44,182 Depreciation and amortization 14,527 14,224 29,252 28,533 Total expenses 37,395 36,327 74,969 72,715 Operating income 19,701 19,535 38,613 37,908 Other expense Interest expense 14,708 9,427 29,132 18,727 Net income $ 4,993 $ 10,108 $ 9,481 $ 19,181 Company’s share of net income $ 2,105 $ 4,344 $ 3,931 $ 8,667 Basis differential (2) (1,336 ) (1,236 ) (2,701 ) (2,475 ) Income from unconsolidated joint ventures $ 769 $ 3,108 $ 1,230 $ 6,192 _______________ (1) Includes straight-line rent adjustments of approximately $3.2 million and $4.3 million for the three months ended June 30, 2018 and 2017 , respectively, and $5.0 million and $11.3 million for the six months ended June 30, 2018 and 2017 , respectively. (2) Includes straight-line rent adjustments of approximately $0.7 million and $0.8 million for the three months ended June 30, 2018 and 2017 , respectively, and $1.4 million and $1.5 million for the six months ended June 30, 2018 and 2017 , respectively. Also includes net above-/below-market rent adjustments of approximately $0.4 million and $0.4 million for the three months ended June 30, 2018 and 2017 , respectively, and $0.8 million and $0.9 million for the six months ended June 30, 2018 and 2017 , respectively.

Noncontrolling Interests (Table

Noncontrolling Interests (Tables)	6 Months Ended
Noncontrolling Interests (Tables)	Jun. 30, 2018
Noncontrolling Interest [Line Items]
Distributions Declared to OP, LTIP, OPP and MYLTIP Units [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 in 2018 : Record Date Payment Date Dividend (Per Share) Distribution (Per Unit) 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 Common Units [Table Text Block]	The following table reflects the activity of noncontrolling interests—redeemable partnership units of Boston Properties Limited Partnership for the six months ended June 30, 2018 and 2017 (in thousands): Balance at December 31, 2017 $ 2,292,263 Contributions 34,973 Net income 35,311 Distributions (28,708 ) Conversion of redeemable partnership units (1,196 ) Unearned compensation (13,443 ) Cumulative effect of a change in accounting principle 563 Other comprehensive income 310 Adjustment to reflect redeemable partnership units at redemption value (84,641 ) Balance at June 30, 2018 $ 2,235,432 Balance at December 31, 2016 $ 2,262,040 Contributions 31,532 Net income 26,933 Distributions (26,977 ) Conversion of redeemable partnership units (16,422 ) Unearned compensation (12,344 ) Cumulative effect of a change in accounting principle (1,763 ) Other comprehensive loss (104 ) Adjustment to reflect redeemable partnership units at redemption value (92,740 ) Balance at June 30, 2017 $ 2,170,155
Schedule Of Noncontrolling Interest Property Partnerships [Table Text Block]	The following table reflects the activity of the noncontrolling interests — property partnerships for the six months ended June 30, 2018 and 2017 (in thousands): Balance at December 31, 2017 $ 1,683,760 Capital contributions 27,532 Net income 31,634 Accumulated other comprehensive income 288 Distributions (44,033 ) Balance at June 30, 2018 $ 1,699,181 Balance at December 31, 2016 $ 1,530,647 Capital contributions 133,072 Net income 19,627 Accumulated other comprehensive loss (2,416 ) Distributions (26,949 ) Balance at June 30, 2017 $ 1,653,981
Noncontrolling Interests [Member]
Noncontrolling Interest [Line Items]
Distributions Declared to OP, LTIP, OPP and MYLTIP Units [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 and 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 6, 2018 issuance date) paid in 2018 : Record Date Payment Date Distributions per OP Unit and LTIP Unit Distributions per MYLTIP Unit 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 _ Partne26

Stockholders' Equity / Partners' Capital Tables (Tables)	6 Months Ended
Stockholders' Equity / Partners' Capital Tables (Tables)	Jun. 30, 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 in 2018 : Record Date Payment Date Dividend (Per Share) Distribution (Per Unit) 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 Cumulative Redeemable 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 during 2018 : Record Date Payment Date Dividend (Per Share) August 3, 2018 August 15, 2018 $32.8125 May 4, 2018 May 15, 2018 $32.8125 February 2, 2018 February 15, 2018 $32.8125

Earnings Per Share _ Common U27

Earnings Per Share / Common Unit (Tables)	6 Months Ended
Earnings Per Share / Common Unit (Tables)	Jun. 30, 2018
Entity Information [Line Items]
Computation Of Basic And Diluted Earnings Per Share	Three months ended June 30, 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 $ 128,681 154,415 $ 0.83 Allocation of undistributed earnings to participating securities (16 ) — — Net income attributable to Boston Properties, Inc. common shareholders $ 128,665 154,415 $ 0.83 Effect of Dilutive Securities: Stock Based Compensation — 156 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 128,665 154,571 $ 0.83 Three months ended June 30, 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 $ 133,709 154,177 $ 0.87 Allocation of undistributed earnings to participating securities (43 ) — — Net income attributable to Boston Properties, Inc. common shareholders $ 133,666 154,177 $ 0.87 Effect of Dilutive Securities: Stock Based Compensation — 154 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 133,666 154,331 $ 0.87 Six months ended June 30, 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 $ 304,682 154,400 $ 1.97 Allocation of undistributed earnings to participating securities (142 ) — — Net income attributable to Boston Properties, Inc. common shareholders $ 304,540 154,400 $ 1.97 Effect of Dilutive Securities: Stock Based Compensation — 238 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 304,540 154,638 $ 1.97 Six months ended June 30, 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 $ 230,764 154,019 $ 1.50 Allocation of undistributed earnings to participating securities (9 ) — — Net income attributable to Boston Properties, Inc. common shareholders $ 230,755 154,019 $ 1.50 Effect of Dilutive Securities: Stock Based Compensation — 254 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 230,755 154,273 $ 1.50
Boston Properties Limited Partnership
Entity Information [Line Items]
Computation Of Basic And Diluted Earnings Per Share	Three months ended June 30, 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 $ 145,961 171,916 $ 0.85 Allocation of undistributed earnings to participating securities (18 ) — — Net income attributable to Boston Properties Limited Partnership common unitholders $ 145,943 171,916 $ 0.85 Effect of Dilutive Securities: Stock Based Compensation — 156 — Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 145,943 172,072 $ 0.85 Three months ended June 30, 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 $ 151,844 171,675 $ 0.88 Allocation of undistributed earnings to participating securities (48 ) — — Net income attributable to Boston Properties Limited Partnership common unitholders $ 151,796 171,675 $ 0.88 Effect of Dilutive Securities: Stock Based Compensation — 154 — Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 151,796 171,829 $ 0.88 Six months ended June 30, 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 $ 346,868 171,892 $ 2.02 Allocation of undistributed earnings to participating securities (158 ) — — Net income attributable to Boston Properties Limited Partnership common unitholders $ 346,710 171,892 $ 2.02 Effect of Dilutive Securities: Stock Based Compensation — 238 (0.01 ) Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 346,710 172,130 $ 2.01 Six months ended June 30, 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 $ 262,506 171,628 $ 1.53 Allocation of undistributed earnings to participating securities (10 ) — — Net income attributable to Boston Properties Limited Partnership common unitholders $ 262,496 171,628 $ 1.53 Effect of Dilutive Securities: Stock Based Compensation — 254 — Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 262,496 171,882 $ 1.53

Segment Information (Tables)

