Boston Properties LTD Partnership 10-Q 7 Nov 18 2018 Q3 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Nov. 02, 2018
Entity Information [Line Items]
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
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		154,440,500
Boston Properties Limited Partnership
Entity Information [Line Items]
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
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	Sep. 30, 2018	Dec. 31, 2017
ASSETS
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $7,426,998 and $7,172,718 at September 30, 2018 and December 31, 2017, respectively)	$ 21,687,639	$ 21,096,642
Less: accumulated depreciation (amounts related to VIEs of $(942,678) and $(854,172) at September 30, 2018 and December 31, 2017, respectively)	(4,838,496)	(4,589,634)
Total real estate	16,849,143	16,507,008
Cash and cash equivalents (amounts related to VIEs of $284,053 and $304,955 at September 30, 2018 and December 31, 2017, respectively)	322,502	434,767
Cash held in escrows (amounts related to VIEs of $6,118 and $6,135 at September 30, 2018 and December 31, 2017, respectively)	101,282	70,602
Investments in securities	31,376	29,161
Tenant and other receivables (amounts related to VIEs of $42,193 and $27,057 at September 30, 2018 and December 31, 2017, respectively)	98,502	92,186
Related party note receivable	80,000	0
Accrued rental income (amounts related to VIEs of $269,794 and $242,589 at September 30, 2018 and December 31, 2017, respectively)	926,274	861,575
Deferred charges, net (amounts related to VIEs of $261,951 and $281,678 at September 30, 2018 and December 31, 2017, respectively)	669,545	679,038
Prepaid expenses and other assets (amounts related to VIEs of $62,325 and $33,666 at September 30, 2018 and December 31, 2017, respectively)	133,443	77,971
Investments in unconsolidated joint ventures	925,431	619,925
Total assets	20,137,498	19,372,233
Liabilities:
Mortgage notes payable, net (amounts related to VIEs of $2,931,852 and $2,939,183 at September 30, 2018 and December 31, 2017, respectively)	2,967,548	2,979,281
Unsecured senior notes, net	7,253,786	7,247,330
Unsecured line of credit	170,000	45,000
Unsecured term loan, net	498,368	0
Accounts payable and accrued expenses (amounts related to VIEs of $78,893 and $106,683 at September 30, 2018 and December 31, 2017, respectively)	315,462	331,500
Dividends and distributions payable	165,118	139,040
Accrued interest payable (amounts related to VIEs of $6,659 and $6,907 at September 30, 2018 and December 31, 2017, respectively)	92,809	83,646
Other liabilities (amounts related to VIEs of $200,306 and $164,806 at September 30, 2018 and December 31, 2017, respectively)	468,433	443,980
Total liabilities	11,931,524	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 September 30, 2018 and December 31, 2017	200,000	200,000
Common stock, $0.01 par value, 250,000,000 shares authorized, 154,519,139 and 154,404,186 issued and 154,440,239 and 154,325,286 outstanding at September 30, 2018 and December 31, 2017, respectively	1,544	1,543
Additional paid-in capital	6,400,193	6,377,908
Dividends in excess of earnings	(677,312)	(712,343)
Treasury common stock at cost, 78,900 shares at September 30, 2018 and December 31, 2017	(2,722)	(2,722)
Accumulated other comprehensive loss	(45,137)	(50,429)
Total stockholders’ equity attributable to Boston Properties, Inc.	5,876,566	5,813,957
Noncontrolling interests:
Common units of Boston Properties Limited Partnership	618,380	604,739
Property partnerships	1,711,028	1,683,760
Total equity / capital	8,205,974	8,102,456
Total liabilities and equity / capital	20,137,498	19,372,233
Boston Properties Limited Partnership
ASSETS
Real estate, at cost (amounts related to variable interest entities (“VIEs”) of $7,426,998 and $7,172,718 at September 30, 2018 and December 31, 2017, respectively)	21,281,726	20,685,164
Less: accumulated depreciation (amounts related to VIEs of $(942,678) and $(854,172) at September 30, 2018 and December 31, 2017, respectively)	(4,741,280)	(4,496,959)
Total real estate	16,540,446	16,188,205
Cash and cash equivalents (amounts related to VIEs of $284,053 and $304,955 at September 30, 2018 and December 31, 2017, respectively)	322,502	434,767
Cash held in escrows (amounts related to VIEs of $6,118 and $6,135 at September 30, 2018 and December 31, 2017, respectively)	101,282	70,602
Investments in securities	31,376	29,161
Tenant and other receivables (amounts related to VIEs of $42,193 and $27,057 at September 30, 2018 and December 31, 2017, respectively)	98,502	92,186
Related party note receivable	80,000	0
Accrued rental income (amounts related to VIEs of $269,794 and $242,589 at September 30, 2018 and December 31, 2017, respectively)	926,274	861,575
Deferred charges, net (amounts related to VIEs of $261,951 and $281,678 at September 30, 2018 and December 31, 2017, respectively)	669,545	679,038
Prepaid expenses and other assets (amounts related to VIEs of $62,325 and $33,666 at September 30, 2018 and December 31, 2017, respectively)	133,443	77,971
Investments in unconsolidated joint ventures	925,431	619,925
Total assets	19,828,801	19,053,430
Liabilities:
Mortgage notes payable, net (amounts related to VIEs of $2,931,852 and $2,939,183 at September 30, 2018 and December 31, 2017, respectively)	2,967,548	2,979,281
Unsecured senior notes, net	7,253,786	7,247,330
Unsecured line of credit	170,000	45,000
Unsecured term loan, net	498,368	0
Accounts payable and accrued expenses (amounts related to VIEs of $78,893 and $106,683 at September 30, 2018 and December 31, 2017, respectively)	315,462	331,500
Dividends and distributions payable	165,118	139,040
Accrued interest payable (amounts related to VIEs of $6,659 and $6,907 at September 30, 2018 and December 31, 2017, respectively)	92,809	83,646
Other liabilities (amounts related to VIEs of $200,306 and $164,806 at September 30, 2018 and December 31, 2017, respectively)	468,433	443,980
Total liabilities	11,931,524	11,269,777
Commitments and contingencies	0	0
Noncontrolling interest:
Redeemable partnership units—16,804,929 and 16,810,378 common units and 992,321 and 818,343 long term incentive units outstanding at redemption value at September 30, 2018 and December 31, 2017, respectively	2,190,664	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 September 30, 2018 and December 31, 2017	193,623	193,623
Noncontrolling interests:
Boston Properties Limited Partnership partners’ capital—1,722,375 and 1,719,540 general partner units and 152,717,864 and 152,605,746 limited partner units outstanding at September 30, 2018 and December 31, 2017, respectively	3,801,962	3,614,007
Noncontrolling interests in property partnerships	1,711,028	1,683,760
Total equity / capital	5,706,613	5,491,390
Total liabilities and equity / capital	$ 19,828,801	$ 19,053,430

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 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	154,519,139	154,404,186
Common stock, shares outstanding	154,440,239	154,325,286
Treasury common stock at cost, shares	78,900	78,900
General Partners' Capital Account, Units Outstanding	1,722,375
Limited Partners' Capital Account, Units Outstanding	152,717,864
Real Estate Investment Property, at Cost	$ 21,687,639	$ 21,096,642
Accumulated depreciation	(4,838,496)	(4,589,634)
Cash and Cash Equivalents	322,502	434,767
Cash held in escrow	101,282	70,602
Tenant and other receivables	98,502	92,186
Accrued rental income	926,274	861,575
Deferred Charges, net	669,545	679,038
Prepaid expense and other assets	133,443	77,971
Mortgage notes payable, net	2,967,548	2,979,281
Accounts payable and accrued expenses	315,462	331,500
Accrued interest payable	92,809	83,646
Other Liabilities	$ 468,433	$ 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	16,804,929	16,810,378
NonControlling Interest Redeemable Partnership Units Common Units Long Term Incentive Units At Redemption Value Shares Outstanding	992,321	818,343
General Partners' Capital Account, Units Outstanding	1,722,375	1,719,540
Limited Partners' Capital Account, Units Outstanding	152,717,864	152,605,746
Real Estate Investment Property, at Cost	$ 21,281,726	$ 20,685,164
Accumulated depreciation	(4,741,280)	(4,496,959)
Cash and Cash Equivalents	322,502	434,767
Cash held in escrow	101,282	70,602
Tenant and other receivables	98,502	92,186
Accrued rental income	926,274	861,575
Deferred Charges, net	669,545	679,038
Prepaid expense and other assets	133,443	77,971
Mortgage notes payable, net	2,967,548	2,979,281
Accounts payable and accrued expenses	315,462	331,500
Accrued interest payable	92,809	83,646
Other Liabilities	$ 468,433	$ 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	$ 7,426,998	$ 7,172,718
Accumulated depreciation	(942,678)	(854,172)
Cash and Cash Equivalents	284,053	304,955
Cash held in escrow	6,118	6,135
Tenant and other receivables	42,193	27,057
Accrued rental income	269,794	242,589
Deferred Charges, net	261,951	281,678
Prepaid expense and other assets	62,325	33,666
Mortgage notes payable, net	2,931,852	2,939,183
Accounts payable and accrued expenses	78,893	106,683
Accrued interest payable	6,659	6,907
Other Liabilities	200,306	164,806
VIE | Boston Properties Limited Partnership
Real Estate Investment Property, at Cost	7,426,998	7,172,718
Accumulated depreciation	(942,678)	(854,172)
Cash and Cash Equivalents	284,053	304,955
Cash held in escrow	6,118	6,135
Tenant and other receivables	42,193	27,057
Accrued rental income	269,794	242,589
Deferred Charges, net	261,951	281,678
Prepaid expense and other assets	62,325	33,666
Mortgage notes payable, net	2,931,852	2,939,183
Accounts payable and accrued expenses	78,893	106,683
Accrued interest payable	6,659	6,907
Other Liabilities	$ 200,306	$ 164,806

Consolidated Statements Of Oper

Consolidated Statements Of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue
Base rent	$ 525,875	$ 513,269	$ 1,561,821	$ 1,537,373
Recoveries from tenants	102,424	94,476	292,801	272,803
Parking and other	26,552	26,092	79,590	78,164
Total rental revenue	654,851	633,837	1,934,212	1,888,340
Hotel revenue	13,664	13,064	37,373	33,859
Development and management services	15,253	10,811	32,963	24,648
Direct reimbursements of payroll and related costs from management services contracts	2,516	0	7,371	0
Total revenue	686,284	657,712	2,011,919	1,946,847
Expenses
Rental	247,989	237,341	726,108	696,082
Hotel	8,828	8,447	25,642	23,942
General and administrative	29,677	25,792	94,039	84,319
Payroll and related costs from management services contracts	2,516	0	7,371	0
Transaction costs	914	239	1,409	572
Depreciation and amortization	157,996	152,164	480,210	463,288
Total expenses	447,920	423,983	1,334,779	1,268,203
Operating income	238,364	233,729	677,140	678,644
Other income (expense)
Income (loss) from unconsolidated joint ventures	(4,313)	843	(3,083)	7,035
Gains on sales of real estate	7,863	2,891	122,552	6,791
Interest and other income	2,822	1,329	7,049	3,447
Gains from investments in securities	1,075	944	1,454	2,716
Gains from early extinguishments of debt	0	0	0	14,354
Interest expense	(95,366)	(92,032)	(277,790)	(282,709)
Net income	150,445	147,704	527,322	430,278
Net income attributable to noncontrolling interests
Noncontrolling interests in property partnerships	(14,850)	(14,340)	(46,484)	(33,967)
Noncontrolling interest—common units of Boston Properties Limited Partnership	(13,852)	(13,402)	(49,128)	(40,350)
Net income attributable to the Company	121,743	119,962	431,710	355,961
Preferred dividends / distributions	(2,625)	(2,625)	(7,875)	(7,875)
Net income attributable to the Company's common shareholders / unitholders	$ 119,118	$ 117,337	$ 423,835	$ 348,086
Basic earnings per common share / unit attributable to the Company's common shareholders / unitholders
Net income (in dollars per share / unit)	$ 0.77	$ 0.76	$ 2.74	$ 2.26
Weighted average number of common shares / units outstanding	154,440	154,355	154,414	154,132
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)	$ 0.77	$ 0.76	$ 2.74	$ 2.26
Weighted average number of common and common equivalent shares / units outstanding (in shares / units)	154,678	154,483	154,652	154,344
Boston Properties Limited Partnership
Revenue
Base rent	$ 525,875	$ 513,269	$ 1,561,821	$ 1,537,373
Recoveries from tenants	102,424	94,476	292,801	272,803
Parking and other	26,552	26,092	79,590	78,164
Total rental revenue	654,851	633,837	1,934,212	1,888,340
Hotel revenue	13,664	13,064	37,373	33,859
Development and management services	15,253	10,811	32,963	24,648
Direct reimbursements of payroll and related costs from management services contracts	2,516	0	7,371	0
Total revenue	686,284	657,712	2,011,919	1,946,847
Expenses
Rental	247,989	237,341	726,108	696,082
Hotel	8,828	8,447	25,642	23,942
General and administrative	29,677	25,792	94,039	84,319
Payroll and related costs from management services contracts	2,516	0	7,371	0
Transaction costs	914	239	1,409	572
Depreciation and amortization	156,056	150,210	474,383	457,102
Total expenses	445,980	422,029	1,328,952	1,262,017
Operating income	240,304	235,683	682,967	684,830
Other income (expense)
Income (loss) from unconsolidated joint ventures	(4,313)	843	(3,083)	7,035
Gains on sales of real estate	9,154	2,891	126,831	7,368
Interest and other income	2,822	1,329	7,049	3,447
Gains from investments in securities	1,075	944	1,454	2,716
Gains from early extinguishments of debt	0	0	0	14,354
Interest expense	(95,366)	(92,032)	(277,790)	(282,709)
Net income	153,676	149,658	537,428	437,041
Net income attributable to noncontrolling interests
Noncontrolling interests in property partnerships	(14,850)	(14,340)	(46,484)	(33,967)
Net income attributable to the Company	138,826	135,318	490,944	403,074
Preferred dividends / distributions	(2,625)	(2,625)	(7,875)	(7,875)
Net income attributable to the Company's common shareholders / unitholders	$ 136,201	$ 132,693	$ 483,069	$ 395,199
Basic earnings per common share / unit attributable to the Company's common shareholders / unitholders
Net income (in dollars per share / unit)	$ 0.79	$ 0.77	$ 2.81	$ 2.30
Weighted average number of common shares / units outstanding	171,928	171,691	171,904	171,649
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)	$ 0.79	$ 0.77	$ 2.81	$ 2.30
Weighted average number of common and common equivalent shares / units outstanding (in shares / units)	172,166	171,819	172,142	171,861

