Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Net income	$ 408,647	$ 993,786
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	539,815	515,738
Amortization of right of use assets - operating leases	3,208	1,667
Non-cash compensation expense	43,098	36,152
Loss from unconsolidated joint ventures	1,745	5,410
Distributions of net cash flow from operations of unconsolidated joint ventures	18,462	22,285
Gains from investments in securities	(3,744)	(965)
Allowance for current expected credit losses	(758)	1,997
Non-cash portion of interest expense	17,584	17,397
Settlement of accreted debt discount on redemption of unsecured senior notes	(6,290)	0
Loss from early extinguishment of debt	898	0
Gains on sales of real estate	(8,104)	(613,723)
Change in assets and liabilities:
Tenant and other receivables, net	13,738	18,543
Notes receivable, net	(419)	(395)
Accrued rental income, net	(74,283)	(85,843)
Prepaid expenses and other assets	(61,019)	(60,365)
Lease liabilities - operating leases	(24,023)	1,157
Accounts payable and accrued expenses	26,097	8,273
Accrued interest payable	(18,237)	(1,202)
Other liabilities	(51,938)	(24,868)
Tenant leasing costs	(37,618)	(52,621)
Total adjustments	378,212	(211,363)
Net cash provided by operating activities	786,859	782,423
Cash flows from investing activities:
Acquisitions of real estate	(218,679)	(135,698)
Construction in progress	(381,104)	(358,824)
Building and other capital improvements	(103,840)	(116,894)
Tenant improvements	(218,878)	(172,401)
Proceeds from sales of real estate	0	505,679
Capital contributions to unconsolidated joint ventures	(95,462)	(158,374)
Capital distributions from unconsolidated joint ventures	122	55,123
Proceeds from sale of investment in unconsolidated joint venture	17,789	0
Issuance of notes receivable, net	0	(9,800)
Investments in securities, net	1,684	2,778
Net cash used in investing activities	(998,368)	(388,411)
Cash flows from financing activities:
Repayments of mortgage notes payable	(13,261)	(12,795)
Proceeds from unsecured senior notes	1,695,996	1,248,125
Redemption of unsecured senior notes	(843,710)	0
Borrowings on unsecured line of credit	300,000	265,000
Repayments of unsecured line of credit	(300,000)	(265,000)
Repayment of unsecured term loan	(500,000)	0
Redemption of preferred stock	(200,000)	0
Payments on finance lease obligations	1,250	0
Deferred financing costs	(20,770)	(10,416)
Debt prepayment and extinguishment costs	(185)	0
Net proceeds from equity transactions	20,028	3,276
Dividends and distributions	(513,381)	(516,572)
Contributions from noncontrolling interests in property partnerships	13,738	7,364
Distributions to noncontrolling interests in property partnerships	(65,604)	(40,091)
Net cash provided by (used in) financing activities	(425,899)	678,891
Net increase (decrease) in cash and cash equivalents and cash held in escrows	(637,408)	1,072,903
Cash and cash equivalents and cash held in escrows, beginning of period	1,719,329	691,886
Cash and cash equivalents and cash held in escrows, end of period	1,081,921	1,764,789
Reconciliation of cash and cash equivalents and cash held in escrow
Cash and cash equivalents, beginning of period	1,668,742	644,950
Cash held in escrows, beginning of period	50,587	46,936
Cash and cash equivalents, end of period	1,002,728	1,714,783
Cash held in escrows,end of period	79,193	50,006
Supplemental disclosures:
Cash paid for interest	358,015	335,591
Interest capitalized	36,632	41,329
Non-cash investing and financing activities:
Write-off of fully depreciated real estate	(159,108)	(73,584)
Change in real estate included in accounts payable and accrued expenses	(22,104)	(30,924)
Right-of-use assets obtained in exchange for operating lease liabilities	26,887	0
Accrued rental income, net deconsolidated	0	(4,558)
Tenant leasing costs, net deconsolidated	0	(3,462)
Building and other capital improvements, net deconsolidated	0	(111,889)
Tenant improvements, net deconsolidated	0	(12,331)
Investment in unconsolidated joint venture recorded upon deconsolidation	0	347,898
Dividends and distributions declared but not paid	169,739	171,070
Conversions of noncontrolling interests to stockholders’ equity	8,033	26,682
Issuance of restricted securities to employees and non-employee directors	44,257	43,244