Segment Information (Tables)	6 Months Ended
Segment Information (Tables)	Jun. 30, 2018
Segment Reporting [Abstract]
Schedule Of Reconciliation Of Net Operating Income To Net Income	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 three and six months ended June 30, 2018 and 2017 . Boston Properties, Inc. Three months ended June 30, Six months ended June 30, 2018 2017 2018 2017 (in thousands) Net income attributable to Boston Properties, Inc. common shareholders $ 128,681 $ 133,709 $ 304,682 $ 230,764 Add: Preferred dividends 2,625 2,625 5,250 5,250 Noncontrolling interest—common units of Boston Properties Limited Partnership 14,859 15,473 35,311 26,933 Noncontrolling interests in property partnerships 14,400 15,203 31,634 19,627 Interest expense 92,204 95,143 182,424 190,677 Depreciation and amortization expense 156,417 151,919 322,214 311,124 Transaction costs 474 299 495 333 Payroll and related costs from management services contracts 1,970 — 4,855 — General and administrative expense 28,468 27,141 64,362 58,527 Less: Gains on sales of real estate 18,292 3,767 114,689 3,900 Gains from early extinguishments of debt — 14,354 — 14,354 Gains from investments in securities 505 730 379 1,772 Interest and other income 2,579 1,504 4,227 2,118 Income from unconsolidated joint ventures 769 3,108 1,230 6,192 Direct reimbursements of payroll and related costs from management services contracts 1,970 — 4,855 — Development and management services revenue 9,305 7,365 17,710 13,837 Net Operating Income $ 406,678 $ 410,684 $ 808,137 $ 801,062 Boston Properties Limited Partnership Three months ended June 30, Six months ended June 30, 2018 2017 2018 2017 (in thousands) Net income attributable to Boston Properties Limited Partnership common unitholders $ 145,961 $ 151,844 $ 346,868 $ 262,506 Add: Preferred distributions 2,625 2,625 5,250 5,250 Noncontrolling interests in property partnerships 14,400 15,203 31,634 19,627 Interest expense 92,204 95,143 182,424 190,677 Depreciation and amortization expense 154,474 149,834 318,327 306,892 Transaction costs 474 299 495 333 Payroll and related costs from management services contracts 1,970 — 4,855 — General and administrative expense 28,468 27,141 64,362 58,527 Less: Gains on sales of real estate 18,770 4,344 117,677 4,477 Gains from early extinguishments of debt — 14,354 — 14,354 Gains from investments in securities 505 730 379 1,772 Interest and other income 2,579 1,504 4,227 2,118 Income from unconsolidated joint ventures 769 3,108 1,230 6,192 Direct reimbursements of payroll and related costs from management services contracts 1,970 — 4,855 — Development and management services revenue 9,305 7,365 17,710 13,837 Net Operating Income $ 406,678 $ 410,684 $ 808,137 $ 801,062
Schedule Of Segment Information By Geographic Area And Property Type	Information by geographic area and property type (dollars in thousands): For the three months ended June 30, 2018 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 207,810 $ 234,006 $ 93,482 $ 98,505 $ 633,803 Residential 1,195 — — 3,604 4,799 Hotel 14,607 — — — 14,607 Total 223,612 234,006 93,482 102,109 653,209 % of Grand Totals 34.23 % 35.83 % 14.31 % 15.63 % 100.00 % Rental Expenses: Office 77,147 91,838 31,214 34,678 234,877 Residential 706 — — 2,207 2,913 Hotel 8,741 — — — 8,741 Total 86,594 91,838 31,214 36,885 246,531 % of Grand Totals 35.12 % 37.26 % 12.66 % 14.96 % 100.00 % Net operating income $ 137,018 $ 142,168 $ 62,268 $ 65,224 $ 406,678 % of Grand Totals 33.69 % 34.96 % 15.31 % 16.04 % 100.00 % For the three months ended June 30, 2017 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 191,760 $ 251,844 $ 85,483 $ 102,870 $ 631,957 Residential 1,153 — — 3,057 4,210 Hotel 13,375 — — — 13,375 Total 206,288 251,844 85,483 105,927 649,542 % of Grand Totals 31.76 % 38.77 % 13.16 % 16.31 % 100.00 % Rental Expenses: Office 74,160 93,110 25,938 35,611 228,819 Residential 545 — — 1,090 1,635 Hotel 8,404 — — — 8,404 Total 83,109 93,110 25,938 36,701 238,858 % of Grand Totals 34.79 % 38.98 % 10.86 % 15.37 % 100.00 % Net operating income $ 123,179 $ 158,734 $ 59,545 $ 69,226 $ 410,684 % of Grand Totals 29.99 % 38.65 % 14.50 % 16.86 % 100.00 % For the six months ended June 30, 2018 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 412,807 $ 476,404 $ 183,375 $ 197,817 $ 1,270,403 Residential 2,347 — — 6,611 8,958 Hotel 23,709 — — — 23,709 Total 438,863 476,404 183,375 204,428 1,303,070 % of Grand Totals 33.68 % 36.56 % 14.07 % 15.69 % 100.00 % Rental Expenses: Office 157,471 185,600 58,842 71,021 472,934 Residential 1,220 — — 3,965 5,185 Hotel 16,814 — — — 16,814 Total 175,505 185,600 58,842 74,986 494,933 % of Grand Totals 35.46 % 37.50 % 11.89 % 15.15 % 100.00 % Net operating income $ 263,358 $ 290,804 $ 124,533 $ 129,442 $ 808,137 % of Grand Totals 32.59 % 35.98 % 15.41 % 16.02 % 100.00 % For the six months ended June 30, 2017 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 377,196 $ 493,414 $ 170,124 $ 205,603 $ 1,246,337 Residential 2,292 — — 5,874 8,166 Hotel 20,795 — — — 20,795 Total 400,283 493,414 170,124 211,477 1,275,298 % of Grand Totals 31.39 % 38.69 % 13.34 % 16.58 % 100.00 % Rental Expenses: Office 149,416 184,794 50,412 70,933 455,555 Residential 1,040 — — 2,146 3,186 Hotel 15,495 — — — 15,495 Total 165,951 184,794 50,412 73,079 474,236 % of Grand Totals 34.99 % 38.97 % 10.63 % 15.41 % 100.00 % Net operating income $ 234,332 $ 308,620 $ 119,712 $ 138,398 $ 801,062 % of Grand Totals 29.25 % 38.53 % 14.94 % 17.28 % 100.00 %

Organization (Details)

Organization (Details) ft² in Millions	6 Months Ended	12 Months Ended
Organization (Details) ft² in Millions	Jun. 30, 2018ft²seriesReal_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 \| series	1
Commercial Real Estate Properties [Member]
Real Estate Properties [Line Items]
Number of real estate properties	178
Net Rentable Area (in sf) \| ft²	50.2
Total Properties Under Construction [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	12
Net Rentable Area (in sf) \| ft²	6
Total Office Properties [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	166
Office Properties Under Construction [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	9
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	3
Retail Properties [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	5
Hotel Property [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	1
Series B Cumulative Redeemable Preferred Stock [Member]
Real Estate Properties [Line Items]
Ratio of depository shares to shares of Series B Preferred Stock	0.01
Series B, Shares Outstanding (in shares) \| shares	80,000	80,000
Series B, Dividend Rate, Percentage	5.25%
Depository shares of Series B Cumulative Redeemable Preferred [Member]
Real Estate Properties [Line Items]
Series B, Shares Outstanding (in shares) \| shares	8,000,000
Series B Preferred Units [Member]
Real Estate Properties [Line Items]
Series B, Shares Outstanding (in shares) \| shares	80,000