Consolidated Statements Of Comp

Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net income		$ 150,445	$ 147,704	$ 527,322	$ 430,278
Other comprehensive income (loss):
Effective portion of interest rate contracts		1,325	0	1,325	(6,133)
Amortization of interest rate contracts	[1]	1,666	1,665	4,998	4,368
Other comprehensive income (loss)		2,991	1,665	6,323	(1,765)
Comprehensive income		153,436	149,369	533,645	428,513
Comprehensive income attributable to noncontrolling interests		(28,702)	(27,742)	(95,612)	(74,317)
Other comprehensive (income) loss attributable to noncontrolling interests		(433)	(300)	(1,031)	2,220
Comprehensive income attributable to the Company		124,301	121,327	437,002	356,416
Boston Properties Limited Partnership
Net income		153,676	149,658	537,428	437,041
Other comprehensive income (loss):
Effective portion of interest rate contracts		1,325	0	1,325	(6,133)
Amortization of interest rate contracts	[2]	1,666	1,665	4,998	4,368
Other comprehensive income (loss)		2,991	1,665	6,323	(1,765)
Comprehensive income		156,667	151,323	543,751	435,276
Comprehensive income attributable to noncontrolling interests		(14,994)	(14,484)	(46,916)	(31,695)
Comprehensive income attributable to the Company		$ 141,673	$ 136,839	$ 496,835	$ 403,581
[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		492,000
Conversion of operating partnership units to Common Stock, value	0	$ 5		16,807				(16,812)
Allocated net income for the year	430,278				355,961			74,317
Dividends/distributions declared	(395,026)				(354,734)			(40,292)
Shares issued pursuant to stock purchase plan, shares		6,000
Shares issued pursuant to stock purchase plan, value	795			795
Net activity from stock option and incentive plan, shares		34,000
Net activity from stock option and incentive plan, value	29,191	$ 0		2,920				26,271
Cumulative effect of a change in accounting principle	(2,035)				(272)			(1,763)
Contributions from noncontrolling interests in property partnerships	147,772							147,772
Distributions to noncontrolling interests in property partnerships	(41,439)							(41,439)
Effective portion of interest rate contracts	(6,133)						(3,304)	(2,829)
Amortization of interest rate contracts	4,368						3,759	609
Reallocation of noncontrolling interest	0			16,986				(16,986)
Equity, value at Sep. 30, 2017	8,099,695	$ 1,543	200,000	6,370,932	(692,739)	(2,722)	(51,796)	2,274,477
Equity, shares at Sep. 30, 2017		154,322,000
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		60,000
Conversion of operating partnership units to Common Stock, value		$ 1		2,111				(2,112)
Allocated net income for the year	$ 527,322				431,710			95,612
Dividends/distributions declared	(447,342)				(401,612)			(45,730)
Shares issued pursuant to stock purchase plan, shares		6,000
Shares issued pursuant to stock purchase plan, value	797			797
Net activity from stock option and incentive plan, shares		49,000
Net activity from stock option and incentive plan, value	30,570			1,354				29,216
Cumulative effect of a change in accounting principle	5,496				4,933			563
Contributions from noncontrolling interests in property partnerships	37,148							37,148
Distributions to noncontrolling interests in property partnerships	(56,796)							(56,796)
Effective portion of interest rate contracts	1,325						1,190	135
Amortization of interest rate contracts	4,998						4,102	896
Reallocation of noncontrolling interest				18,023				(18,023)
Equity, value at Sep. 30, 2018	$ 8,205,974	$ 1,544	$ 200,000	$ 6,400,193	$ (677,312)	$ (2,722)	$ (45,137)	$ 2,329,408
Equity, shares at Sep. 30, 2018	154,440,239	154,440,000

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		4,937
Net income allocable to general and limited partner units		362,724
Distributions		(354,734)
Other comprehensive income		455
Cumulative effect of a change in accounting principle	$ (2,035)	(272)
Unearned compensation		(1,222)
Conversion of redeemable partnership units		16,812
Adjustment to reflect redeemable partnership units at redemption value		103,556
Ending Balance at Sep. 30, 2017		3,943,973
Beginning Balance at Dec. 31, 2017		3,807,630
Contributions		2,039
Net income allocable to general and limited partner units		441,816
Distributions		(401,612)
Other comprehensive income		5,292
Cumulative effect of a change in accounting principle	$ 5,496	4,933
Unearned compensation		112
Conversion of redeemable partnership units		2,112
Adjustment to reflect redeemable partnership units at redemption value		133,263
Ending Balance at Sep. 30, 2018		$ 3,995,585

Consolidated Statements Of Cash

Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net income	$ 527,322	$ 430,278
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	480,210	463,288
Non-cash compensation expense	31,700	27,260
Loss (income) from unconsolidated joint ventures	3,083	(7,035)
Distributions of net cash flow from operations of unconsolidated joint ventures	3,988	8,563
Gains from investments in securities	(1,454)	(2,716)
Gains from early extinguishments of debt	0	(14,354)
Non-cash portion of interest expense	15,922	(6,667)
Gains on sales of real estate	(122,552)	(6,791)
Change in assets and liabilities:
Tenant and other receivables, net	1,578	12,528
Accrued rental income, net	(41,519)	(36,012)
Prepaid expenses and other assets	(51,938)	(13,633)
Accounts payable and accrued expenses	6,354	7,861
Accrued interest payable	8,860	(144,833)
Other liabilities	(1,561)	(65,073)
Tenant leasing costs	(89,366)	(67,699)
Total adjustments	243,305	154,687
Net cash provided by operating activities	770,627	584,965
Cash flows from investing activities:
Acquisitions of real estate	0	(15,953)
Construction in progress	(530,389)	(452,283)
Building and other capital improvements	(140,969)	(162,395)
Tenant improvements	(129,450)	(152,749)
Proceeds from sales of real estate	175,577	29,810
Capital contributions to unconsolidated joint ventures	(314,075)	(89,874)
Capital distributions from unconsolidated joint ventures	0	251,000
Issuance of related party note receivable	(80,000)	0
Investments in securities, net	(761)	(1,451)
Net cash used in investing activities	(1,020,067)	(593,895)
Cash flows from financing activities:
Proceeds from mortgage notes payable	0	2,300,000
Repayments of mortgage notes payable	(14,677)	(1,313,890)
Borrowings on unsecured line of credit	580,000	470,000
Repayments of unsecured line of credit	(455,000)	(470,000)
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	(463)
Payments on real estate financing transactions	(960)	(1,306)
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)	(44,083)
Debt prepayment and extinguishment costs	0	(90)
Net proceeds from equity transactions	(333)	241
Dividends and distributions	(421,264)	(394,900)
Contributions from noncontrolling interests in property partnerships	37,148	38,196
Distributions to noncontrolling interests in property partnerships	(56,796)	(41,605)
Net cash provided by financing activities	167,855	165,676
Net increase (decrease) in cash and cash equivalents and cash held in escrows	(81,585)	156,746
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	423,784	576,834
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	322,502	493,055
Cash held in escrows, end of period	101,282	83,779
Supplemental disclosures:
Cash paid for interest	303,203	477,189
Interest capitalized	51,594	43,286
Non-cash investing and financing activities:
Write-off of fully depreciated real estate	(100,118)	(103,972)
Additions to real estate included in accounts payable and accrued expenses	(11,746)	36,609
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	165,118	130,434
Conversions of noncontrolling interests to stockholders’ equity / partners' capital	2,112	16,812
Issuance of restricted securities to employees	37,342	35,711
Boston Properties Limited Partnership
Cash flows from operating activities:
Net income	537,428	437,041
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	474,383	457,102
Non-cash compensation expense	31,700	27,260
Loss (income) from unconsolidated joint ventures	3,083	(7,035)
Distributions of net cash flow from operations of unconsolidated joint ventures	3,988	8,563
Gains from investments in securities	(1,454)	(2,716)
Gains from early extinguishments of debt	0	(14,354)
Non-cash portion of interest expense	15,922	(6,667)
Gains on sales of real estate	(126,831)	(7,368)
Change in assets and liabilities:
Tenant and other receivables, net	1,578	12,528
Accrued rental income, net	(41,519)	(36,012)
Prepaid expenses and other assets	(51,938)	(13,633)
Accounts payable and accrued expenses	6,354	7,861
Accrued interest payable	8,860	(144,833)
Other liabilities	(1,561)	(65,073)
Tenant leasing costs	(89,366)	(67,699)
Total adjustments	233,199	147,924
Net cash provided by operating activities	770,627	584,965
Cash flows from investing activities:
Acquisitions of real estate	0	(15,953)
Construction in progress	(530,389)	(452,283)
Building and other capital improvements	(140,969)	(162,395)
Tenant improvements	(129,450)	(152,749)
Proceeds from sales of real estate	175,577	29,810
Capital contributions to unconsolidated joint ventures	(314,075)	(89,874)
Capital distributions from unconsolidated joint ventures	0	251,000
Issuance of related party note receivable	(80,000)	0
Investments in securities, net	(761)	(1,451)
Net cash used in investing activities	(1,020,067)	(593,895)
Cash flows from financing activities:
Proceeds from mortgage notes payable	0	2,300,000
Repayments of mortgage notes payable	(14,677)	(1,313,890)
Borrowings on unsecured line of credit	580,000	470,000
Repayments of unsecured line of credit	(455,000)	(470,000)
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	(463)
Payments on real estate financing transactions	(960)	(1,306)
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)	(44,083)
Debt prepayment and extinguishment costs	0	(90)
Net proceeds from equity transactions	(333)	241
Dividends and distributions	(421,264)	(394,900)
Contributions from noncontrolling interests in property partnerships	37,148	38,196
Distributions to noncontrolling interests in property partnerships	(56,796)	(41,605)
Net cash provided by financing activities	167,855	165,676
Net increase (decrease) in cash and cash equivalents and cash held in escrows	(81,585)	156,746
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	423,784	576,834
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	322,502	493,055
Cash held in escrows, end of period	101,282	83,779
Supplemental disclosures:
Cash paid for interest	303,203	477,189
Interest capitalized	51,594	43,286
Non-cash investing and financing activities:
Write-off of fully depreciated real estate	(100,118)	(102,795)
Additions to real estate included in accounts payable and accrued expenses	(11,746)	36,609
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	165,118	130,434
Conversions of noncontrolling interests to stockholders’ equity / partners' capital	2,112	16,812
Issuance of restricted securities to employees	$ 37,342	$ 35,711

Organization

Organization	9 Months Ended
	Sep. 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 September 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 earned 2012 OPP Units, the 2013 MYLTIP Units, the 2014 MYLTIP Units and the 2015 MYLTIP Units), whether vested or not, will receive the same quarterly per unit distributions as OP Units, which equal per share dividends on Common Stock (See Notes 7 , 8 and 10 ). At September 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 September 30, 2018 , the Company owned or had interests in a portfolio of 200 commercial real estate properties (the “Properties”) aggregating approximately 52.7 million net rentable square feet of primarily Class A office properties, including fourteen properties under construction/redevelopment totaling approximately 7.5 million net rentable square feet. At September 30, 2018 , the Properties consisted of: • 180 office properties (including twelve properties under construction/redevelopment); • thirteen retail properties; • six residential properties (including two properties under construction); and • one hotel. The Company considers Class A office properties to be well-located buildings that are professionally managed and maintained, attract high-quality tenants and command upper-tier rental rates, and that are modern structures or have been modernized to compete with newer buildings.

Basis Of Presentation And Summa

Basis Of Presentation And Summary Of Significant Accounting Policies	9 Months Ended
	Sep. 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 related party note receivable and mortgage notes payable using discounted cash flow analysis by discounting the spread between the future contractual interest payments and hypothetical future interest payments on note receivables / mortgage debt based on current market rates for similar securities. In determining the current market rates, the Company adds its estimates of market spreads to the quoted yields on federal government treasury securities with similar maturity dates to its debt. The inputs used in determining the fair value of the Company’s related party note receivable and 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, related party note receivable, 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 September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Related party note receivable $ 80,000 $ 80,000 $ — $ — Mortgage notes payable, net $ 2,967,548 $ 2,898,871 $ 2,979,281 $ 3,042,920 Unsecured senior notes, net 7,253,786 7,174,434 7,247,330 7,461,615 Unsecured line of credit 170,000 170,287 45,000 45,000 Unsecured term loan, net 498,368 502,110 — — Total $ 10,889,702 $ 10,745,702 $ 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 September 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 Office Tower Developer LLC joint ventures, which own 7750 Wisconsin Avenue and 100 Causeway Street (which is the office component of The Hub on Causeway mixed-use development project), respectively, are VIEs. The Company 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 nine months ended September 30, 2018, the Company recognized approximately $2.5 million and $7.4 million , respectively, of expenses consisting of payroll and related costs from management services contracts and recognized corresponding revenue of approximately $2.5 million and $7.4 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 $7.7 million , an increase to net cash used in investing activities totaling approximately $28.5 million , a decrease to net cash provided by financing activities totaling approximately $0.2 million , and a corresponding decrease to the net increase in cash and cash equivalents and cash held in escrows totaling approximately $20.6 million from amounts previously reported for the nine months ended September 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 September 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 (1) simplifies transition requirements for both lessees and lessors by adding an option that permits an organization to apply the transition provisions of the new standard at its adoption date instead of at the earliest comparative period presented in its financial statements and (2) allows lessors to elect, as a practical expedient, by class of underlying asset, to not separate nonlease components from the associated lease component and, instead, to account for those components as a single component if the nonlease components otherwise would be accounted for under the new revenue guidance (ASC 606) and both of the following are met: (1) The timing and pattern of transfer of the nonlease component(s) and associated lease components are the same; and (2) the lease component, if accounted for separately, would be classified as an operating lease. If the nonlease component or components associated with the lease component are the predominant component of the combined component, an entity is required to account for the combined component in accordance with ASC 606. Certain disclosures are required if applying this practical expedient. 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 non-incremental 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. Financial Instruments - Credit Losses In June 2016, the FASB issued ASU 2016-13, “Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments” (“ASU 2016-13”). ASU 2016-13 is intended to provide financial statement users with more decision-useful information about the expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date. To achieve this objective, ASU 2016-13 replaces the current incurred loss impairment methodology with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. ASU 2016-13 is effective for the Company for reporting periods beginning after December 15, 2019, with early adoption permitted. The Company is assessing the potential impact that the adoption of ASU 2016-13 will have on its consolidated financial statements. Fair Value Measurement In August 2018, the FASB issued ASU 2018-13, “Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement” (“ASU 2018-13”). ASU 2018-13 is intended to improve the effectiveness of disclosures required by entities regarding recurring and nonrecurring fair value measurements. ASU 2018-13 is effective for the Company for reporting periods beginning after December 15, 2019, with early adoption permitted. The adoption of ASU 2018-13 will not have a material impact on the Company's consolidated financial statements. Consolidation In October 2018, the FASB issued ASU 2018-17, “Consolidation (Topic 810): Targeted Improvements to Related Party Guidance for Variable Interest Entities” (“ASU 2018-17”). ASU 2018-17 is intended to improve the accounting when considering indirect interests held through related parties under common control for determining whether fees paid to decision makers and service providers are variable interests. ASU 2018-17 is effective for the Company for reporting periods beginning after December 15, 2019, with early adoption permitted. The Company is assessing the potential impact that the adoption of ASU 2018-17 will have on its consolidated financial statements.

Real Estate

Real Estate	9 Months Ended
	Sep. 30, 2018
Real Estate [Abstract]
Real Estate	3. Real Estate Boston Properties, Inc. Real estate consisted of the following at September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Land $ 5,108,491 $ 5,080,679 Land held for future development (1) 205,096 204,925 Buildings and improvements 12,949,543 12,284,164 Tenant improvements 2,322,552 2,219,608 Furniture, fixtures and equipment 44,696 37,928 Construction in progress 1,057,261 1,269,338 Total 21,687,639 21,096,642 Less: Accumulated depreciation (4,838,496 ) (4,589,634 ) $ 16,849,143 $ 16,507,008 _______________ (1) Includes pre-development costs. Boston Properties Limited Partnership Real estate consisted of the following at September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Land $ 5,005,507 $ 4,976,303 Land held for future development (1) 205,096 204,925 Buildings and improvements 12,646,614 11,977,062 Tenant improvements 2,322,552 2,219,608 Furniture, fixtures and equipment 44,696 37,928 Construction in progress 1,057,261 1,269,338 Total 21,281,726 20,685,164 Less: Accumulated depreciation (4,741,280 ) (4,496,959 ) $ 16,540,446 $ 16,188,205 _______________ (1) Includes pre-development costs. Development On January 24, 2018, the Company entered into a lease agreement with an affiliate of Leidos Holdings, Inc. for a build-to-suit project with approximately 276,000 net rentable square feet of Class A office space at the Company's 17Fifty Presidents Street development project located in Reston, Virginia. Concurrently with the execution of the lease, the Company commenced development of the project and expects the building to be completed and available for occupancy during the second quarter of 2020. On January 31, 2018, the Company partially placed in-service its Signature at Reston development project comprised of 508 apartment units and retail space aggregating approximately 518,000 square feet located in Reston, Virginia. This project was completed and fully placed in-service on June 7, 2018. On February 23, 2018, the Company entered into a lease agreement with Fannie Mae to lease approximately 850,000 net rentable square feet of Class A office space at the Company's Reston Gateway development project located in Reston, Virginia. The initial phase of the project will consist of two Class A office buildings aggregating approximately 1.1 million net rentable square feet. On August 31, 2018, the Company commenced development of the project. On June 20, 2018, the Company partially placed in-service its Proto Kendall Square development project comprised of 280 apartment units and retail space aggregating approximately 167,000 square feet located in Cambridge, Massachusetts. This project was completed and fully placed in-service on September 1, 2018. On August 7, 2018, the Company entered into an agreement with a third party to (1) share certain pre-development costs during the pre-lease period and (2) to form a joint venture to thereafter own and develop a leasehold interest in 343 Madison Avenue located in New York City, which will support a Class A office tower with approximately 850,000 net rentable square feet. The Company will serve as development manager of the project and will own a 55% interest in the joint venture. In 2016, the Company was selected by the Metropolitan Transportation Authority ("MTA") as the developer of the project and will enter into a pre-lease agreement and a 99 -year ground lease with the MTA for the site. There can be no assurances that the transaction will be completed on the terms currently contemplated, or at all. The Company exercised its option to acquire land parcels at its Carnegie Center property located in Princeton, New Jersey for a purchase price of approximately $42.4 million . The seller will be entitled to receive additional payments in the future aggregating approximately $9.2 million , which are contingent on the development of each of the parcels. The land parcels will support approximately 1.7 million square feet of development. There can be no assurances that the transaction will be completed on the terms currently contemplated, or at all. 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 $1.7 million and $4.9 million of net income to the Company for the three and nine months ended September 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 $0.3 million of net income to the Company for the period from January 1, 2018 through May 23, 2018 and contributed approximately $0.1 million and $0.4 million of net income to the Company for the three and nine months ended September 30, 2017 , respectively. On August 30, 2018, the Company entered into a binding agreement for the sale of its 1333 New Hampshire Avenue property located in Washington, DC for a gross sale price of approximately $136.5 million . 1333 New Hampshire Avenue is an approximately 316,000 net rentable square foot Class A office property. The sale is subject to the satisfaction of customary closing conditions and there can be no assurance that the sale will be completed on the terms currently contemplated or at all. On September 27, 2018, the Company completed the sale of its Quorum Office Park property located in Chelmsford, Massachusetts for a gross sale price of approximately $35.3 million . Net cash proceeds totaled approximately $34.3 million , resulting in a gain on sale of real estate totaling approximately $7.9 million for Boston Properties, Inc. and approximately $9.2 million for Boston Properties Limited Partnership. Quorum Office Park is an approximately 268,000 net rentable square foot Class A office property. Quorum Office Park contributed approximately $0.2 million and $0.7 million of net income to the Company for the period from July 1, 2018 through September 26, 2018 and the period from January 1, 2018 through September 26, 2018, respectively, and contributed approximately $0.3 million and $0.7 million of net income to the Company for the three and nine months ended September 30, 2017, respectively.

Investments in Unconsolidated J

Investments in Unconsolidated Joint Ventures	9 Months Ended
	Sep. 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 September 30, 2018 and December 31, 2017 : Nominal % Ownership Carrying Value of Investment (1) Entity Properties September 30, 2018 December 31, 2017 (in thousands) Square 407 Limited Partnership Market Square North 50.0 % $ (6,870 ) $ (8,258 ) The Metropolitan Square Associates LLC Metropolitan Square 20.0 % 1,220 3,339 BP/CRF 901 New York Avenue LLC 901 New York Avenue 25.0 % (2) (12,454 ) (13,811 ) WP Project Developer LLC Wisconsin Place Land and Infrastructure 33.3 % (3) 38,667 39,710 Annapolis Junction NFM LLC Annapolis Junction 50.0 % (4) 17,309 18,381 540 Madison Venture LLC 540 Madison Avenue 60.0 % 66,492 66,179 500 North Capitol Venture LLC 500 North Capitol Street, NW 30.0 % (4,699 ) (3,876 ) 501 K Street LLC 1001 6th Street 50.0 % (5) 42,584 42,657 Podium Developer LLC The Hub on Causeway - Podium 50.0 % 68,919 67,120 Residential Tower Developer LLC The Hub on Causeway - Residential 50.0 % 46,655 28,212 Hotel Tower Developer LLC The Hub on Causeway - Hotel Air Rights 50.0 % 2,738 1,690 Office Tower Developer LLC 100 Causeway Street 50.0 % (6) 12,232 — 1265 Main Office JV LLC 1265 Main Street 50.0 % 4,313 4,641 BNY Tower Holdings LLC Dock 72 50.0 % 72,100 72,104 CA-Colorado Center Limited Partnership Colorado Center 50.0 % 253,334 254,440 7750 Wisconsin Avenue LLC 7750 Wisconsin Avenue 50.0 % (6) 69,007 21,452 BP-M 3HB Venture LLC 3 Hudson Boulevard 25.0 % 46,240 — SMBP Venture LP Santa Monica Business Park 55.0 % 183,621 — $ 901,408 $ 593,980 _______________ (1) Investments with deficit balances aggregating approximately $24.0 million and $25.9 million at September 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 to the Consolidated Financial Statements). 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: September 30, 2018 December 31, 2017 (in thousands) ASSETS Real estate and development in process, net $ 3,475,909 $ 1,768,996 Other assets 523,177 367,743 Total assets $ 3,999,086 $ 2,136,739 LIABILITIES AND MEMBERS’/PARTNERS’ EQUITY Mortgage and notes payable, net $ 1,975,260 $ 1,437,440 Other liabilities 589,394 99,215 Members’/Partners’ equity 1,434,432 600,084 Total liabilities and members’/partners’ equity $ 3,999,086 $ 2,136,739 Company’s share of equity $ 593,427 $ 286,495 Basis differentials (1) 307,981 307,485 Carrying value of the Company’s investments in unconsolidated joint ventures (2) $ 901,408 $ 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 September 30, 2018 and December 31, 2017 , there was an aggregate basis differential of approximately $318.2 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 $24.0 million and $25.9 million at September 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 September 30, Nine months ended September 30, 2018 2017 2018 2017 (in thousands) Total revenue (1) $ 76,177 $ 55,516 $ 189,759 $ 166,139 Expenses Operating 29,522 23,128 75,239 67,310 Depreciation and amortization (2) 44,993 16,440 74,245 44,973 Total expenses 74,515 39,568 149,484 112,283 Operating income 1,662 15,948 40,275 53,856 Other expense Interest expense 19,861 13,088 48,993 31,815 Net income (loss) $ (18,199 ) $ 2,860 $ (8,718 ) $ 22,041 Company’s share of net income (loss) $ (2,858 ) $ 2,909 $ 1,073 $ 11,576 Basis differential (3) (1,455 ) (2,066 ) (4,156 ) (4,541 ) Income (loss) from unconsolidated joint ventures (2) $ (4,313 ) $ 843 $ (3,083 ) $ 7,035 _______________ (1) Includes straight-line rent adjustments of approximately $4.8 million and $5.1 million for the three months ended September 30, 2018 and 2017 , respectively, and $9.8 million and $16.4 million for the nine months ended September 30, 2018 and 2017 , respectively. (2) During the three months ended September 30, 2018, the joint venture that owns Metropolitan Square, in Washington, DC, commenced a renovation project and recorded accelerated depreciation of approximately $22.4 million related to the remaining book value of the asset to be replaced. The Company's share of the accelerated depreciation totaled approximately $4.5 million . (3) Includes straight-line rent adjustments of approximately $0.5 million and $0.7 million for the three months ended September 30, 2018 and 2017 , respectively, and $1.9 million and $2.2 million for the nine months ended September 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 September 30, 2018 and 2017 , respectively, and $1.2 million and $1.3 million for the nine months ended September 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. As of September 30, 2018, approximately $8.2 million had been drawn under the loan. The Hub on Causeway - Residential is an approximately 320,000 square foot project comprised of 440 residential units located in Boston, Massachusetts. On April 27, 2018, a joint venture in which the Company has a 60% interest refinanced the mortgage loan collateralized by its 540 Madison Avenue property located in New York City totaling $120.0 million . The mortgage loan bears interest at a variable rate equal to LIBOR plus 1.10% per annum and matures on June 5, 2023. The previous mortgage loan bore interest at a variable rate equal to LIBOR plus 1.50% per annum and was scheduled to mature on June 5, 2018. 540 Madison Avenue is an approximately 284,000 net rentable square foot Class A office property. On July 13, 2018, the Company entered into a joint venture with a third party to acquire a development site at 3 Hudson Boulevard that, upon the future acquisition of additional available development rights, can accommodate a Class A office tower with up to 2.0 million net rentable square feet located on the entire square block between 11th Avenue and Hudson Boulevard Park from West 34th Street to West 35th Street in New York City. The Company owns a 25% interest in and is the managing member of the joint venture. The acquisition includes improvements consisting of excavation work and foundation elements that are currently being constructed on the site. The Company contributed cash totaling approximately $45.6 million at closing and will contribute approximately $62.2 million in the future for its initial capital contribution, a portion of which will fund the remaining costs to complete the foundation elements to grade for the future office building. In addition, the Company 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. The loan has been reflected as a Related Party Note Receivable on the Company’s Consolidated Balance Sheets. The Company's policy is to record notes receivable at their unamortized cost, net of any unamortized deferred fees or costs, premiums or discounts and an allowance for loan losses. Loan fees and direct costs associated with loans originated by the Company are deferred and amortized over the term of the note as interest income. On July 19, 2018, the Company entered into a joint venture to acquire Santa Monica Business Park in the Ocean Park neighborhood of Santa Monica, California for a net purchase price of approximately $626.7 million , including $11.5 million of seller funded leasing costs after the effective date of the purchase and sale agreement. Santa Monica Business Park is a 47 -acre office park consisting of 21 buildings totaling approximately 1.2 million net rentable square feet. Approximately 70% of the rentable square footage is subject to a ground lease with 80 years remaining, including renewal periods. The ground lease provides the joint venture with the right to purchase the land underlying the properties in 2028 with subsequent purchase rights every 15 years. Canada Pension Plan Investment Board invested approximately $147.0 million for a 45% ownership interest in the joint venture. The Company is providing customary operating, property management and leasing services to, and invested approximately $179.7 million , in the joint venture. The acquisition was completed with $300.0 million of financing. The mortgage financing bears interest at a variable rate equal to LIBOR plus 1.28% per annum and matures on July 19, 2025. At closing, the borrower under the loan, which is a subsidiary of the joint venture, entered into interest rate swap contracts with notional amounts aggregating $300.0 million through April 1, 2025, resulting in a fixed rate of approximately 4.063% per annum through the expiration of the interest rate swap contracts. At September 30, 2018, the unconsolidated joint venture has recorded the changes in fair value of the interest rate swap contracts aggregating approximately $2.4 million as an asset and accumulated other comprehensive income on its balance sheet. At September 30, 2018, the Company has recognized its share of the fair value totaling approximately $1.3 million as an increase to its Investments in Unconsolidated Joint Ventures and Accumulated Other Comprehensive Loss on the Company's Consolidated Balance Sheets. The following table summarizes the allocation of the joint venture's aggregate purchase price for Santa Monica Business Park at the date of acquisition (in thousands). Land and improvements $ 100,525 Leasehold interest in land 248,944 Site improvements 13,381 Building and improvements 593,759 Tenant improvements 31,338 In-place lease intangibles 47,783 Above-market lease intangible 4,495 Below-market lease intangible (17,504 ) Capital lease obligation (396,008 ) Net assets acquired $ 626,713 On July 27, 2018, the Company entered into a joint venture with its partner at The Hub on Causeway mixed-use development in Boston, Massachusetts to acquire the air rights for the development of an approximately 627,000 net rentable square foot Class A office tower at the site to be known as 100 Causeway Street. 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 the co-development manager for the project. The joint venture partner contributed an air rights parcel and improvements, with a fair value of approximately $41.3 million , for its initial 50% interest in the joint venture. The Company contributed improvements totaling approximately $3.9 million and will contribute cash totaling approximately $37.4 million for its initial 50% interest.

Debt

Debt	9 Months Ended
	Sep. 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 September 30, 2018 , Boston Properties Limited Partnership had $500.0 million of borrowings outstanding under its Delayed Draw Facility, $170.0 million of borrowings outstanding under its Revolving Facility and outstanding letters of credit totaling approximately $0.3 million , with the ability to borrow approximately $1.3 billion .