Basis Of Presentation And Sum30

Basis Of Presentation And Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Entity Information [Line Items]
Payroll and related costs from management services contracts	$ 1,970	$ 0	$ 4,855	$ 0
Direct reimbursements of payroll and related costs from management services contracts	1,970	0	4,855	0
Net Cash Provided by (Used in) Operating Activities			560,846	364,809
Cumulative effect of a change in accounting principle			5,496	(2,035)
Net Cash Provided by (Used in) Investing Activities			485,801	547,678
Net Cash Provided by (Used in) Financing Activities			(146,646)	(302,561)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect			(221,691)	(119,692)
Interest Expense	92,204	95,143	182,424	190,677
Boston Properties Limited Partnership
Entity Information [Line Items]
Payroll and related costs from management services contracts	1,970	0	4,855	0
Direct reimbursements of payroll and related costs from management services contracts	1,970	0	4,855	0
Net Cash Provided by (Used in) Operating Activities			560,846	364,809
Cumulative effect of a change in accounting principle			4,933	(272)
Net Cash Provided by (Used in) Investing Activities			485,801	547,678
Net Cash Provided by (Used in) Financing Activities			(146,646)	(302,561)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect			(221,691)	(119,692)
Interest Expense	92,204	$ 95,143	182,424	190,677
Dividends In Excess Of Earnings [Member]
Entity Information [Line Items]
Cumulative effect of a change in accounting principle			4,933	(272)
Noncontrolling Interests [Member]
Entity Information [Line Items]
Cumulative effect of a change in accounting principle			563	(1,763)
Noncontrolling Interests [Member] \| Boston Properties Limited Partnership
Entity Information [Line Items]
Cumulative effect of a change in accounting principle			563	(1,763)
Accounting Standards Update 2014-09 [Member]
Entity Information [Line Items]
Payroll and related costs from management services contracts	2,000		4,900
Direct reimbursements of payroll and related costs from management services contracts	2,000		4,900
Cumulative effect of a change in accounting principle			4,900
Accounting Standards Update 2014-09 [Member] \| Boston Properties Limited Partnership
Entity Information [Line Items]
Cumulative effect of a change in accounting principle			4,900
Accounting Standards Update 2014-09 [Member] \| Noncontrolling Interests [Member]
Entity Information [Line Items]
Cumulative effect of a change in accounting principle			600
Accounting Standards Update 2014-09 [Member] \| Noncontrolling Interests [Member] \| Boston Properties Limited Partnership
Entity Information [Line Items]
Cumulative effect of a change in accounting principle			$ 600
Accounting Standards Update 2016-18 [Member]
Entity Information [Line Items]
Net Cash Provided by (Used in) Operating Activities				(7,500)
Net Cash Provided by (Used in) Investing Activities				8,200
Net Cash Provided by (Used in) Financing Activities				100
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect				$ 15,800
Accounting Standards Update 2017-12 [Member]
Entity Information [Line Items]
Interest Expense	$ 1,700

Basis Of Presentation And Sum31

Basis Of Presentation And Summary Of Significant Accounting Policies (Carrying Value Of Indebtedness And Corresponding Estimate Of Fair Value) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Summary Of Significant Accounting Policies [Line Items]
Mortgage notes payable, net	$ 2,972,052	$ 2,979,281
Unsecured senior notes, net	7,251,578	7,247,330
Unsecured line of credit	0	45,000
Unsecured term loan, net	498,248	0
Carrying Amount [Member]
Summary Of Significant Accounting Policies [Line Items]
Mortgage notes payable, net	2,972,052	2,979,281
Unsecured senior notes, net	7,251,578	7,247,330
Unsecured line of credit	0	45,000
Unsecured term loan, net	498,248	0
Total	10,721,878	10,271,611
Estimated Fair Value [Member]
Summary Of Significant Accounting Policies [Line Items]
Mortgage notes payable, net	2,938,167	3,042,920
Unsecured senior notes, net	7,188,261	7,461,615
Unsecured line of credit	0	45,000
Unsecured term loan, net	500,181	0
Total	$ 10,626,609	$ 10,549,535

Real Estate Properties Table (D

Real Estate Properties Table (Details) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land		$ 5,108,880	$ 5,080,679
Land held for future development	[1]	210,902	204,925
Buildings and improvements		12,720,779	12,284,164
Tenant improvements		2,278,755	2,219,608
Furniture, fixtures and equipment		44,164	37,928
Construction in Progress		1,163,040	1,269,338
Total		21,526,520	21,096,642
Accumulated depreciation		(4,745,590)	(4,589,634)
Total real estate		16,780,930	16,507,008
Boston Properties Limited Partnership
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land		5,005,471	4,976,303
Land held for future development	[1]	210,902	204,925
Buildings and improvements		12,416,577	11,977,062
Tenant improvements		2,278,755	2,219,608
Furniture, fixtures and equipment		44,164	37,928
Construction in Progress		1,163,040	1,269,338
Total		21,118,909	20,685,164
Accumulated depreciation		(4,649,907)	(4,496,959)
Total real estate		$ 16,469,002	$ 16,188,205

[1]	Includes pre-development costs.

Real Estate Narrative (Details)

Real Estate Narrative (Details) $ in Thousands

May 24, 2018USD ($)ft²

Feb. 23, 2018ft²

Jan. 09, 2018USD ($)ft²

Jan. 08, 2018USD ($)

May 23, 2018USD ($)

Jun. 30, 2018USD ($)

Jun. 30, 2017USD ($)

May 23, 2018USD ($)

Jun. 30, 2018USD ($)

Jun. 30, 2017USD ($)

Jun. 20, 2018ft²apartments

Jun. 07, 2018ft²apartments

Jan. 24, 2018ft²

Real Estate [Line Items]

Proceeds from sales of real estate

$ 141,249

$ 17,049

Gains on sales of real estate

$ 18,292

$ 3,767

114,689

3,900

17Fifty Presidents Street [Member]

Real Estate [Line Items]

Net Rentable Area (in sf) | ft²

276,000

Signature at Reston [Member]

Real Estate [Line Items]

Net Rentable Area (in sf) | ft²

518,000

Number of apartment units | apartments

508

Reston Gateway [Member]

Real Estate [Line Items]

Net Rentable Area (in sf) | ft²

1,100,000

Square Footage Of Signed Lease | ft²

850,000

Proto Kendall Square [Member]

Real Estate [Line Items]

Net Rentable Area (in sf) | ft²

167,000

Number of apartment units | apartments

280

Boston Properties Limited Partnership

Real Estate [Line Items]

Proceeds from sales of real estate

141,249

17,049

Gains on sales of real estate

$ 18,770

4,344

$ 117,677

4,477

500 E Street [Member]

Real Estate [Line Items]

Net Rentable Area (in sf) | ft²

262,000

Net Contractual Sales Price

$ 118,600

Net income (loss)

$ 100

1,600

3,200

Proceeds from sales of real estate

116,100

Gains on sales of real estate

96,400

500 E Street [Member] | Boston Properties Limited Partnership

Real Estate [Line Items]

Gains on sales of real estate

$ 98,900

91 Hartwell Avenue [Member]

Real Estate [Line Items]

Net Rentable Area (in sf) | ft²

119,000

Gross Sale Price

$ 22,200

Net income (loss)