Commitments And Contingencies

Commitments And Contingencies	9 Months Ended
	Sep. 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 $7.8 million . Certain of the Company’s joint venture agreements include provisions whereby, at certain specified times, each partner has the right to initiate a purchase or sale of its interest in the joint ventures. With limited exception, under these provisions, the Company is not compelled to purchase the interest of its outside joint venture partners. From time to time, under certain of the Company’s joint venture agreements, if certain return thresholds are achieved, either the Company or its partners will be entitled to an additional promoted interest or payments. See also Note 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 September 30, 2018 , the maximum funding obligation under the guarantee was approximately $126.4 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 September 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 September 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, 2016 and 2017, the Company received distributions of approximately $7.7 million , $8.1 million , $1.4 million and $0.4 million , respectively. On September 13, 2018, the Company received a sixth interim distribution totaling approximately $0.3 million , leaving a remaining claim of approximately $27.2 million . The Company will continue to evaluate whether to attempt to sell the remaining claim or wait until the trustee distributes proceeds from the Lehman Brothers estate. Given the inherent uncertainties in bankruptcy proceedings, there can be no assurance as to the timing or amount of additional proceeds, if any, that the Company may ultimately realize on the remaining claim, whether by sale to a third party or by one or more distributions from the trustee. Accordingly, the Company has not recorded any estimated recoveries associated with this gain contingency within its Consolidated Financial Statements at September 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	9 Months Ended
	Sep. 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 September 30, 2018 , the noncontrolling interests in Boston Properties Limited Partnership consisted of 16,804,929 OP Units, 992,321 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 nine months ended September 30, 2018 , 61,021 OP Units were presented by the holders for redemption (including 47,985 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 September 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 September 28, 2018 October 31, 2018 $0.95 $0.095 June 29, 2018 July 31, 2018 $0.80 $0.080 March 29, 2018 April 30, 2018 $0.80 $0.080 December 29, 2017 January 30, 2018 $0.80 $0.080 A holder of an OP Unit may present the OP Unit to Boston Properties Limited Partnership for redemption at any time (subject to restrictions agreed upon at the time of issuance of OP Units to particular holders that may restrict such redemption right for a period of time, generally one year from issuance). Upon presentation of an OP Unit for redemption, Boston Properties Limited Partnership must redeem the OP Unit for cash equal to the then value of a share of common stock of Boston Properties, Inc. Boston Properties, Inc. may, in its sole discretion, elect to assume and satisfy the redemption obligation by paying either cash or issuing one share of Common Stock. The value of the OP Units not owned by Boston Properties, Inc. and LTIP Units (including the 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units and 2015 MYLTIP Units), assuming that all conditions had been met for the conversion thereof, had all of such units been redeemed at September 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 $123.09 per share on September 28, 2018. Boston Properties Limited Partnership The following table reflects the activity of noncontrolling interests—redeemable partnership units of Boston Properties Limited Partnership for the nine months ended September 30, 2018 and 2017 (in thousands): Balance at December 31, 2017 $ 2,292,263 Contributions 34,970 Net income 49,128 Distributions (45,730 ) Conversion of redeemable partnership units (2,112 ) Unearned compensation (5,754 ) Cumulative effect of a change in accounting principle 563 Other comprehensive income 599 Adjustment to reflect redeemable partnership units at redemption value (133,263 ) Balance at September 30, 2018 $ 2,190,664 Balance at December 31, 2016 $ 2,262,040 Contributions 31,465 Net income 40,350 Distributions (40,292 ) Conversion of redeemable partnership units (16,812 ) Unearned compensation (5,194 ) Cumulative effect of a change in accounting principle (1,763 ) Other comprehensive income 52 Adjustment to reflect redeemable partnership units at redemption value (103,556 ) Balance at September 30, 2017 $ 2,166,290 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 September 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 September 30, 2018 , the Company had contributed an aggregate of approximately $22.6 million of preferred equity to the venture. Also, under the joint venture agreement, (a) from and after the stabilization date, the partner has the right to cause the Company to purchase all (but not less than all) of the partner’s interest and (b) from and after the third anniversary of the stabilization date, the Company has the right to acquire all (but not less than all) of the partner’s interest, in each case at an agreed upon purchase price or appraised value. In addition, if certain threshold returns are achieved the partner will be entitled to receive an additional promoted interest with respect to cash flow distributions. The term stabilization date is defined in the agreement to generally mean the first date after completion upon which Salesforce Tower is (1) at least 90% leased and (2) 50% occupied by tenants that are paying rent. The stabilization date is expected to occur in the fourth quarter of 2018. The Company expects the partner to exercise its right and to close on the purchase of the partner's interest by the end of the first half of 2019. The following table reflects the activity of the noncontrolling interests — property partnerships for the nine months ended September 30, 2018 and 2017 (in thousands): Balance at December 31, 2017 $ 1,683,760 Capital contributions 37,148 Net income 46,484 Accumulated other comprehensive income 432 Distributions (56,796 ) Balance at September 30, 2018 $ 1,711,028 Balance at December 31, 2016 $ 1,530,647 Capital contributions 147,772 Net income 33,967 Accumulated other comprehensive loss (2,272 ) Distributions (41,439 ) Balance at September 30, 2017 $ 1,668,675

Stockholders' Equity _ Partners

Stockholders' Equity / Partners' Capital	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Stockholders' Equity / Partners' Capital	8. Stockholders’ Equity / Partners’ Capital As of September 30, 2018 , Boston Properties, Inc. had 154,440,239 shares of Common Stock outstanding. As of September 30, 2018 , Boston Properties, Inc. owned 1,722,375 general partnership units and 152,717,864 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 nine months ended September 30, 2018 , Boston Properties, Inc. issued 61,021 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) September 28, 2018 October 31, 2018 $0.95 $0.95 June 29, 2018 July 31, 2018 $0.80 $0.80 March 29, 2018 April 30, 2018 $0.80 $0.80 December 29, 2017 January 30, 2018 $0.80 $0.80 Preferred Stock As of September 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) November 2, 2018 November 15, 2018 $32.8125 August 3, 2018 August 15, 2018 $32.8125 May 4, 2018 May 15, 2018 $32.8125 February 2, 2018 February 15, 2018 $32.8125

Earnings Per Share _ Common Uni

Earnings Per Share / Common Unit	9 Months Ended
	Sep. 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 September 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 $ 119,118 154,440 $ 0.77 Effect of Dilutive Securities: Stock Based Compensation — 238 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 119,118 154,678 $ 0.77 Three months ended September 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 $ 117,337 154,355 $ 0.76 Allocation of undistributed earnings to participating securities (7 ) — — Net income attributable to Boston Properties, Inc. common shareholders $ 117,330 154,355 $ 0.76 Effect of Dilutive Securities: Stock Based Compensation — 128 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 117,330 154,483 $ 0.76 Nine months ended September 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 $ 423,835 154,414 $ 2.74 Allocation of undistributed earnings to participating securities (87 ) — — Net income attributable to Boston Properties, Inc. common shareholders $ 423,748 154,414 $ 2.74 Effect of Dilutive Securities: Stock Based Compensation — 238 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 423,748 154,652 $ 2.74 Nine months ended September 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 $ 348,086 154,132 $ 2.26 Allocation of undistributed earnings to participating securities (15 ) — — Net income attributable to Boston Properties, Inc. common shareholders $ 348,071 154,132 $ 2.26 Effect of Dilutive Securities: Stock Based Compensation — 212 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 348,071 154,344 $ 2.26 Boston Properties Limited Partnership The following table provides a reconciliation of both the net income attributable to Boston Properties Limited Partnership common unitholders and the number of common units used in the computation of basic earnings per common unit, which is calculated by dividing net income attributable to Boston Properties Limited Partnership common unitholders by the weighted-average number of common units outstanding during the period. Unvested share-based payment awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid) are also participating securities. As such, unvested restricted common stock of Boston Properties, Inc. and Boston Properties Limited Partnership’s LTIP Units, 2012 OPP Units and MYLTIP Units are considered participating securities. Participating securities are included in the computation of basic earnings per common unit using the two -class method. Participating securities are included in the computation of diluted earnings per common unit using the if-converted method if the impact is dilutive. Because the 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units and 2015 MYLTIP Units required, and the 2016-2018 MYLTIP Units require, Boston Properties, Inc. to outperform absolute and relative return thresholds, unless such thresholds have been met by the end of the applicable reporting period, Boston Properties Limited Partnership excludes such units from the diluted earnings per common unit calculation. Other potentially dilutive common units and the related impact on earnings are considered when calculating diluted earnings per common unit. Included in the number of units (the denominator) below are approximately 17,488,000 and 17,336,000 redeemable common units for the three months ended September 30, 2018 and 2017 , respectively, and 17,490,000 and 17,517,000 redeemable common units for the nine months ended September 30, 2018 and 2017 , respectively. Three months ended September 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 $ 136,201 171,928 $ 0.79 Effect of Dilutive Securities: Stock Based Compensation — 238 — Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 136,201 172,166 $ 0.79 Three months ended September 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 $ 132,693 171,691 $ 0.77 Allocation of undistributed earnings to participating securities (8 ) — — Net income attributable to Boston Properties Limited Partnership common unitholders $ 132,685 171,691 $ 0.77 Effect of Dilutive Securities: Stock Based Compensation — 128 — Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 132,685 171,819 $ 0.77 Nine months ended September 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 $ 483,069 171,904 $ 2.81 Allocation of undistributed earnings to participating securities (97 ) — — Net income attributable to Boston Properties Limited Partnership common unitholders $ 482,972 171,904 $ 2.81 Effect of Dilutive Securities: Stock Based Compensation — 238 — Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 482,972 172,142 $ 2.81 Nine months ended September 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 $ 395,199 171,649 $ 2.30 Allocation of undistributed earnings to participating securities (17 ) — — Net income attributable to Boston Properties Limited Partnership common unitholders $ 395,182 171,649 $ 2.30 Effect of Dilutive Securities: Stock Based Compensation — 212 — Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 395,182 171,861 $ 2.30

Stock Option and Incentive Plan

Stock Option and Incentive Plan	9 Months Ended
	Sep. 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 1,000 basis points or more below the index to a maximum of 200% of target if the Company's TSR is equal to or greater than 1,000 basis points above the index, on a straight-line basis, depending on the value and linear interpolation between zero and maximum. Earned awards measured on the basis of relative TSR performance are subject to an absolute TSR component in the form of modifiers that (A) reduce the level of earned awards in the event Boston Properties, Inc.’s annualized TSR is 0% or less and (B) cause some awards to be earned in the event Boston Properties, Inc.’s annualized TSR is 12% or more even though on a relative basis alone Boston Properties, Inc.’s TSR would not result in any earned awards. Earned awards (if any) will vest 50% on February 5, 2021 and 50% on February 5, 2022, based on continued employment. Vesting will be accelerated in the event of a change in control, termination of employment by Boston Properties, Inc. without cause, or termination of employment by the award recipient for good reason, death, disability or retirement. If there is a change of control prior to February 5, 2021, earned awards will be calculated based on TSR performance up to the date of the change of control. The 2018 MYLTIP awards are in the form of LTIP Units issued on the grant date which (i) are subject to forfeiture to the extent awards are not earned and (ii) prior to the performance measurement date are only entitled to one-tenth ( 10% ) of the regular quarterly distributions payable on common partnership units. Under ASC 718, the 2018 MYLTIP awards have an aggregate value of approximately $13.3 million , which amount will generally be amortized into earnings over the four -year plan period under the graded vesting method. On February 4, 2018, the measurement period for the Company’s 2015 MYLTIP awards ended and, based on Boston Properties, Inc.’s relative TSR performance, the final awards were determined to be 22.0% of target or an aggregate of approximately $3.6 million (after giving effect to voluntary employee separations). As a result, an aggregate of 337,847 2015 MYLTIP Units that had been previously granted were automatically forfeited. During the nine months ended September 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 nine months ended September 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 $7.5 million for the three months ended September 30, 2018 and 2017 , respectively, and $30.1 million and $25.6 million for the nine months ended September 30, 2018 and 2017 , respectively. At September 30, 2018 , there was (1) an aggregate of approximately $27.3 million of unrecognized compensation expense related to unvested restricted stock, LTIP Units and 2015 MYLTIP Units and (2) an aggregate of approximately $18.8 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 2.5 years.

Segment Information

Segment Information	9 Months Ended
	Sep. 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 nine months ended September 30, 2018 and 2017 . Boston Properties, Inc. Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (in thousands) Net income attributable to Boston Properties, Inc. common shareholders $ 119,118 $ 117,337 $ 423,835 $ 348,086 Add: Preferred dividends 2,625 2,625 7,875 7,875 Noncontrolling interest—common units of Boston Properties Limited Partnership 13,852 13,402 49,128 40,350 Noncontrolling interests in property partnerships 14,850 14,340 46,484 33,967 Interest expense 95,366 92,032 277,790 282,709 Depreciation and amortization expense 157,996 152,164 480,210 463,288 Transaction costs 914 239 1,409 572 Payroll and related costs from management services contracts 2,516 — 7,371 — General and administrative expense 29,677 25,792 94,039 84,319 Less: Gains from early extinguishments of debt — — — 14,354 Gains from investments in securities 1,075 944 1,454 2,716 Interest and other income 2,822 1,329 7,049 3,447 Gains on sales of real estate 7,863 2,891 122,552 6,791 Income (loss) from unconsolidated joint ventures (4,313 ) 843 (3,083 ) 7,035 Direct reimbursements of payroll and related costs from management services contracts 2,516 — 7,371 — Development and management services revenue 15,253 10,811 32,963 24,648 Net Operating Income $ 411,698 $ 401,113 $ 1,219,835 $ 1,202,175 Boston Properties Limited Partnership Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (in thousands) Net income attributable to Boston Properties Limited Partnership common unitholders $ 136,201 $ 132,693 $ 483,069 $ 395,199 Add: Preferred distributions 2,625 2,625 7,875 7,875 Noncontrolling interests in property partnerships 14,850 14,340 46,484 33,967 Interest expense 95,366 92,032 277,790 282,709 Depreciation and amortization expense 156,056 150,210 474,383 457,102 Transaction costs 914 239 1,409 572 Payroll and related costs from management services contracts 2,516 — 7,371 — General and administrative expense 29,677 25,792 94,039 84,319 Less: Gains from early extinguishments of debt — — — 14,354 Gains from investments in securities 1,075 944 1,454 2,716 Interest and other income 2,822 1,329 7,049 3,447 Gains on sales of real estate 9,154 2,891 126,831 7,368 Income (loss) from unconsolidated joint ventures (4,313 ) 843 (3,083 ) 7,035 Direct reimbursements of payroll and related costs from management services contracts 2,516 — 7,371 — Development and management services revenue 15,253 10,811 32,963 24,648 Net Operating Income $ 411,698 $ 401,113 $ 1,219,835 $ 1,202,175 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 from early extinguishments of debt, gains from investments in securities, interest and other income, gains on sales of real estate, income (loss) 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 from early extinguishments of debt, gains from investments in securities, interest and other income, gains on sales of real estate, income (loss) 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 September 30, 2018 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 210,277 $ 237,944 $ 102,035 $ 98,275 $ 648,531 Residential 1,905 — — 4,415 6,320 Hotel 13,664 — — — 13,664 Total 225,846 237,944 102,035 102,690 668,515 % of Grand Totals 33.78 % 35.60 % 15.26 % 15.36 % 100.00 % Rental Expenses: Office 78,089 96,795 34,016 35,365 244,265 Residential 1,159 — — 2,565 3,724 Hotel 8,828 — — — 8,828 Total 88,076 96,795 34,016 37,930 256,817 % of Grand Totals 34.30 % 37.68 % 13.25 % 14.77 % 100.00 % Net operating income $ 137,770 $ 141,149 $ 68,019 $ 64,760 $ 411,698 % of Grand Totals 33.46 % 34.29 % 16.52 % 15.73 % 100.00 % For the three months ended September 30, 2017 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 196,687 $ 242,071 $ 87,162 $ 103,622 $ 629,542 Residential 1,228 — — 3,067 4,295 Hotel 13,064 — — — 13,064 Total 210,979 242,071 87,162 106,689 646,901 % of Grand Totals 32.61 % 37.43 % 13.47 % 16.49 % 100.00 % Rental Expenses: Office 76,086 95,775 26,792 37,111 235,764 Residential 512 — — 1,065 1,577 Hotel 8,447 — — — 8,447 Total 85,045 95,775 26,792 38,176 245,788 % of Grand Totals 34.60 % 38.97 % 10.90 % 15.53 % 100.00 % Net operating income $ 125,934 $ 146,296 $ 60,370 $ 68,513 $ 401,113 % of Grand Totals 31.40 % 36.47 % 15.05 % 17.08 % 100.00 % For the nine months ended September 30, 2018 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 623,084 $ 714,348 $ 285,410 $ 296,092 $ 1,918,934 Residential 4,252 — — 11,026 15,278 Hotel 37,373 — — — 37,373 Total 664,709 714,348 285,410 307,118 1,971,585 % of Grand Totals 33.71 % 36.23 % 14.48 % 15.58 % 100.00 % Rental Expenses: Office 235,560 282,395 92,858 106,386 717,199 Residential 2,379 — — 6,530 8,909 Hotel 25,642 — — — 25,642 Total 263,581 282,395 92,858 112,916 751,750 % of Grand Totals 35.06 % 37.57 % 12.35 % 15.02 % 100.00 % Net operating income $ 401,128 $ 431,953 $ 192,552 $ 194,202 $ 1,219,835 % of Grand Totals 32.88 % 35.41 % 15.79 % 15.92 % 100.00 % For the nine months ended September 30, 2017 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 573,883 $ 735,485 $ 257,286 $ 309,225 $ 1,875,879 Residential 3,520 — — 8,941 12,461 Hotel 33,859 — — — 33,859 Total 611,262 735,485 257,286 318,166 1,922,199 % of Grand Totals 31.80 % 38.27 % 13.38 % 16.55 % 100.00 % Rental Expenses: Office 225,502 280,569 77,204 108,044 691,319 Residential 1,552 — — 3,211 4,763 Hotel 23,942 — — — 23,942 Total 250,996 280,569 77,204 111,255 720,024 % of Grand Totals 34.86 % 38.97 % 10.72 % 15.45 % 100.00 % Net operating income $ 360,266 $ 454,916 $ 180,082 $ 206,911 $ 1,202,175 % of Grand Totals 29.97 % 37.84 % 14.98 % 17.21 % 100.00 %

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2018
Subsequent Events [Abstract]
Subsequent Events [Text Block]	12. Subsequent Events The Company has evaluated subsequent events and transactions through November 7, 2018, the date the Consolidated Financial Statements were available to be issued. There were no events or transactions that occurred that would require recognition or disclosure in the Consolidated Financial Statements.