$ 100

$ 300

Proceeds from sales of real estate

21,700

Gains on sales of real estate

15,500

91 Hartwell Avenue [Member] | Boston Properties Limited Partnership

Real Estate [Line Items]

Gains on sales of real estate

$ 15,900

Investments in Unconsolidated34

Investments in Unconsolidated Joint Ventures (Investments in Unconsolidated Joint Ventures) (Details) $ in Thousands		6 Months Ended
		Jun. 30, 2018USD ($)ft²Land_ParcelsBuildingspayments	Dec. 31, 2017USD ($)
Schedule of Equity Method Investments [Line Items]
Mortgage notes payable, net		$ 2,972,052	$ 2,979,281
Carrying Value of investment		(462,869)	(443,980)
Carrying value of the Company's investments in unconsolidated joint ventures		$ 682,507	619,925
Square 407 Limited Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Market Square North
Ownership Percentage		50.00%
Carrying Value of investment	[1]	$ (7,371)	(8,258)
The Metropolitan Square Associates LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Metropolitan Square
Ownership Percentage		20.00%
Carrying value of the Company's investments in unconsolidated joint ventures	[1]	$ 4,628	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%
Carrying Value of investment	[1]	$ (12,824)	(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%
Carrying value of the Company's investments in unconsolidated joint ventures	[1]	$ 39,015	39,710
Annapolis Junction NFM, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Annapolis Junction
Ownership Percentage	[4]	50.00%
Carrying value of the Company's investments in unconsolidated joint ventures	[1]	$ 17,597	18,381
Number of real estate properties \| Buildings		4
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%
Carrying value of the Company's investments in unconsolidated joint ventures	[1]	$ 66,385	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%
Carrying Value of investment	[1]	$ (4,416)	(3,876)
501 K Street LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		1001 6th Street
Ownership Percentage	[5]	50.00%
Carrying value of the Company's investments in unconsolidated joint ventures	[1]	$ 42,646	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
Ownership Percentage		50.00%
Carrying value of the Company's investments in unconsolidated joint ventures	[1]	$ 72,900	67,120
Residential Tower Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		The Hub on Causeway - Residential
Ownership Percentage	[6]	50.00%
Carrying value of the Company's investments in unconsolidated joint ventures	[1]	$ 38,958	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%
Carrying value of the Company's investments in unconsolidated joint ventures	[1]	$ 2,046	1,690
1265 Main Office JV LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		1265 Main Street
Ownership Percentage		50.00%
Carrying value of the Company's investments in unconsolidated joint ventures	[1]	$ 4,413	4,641
BNY Tower Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Dock 72 at the Brooklyn Navy Yard
Ownership Percentage		50.00%
Carrying value of the Company's investments in unconsolidated joint ventures	[1]	$ 71,651	72,104
CA-Colorado Center Limited Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Properties		Colorado Center
Ownership Percentage		50.00%
Carrying value of the Company's investments in unconsolidated joint ventures	[1]	$ 253,864	254,440
7750 Wisconsin Avenue LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties		7750 Wisconsin Avenue
Ownership Percentage	[6]	50.00%
Carrying value of the Company's investments in unconsolidated joint ventures	[1]	$ 68,404	21,452
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Carrying Value of investment		24,600	25,900
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Mortgage notes payable, net		1,524,951	1,437,440
Carrying Value of investment		(126,179)	(99,215)
Carrying value of the Company's investments in unconsolidated joint ventures	[1],[7]	$ 657,896	$ 593,980

[1]	Investments with deficit balances aggregating approximately $24.6 million and $25.9 million at June 30, 2018 and December 31, 2017, respectively, have been reflected 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 four 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 2).
[7]	Investments with deficit balances aggregating approximately $24.6 million and $25.9 million at June 30, 2018 and December 31, 2017, respectively, have been reflected within Other Liabilities in the Company’s Consolidated Balance Sheet

Investments in Unconsolidated35

Investments in Unconsolidated Joint Ventures (Balance Sheets of the Unconsolidated Joint Ventures) (Details) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
ASSETS
Real estate and development in process, net		$ 16,780,930	$ 16,507,008
Liabilities and Members'/Partners' Equity [Abstract]
Mortgage notes payable, net		2,972,052	2,979,281
Other Liabilities		462,869	443,980
Total liabilities and equity / capital		19,961,163	19,372,233
Carrying value of the Company's investments in unconsolidated joint ventures		682,507	619,925
Unconsolidated Joint Ventures [Member]
ASSETS
Real estate and development in process, net		1,938,438	1,768,996
Other assets		397,442	367,743
Total assets		2,335,880	2,136,739
Liabilities and Members'/Partners' Equity [Abstract]
Mortgage notes payable, net		1,524,951	1,437,440
Other Liabilities		126,179	99,215
Members'/Partners' equity		684,750	600,084
Total liabilities and equity / capital		2,335,880	2,136,739
Company's share of equity		349,576	286,495
Basis differentials	[1]	308,320	307,485
Carrying value of the Company's investments in unconsolidated joint ventures	[2],[3]	657,896	593,980
Unconsolidated Joint Ventures [Member]
Liabilities and Members'/Partners' Equity [Abstract]
Other Liabilities		(24,600)	(25,900)
Basis differentials		$ 319,700	$ 322,500

[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 June 30, 2018 and December 31, 2017, there was an aggregate basis differential of approximately $319.7 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 $24.6 million and $25.9 million at June 30, 2018 and December 31, 2017, respectively, have been reflected within Other Liabilities in the Company’s Consolidated Balance Sheet
[3]	Investments with deficit balances aggregating approximately $24.6 million and $25.9 million at June 30, 2018 and December 31, 2017, respectively, have been reflected within Other Liabilities in the Company’s Consolidated Balance Sheets.

Investments in Unconsolidated36

Investments in Unconsolidated Joint Ventures (Statements of Operations of the Joint Ventures) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Schedule of Equity Method Investments [Line Items]
Total revenue		$ 664,484	$ 656,907	$ 1,325,635	$ 1,289,135
Expenses
Depreciation and amortization		156,417	151,919	322,214	311,124
Total expenses		433,860	418,217	886,859	844,220
Operating income		230,624	238,690	438,776	444,915
Other expense
Interest expense		92,204	95,143	182,424	190,677
Net income		160,565	167,010	376,877	282,574
Income from unconsolidated joint ventures		769	3,108	1,230	6,192
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Total revenue	[1]	57,096	55,862	113,582	110,623
Expenses
Operating		22,868	22,103	45,717	44,182
Depreciation and amortization		14,527	14,224	29,252	28,533
Total expenses		37,395	36,327	74,969	72,715
Operating income		19,701	19,535	38,613	37,908
Other expense
Interest expense		14,708	9,427	29,132	18,727
Net income		4,993	10,108	9,481	19,181
Company's share of net income		2,105	4,344	3,931	8,667
Basis differential	[2]	(1,336)	(1,236)	(2,701)	(2,475)
Income from unconsolidated joint ventures		769	3,108	1,230	6,192
Straight-line rent adjustments		3,200	4,300	5,000	11,300
Colorado Center [Member] \| Unconsolidated Joint Ventures [Member]
Other expense
Straight-line rent adjustments		700	800	1,400	1,500
"Above" and "below" market rent adjustments, net		$ 400	$ 400	$ 800	$ 900

[1]	Includes straight-line rent adjustments of approximately $3.2 million and $4.3 million for the three months ended June 30, 2018 and 2017, respectively, and $5.0 million and $11.3 million for the six months ended June 30, 2018 and 2017
[2]	Includes straight-line rent adjustments of approximately $0.7 million and $0.8 million for the three months ended June 30, 2018 and 2017, respectively, and $1.4 million and $1.5 million for the six months ended June 30, 2018 and 2017, respectively. Also includes net above-/below-market rent adjustments of approximately $0.4 million and $0.4 million for the three months ended June 30, 2018 and 2017, respectively, and $0.8 million and $0.9 million for the six months ended June 30, 2018 and 2017

Investments in Unconsolidated37

Investments in Unconsolidated Joint Ventures Narrative (Details) $ in Thousands	Apr. 27, 2018USD ($)ft²	Apr. 26, 2018	Apr. 19, 2018USD ($)ft²yrapartments	Jun. 30, 2018USD ($)	Dec. 31, 2017USD ($)
Schedule of Equity Method Investments [Line Items]
Mortgage notes payable, net				$ 2,972,052	$ 2,979,281
The Hub on Causeway - Residential [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage			50.00%
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
Net Rentable Area (in sf) \| ft²			320,000
Number of apartment units \| apartments			440
540 Madison Avenue [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage	60.00%
Mortgage notes payable, net	$ 120,000
Debt Instrument, Basis Spread on Variable Rate	1.10%	1.50%
Net Rentable Area (in sf) \| ft²	284,000

Debt (Details)

Debt (Details) - USD ($) $ in Thousands	6 Months Ended
Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Apr. 24, 2018	Dec. 31, 2017	Apr. 24, 2017	Apr. 23, 2017
Debt Instrument [Line Items]
Unsecured term loan, net	$ 498,248		$ 0
Long-term Line of Credit	$ 0		$ 45,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity				$ 1,500,000	$ 1,000,000
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.125%
Letters of Credit Outstanding, Amount	$ 1,600
Line of Credit Facility, Remaining Borrowing Capacity	$ 1,500,000
Delayed Draw Facility [Member]
Debt Instrument [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	$ 500,000
Interest Rate Based on LIBOR or CDOR [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Margin added to Calculated Interest Rate	0.825%
Interest Rate Based on LIBOR or CDOR [Member] \| Delayed Draw Facility [Member]
Debt Instrument [Line Items]
Margin added to Calculated Interest Rate	0.90%	0.90%

Commitments And Contingencies (

Commitments And Contingencies (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2009	May 19, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jan. 10, 2014
Commitments And Contingencies [Line Items]
Letter of credit and performance obligations	$ 9.3
Property insurance program per occurrence limits	1,000
Per occurrence limit for NBCR Coverage	1,000
Value of program trigger	$ 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	144.7
Property insurance program per occurrence limits	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			$ 0.4	$ 1.4	$ 8.1	$ 7.7
Bankruptcy remaining claim amount allowed by court to creditor	27.6
601 Lexington Avenue [Member]
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

Noncontrolling Interests (Narra

Noncontrolling Interests (Narrative) (Details) - Boston Properties Limited Partnership	Jun. 30, 2018shares
Noncontrolling Interests [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Operating Partnership (OP) Units (in shares)	16,831,182
Long-Term Incentive Plan (LTIP) Units (in shares)	992,387
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
2013 MYLTIP [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2013 MYLTIP (in units)	68,889
2014 MYLTIP [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2014 MYLTIP (in units)	23,187
2015 MYLTIP [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2015 MYLTIPS (in units)	28,724
2016 MYLTIP [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2016 MYLTIPs (in units)	471,579
2017 MYLTIP [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2017 MYLTIP (in units)	398,871
2018 MYLTIP [Member]
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 ($)shares	Jun. 30, 2018USD ($)sharesyr$ / shares
OP Units [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
OP Units for redemption (in shares)		34,741
Redemption of OP units issued on conversion of LTIP Units (in shares)		31,741
Restriction on redemption of OP Unit to Common Stock (in years) \| yr		1
Redemption of OP Unit equivalent to Common Stock (in shares)		1
Common units of operating partnership if converted value \| $		$ 2,200
Closing price of common stock (in dollars per share) \| $ / shares		$ 125.42
2015 MYLTIP [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
2015 MYLTIP Units Forfeited	337,847
Boston Properties Limited Partnership \| OP Units [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
MYLTIP distribution prior to measurement date		10.00%
Boston Properties Limited Partnership \| 2016 MYLTIP [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2016 MYLTIPs (in units)		471,579
Boston Properties Limited Partnership \| 2017 MYLTIP [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
2017 MYLTIP (in units)		398,871
Boston Properties Limited Partnership \| 2018 MYLTIP [Member]
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	Apr. 30, 2018	Jan. 30, 2018	Jun. 14, 2018
Dividends Payable [Line Items]
Distributions Declared To OP And LTIP Units Per Unit			$ 0.80
Distributions Declared To MYLTIP Units Per Unit (in dollars per unit)			$ 0.080
Distributions made to OP and LTIP units per unit (in dollars per unit)	$ 0.80	$ 0.80
Distribution paid to MYLTIP Units (in dollars per unit)	$ 0.080	$ 0.080

Noncontrolling Interests Comm43

Noncontrolling Interests Common units for Boston Properties Limited Partnership (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Noncontrolling Interest [Line Items]
Conversion of redeemable partnership units		$ 0
Cumulative effect of a change in accounting principle	$ 5,496	(2,035)
Other comprehensive income (loss)	(47,695)		$ (50,429)
Noncontrolling Interests [Member]
Noncontrolling Interest [Line Items]
Conversion of redeemable partnership units	11,328	10,840
Cumulative effect of a change in accounting principle	563	(1,763)
Boston Properties Limited Partnership
Noncontrolling Interest [Line Items]
Cumulative effect of a change in accounting principle	4,933	(272)
Boston Properties Limited Partnership \| Noncontrolling Interests [Member]
Noncontrolling Interest [Line Items]
Beginning balance	2,292,263	2,262,040
Contributions	34,973	31,532
Net income	35,311	26,933
Distributions	(28,708)	(26,977)
Conversion of redeemable partnership units	(1,196)	(16,422)
Unearned compensation	(13,443)	(12,344)
Cumulative effect of a change in accounting principle	563	(1,763)
Other comprehensive income (loss)	310	(104)
Adjustments to reflect redeemable preferred units at redemption value	(84,641)	(92,740)
Ending balance	$ 2,235,432	$ 2,170,155

Noncontrolling Interests (Prope

Noncontrolling Interests (Property Partnerships) (Narrative) (Details) - USD ($) $ in Thousands	May 12, 2016	Jun. 30, 2018	Dec. 31, 2017
Noncontrolling Interest [Line Items]
Noncontrolling Interest in Limited Partnerships		$ 1,699,181	$ 1,683,760
Salesforce Tower[Member] \| Consolidated Properties [Member]
Noncontrolling Interest [Line Items]
Portion of project costs covered by a construction loan	50.00%
Portion of costs funded (in percentage)	50.00%
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners	5.00%
Debt Instrument, Basis Spread on Variable Rate	3.00%
Salesforce Tower[Member] \| Parent Company [Member] \| Consolidated Properties [Member]
Noncontrolling Interest [Line Items]
Costs funded (in percentage)	2.50%
Preferred equity funded		$ 20,700