Basis Of Presentation And Sum_2

Basis Of Presentation And Summary Of Significant Accounting Policies Recent Accounting Pronouncements (Policies)	9 Months Ended
	Sep. 30, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New 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 nine months ended September 30, 2018, the Company recognized approximately $2.5 million and $7.4 million , respectively, of expenses consisting of payroll and related costs from management services contracts and recognized corresponding revenue of approximately $2.5 million and $7.4 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 $7.7 million , an increase to net cash used in investing activities totaling approximately $28.5 million , a decrease to net cash provided by financing activities totaling approximately $0.2 million , and a corresponding decrease to the net increase in cash and cash equivalents and cash held in escrows totaling approximately $20.6 million from amounts previously reported for the nine months ended September 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 September 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 (1) simplifies transition requirements for both lessees and lessors by adding an option that permits an organization to apply the transition provisions of the new standard at its adoption date instead of at the earliest comparative period presented in its financial statements and (2) allows lessors to elect, as a practical expedient, by class of underlying asset, to not separate nonlease components from the associated lease component and, instead, to account for those components as a single component if the nonlease components otherwise would be accounted for under the new revenue guidance (ASC 606) and both of the following are met: (1) The timing and pattern of transfer of the nonlease component(s) and associated lease components are the same; and (2) the lease component, if accounted for separately, would be classified as an operating lease. If the nonlease component or components associated with the lease component are the predominant component of the combined component, an entity is required to account for the combined component in accordance with ASC 606. Certain disclosures are required if applying this practical expedient. 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 non-incremental 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. Financial Instruments - Credit Losses In June 2016, the FASB issued ASU 2016-13, “Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments” (“ASU 2016-13”). ASU 2016-13 is intended to provide financial statement users with more decision-useful information about the expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date. To achieve this objective, ASU 2016-13 replaces the current incurred loss impairment methodology with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. ASU 2016-13 is effective for the Company for reporting periods beginning after December 15, 2019, with early adoption permitted. The Company is assessing the potential impact that the adoption of ASU 2016-13 will have on its consolidated financial statements. Fair Value Measurement In August 2018, the FASB issued ASU 2018-13, “Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement” (“ASU 2018-13”). ASU 2018-13 is intended to improve the effectiveness of disclosures required by entities regarding recurring and nonrecurring fair value measurements. ASU 2018-13 is effective for the Company for reporting periods beginning after December 15, 2019, with early adoption permitted. The adoption of ASU 2018-13 will not have a material impact on the Company's consolidated financial statements. Consolidation In October 2018, the FASB issued ASU 2018-17, “Consolidation (Topic 810): Targeted Improvements to Related Party Guidance for Variable Interest Entities” (“ASU 2018-17”). ASU 2018-17 is intended to improve the accounting when considering indirect interests held through related parties under common control for determining whether fees paid to decision makers and service providers are variable interests. ASU 2018-17 is effective for the Company for reporting periods beginning after December 15, 2019, with early adoption permitted. The Company is assessing the potential impact that the adoption of ASU 2018-17 will have on its consolidated financial statements.
Revenue from Contracts with Customers [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 nine months ended September 30, 2018, the Company recognized approximately $2.5 million and $7.4 million , respectively, of expenses consisting of payroll and related costs from management services contracts and recognized corresponding revenue of approximately $2.5 million and $7.4 million , respectively, reflecting the direct reimbursements of such costs from the unconsolidated joint venture entities and third-party property owners.
Statement of Cash Flows [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 $7.7 million , an increase to net cash used in investing activities totaling approximately $28.5 million , a decrease to net cash provided by financing activities totaling approximately $0.2 million , and a corresponding decrease to the net increase in cash and cash equivalents and cash held in escrows totaling approximately $20.6 million from amounts previously reported for the nine months ended September 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 September 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.
Leases [Policy Text Block]	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 (1) simplifies transition requirements for both lessees and lessors by adding an option that permits an organization to apply the transition provisions of the new standard at its adoption date instead of at the earliest comparative period presented in its financial statements and (2) allows lessors to elect, as a practical expedient, by class of underlying asset, to not separate nonlease components from the associated lease component and, instead, to account for those components as a single component if the nonlease components otherwise would be accounted for under the new revenue guidance (ASC 606) and both of the following are met: (1) The timing and pattern of transfer of the nonlease component(s) and associated lease components are the same; and (2) the lease component, if accounted for separately, would be classified as an operating lease. If the nonlease component or components associated with the lease component are the predominant component of the combined component, an entity is required to account for the combined component in accordance with ASC 606. Certain disclosures are required if applying this practical expedient. 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 non-incremental 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.
Fair Value Measurement, Policy [Policy Text Block]	Fair Value Measurement In August 2018, the FASB issued ASU 2018-13, “Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement” (“ASU 2018-13”). ASU 2018-13 is intended to improve the effectiveness of disclosures required by entities regarding recurring and nonrecurring fair value measurements. ASU 2018-13 is effective for the Company for reporting periods beginning after December 15, 2019, with early adoption permitted. The adoption of ASU 2018-13 will not have a material impact on the Company's consolidated financial statements.
Consolidation, Variable Interest Entity, Policy [Policy Text Block]	Consolidation In October 2018, the FASB issued ASU 2018-17, “Consolidation (Topic 810): Targeted Improvements to Related Party Guidance for Variable Interest Entities” (“ASU 2018-17”). ASU 2018-17 is intended to improve the accounting when considering indirect interests held through related parties under common control for determining whether fees paid to decision makers and service providers are variable interests. ASU 2018-17 is effective for the Company for reporting periods beginning after December 15, 2019, with early adoption permitted. The Company is assessing the potential impact that the adoption of ASU 2018-17 will have on its consolidated financial statements.
Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue from Contracts with Customers [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 Sum_3

Basis Of Presentation And Summary Of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 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, related party note receivable, 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 September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Related party note receivable $ 80,000 $ 80,000 $ — $ — Mortgage notes payable, net $ 2,967,548 $ 2,898,871 $ 2,979,281 $ 3,042,920 Unsecured senior notes, net 7,253,786 7,174,434 7,247,330 7,461,615 Unsecured line of credit 170,000 170,287 45,000 45,000 Unsecured term loan, net 498,368 502,110 — — Total $ 10,889,702 $ 10,745,702 $ 10,271,611 $ 10,549,535

Real Estate (Tables)

Real Estate (Tables)	9 Months Ended
	Sep. 30, 2018
Entity Information [Line Items]
Schedule of Real Estate Properties [Table Text Block]	Boston Properties, Inc. Real estate consisted of the following at September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Land $ 5,108,491 $ 5,080,679 Land held for future development (1) 205,096 204,925 Buildings and improvements 12,949,543 12,284,164 Tenant improvements 2,322,552 2,219,608 Furniture, fixtures and equipment 44,696 37,928 Construction in progress 1,057,261 1,269,338 Total 21,687,639 21,096,642 Less: Accumulated depreciation (4,838,496 ) (4,589,634 ) $ 16,849,143 $ 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 September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Land $ 5,005,507 $ 4,976,303 Land held for future development (1) 205,096 204,925 Buildings and improvements 12,646,614 11,977,062 Tenant improvements 2,322,552 2,219,608 Furniture, fixtures and equipment 44,696 37,928 Construction in progress 1,057,261 1,269,338 Total 21,281,726 20,685,164 Less: Accumulated depreciation (4,741,280 ) (4,496,959 ) $ 16,540,446 $ 16,188,205 _______________ (1) Includes pre-development costs.

Investments in Unconsolidated_2

Investments in Unconsolidated Joint Ventures (Tables)	9 Months Ended
	Sep. 30, 2018
Schedule of Equity Method Investments [Line Items]
Investments In Unconsolidated Joint Ventures	The investments in unconsolidated joint ventures consist of the following at September 30, 2018 and December 31, 2017 : Nominal % Ownership Carrying Value of Investment (1) Entity Properties September 30, 2018 December 31, 2017 (in thousands) Square 407 Limited Partnership Market Square North 50.0 % $ (6,870 ) $ (8,258 ) The Metropolitan Square Associates LLC Metropolitan Square 20.0 % 1,220 3,339 BP/CRF 901 New York Avenue LLC 901 New York Avenue 25.0 % (2) (12,454 ) (13,811 ) WP Project Developer LLC Wisconsin Place Land and Infrastructure 33.3 % (3) 38,667 39,710 Annapolis Junction NFM LLC Annapolis Junction 50.0 % (4) 17,309 18,381 540 Madison Venture LLC 540 Madison Avenue 60.0 % 66,492 66,179 500 North Capitol Venture LLC 500 North Capitol Street, NW 30.0 % (4,699 ) (3,876 ) 501 K Street LLC 1001 6th Street 50.0 % (5) 42,584 42,657 Podium Developer LLC The Hub on Causeway - Podium 50.0 % 68,919 67,120 Residential Tower Developer LLC The Hub on Causeway - Residential 50.0 % 46,655 28,212 Hotel Tower Developer LLC The Hub on Causeway - Hotel Air Rights 50.0 % 2,738 1,690 Office Tower Developer LLC 100 Causeway Street 50.0 % (6) 12,232 — 1265 Main Office JV LLC 1265 Main Street 50.0 % 4,313 4,641 BNY Tower Holdings LLC Dock 72 50.0 % 72,100 72,104 CA-Colorado Center Limited Partnership Colorado Center 50.0 % 253,334 254,440 7750 Wisconsin Avenue LLC 7750 Wisconsin Avenue 50.0 % (6) 69,007 21,452 BP-M 3HB Venture LLC 3 Hudson Boulevard 25.0 % 46,240 — SMBP Venture LP Santa Monica Business Park 55.0 % 183,621 — $ 901,408 $ 593,980 _______________ (1) Investments with deficit balances aggregating approximately $24.0 million and $25.9 million at September 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 to the Consolidated Financial Statements).
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: September 30, 2018 December 31, 2017 (in thousands) ASSETS Real estate and development in process, net $ 3,475,909 $ 1,768,996 Other assets 523,177 367,743 Total assets $ 3,999,086 $ 2,136,739 LIABILITIES AND MEMBERS’/PARTNERS’ EQUITY Mortgage and notes payable, net $ 1,975,260 $ 1,437,440 Other liabilities 589,394 99,215 Members’/Partners’ equity 1,434,432 600,084 Total liabilities and members’/partners’ equity $ 3,999,086 $ 2,136,739 Company’s share of equity $ 593,427 $ 286,495 Basis differentials (1) 307,981 307,485 Carrying value of the Company’s investments in unconsolidated joint ventures (2) $ 901,408 $ 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 September 30, 2018 and December 31, 2017 , there was an aggregate basis differential of approximately $318.2 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 $24.0 million and $25.9 million at September 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 September 30, Nine months ended September 30, 2018 2017 2018 2017 (in thousands) Total revenue (1) $ 76,177 $ 55,516 $ 189,759 $ 166,139 Expenses Operating 29,522 23,128 75,239 67,310 Depreciation and amortization (2) 44,993 16,440 74,245 44,973 Total expenses 74,515 39,568 149,484 112,283 Operating income 1,662 15,948 40,275 53,856 Other expense Interest expense 19,861 13,088 48,993 31,815 Net income (loss) $ (18,199 ) $ 2,860 $ (8,718 ) $ 22,041 Company’s share of net income (loss) $ (2,858 ) $ 2,909 $ 1,073 $ 11,576 Basis differential (3) (1,455 ) (2,066 ) (4,156 ) (4,541 ) Income (loss) from unconsolidated joint ventures (2) $ (4,313 ) $ 843 $ (3,083 ) $ 7,035 _______________ (1) Includes straight-line rent adjustments of approximately $4.8 million and $5.1 million for the three months ended September 30, 2018 and 2017 , respectively, and $9.8 million and $16.4 million for the nine months ended September 30, 2018 and 2017 , respectively. (2) During the three months ended September 30, 2018, the joint venture that owns Metropolitan Square, in Washington, DC, commenced a renovation project and recorded accelerated depreciation of approximately $22.4 million related to the remaining book value of the asset to be replaced. The Company's share of the accelerated depreciation totaled approximately $4.5 million . (3) Includes straight-line rent adjustments of approximately $0.5 million and $0.7 million for the three months ended September 30, 2018 and 2017 , respectively, and $1.9 million and $2.2 million for the nine months ended September 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 September 30, 2018 and 2017 , respectively, and $1.2 million and $1.3 million for the nine months ended September 30, 2018 and 2017 , respectively.
SMBP Venture LP [Member]
Schedule of Equity Method Investments [Line Items]
Schedule of Asset Acquistion [Table Text Block]	The following table summarizes the allocation of the joint venture's aggregate purchase price for Santa Monica Business Park at the date of acquisition (in thousands). Land and improvements $ 100,525 Leasehold interest in land 248,944 Site improvements 13,381 Building and improvements 593,759 Tenant improvements 31,338 In-place lease intangibles 47,783 Above-market lease intangible 4,495 Below-market lease intangible (17,504 ) Capital lease obligation (396,008 ) Net assets acquired $ 626,713

Noncontrolling Interests (Table

Noncontrolling Interests (Tables)	9 Months Ended
	Sep. 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) September 28, 2018 October 31, 2018 $0.95 $0.95 June 29, 2018 July 31, 2018 $0.80 $0.80 March 29, 2018 April 30, 2018 $0.80 $0.80 December 29, 2017 January 30, 2018 $0.80 $0.80
Schedule Of Noncontrolling Interest Common Units [Table Text Block]	The following table reflects the activity of noncontrolling interests—redeemable partnership units of Boston Properties Limited Partnership for the nine months ended September 30, 2018 and 2017 (in thousands): Balance at December 31, 2017 $ 2,292,263 Contributions 34,970 Net income 49,128 Distributions (45,730 ) Conversion of redeemable partnership units (2,112 ) Unearned compensation (5,754 ) Cumulative effect of a change in accounting principle 563 Other comprehensive income 599 Adjustment to reflect redeemable partnership units at redemption value (133,263 ) Balance at September 30, 2018 $ 2,190,664 Balance at December 31, 2016 $ 2,262,040 Contributions 31,465 Net income 40,350 Distributions (40,292 ) Conversion of redeemable partnership units (16,812 ) Unearned compensation (5,194 ) Cumulative effect of a change in accounting principle (1,763 ) Other comprehensive income 52 Adjustment to reflect redeemable partnership units at redemption value (103,556 ) Balance at September 30, 2017 $ 2,166,290
Schedule Of Noncontrolling Interest Property Partnerships [Table Text Block]	The following table reflects the activity of the noncontrolling interests — property partnerships for the nine months ended September 30, 2018 and 2017 (in thousands): Balance at December 31, 2017 $ 1,683,760 Capital contributions 37,148 Net income 46,484 Accumulated other comprehensive income 432 Distributions (56,796 ) Balance at September 30, 2018 $ 1,711,028 Balance at December 31, 2016 $ 1,530,647 Capital contributions 147,772 Net income 33,967 Accumulated other comprehensive loss (2,272 ) Distributions (41,439 ) Balance at September 30, 2017 $ 1,668,675
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 September 28, 2018 October 31, 2018 $0.95 $0.095 June 29, 2018 July 31, 2018 $0.80 $0.080 March 29, 2018 April 30, 2018 $0.80 $0.080 December 29, 2017 January 30, 2018 $0.80 $0.080