Noncontrolling Interests Proper

Noncontrolling Interests Property Partnerships (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Activity of Noncontrolling Interests [Roll Forward]
Beginning Balance			$ 1,683,760
Capital contributions			(27,532)	$ (133,072)
Net income	$ 14,400	$ 15,203	31,634	19,627
Accumulated other comprehensive income	(299)	2,738	(598)	2,520
Ending Balance	1,699,181		1,699,181
Property Partnerships Member
Activity of Noncontrolling Interests [Roll Forward]
Beginning Balance			1,683,760	1,530,647
Capital contributions			27,532	133,072
Net income			31,634	19,627
Accumulated other comprehensive income			288	(2,416)
Distributions			(44,033)	(26,949)
Ending Balance	$ 1,699,181	$ 1,653,981	$ 1,699,181	$ 1,653,981

Stockholders' Equity _ Partne46

Stockholders' Equity / Partners' Capital Narrative (Details)	Jun. 02, 2017USD ($)yr	Jun. 30, 2018USD ($)$ / sharesshares	Mar. 27, 2018$ / shares	Dec. 31, 2017USD ($)$ / sharesshares	Jun. 03, 2014USD ($)
Class of Stock [Line Items]
Common stock, shares outstanding		154,411,529		154,325,286
General Partners' Capital Account, Units Outstanding		1,722,351
Limited Partners' Capital Account, Units Outstanding		152,689,178
Shares of Common Stock in connection with the redemption of an equal number of OP Units (in shares)		34,741
Common Stock, Value, Issued \| $		$ 1,544,000		$ 1,543,000
ATM Program [Member]
Class of Stock [Line Items]
At the market stock offering program, aggregate value of common stock \| $	$ 600,000,000				$ 600,000,000
At Market Stock Offering Program Maximum Length Of Sale In Years \| yr	3
Common Stock, Value, Issued \| $		$ 0
Series B Cumulative Redeemable Preferred Stock [Member]
Class of Stock [Line Items]
Series B, Shares Outstanding (in shares)		80,000		80,000
Series B, Dividend Rate, Percentage		5.25%
Series B, Liquidation Preference Per Share (dollars per share) \| $ / shares		$ 2,500	$ 2,500	$ 2,500
Ratio of depository shares to shares of Series B Preferred Stock		0.01
Depository shares of Series B Cumulative Redeemable Preferred [Member]
Class of Stock [Line Items]
Series B, Shares Outstanding (in shares)		8,000,000
Series B, Liquidation Preference Per Share (dollars per share) \| $ / shares		$ 25	$ 25
Boston Properties Limited Partnership
Class of Stock [Line Items]
General Partners' Capital Account, Units Outstanding		1,722,351		1,719,540
Limited Partners' Capital Account, Units Outstanding		152,689,178		152,605,746
Boston Properties Limited Partnership \| Series B Cumulative Redeemable Preferred Stock [Member]
Class of Stock [Line Items]
Series B, Shares Outstanding (in shares)		80,000		80,000
Series B, Liquidation Preference Per Share (dollars per share) \| $ / shares		$ 2,500		$ 2,500

Stockholders' Equity _ Partne47

Stockholders' Equity / Partners' Capital Stockholders' Equity / Partners' Capital Dividends / Distributions (Details) - $ / shares	May 15, 2018	Apr. 30, 2018	Feb. 15, 2018	Jan. 30, 2018	Jun. 14, 2018
Entity Information [Line Items]
Dividends Payable, Amount Per Share / Unit					$ 0.80
Dividends, Per Share / Unit		$ 0.80		$ 0.80
Boston Properties Limited Partnership
Entity Information [Line Items]
Dividends Payable, Amount Per Share / Unit					0.80
Dividends, Per Share / Unit		$ 0.80		$ 0.80
Series B Cumulative Redeemable Preferred Stock [Member]
Entity Information [Line Items]
Dividends Payable, Amount Per Share / Unit					$ 32.8125
Dividends, Per Share / Unit	$ 32.8125		$ 32.8125

Earnings Per Share _ Common U48

Earnings Per Share / Common Unit (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Basic Earnings:
Net income attributable to the Company's common shareholders / unitholders	$ 128,681	$ 133,709	$ 304,682	$ 230,764
Net income attributable to the Company's common shareholders / unitholders (in shares / units)	154,415,000	154,177,000	154,400,000	154,019,000
Net income (in dollars per share / unit)	$ 0.83	$ 0.87	$ 1.97	$ 1.50
Allocation of undistributed earnings to participating securities (numerator)	$ (16)	$ (43)	$ (142)	$ (9)
Allocation of undistributed earnings to participating securities (in shares)	0	0	0	0
Allocation of undistributed earnings to participating securities (in dollars per shares / units)	$ 0	$ 0	$ 0	$ 0
Net income attributable to the Company's common shareholders / unitholders	$ 128,665	$ 133,666	$ 304,540	$ 230,755
Net income attributable to the Company's common shareholders / unitholders (in shares / units)	154,415,000	154,177,000	154,400,000	154,019,000
Net income attributable to the Company's common shareholders / unitholders (in dollars per share / unit)	$ 0.83	$ 0.87	$ 1.97	$ 1.50
Effect of Dilutive Securities:
Stock Based Compensation, Income (Numerator)	$ 0	$ 0	$ 0	$ 0
Stock Based Compensation, Shares / Units (Denominator)	156,000	154,000	238,000	254,000
Stock Based Compensation, Per Share / Unit Amount (in dollars per share / unit)	$ 0	$ 0	$ 0	$ 0
Diluted Earnings:
Net income attributable to the Company's common shareholders / unitholders (Numerator)	$ 128,665	$ 133,666	$ 304,540	$ 230,755
Net income attributable to to the Company's shareholders / unitholder (number of shares)	154,571,000	154,331,000	154,638,000	154,273,000
Diluted Earnings: Net income, Per Share Amount (in dollars per share / unit)	$ 0.83	$ 0.87	$ 1.97	$ 1.50
Boston Properties Limited Partnership
Entity Information [Line Items]
Redeemable Common Units	17,501,000	17,498,000	17,492,000	17,609,000
Basic Earnings:
Net income attributable to the Company's common shareholders / unitholders	$ 145,961	$ 151,844	$ 346,868	$ 262,506
Net income attributable to the Company's common shareholders / unitholders (in shares / units)	171,916,000	171,675,000	171,892,000	171,628,000
Net income (in dollars per share / unit)	$ 0.85	$ 0.88	$ 2.02	$ 1.53
Allocation of undistributed earnings to participating securities (numerator)	$ (18)	$ (48)	$ (158)	$ (10)
Allocation of undistributed earnings to participating securities (in shares)	0	0	0	0
Allocation of undistributed earnings to participating securities (in dollars per shares / units)	$ 0	$ 0	$ 0	$ 0
Net income attributable to the Company's common shareholders / unitholders	$ 145,943	$ 151,796	$ 346,710	$ 262,496
Net income attributable to the Company's common shareholders / unitholders (in shares / units)	171,916,000	171,675,000	171,892,000	171,628,000
Net income attributable to the Company's common shareholders / unitholders (in dollars per share / unit)	$ 0.85	$ 0.88	$ 2.02	$ 1.53
Effect of Dilutive Securities:
Stock Based Compensation, Income (Numerator)	$ 0	$ 0	$ 0	$ 0
Stock Based Compensation, Shares / Units (Denominator)	156,000	154,000	238,000	254,000
Stock Based Compensation, Per Share / Unit Amount (in dollars per share / unit)	$ 0	$ 0	$ (0.01)	$ 0
Diluted Earnings:
Net income attributable to the Company's common shareholders / unitholders (Numerator)	$ 145,943	$ 151,796	$ 346,710	$ 262,496
Net income attributable to to the Company's shareholders / unitholder (number of shares)	172,072,000	171,829,000	172,130,000	171,882,000
Diluted Earnings: Net income, Per Share Amount (in dollars per share / unit)	$ 0.85	$ 0.88	$ 2.01	$ 1.53