Stockholders' Equity _ Partne_2

Stockholders' Equity / Partners' Capital Tables (Tables)	9 Months Ended
	Sep. 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) September 28, 2018 October 31, 2018 $0.95 $0.95 June 29, 2018 July 31, 2018 $0.80 $0.80 March 29, 2018 April 30, 2018 $0.80 $0.80 December 29, 2017 January 30, 2018 $0.80 $0.80
Series B 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) November 2, 2018 November 15, 2018 $32.8125 August 3, 2018 August 15, 2018 $32.8125 May 4, 2018 May 15, 2018 $32.8125 February 2, 2018 February 15, 2018 $32.8125

Earnings Per Share _ Common U_2

Earnings Per Share / Common Unit (Tables)	9 Months Ended
	Sep. 30, 2018
Entity Information [Line Items]
Computation Of Basic And Diluted Earnings Per Share	Three months ended September 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 $ 119,118 154,440 $ 0.77 Effect of Dilutive Securities: Stock Based Compensation — 238 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 119,118 154,678 $ 0.77 Three months ended September 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 $ 117,337 154,355 $ 0.76 Allocation of undistributed earnings to participating securities (7 ) — — Net income attributable to Boston Properties, Inc. common shareholders $ 117,330 154,355 $ 0.76 Effect of Dilutive Securities: Stock Based Compensation — 128 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 117,330 154,483 $ 0.76 Nine months ended September 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 $ 423,835 154,414 $ 2.74 Allocation of undistributed earnings to participating securities (87 ) — — Net income attributable to Boston Properties, Inc. common shareholders $ 423,748 154,414 $ 2.74 Effect of Dilutive Securities: Stock Based Compensation — 238 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 423,748 154,652 $ 2.74 Nine months ended September 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 $ 348,086 154,132 $ 2.26 Allocation of undistributed earnings to participating securities (15 ) — — Net income attributable to Boston Properties, Inc. common shareholders $ 348,071 154,132 $ 2.26 Effect of Dilutive Securities: Stock Based Compensation — 212 — Diluted Earnings: Net income attributable to Boston Properties, Inc. common shareholders $ 348,071 154,344 $ 2.26
Boston Properties Limited Partnership
Entity Information [Line Items]
Computation Of Basic And Diluted Earnings Per Share	Three months ended September 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 $ 136,201 171,928 $ 0.79 Effect of Dilutive Securities: Stock Based Compensation — 238 — Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 136,201 172,166 $ 0.79 Three months ended September 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 $ 132,693 171,691 $ 0.77 Allocation of undistributed earnings to participating securities (8 ) — — Net income attributable to Boston Properties Limited Partnership common unitholders $ 132,685 171,691 $ 0.77 Effect of Dilutive Securities: Stock Based Compensation — 128 — Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 132,685 171,819 $ 0.77 Nine months ended September 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 $ 483,069 171,904 $ 2.81 Allocation of undistributed earnings to participating securities (97 ) — — Net income attributable to Boston Properties Limited Partnership common unitholders $ 482,972 171,904 $ 2.81 Effect of Dilutive Securities: Stock Based Compensation — 238 — Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 482,972 172,142 $ 2.81 Nine months ended September 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 $ 395,199 171,649 $ 2.30 Allocation of undistributed earnings to participating securities (17 ) — — Net income attributable to Boston Properties Limited Partnership common unitholders $ 395,182 171,649 $ 2.30 Effect of Dilutive Securities: Stock Based Compensation — 212 — Diluted Earnings: Net income attributable to Boston Properties Limited Partnership common unitholders $ 395,182 171,861 $ 2.30

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 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 nine months ended September 30, 2018 and 2017 . Boston Properties, Inc. Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (in thousands) Net income attributable to Boston Properties, Inc. common shareholders $ 119,118 $ 117,337 $ 423,835 $ 348,086 Add: Preferred dividends 2,625 2,625 7,875 7,875 Noncontrolling interest—common units of Boston Properties Limited Partnership 13,852 13,402 49,128 40,350 Noncontrolling interests in property partnerships 14,850 14,340 46,484 33,967 Interest expense 95,366 92,032 277,790 282,709 Depreciation and amortization expense 157,996 152,164 480,210 463,288 Transaction costs 914 239 1,409 572 Payroll and related costs from management services contracts 2,516 — 7,371 — General and administrative expense 29,677 25,792 94,039 84,319 Less: Gains from early extinguishments of debt — — — 14,354 Gains from investments in securities 1,075 944 1,454 2,716 Interest and other income 2,822 1,329 7,049 3,447 Gains on sales of real estate 7,863 2,891 122,552 6,791 Income (loss) from unconsolidated joint ventures (4,313 ) 843 (3,083 ) 7,035 Direct reimbursements of payroll and related costs from management services contracts 2,516 — 7,371 — Development and management services revenue 15,253 10,811 32,963 24,648 Net Operating Income $ 411,698 $ 401,113 $ 1,219,835 $ 1,202,175 Boston Properties Limited Partnership Three months ended September 30, Nine months ended September 30, 2018 2017 2018 2017 (in thousands) Net income attributable to Boston Properties Limited Partnership common unitholders $ 136,201 $ 132,693 $ 483,069 $ 395,199 Add: Preferred distributions 2,625 2,625 7,875 7,875 Noncontrolling interests in property partnerships 14,850 14,340 46,484 33,967 Interest expense 95,366 92,032 277,790 282,709 Depreciation and amortization expense 156,056 150,210 474,383 457,102 Transaction costs 914 239 1,409 572 Payroll and related costs from management services contracts 2,516 — 7,371 — General and administrative expense 29,677 25,792 94,039 84,319 Less: Gains from early extinguishments of debt — — — 14,354 Gains from investments in securities 1,075 944 1,454 2,716 Interest and other income 2,822 1,329 7,049 3,447 Gains on sales of real estate 9,154 2,891 126,831 7,368 Income (loss) from unconsolidated joint ventures (4,313 ) 843 (3,083 ) 7,035 Direct reimbursements of payroll and related costs from management services contracts 2,516 — 7,371 — Development and management services revenue 15,253 10,811 32,963 24,648 Net Operating Income $ 411,698 $ 401,113 $ 1,219,835 $ 1,202,175
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 September 30, 2018 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 210,277 $ 237,944 $ 102,035 $ 98,275 $ 648,531 Residential 1,905 — — 4,415 6,320 Hotel 13,664 — — — 13,664 Total 225,846 237,944 102,035 102,690 668,515 % of Grand Totals 33.78 % 35.60 % 15.26 % 15.36 % 100.00 % Rental Expenses: Office 78,089 96,795 34,016 35,365 244,265 Residential 1,159 — — 2,565 3,724 Hotel 8,828 — — — 8,828 Total 88,076 96,795 34,016 37,930 256,817 % of Grand Totals 34.30 % 37.68 % 13.25 % 14.77 % 100.00 % Net operating income $ 137,770 $ 141,149 $ 68,019 $ 64,760 $ 411,698 % of Grand Totals 33.46 % 34.29 % 16.52 % 15.73 % 100.00 % For the three months ended September 30, 2017 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 196,687 $ 242,071 $ 87,162 $ 103,622 $ 629,542 Residential 1,228 — — 3,067 4,295 Hotel 13,064 — — — 13,064 Total 210,979 242,071 87,162 106,689 646,901 % of Grand Totals 32.61 % 37.43 % 13.47 % 16.49 % 100.00 % Rental Expenses: Office 76,086 95,775 26,792 37,111 235,764 Residential 512 — — 1,065 1,577 Hotel 8,447 — — — 8,447 Total 85,045 95,775 26,792 38,176 245,788 % of Grand Totals 34.60 % 38.97 % 10.90 % 15.53 % 100.00 % Net operating income $ 125,934 $ 146,296 $ 60,370 $ 68,513 $ 401,113 % of Grand Totals 31.40 % 36.47 % 15.05 % 17.08 % 100.00 % For the nine months ended September 30, 2018 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 623,084 $ 714,348 $ 285,410 $ 296,092 $ 1,918,934 Residential 4,252 — — 11,026 15,278 Hotel 37,373 — — — 37,373 Total 664,709 714,348 285,410 307,118 1,971,585 % of Grand Totals 33.71 % 36.23 % 14.48 % 15.58 % 100.00 % Rental Expenses: Office 235,560 282,395 92,858 106,386 717,199 Residential 2,379 — — 6,530 8,909 Hotel 25,642 — — — 25,642 Total 263,581 282,395 92,858 112,916 751,750 % of Grand Totals 35.06 % 37.57 % 12.35 % 15.02 % 100.00 % Net operating income $ 401,128 $ 431,953 $ 192,552 $ 194,202 $ 1,219,835 % of Grand Totals 32.88 % 35.41 % 15.79 % 15.92 % 100.00 % For the nine months ended September 30, 2017 : Boston New York San Francisco Washington, DC Total Rental Revenue: Office $ 573,883 $ 735,485 $ 257,286 $ 309,225 $ 1,875,879 Residential 3,520 — — 8,941 12,461 Hotel 33,859 — — — 33,859 Total 611,262 735,485 257,286 318,166 1,922,199 % of Grand Totals 31.80 % 38.27 % 13.38 % 16.55 % 100.00 % Rental Expenses: Office 225,502 280,569 77,204 108,044 691,319 Residential 1,552 — — 3,211 4,763 Hotel 23,942 — — — 23,942 Total 250,996 280,569 77,204 111,255 720,024 % of Grand Totals 34.86 % 38.97 % 10.72 % 15.45 % 100.00 % Net operating income $ 360,266 $ 454,916 $ 180,082 $ 206,911 $ 1,202,175 % of Grand Totals 29.97 % 37.84 % 14.98 % 17.21 % 100.00 %

Organization (Details)

Organization (Details) ft² in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2018ft²Real_Estate_Propertiesseriesyrshares	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	200
Net Rentable Area (in sf) | ft²	52.7
Total Properties Under Construction [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	14
Net Rentable Area (in sf) | ft²	7.5
Total Office Properties [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	180
Office Properties Under Construction [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	12
Residential Properties [Member]
Real Estate Properties [Line Items]
Number of real estate properties	6
Residential Properties Under Construction [Member]
Real Estate Properties [Line Items]
Number of real estate properties	2
Retail Properties [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	13
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 Sum_4

Basis Of Presentation And Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Entity Information [Line Items]
Payroll and related costs from management services contracts	$ 2,516	$ 0	$ 7,371	$ 0
Direct reimbursements of payroll and related costs from management services contracts	2,516	0	7,371	0
Net Cash Provided by (Used in) Operating Activities			770,627	584,965
Cumulative effect of a change in accounting principle			5,496	(2,035)
Net Cash Provided by (Used in) Investing Activities			1,020,067	593,895
Net Cash Provided by (Used in) Financing Activities			167,855	165,676
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect			(81,585)	156,746
Interest Expense	95,366	92,032	277,790	282,709
Boston Properties Limited Partnership
Entity Information [Line Items]
Payroll and related costs from management services contracts	2,516	0	7,371	0
Direct reimbursements of payroll and related costs from management services contracts	2,516	0	7,371	0
Net Cash Provided by (Used in) Operating Activities			770,627	584,965
Cumulative effect of a change in accounting principle			4,933	(272)
Net Cash Provided by (Used in) Investing Activities			1,020,067	593,895
Net Cash Provided by (Used in) Financing Activities			167,855	165,676
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect			(81,585)	156,746
Interest Expense	95,366	$ 92,032	277,790	282,709
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	2,500		7,400
Direct reimbursements of payroll and related costs from management services contracts	2,500		7,400
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				(7,700)
Net Cash Provided by (Used in) Investing Activities				28,500
Net Cash Provided by (Used in) Financing Activities				(200)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect				$ (20,600)
Accounting Standards Update 2017-12 [Member]
Entity Information [Line Items]
Interest Expense	$ 1,700

Basis Of Presentation And Sum_5

Basis Of Presentation And Summary Of Significant Accounting Policies (Carrying Value Of note receivable, Indebtedness And Corresponding Estimate Of Fair Value) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Summary Of Significant Accounting Policies [Line Items]
Related party note receivable	$ 80,000	$ 0
Mortgage notes payable, net	2,967,548	2,979,281
Unsecured senior notes, net	7,253,786	7,247,330
Unsecured line of credit	170,000	45,000
Unsecured term loan, net	498,368	0
Carrying Amount [Member]
Summary Of Significant Accounting Policies [Line Items]
Related party note receivable	80,000	0
Mortgage notes payable, net	2,967,548	2,979,281
Unsecured senior notes, net	7,253,786	7,247,330
Unsecured line of credit	170,000	45,000
Unsecured term loan, net	498,368	0
Total	10,889,702	10,271,611
Estimated Fair Value [Member]
Summary Of Significant Accounting Policies [Line Items]
Related party note receivable	80,000	0
Mortgage notes payable, net	2,898,871	3,042,920
Unsecured senior notes, net	7,174,434	7,461,615
Unsecured line of credit	170,287	45,000
Unsecured term loan, net	502,110	0
Total	$ 10,745,702	$ 10,549,535

Real Estate Properties Table (D

Real Estate Properties Table (Details) - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land		$ 5,108,491	$ 5,080,679
Land held for future development	[1]	205,096	204,925
Buildings and improvements		12,949,543	12,284,164
Tenant improvements		2,322,552	2,219,608
Furniture, fixtures and equipment		44,696	37,928
Construction in progress		1,057,261	1,269,338
Total		21,687,639	21,096,642
Accumulated depreciation		(4,838,496)	(4,589,634)
Total real estate		16,849,143	16,507,008
Boston Properties Limited Partnership
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Land		5,005,507	4,976,303
Land held for future development	[1]	205,096	204,925
Buildings and improvements		12,646,614	11,977,062
Tenant improvements		2,322,552	2,219,608
Furniture, fixtures and equipment		44,696	37,928
Construction in progress		1,057,261	1,269,338
Total		21,281,726	20,685,164
Accumulated depreciation		(4,741,280)	(4,496,959)
Total real estate		$ 16,540,446	$ 16,188,205
[1]	Includes pre-development costs.

Real Estate Narrative (Details)

Real Estate Narrative (Details) $ in Thousands

Sep. 27, 2018USD ($)ft²

May 24, 2018USD ($)ft²

Feb. 23, 2018ft²Buildings

Jan. 09, 2018USD ($)ft²

Jan. 08, 2018USD ($)

Sep. 30, 2018USD ($)ft²

Sep. 26, 2018USD ($)

Sep. 30, 2017USD ($)

May 23, 2018USD ($)

Sep. 30, 2018USD ($)ft²

Sep. 26, 2018USD ($)

Sep. 30, 2017USD ($)

Sep. 01, 2018ft²apartments

Aug. 30, 2018USD ($)ft²

Aug. 07, 2018ft²

Jun. 07, 2018ft²apartments

Jan. 24, 2018ft²

Real Estate [Line Items]

Proceeds from sales of real estate

$ 175,577

$ 29,810

Gains on sales of real estate

$ 7,863

$ 2,891

122,552

6,791

Boston Properties Limited Partnership

Real Estate [Line Items]

Proceeds from sales of real estate

175,577

29,810

Gains on sales of real estate

$ 9,154

2,891

$ 126,831

7,368

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

Number of real estate properties | Buildings

2

Proto Kendall Square [Member]

Real Estate [Line Items]

Net Rentable Area (in sf) | ft²

167,000

Number of apartment units | apartments

280

343 Madison Avenue [Member]

Real Estate [Line Items]

Net Rentable Area (in sf) | ft²

850,000

Ownership Percentage by the Company

55.00%

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

1,700

4,900

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

400

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

1333 New Hampshire Avenue [Member]

Real Estate [Line Items]

Net Rentable Area (in sf) | ft²

316,000

Gross Sale Price

$ 136,500

Quorum Office Park [Member]

Real Estate [Line Items]

Net Rentable Area (in sf) | ft²

268,000

Gross Sale Price

$ 35,300

Net income (loss)

$ 200

$ 300

$ 700

$ 700

Proceeds from sales of real estate

34,300

Gains on sales of real estate

7,900

Quorum Office Park [Member] | Boston Properties Limited Partnership

Real Estate [Line Items]

Gains on sales of real estate

$ 9,200

Carnegie Center purchase option [Member]

Real Estate [Line Items]

Net Rentable Area (in sf) | ft²

1,700,000

1,700,000

Aggregate purchase price

$ 42,400

$ 42,400

Deferred purchase price

$ 9,200

$ 9,200

Investments in Unconsolidated_3

Investments in Unconsolidated Joint Ventures (Investments in Unconsolidated Joint Ventures) (Details) $ in Thousands		Jul. 13, 2018ft²	Sep. 30, 2018USD ($)ft²Land_ParcelsBuildingspayments		Jul. 27, 2018ft²	Dec. 31, 2017USD ($)
Schedule of Equity Method Investments [Line Items]
Carrying Value of investment			$ (468,433)			$ (443,980)
Carrying value of the Company's investments in unconsolidated joint ventures			$ 925,431			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]		$ (6,870)			(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]		$ 1,220			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]		$ (12,454)			(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]		$ 38,667			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]		$ 17,309			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]		$ 66,492			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]		$ (4,699)			(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]		$ 42,584			42,657
Potential additonal payments to joint venture partner | payments			2
Minimum square footage to make a potential additional payment to joint venture partner (in sqft) | ft²			520,000
Podium Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties			The Hub on Causeway - Podium
Ownership Percentage			50.00%
Carrying value of the Company's investments in unconsolidated joint ventures	[1]		$ 68,919			67,120
Residential Tower Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties			The Hub on Causeway - Residential
Ownership Percentage			50.00%
Carrying value of the Company's investments in unconsolidated joint ventures	[1]		$ 46,655			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]		$ 2,738			1,690
Office Tower Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties			100 Causeway Street
Ownership Percentage			50.00%	[6]	50.00%
Carrying value of the Company's investments in unconsolidated joint ventures	[1]		$ 12,232			0
Net Rentable Area (in sf) | ft²					627,000
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]		$ 4,313			4,641
BNY Tower Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties			Dock 72
Ownership Percentage			50.00%
Carrying value of the Company's investments in unconsolidated joint ventures	[1]		$ 72,100			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]		$ 253,334			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]		$ 69,007			21,452
BP-M 3HB Venture LLC [Member]
Schedule of Equity Method Investments [Line Items]
Debt Instrument, Basis Spread on Variable Rate		3.50%
Properties			3 Hudson Boulevard
Ownership Percentage		25.00%	25.00%
Carrying value of the Company's investments in unconsolidated joint ventures	[1]		$ 46,240			0
Net Rentable Area (in sf) | ft²		2,000,000
SMBP Venture LP [Member]
Schedule of Equity Method Investments [Line Items]
Properties			Santa Monica Business Park
Ownership Percentage			55.00%
Carrying value of the Company's investments in unconsolidated joint ventures	[1]		$ 183,621			0
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Carrying Value of investment			24,000			25,900
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Carrying Value of investment			(589,394)			(99,215)
Carrying value of the Company's investments in unconsolidated joint ventures	[1],[7]		$ 901,408			$ 593,980
[1]	Investments with deficit balances aggregating approximately $24.0 million and $25.9 million at September 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 to the Consolidated Financial Statements).
[7]	Investments with deficit balances aggregating approximately $24.0 million and $25.9 million at September 30, 2018 and December 31, 2017, respectively, have been reflected within Other Liabilities in the Company’s Consolidated Balance Sheet

Investments in Unconsolidated_4

Investments in Unconsolidated Joint Ventures (Balance Sheets of the Unconsolidated Joint Ventures) (Details) - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017
ASSETS
Real estate and development in process, net		$ 16,849,143	$ 16,507,008
Liabilities and Members'/Partners' Equity [Abstract]
Mortgage notes payable, net		2,967,548	2,979,281
Other Liabilities		468,433	443,980
Total liabilities and equity / capital		20,137,498	19,372,233
Carrying value of the Company's investments in unconsolidated joint ventures		925,431	619,925
Unconsolidated Joint Ventures [Member]
ASSETS
Real estate and development in process, net		3,475,909	1,768,996
Other assets		523,177	367,743
Total assets		3,999,086	2,136,739
Liabilities and Members'/Partners' Equity [Abstract]
Mortgage notes payable, net		1,975,260	1,437,440
Other Liabilities		589,394	99,215
Members'/Partners' equity		1,434,432	600,084
Total liabilities and equity / capital		3,999,086	2,136,739
Company's share of equity		593,427	286,495
Basis differentials	[1]	307,981	307,485
Carrying value of the Company's investments in unconsolidated joint ventures	[2],[3]	901,408	593,980
Unconsolidated Joint Ventures [Member]
Liabilities and Members'/Partners' Equity [Abstract]
Other Liabilities		(24,000)	(25,900)
Basis differentials		$ 318,200	$ 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 September 30, 2018 and December 31, 2017, there was an aggregate basis differential of approximately $318.2 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 $24.0 million and $25.9 million at September 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 $24.0 million and $25.9 million at September 30, 2018 and December 31, 2017, respectively, have been reflected within Other Liabilities in the Company’s Consolidated Balance Sheets.

Investments in Unconsolidated_5

Investments in Unconsolidated Joint Ventures (Statements of Operations of the Joint Ventures) (Details) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2018		Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Schedule of Equity Method Investments [Line Items]
Total revenue		$ 686,284		$ 657,712	$ 2,011,919	$ 1,946,847
Expenses
Depreciation and amortization		157,996		152,164	480,210	463,288
Total expenses		447,920		423,983	1,334,779	1,268,203
Operating income		238,364		233,729	677,140	678,644
Other expense
Interest expense		95,366		92,032	277,790	282,709
Net income (loss)		150,445		147,704	527,322	430,278
Income (loss) from unconsolidated joint ventures		(4,313)		843	(3,083)	7,035
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Total revenue	[1]	76,177		55,516	189,759	166,139
Expenses
Operating		29,522		23,128	75,239	67,310
Depreciation and amortization		44,993	[2]	16,440	74,245	44,973
Total expenses		74,515		39,568	149,484	112,283
Operating income		1,662		15,948	40,275	53,856
Other expense
Interest expense		19,861		13,088	48,993	31,815
Net income (loss)		(18,199)		2,860	(8,718)	22,041
Company's share of net income (loss)		(2,858)		2,909	1,073	11,576
Basis differential	[3]	(1,455)		(2,066)	(4,156)	(4,541)
Income (loss) from unconsolidated joint ventures		(4,313)		843	(3,083)	7,035
Straight-line rent adjustments		4,800		5,100	9,800	16,400
The Metropolitan Square Associates LLC [Member]
Expenses
Depreciation and amortization		22,400
The Metropolitan Square Associates LLC [Member] | BXP [Member]
Expenses
Depreciation and amortization		4,500
Colorado Center [Member] | Unconsolidated Joint Ventures [Member]
Other expense
Straight-line rent adjustments		500		700	1,900	2,200
"Above" and "below" market rent adjustments, net		$ 400		$ 400	$ 1,200	$ 1,300
[1]	Includes straight-line rent adjustments of approximately $4.8 million and $5.1 million for the three months ended September 30, 2018 and 2017, respectively, and $9.8 million and $16.4 million for the nine months ended September 30, 2018 and 2017
[2]	During the three months ended September 30, 2018, the joint venture that owns Metropolitan Square, in Washington, DC, commenced a renovation project and recorded accelerated depreciation of approximately $22.4 million related to the remaining book value of the asset to be replaced. The Company's share of the accelerated depreciation totaled approximately $4.5 million.
[3]	Includes straight-line rent adjustments of approximately $0.5 million and $0.7 million for the three months ended September 30, 2018 and 2017, respectively, and $1.9 million and $2.2 million for the nine months ended September 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 September 30, 2018 and 2017, respectively, and $1.2 million and $1.3 million for the nine months ended September 30, 2018 and 2017

Investments in Unconsolidated_6

Investments in Unconsolidated Joint Ventures Narrative (Details) $ in Thousands	Jul. 27, 2018USD ($)ft²yr	Jul. 19, 2018USD ($)ft²ayrBuildings	Jul. 13, 2018USD ($)ft²	Apr. 27, 2018USD ($)ft²	Apr. 26, 2018	Apr. 19, 2018USD ($)ft²yrapartments	Sep. 30, 2018USD ($)		Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Schedule of Equity Method Investments [Line Items]
Mortgage notes payable, net							$ 2,967,548			$ 2,979,281
Payments to Acquire Equity Method Investments							314,075		$ 89,874
Accumulated other comprehensive loss							$ (45,137)			$ (50,429)
100 Causeway Street [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage	50.00%						50.00%	[1]
Payment for improvements for equity method investment	$ 3,900
Net Rentable Area (in sf) | ft²	627,000
Payments to Acquire Equity Method Investments	$ 37,400
Term of Lease Signed (in years) | yr	20
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
Construction Loan						$ 8,200
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
Three Hudson Boulevard [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage			25.00%				25.00%
Mortgage notes payable, net			$ 80,000
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
Future payments to acquire equity method investments			$ 62,200
Santa Monica Business Park [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage							55.00%
Accumulated other comprehensive loss							$ 2,400
Santa Monica Business Park [Member] | Santa Monica Business Park [Member]
Schedule of Equity Method Investments [Line Items]
Mortgage notes payable, net		$ 300,000
Debt Instrument, Basis Spread on Variable Rate		1.28%
Net Rentable Area (in sf) | ft²		1,200,000
Payments to Acquire Equity Method Investments		$ 179,700
Aggregate purchase price		626,700
seller funded leasing costs		$ 11,500
Area of Land | a		47
number of buildings | Buildings		21
rentable square feet subject to a ground lease (percetnage)		70.00%
Term of Lease Signed (in years) | yr		80
Derivative, Notional Amount		$ 300,000
Derivative, Fixed Interest Rate		4.063%
Joint venture partner [Member] | 100 Causeway Street [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage	50.00%
Payments to Acquire Equity Method Investments	$ 41,300
Joint venture partner [Member] | Santa Monica Business Park [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		45.00%
Payments to Acquire Equity Method Investments		$ 147,000
BXP [Member]
Schedule of Equity Method Investments [Line Items]
Accumulated other comprehensive loss							$ 1,300
[1]	This entity is a VIE (See Note 2 to the Consolidated Financial Statements).

Investments in Unconsolidated_7

Investments in Unconsolidated Joint Ventures Purchase price allocation table (Details) - Santa Monica Business Park [Member] $ in Thousands	Jul. 19, 2018USD ($)
Schedule of Asset Acquisition [Line Items]
Land and improvements	$ 100,525
Leasehold interest in land	248,944
Site improvements	13,381
Building and improvements	593,759
Tenant improvements	31,338
In-place lease intangibles	47,783
Above-market lease intangible	4,495
Below-market lease intangible	(17,504)
Capital lease obligation	(396,008)
Net assets acquired	$ 626,713

Debt (Details)

Debt (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Apr. 24, 2018	Dec. 31, 2017	Apr. 24, 2017	Apr. 23, 2017
Debt Instrument [Line Items]
Unsecured term loan, net	$ 498,368		$ 0
Long-term Line of Credit	$ 170,000		$ 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%
Unsecured term loan, net	$ 170,000
Letters of Credit Outstanding, Amount	300
Line of Credit Facility, Remaining Borrowing Capacity	1,300,000
Delayed Draw Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity				$ 500,000
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	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2009	Sep. 13, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jan. 10, 2014
Commitments And Contingencies [Line Items]
Letter of credit and performance obligations	$ 7.8
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	126.4
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			$ 0.3	$ 0.4	$ 1.4	$ 8.1	$ 7.7
Bankruptcy remaining claim amount allowed by court to creditor	27.2
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	Sep. 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)	16,804,929
Long-Term Incentive Plan (LTIP) Units (in shares)	992,321
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 ($)shares	Sep. 30, 2018USD ($)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)		61,021
Redemption of OP units issued on conversion of LTIP Units (in shares)		47,985
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		$ 123.09
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	Jul. 31, 2018	Apr. 30, 2018	Jan. 30, 2018	Sep. 18, 2018
Dividends Payable [Line Items]
Distributions Declared To OP And LTIP Units Per Unit				$ 0.95
Distributions Declared To MYLTIP Units Per Unit (in dollars per unit)				$ 0.095
Distributions made to OP and LTIP units per unit (in dollars per unit)	$ 0.80	$ 0.80	$ 0.80
Distribution paid to MYLTIP Units (in dollars per unit)	$ 0.080	$ 0.080	$ 0.080

Noncontrolling Interests Comm_2

Noncontrolling Interests Common units for Boston Properties Limited Partnership (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 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	(45,137)		$ (50,429)
Noncontrolling Interests [Member]
Noncontrolling Interest [Line Items]
Conversion of redeemable partnership units	18,023	16,986
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	34,970	31,465
Net income	49,128	40,350
Distributions	(45,730)	(40,292)
Conversion of redeemable partnership units	(2,112)	(16,812)
Unearned compensation	(5,754)	(5,194)
Cumulative effect of a change in accounting principle	563	(1,763)
Other comprehensive income	599	52
Adjustments to reflect redeemable preferred units at redemption value	(133,263)	(103,556)
Ending balance	$ 2,190,664	$ 2,166,290

Noncontrolling Interests (Prope

Noncontrolling Interests (Property Partnerships) (Narrative) (Details) - USD ($) $ in Thousands	May 12, 2016	Sep. 30, 2018	Dec. 31, 2017
Noncontrolling Interest [Line Items]
Noncontrolling Interest in Limited Partnerships		$ 1,711,028	$ 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		$ 22,600