Stock Option and Incentive Pl49

Stock Option and Incentive Plan Stock Option and Incentive Plan (Narrative) (Details) $ in Millions	Feb. 06, 2018USD ($)yr	Feb. 04, 2018USD ($)shares
2018 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
TSR Measurement, Years \| yr	3
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%
Distributions Percent Before Measurement Date	10.00%
Value of MYLTIP Awards \| $	$ 13.3
MYLTIP Value Amortized Into Earnings, Years \| yr	4
2015 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value of MYLTIP Awards \| $		$ 3.6
Final awards percentage of target		22.00%
2015 MYLTIP Units Forfeited \| shares		337,847
Cohen & Steers Realty Majors Portfolio Index [Member] \| 2018 MYLTIP [Member]
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] \| 2018 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Percentage of Index Used to Compare to TSR	50.00%
MYLTIP vesting 2022 [Member] \| 2018 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Percentage	50.00%
MYLTIP vesting 2021 [Member] \| 2018 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Percentage	50.00%

Stock Option and Incentive Pl50

Stock Option and Incentive Plan Restricted Stock (Narrative) (Details) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018USD ($)$ / sharesshares	Jun. 30, 2017USD ($)	Jun. 30, 2018USD ($)VestingInstallments$ / sharesshares	Jun. 30, 2017USD ($)	Dec. 31, 2017USD ($)shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued \| shares	154,490,429		154,490,429		154,404,186
Common Stock, Value, Issued	$ 1,544		$ 1,544		$ 1,543
Stock based compensation expense	$ 7,900	$ 7,900	$ 22,100	$ 18,100
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued \| shares	20,320		20,320
Employee and director payment per share (in dollars per share) \| $ / shares			$ 0.01
Common Stock, Value, Issued	$ 2,400		$ 2,400
Employee's weighted average cost per share (in dollars per share) \| $ / shares	$ 119.27		$ 119.27
LTIPs (including vested 2012 OPP Awards and vested MYLTIPS) And Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting annual installments \| VestingInstallments			4
Unrecognized compensation expenses	$ 31,700		$ 31,700
Unvested MYLTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expenses	$ 22,400		$ 22,400
Weighted-average period (years)	2 years 7 months 6 days
Boston Properties Limited Partnership \| LTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
LTIP units issued (in shares) \| shares	205,838		205,838
Value of LTIP units issued			$ 22,700
Per unit fair value weighted-average (in dollars per share) \| $ / shares	$ 110.29		$ 110.29
Expected life assumed to calculate per unit fair value per LTIP unit (years)			5 years 8 months 12 days
Risk-free rate			2.63%
Expected price volatility			27.00%
Boston Properties Limited Partnership \| 2018 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
MYLTIP units issued (in shares) \| shares	342,659		342,659
Boston Properties Limited Partnership \| LTIPs and 2018 MYLTIP Units [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

Segment Information (Schedule O

Segment Information (Schedule Of Reconciliation Of Net Operating Income To Net Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net income attributable to the Company's common shareholders / unitholders	$ 128,681	$ 133,709	$ 304,682	$ 230,764
Preferred Stock Dividends / Distributions	(2,625)	(2,625)	(5,250)	(5,250)
Noncontrolling interest-common units of the Operating Partnership	(14,859)	(15,473)	(35,311)	(26,933)
Noncontrolling interest in property partnerships	(14,400)	(15,203)	(31,634)	(19,627)
Interest expense	(92,204)	(95,143)	(182,424)	(190,677)
Depreciation and amortization expense	(156,417)	(151,919)	(322,214)	(311,124)
Transaction costs	(474)	(299)	(495)	(333)
Payroll and related costs from management services contracts	(1,970)	0	(4,855)	0
General and administrative expense	(28,468)	(27,141)	(64,362)	(58,527)
Gains from early extinguishments of debt	0	(14,354)	0	(14,354)
Gains from investments in securities	(505)	(730)	(379)	(1,772)
Interest and other income	(2,579)	(1,504)	(4,227)	(2,118)
Income from unconsolidated joint ventures	(769)	(3,108)	(1,230)	(6,192)
Direct reimbursements of payroll and related costs from management services contracts	(1,970)	0	(4,855)	0
Development and management services income	(9,305)	(7,365)	(17,710)	(13,837)
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	128,681	133,709	304,682	230,764
Preferred Stock Dividends / Distributions	2,625	2,625	5,250	5,250
Noncontrolling interest-common units of the Operating Partnership	14,859	15,473	35,311	26,933
Noncontrolling interest in property partnerships	14,400	15,203	31,634	19,627
Interest expense	92,204	95,143	182,424	190,677
Depreciation and amortization expense	156,417	151,919	322,214	311,124
Transaction costs	474	299	495	333
Payroll and related costs from management services contracts	1,970	0	4,855	0
General and administrative expense	28,468	27,141	64,362	58,527
Gains on sales of real estate	18,292	3,767	114,689	3,900
Gains from early extinguishments of debt	0	14,354	0	14,354
Gains from investments in securities	505	730	379	1,772
Interest and other income	2,579	1,504	4,227	2,118
Income from unconsolidated joint ventures	769	3,108	1,230	6,192
Direct reimbursements of payroll and related costs from management services contracts	1,970	0	4,855	0
Development and management services income	9,305	7,365	17,710	13,837
Net Operating Income	406,678	410,684	808,137	801,062
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	145,961	151,844	346,868	262,506
Preferred Stock Dividends / Distributions	(2,625)	(2,625)	(5,250)	(5,250)
Noncontrolling interest in property partnerships	(14,400)	(15,203)	(31,634)	(19,627)
Interest expense	(92,204)	(95,143)	(182,424)	(190,677)
Depreciation and amortization expense	(154,474)	(149,834)	(318,327)	(306,892)
Transaction costs	(474)	(299)	(495)	(333)
Payroll and related costs from management services contracts	(1,970)	0	(4,855)	0
General and administrative expense	(28,468)	(27,141)	(64,362)	(58,527)
Gains from early extinguishments of debt	0	(14,354)	0	(14,354)
Gains from investments in securities	(505)	(730)	(379)	(1,772)
Interest and other income	(2,579)	(1,504)	(4,227)	(2,118)
Income from unconsolidated joint ventures	(769)	(3,108)	(1,230)	(6,192)
Direct reimbursements of payroll and related costs from management services contracts	(1,970)	0	(4,855)	0
Development and management services income	(9,305)	(7,365)	(17,710)	(13,837)
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	145,961	151,844	346,868	262,506
Preferred Stock Dividends / Distributions	2,625	2,625	5,250	5,250
Noncontrolling interest in property partnerships	14,400	15,203	31,634	19,627
Interest expense	92,204	95,143	182,424	190,677
Depreciation and amortization expense	154,474	149,834	318,327	306,892
Transaction costs	474	299	495	333
Payroll and related costs from management services contracts	1,970	0	4,855	0
General and administrative expense	28,468	27,141	64,362	58,527
Gains on sales of real estate	18,770	4,344	117,677	4,477
Gains from early extinguishments of debt	0	14,354	0	14,354
Gains from investments in securities	505	730	379	1,772
Interest and other income	2,579	1,504	4,227	2,118
Income from unconsolidated joint ventures	769	3,108	1,230	6,192
Direct reimbursements of payroll and related costs from management services contracts	1,970	0	4,855	0
Development and management services income	9,305	7,365	17,710	13,837
Net Operating Income	$ 406,678	$ 410,684	$ 808,137	$ 801,062