Noncontrolling Interests Proper

Noncontrolling Interests Property Partnerships (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Activity of Noncontrolling Interests [Roll Forward]
Beginning Balance			$ 1,683,760
Capital contributions			(37,148)	$ (147,772)
Net income	$ 14,850	$ 14,340	46,484	33,967
Accumulated other comprehensive income (loss)	(433)	(300)	(1,031)	2,220
Ending Balance	1,711,028		1,711,028
Property Partnerships Member
Activity of Noncontrolling Interests [Roll Forward]
Beginning Balance			1,683,760	1,530,647
Capital contributions			37,148	147,772
Net income			46,484	33,967
Accumulated other comprehensive income (loss)			432	(2,272)
Distributions			(56,796)	(41,439)
Ending Balance	$ 1,711,028	$ 1,668,675	$ 1,711,028	$ 1,668,675

Stockholders' Equity _ Partne_3

Stockholders' Equity / Partners' Capital Narrative (Details)	Jun. 02, 2017USD ($)yr	Sep. 30, 2018USD ($)$ / sharesshares	Mar. 27, 2018$ / shares	Dec. 31, 2017USD ($)$ / sharesshares	Jun. 03, 2014USD ($)
Class of Stock [Line Items]
Common stock, shares outstanding		154,440,239		154,325,286
General Partners' Capital Account, Units Outstanding		1,722,375
Limited Partners' Capital Account, Units Outstanding		152,717,864
Shares of Common Stock in connection with the redemption of an equal number of OP Units (in shares)		61,021
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		1,722,375		1,719,540
Limited Partners' Capital Account, Units Outstanding		152,717,864		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 _ Partne_4

Stockholders' Equity / Partners' Capital Stockholders' Equity / Partners' Capital Dividends / Distributions (Details) - $ / shares	Aug. 15, 2018	Jul. 31, 2018	May 15, 2018	Apr. 30, 2018	Feb. 15, 2018	Jan. 30, 2018	Sep. 18, 2018
Entity Information [Line Items]
Dividends Payable, Amount Per Share / Unit							$ 0.95
Dividends, Per Share / Unit		$ 0.80		$ 0.80		$ 0.80
Boston Properties Limited Partnership
Entity Information [Line Items]
Dividends Payable, Amount Per Share / Unit							0.95
Dividends, Per Share / Unit		$ 0.80		$ 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		$ 32.8125

Earnings Per Share _ Common U_3

Earnings Per Share / Common Unit (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Basic Earnings:
Net income attributable to the Company's common shareholders / unitholders	$ 119,118	$ 117,337	$ 423,835	$ 348,086
Net income attributable to the Company's common shareholders / unitholders (in shares / units)	154,440,000	154,355,000	154,414,000	154,132,000
Net income (in dollars per share / unit)	$ 0.77	$ 0.76	$ 2.74	$ 2.26
Allocation of undistributed earnings to participating securities (numerator)		$ (7)	$ (87)	$ (15)
Allocation of undistributed earnings to participating securities (in shares)		0	0	0
Allocation of undistributed earnings to participating securities (in dollars per shares / units)		$ 0	$ 0	$ 0
Net income attributable to the Company's common shareholders / unitholders		$ 117,330	$ 423,748	$ 348,071
Net income attributable to the Company's common shareholders / unitholders (in shares / units)		154,355,000	154,414,000	154,132,000
Net income attributable to the Company's common shareholders / unitholders (in dollars per share / unit)		$ 0.76	$ 2.74	$ 2.26
Effect of Dilutive Securities:
Stock Based Compensation, Income (Numerator)	$ 0	$ 0	$ 0	$ 0
Stock Based Compensation, Shares / Units (Denominator)	238,000	128,000	238,000	212,000
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)	$ 119,118	$ 117,330	$ 423,748	$ 348,071
Net income attributable to to the Company's shareholders / unitholder (number of shares)	154,678,000	154,483,000	154,652,000	154,344,000
Diluted Earnings: Net income, Per Share Amount (in dollars per share / unit)	$ 0.77	$ 0.76	$ 2.74	$ 2.26
Boston Properties Limited Partnership
Entity Information [Line Items]
Redeemable Common Units	17,488,000	17,336,000	17,490,000	17,517,000
Basic Earnings:
Net income attributable to the Company's common shareholders / unitholders	$ 136,201	$ 132,693	$ 483,069	$ 395,199
Net income attributable to the Company's common shareholders / unitholders (in shares / units)	171,928,000	171,691,000	171,904,000	171,649,000
Net income (in dollars per share / unit)	$ 0.79	$ 0.77	$ 2.81	$ 2.30
Allocation of undistributed earnings to participating securities (numerator)		$ (8)	$ (97)	$ (17)
Allocation of undistributed earnings to participating securities (in shares)		0	0	0
Allocation of undistributed earnings to participating securities (in dollars per shares / units)		$ 0	$ 0	$ 0
Net income attributable to the Company's common shareholders / unitholders		$ 132,685	$ 482,972	$ 395,182
Net income attributable to the Company's common shareholders / unitholders (in shares / units)		171,691,000	171,904,000	171,649,000
Net income attributable to the Company's common shareholders / unitholders (in dollars per share / unit)		$ 0.77	$ 2.81	$ 2.30
Effect of Dilutive Securities:
Stock Based Compensation, Income (Numerator)	$ 0	$ 0	$ 0	$ 0
Stock Based Compensation, Shares / Units (Denominator)	238,000	128,000	238,000	212,000
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)	$ 136,201	$ 132,685	$ 482,972	$ 395,182
Net income attributable to to the Company's shareholders / unitholder (number of shares)	172,166,000	171,819,000	172,142,000	171,861,000
Diluted Earnings: Net income, Per Share Amount (in dollars per share / unit)	$ 0.79	$ 0.77	$ 2.81	$ 2.30

Stock Option and Incentive Pl_2

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 Pl_3

Stock Option and Incentive Plan Restricted Stock (Narrative) (Details) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018USD ($)$ / sharesshares	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)VestingInstallments$ / sharesshares	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued | shares	154,519,139		154,519,139		154,404,186
Common Stock, Value, Issued	$ 1,544		$ 1,544		$ 1,543
Stock based compensation expense	$ 7,900	$ 7,500	$ 30,100	$ 25,600
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	$ 27,300		$ 27,300
Unvested MYLTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expenses	$ 18,800		$ 18,800
Weighted-average period (years)	2 years 6 months
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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 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	$ 119,118	$ 117,337	$ 423,835	$ 348,086
Preferred Stock Dividends / Distributions	(2,625)	(2,625)	(7,875)	(7,875)
Noncontrolling interest-common units of the Operating Partnership	(13,852)	(13,402)	(49,128)	(40,350)
Noncontrolling interest in property partnerships	(14,850)	(14,340)	(46,484)	(33,967)
Interest expense	(95,366)	(92,032)	(277,790)	(282,709)
Depreciation and amortization expense	(157,996)	(152,164)	(480,210)	(463,288)
Transaction costs	(914)	(239)	(1,409)	(572)
Payroll and related costs from management services contracts	(2,516)	0	(7,371)	0
General and administrative expense	(29,677)	(25,792)	(94,039)	(84,319)
Gains from early extinguishments of debt	0	0	0	(14,354)
Gains from investments in securities	(1,075)	(944)	(1,454)	(2,716)
Interest and other income	(2,822)	(1,329)	(7,049)	(3,447)
Income (loss) from unconsolidated joint ventures	4,313	(843)	3,083	(7,035)
Direct reimbursements of payroll and related costs from management services contracts	(2,516)	0	(7,371)	0
Development and management services income	(15,253)	(10,811)	(32,963)	(24,648)
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	119,118	117,337	423,835	348,086
Preferred Stock Dividends / Distributions	2,625	2,625	7,875	7,875
Noncontrolling interest-common units of the Operating Partnership	13,852	13,402	49,128	40,350
Noncontrolling interest in property partnerships	14,850	14,340	46,484	33,967
Interest expense	95,366	92,032	277,790	282,709
Depreciation and amortization expense	157,996	152,164	480,210	463,288
Transaction costs	914	239	1,409	572
Payroll and related costs from management services contracts	2,516	0	7,371	0
General and administrative expense	29,677	25,792	94,039	84,319
Gains from early extinguishments of debt	0	0	0	14,354
Gains from investments in securities	1,075	944	1,454	2,716
Interest and other income	2,822	1,329	7,049	3,447
Gains on sales of real estate	7,863	2,891	122,552	6,791
Income (loss) from unconsolidated joint ventures	(4,313)	843	(3,083)	7,035
Direct reimbursements of payroll and related costs from management services contracts	2,516	0	7,371	0
Development and management services income	15,253	10,811	32,963	24,648
Net Operating Income	411,698	401,113	1,219,835	1,202,175
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	136,201	132,693	483,069	395,199
Preferred Stock Dividends / Distributions	(2,625)	(2,625)	(7,875)	(7,875)
Noncontrolling interest in property partnerships	(14,850)	(14,340)	(46,484)	(33,967)
Interest expense	(95,366)	(92,032)	(277,790)	(282,709)
Depreciation and amortization expense	(156,056)	(150,210)	(474,383)	(457,102)
Transaction costs	(914)	(239)	(1,409)	(572)
Payroll and related costs from management services contracts	(2,516)	0	(7,371)	0
General and administrative expense	(29,677)	(25,792)	(94,039)	(84,319)
Gains from early extinguishments of debt	0	0	0	(14,354)
Gains from investments in securities	(1,075)	(944)	(1,454)	(2,716)
Interest and other income	(2,822)	(1,329)	(7,049)	(3,447)
Income (loss) from unconsolidated joint ventures	4,313	(843)	3,083	(7,035)
Direct reimbursements of payroll and related costs from management services contracts	(2,516)	0	(7,371)	0
Development and management services income	(15,253)	(10,811)	(32,963)	(24,648)
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	136,201	132,693	483,069	395,199
Preferred Stock Dividends / Distributions	2,625	2,625	7,875	7,875
Noncontrolling interest in property partnerships	14,850	14,340	46,484	33,967
Interest expense	95,366	92,032	277,790	282,709
Depreciation and amortization expense	156,056	150,210	474,383	457,102
Transaction costs	914	239	1,409	572
Payroll and related costs from management services contracts	2,516	0	7,371	0
General and administrative expense	29,677	25,792	94,039	84,319
Gains from early extinguishments of debt	0	0	0	14,354
Gains from investments in securities	1,075	944	1,454	2,716
Interest and other income	2,822	1,329	7,049	3,447
Gains on sales of real estate	9,154	2,891	126,831	7,368
Income (loss) from unconsolidated joint ventures	(4,313)	843	(3,083)	7,035
Direct reimbursements of payroll and related costs from management services contracts	2,516	0	7,371	0
Development and management services income	15,253	10,811	32,963	24,648
Net Operating Income	$ 411,698	$ 401,113	$ 1,219,835	$ 1,202,175

Segment Information (Schedule_2

Segment Information (Schedule Of Segment Reporting By Geographic Area And Property Type) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 648,531	$ 629,542	$ 1,918,934	$ 1,875,879
Rental Revenue: Residential	6,320	4,295	15,278	12,461
Rental Revenue: Hotel	13,664	13,064	37,373	33,859
Total revenue	$ 668,515	$ 646,901	$ 1,971,585	$ 1,922,199
Rental Revenue: % of Grand Totals	100.00%	100.00%	100.00%	100.00%
Rental Expenses: Office	$ 244,265	$ 235,764	$ 717,199	$ 691,319
Rental Expenses: Residential	3,724	1,577	8,909	4,763
Rental Expenses: Hotel	8,828	8,447	25,642	23,942
Rental Expenses: Total	$ 256,817	$ 245,788	$ 751,750	$ 720,024
Rental Expenses: % Of Grand Totals	100.00%	100.00%	100.00%	100.00%
Net operating Income	$ 411,698	$ 401,113	$ 1,219,835	$ 1,202,175
Net operating Income: % of Grand Totals	100.00%	100.00%	100.00%	100.00%
Boston [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 210,277	$ 196,687	$ 623,084	$ 573,883
Rental Revenue: Residential	1,905	1,228	4,252	3,520
Rental Revenue: Hotel	13,664	13,064	37,373	33,859
Total revenue	$ 225,846	$ 210,979	$ 664,709	$ 611,262
Rental Revenue: % of Grand Totals	33.78%	32.61%	33.71%	31.80%
Rental Expenses: Office	$ 78,089	$ 76,086	$ 235,560	$ 225,502
Rental Expenses: Residential	1,159	512	2,379	1,552
Rental Expenses: Hotel	8,828	8,447	25,642	23,942
Rental Expenses: Total	$ 88,076	$ 85,045	$ 263,581	$ 250,996
Rental Expenses: % Of Grand Totals	34.30%	34.60%	35.06%	34.86%
Net operating Income	$ 137,770	$ 125,934	$ 401,128	$ 360,266
Net operating Income: % of Grand Totals	33.46%	31.40%	32.88%	29.97%
New York [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 237,944	$ 242,071	$ 714,348	$ 735,485
Rental Revenue: Residential	0	0	0	0
Rental Revenue: Hotel	0	0	0	0
Total revenue	$ 237,944	$ 242,071	$ 714,348	$ 735,485
Rental Revenue: % of Grand Totals	35.60%	37.43%	36.23%	38.27%
Rental Expenses: Office	$ 96,795	$ 95,775	$ 282,395	$ 280,569
Rental Expenses: Residential	0	0	0	0
Rental Expenses: Hotel	0	0	0	0
Rental Expenses: Total	$ 96,795	$ 95,775	$ 282,395	$ 280,569
Rental Expenses: % Of Grand Totals	37.68%	38.97%	37.57%	38.97%
Net operating Income	$ 141,149	$ 146,296	$ 431,953	$ 454,916
Net operating Income: % of Grand Totals	34.29%	36.47%	35.41%	37.84%
San Francisco [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 102,035	$ 87,162	$ 285,410	$ 257,286
Rental Revenue: Residential	0	0	0	0
Rental Revenue: Hotel	0	0	0	0
Total revenue	$ 102,035	$ 87,162	$ 285,410	$ 257,286
Rental Revenue: % of Grand Totals	15.26%	13.47%	14.48%	13.38%
Rental Expenses: Office	$ 34,016	$ 26,792	$ 92,858	$ 77,204
Rental Expenses: Residential	0	0	0	0
Rental Expenses: Hotel	0	0	0	0
Rental Expenses: Total	$ 34,016	$ 26,792	$ 92,858	$ 77,204
Rental Expenses: % Of Grand Totals	13.25%	10.90%	12.35%	10.72%
Net operating Income	$ 68,019	$ 60,370	$ 192,552	$ 180,082
Net operating Income: % of Grand Totals	16.52%	15.05%	15.79%	14.98%
Washington, DC [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 98,275	$ 103,622	$ 296,092	$ 309,225
Rental Revenue: Residential	4,415	3,067	11,026	8,941
Rental Revenue: Hotel	0	0	0	0
Total revenue	$ 102,690	$ 106,689	$ 307,118	$ 318,166
Rental Revenue: % of Grand Totals	15.36%	16.49%	15.58%	16.55%
Rental Expenses: Office	$ 35,365	$ 37,111	$ 106,386	$ 108,044
Rental Expenses: Residential	2,565	1,065	6,530	3,211
Rental Expenses: Hotel	0	0	0	0
Rental Expenses: Total	$ 37,930	$ 38,176	$ 112,916	$ 111,255
Rental Expenses: % Of Grand Totals	14.77%	15.53%	15.02%	15.45%
Net operating Income	$ 64,760	$ 68,513	$ 194,202	$ 206,911
Net operating Income: % of Grand Totals	15.73%	17.08%	15.92%	17.21%