Segment Information (Schedule52

Segment Information (Schedule Of Segment Reporting By Geographic Area And Property Type) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 633,803	$ 631,957	$ 1,270,403	$ 1,246,337
Rental Revenue: Residential	4,799	4,210	8,958	8,166
Rental Revenue: Hotel	14,607	13,375	23,709	20,795
Total revenue	$ 653,209	$ 649,542	$ 1,303,070	$ 1,275,298
Rental Revenue: % of Grand Totals	100.00%	100.00%	100.00%	100.00%
Rental Expenses: Office	$ 234,877	$ 228,819	$ 472,934	$ 455,555
Rental Expenses: Residential	2,913	1,635	5,185	3,186
Rental Expenses: Hotel	8,741	8,404	16,814	15,495
Rental Expenses: Total	$ 246,531	$ 238,858	$ 494,933	$ 474,236
Rental Expenses: % Of Grand Totals	100.00%	100.00%	100.00%	100.00%
Net operating Income	$ 406,678	$ 410,684	$ 808,137	$ 801,062
Net operating Income: % of Grand Totals	100.00%	100.00%	100.00%	100.00%
Boston [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 207,810	$ 191,760	$ 412,807	$ 377,196
Rental Revenue: Residential	1,195	1,153	2,347	2,292
Rental Revenue: Hotel	14,607	13,375	23,709	20,795
Total revenue	$ 223,612	$ 206,288	$ 438,863	$ 400,283
Rental Revenue: % of Grand Totals	34.23%	31.76%	33.68%	31.39%
Rental Expenses: Office	$ 77,147	$ 74,160	$ 157,471	$ 149,416
Rental Expenses: Residential	706	545	1,220	1,040
Rental Expenses: Hotel	8,741	8,404	16,814	15,495
Rental Expenses: Total	$ 86,594	$ 83,109	$ 175,505	$ 165,951
Rental Expenses: % Of Grand Totals	35.12%	34.79%	35.46%	34.99%
Net operating Income	$ 137,018	$ 123,179	$ 263,358	$ 234,332
Net operating Income: % of Grand Totals	33.69%	29.99%	32.59%	29.25%
New York [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 234,006	$ 251,844	$ 476,404	$ 493,414
Rental Revenue: Residential	0	0	0	0
Rental Revenue: Hotel	0	0	0	0
Total revenue	$ 234,006	$ 251,844	$ 476,404	$ 493,414
Rental Revenue: % of Grand Totals	35.83%	38.77%	36.56%	38.69%
Rental Expenses: Office	$ 91,838	$ 93,110	$ 185,600	$ 184,794
Rental Expenses: Residential	0	0	0	0
Rental Expenses: Hotel	0	0	0	0
Rental Expenses: Total	$ 91,838	$ 93,110	$ 185,600	$ 184,794
Rental Expenses: % Of Grand Totals	37.26%	38.98%	37.50%	38.97%
Net operating Income	$ 142,168	$ 158,734	$ 290,804	$ 308,620
Net operating Income: % of Grand Totals	34.96%	38.65%	35.98%	38.53%
San Francisco [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 93,482	$ 85,483	$ 183,375	$ 170,124
Rental Revenue: Residential	0	0	0	0
Rental Revenue: Hotel	0	0	0	0
Total revenue	$ 93,482	$ 85,483	$ 183,375	$ 170,124
Rental Revenue: % of Grand Totals	14.31%	13.16%	14.07%	13.34%
Rental Expenses: Office	$ 31,214	$ 25,938	$ 58,842	$ 50,412
Rental Expenses: Residential	0	0	0	0
Rental Expenses: Hotel	0	0	0	0
Rental Expenses: Total	$ 31,214	$ 25,938	$ 58,842	$ 50,412
Rental Expenses: % Of Grand Totals	12.66%	10.86%	11.89%	10.63%
Net operating Income	$ 62,268	$ 59,545	$ 124,533	$ 119,712
Net operating Income: % of Grand Totals	15.31%	14.50%	15.41%	14.94%
Washington, DC [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 98,505	$ 102,870	$ 197,817	$ 205,603
Rental Revenue: Residential	3,604	3,057	6,611	5,874
Rental Revenue: Hotel	0	0	0	0
Total revenue	$ 102,109	$ 105,927	$ 204,428	$ 211,477
Rental Revenue: % of Grand Totals	15.63%	16.31%	15.69%	16.58%
Rental Expenses: Office	$ 34,678	$ 35,611	$ 71,021	$ 70,933
Rental Expenses: Residential	2,207	1,090	3,965	2,146
Rental Expenses: Hotel	0	0	0	0
Rental Expenses: Total	$ 36,885	$ 36,701	$ 74,986	$ 73,079
Rental Expenses: % Of Grand Totals	14.96%	15.37%	15.15%	15.41%
Net operating Income	$ 65,224	$ 69,226	$ 129,442	$ 138,398
Net operating Income: % of Grand Totals	16.04%	16.86%	16.02%	17.28%

Subsequent Events (Details)

Subsequent Events (Details)	Jul. 27, 2018USD ($)ft²yr	Jul. 19, 2018USD ($)ft²ayrBuildings	Jul. 13, 2018USD ($)ft²	Jun. 30, 2018USD ($)	Jun. 30, 2017USD ($)	Aug. 07, 2018ft²yr	Dec. 31, 2017USD ($)
Subsequent Event [Line Items]
mortgage notes				$ 2,972,052,000			$ 2,979,281,000
Payments to Acquire Equity Method Investments				$ 65,250,000	$ 41,491,000
Three Hudson Boulevard [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Ownership Percentage			25.00%
mortgage notes			$ 80,000,000
Debt Instrument, Basis Spread on Variable Rate			3.50%
Net Rentable Area (in sf) \| ft²			2,000,000
Payments to Acquire Equity Method Investments			$ 45,600,000
Future payments to acquire equity method investments			$ 62,200,000
Santa Monica Business Park [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
mortgage notes		$ 300,000,000
Debt Instrument, Basis Spread on Variable Rate		1.28%
Derivative, Notional Amount		$ 300,000,000
Derivative, Average Fixed Interest Rate		4.063%
100 Causeway Street [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Ownership Percentage	50.00%
Payment for improvements for equity method investment	$ 3,900,000
Net Rentable Area (in sf) \| ft²	627,000
Term of Lease Signed (in years) \| yr	20
Payments to Acquire Equity Method Investments	$ 37,400,000
Project estimated budget	$ 270,000,000
343 Madison Avenue [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Net Rentable Area (in sf) \| ft²						900,000
Term of Lease Signed (in years) \| yr						99
Ownership Percentage						55.00%
Santa Monica Business Park [Member] \| Santa Monica Business Park [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Net purchase price		$ 627,500,000
seller funded leasing costs		$ 11,500,000
Area of Land \| a		47
number of buildings \| Buildings		21
Net Rentable Area (in sf) \| 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		$ 180,100,000
Joint venture partner [Member] \| Santa Monica Business Park [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Ownership Percentage		45.00%
Payments to Acquire Equity Method Investments		$ 147,400,000
Joint venture partner [Member] \| 100 Causeway Street [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Ownership Percentage	50.00%
Payments to Acquire Equity Method Investments	$ 41,300,000