Boston Properties Limited Partnership
Net income	415,207	1,012,087
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	533,255	510,400
Amortization of right of use assets - operating leases	3,208	1,667
Non-cash compensation expense	43,098	36,152
Loss from unconsolidated joint ventures	1,745	5,410
Distributions of net cash flow from operations of unconsolidated joint ventures	18,462	22,285
Gains from investments in securities	(3,744)	(965)
Allowance for current expected credit losses	(758)	1,997
Non-cash portion of interest expense	17,584	17,397
Settlement of accreted debt discount on redemption of unsecured senior notes	(6,290)	0
Loss from early extinguishment of debt	898	0
Gains on sales of real estate	(8,104)	(626,686)
Change in assets and liabilities:
Tenant and other receivables, net	13,738	18,543
Notes receivable, net	(419)	(395)
Accrued rental income, net	(74,283)	(85,843)
Prepaid expenses and other assets	(61,019)	(60,365)
Lease liabilities - operating leases	(24,023)	1,157
Accounts payable and accrued expenses	26,097	8,273
Accrued interest payable	(18,237)	(1,202)
Other liabilities	(51,938)	(24,868)
Tenant leasing costs	(37,618)	(52,621)
Total adjustments	371,652	(229,664)
Net cash provided by operating activities	786,859	782,423
Cash flows from investing activities:
Acquisitions of real estate	(218,679)	(135,698)
Construction in progress	(381,104)	(358,824)
Building and other capital improvements	(103,840)	(116,894)
Tenant improvements	(218,878)	(172,401)
Proceeds from sales of real estate	0	505,679
Capital contributions to unconsolidated joint ventures	(95,462)	(158,374)
Capital distributions from unconsolidated joint ventures	122	55,123
Proceeds from sale of investment in unconsolidated joint venture	17,789	0
Issuance of notes receivable, net	0	(9,800)
Investments in securities, net	1,684	2,778
Net cash used in investing activities	(998,368)	(388,411)
Cash flows from financing activities:
Repayments of mortgage notes payable	(13,261)	(12,795)
Proceeds from unsecured senior notes	1,695,996	1,248,125
Redemption of unsecured senior notes	(843,710)	0
Borrowings on unsecured line of credit	300,000	265,000
Repayments of unsecured line of credit	(300,000)	(265,000)
Repayment of unsecured term loan	(500,000)	0
Redemption of preferred stock	(200,000)	0
Payments on finance lease obligations	1,250	0
Deferred financing costs	(20,770)	(10,416)
Debt prepayment and extinguishment costs	(185)	0
Net proceeds from equity transactions	20,028	3,276
Dividends and distributions	(513,381)	(516,572)
Contributions from noncontrolling interests in property partnerships	13,738	7,364
Distributions to noncontrolling interests in property partnerships	(65,604)	(40,091)
Net cash provided by (used in) financing activities	(425,899)	678,891
Net increase (decrease) in cash and cash equivalents and cash held in escrows	(637,408)	1,072,903
Cash and cash equivalents and cash held in escrows, beginning of period	1,719,329	691,886
Cash and cash equivalents and cash held in escrows, end of period	1,081,921	1,764,789
Reconciliation of cash and cash equivalents and cash held in escrow
Cash and cash equivalents, beginning of period	1,668,742	644,950
Cash held in escrows, beginning of period	50,587	46,936
Cash and cash equivalents, end of period	1,002,728	1,714,783
Cash held in escrows,end of period	79,193	50,006
Supplemental disclosures:
Cash paid for interest	358,015	335,591
Interest capitalized	36,632	41,329
Non-cash investing and financing activities:
Write-off of fully depreciated real estate	(157,794)	(73,584)
Change in real estate included in accounts payable and accrued expenses	(22,104)	(30,924)
Right-of-use assets obtained in exchange for operating lease liabilities	26,887	0
Accrued rental income, net deconsolidated	0	(4,558)
Tenant leasing costs, net deconsolidated	0	(3,462)
Building and other capital improvements, net deconsolidated	0	(111,889)
Tenant improvements, net deconsolidated	0	(12,331)
Investment in unconsolidated joint venture recorded upon deconsolidation	0	347,898
Dividends and distributions declared but not paid	169,739	171,070
Conversions of noncontrolling interests to stockholders’ equity	8,033	26,682
Issuance of restricted securities to employees and non-employee directors	$ 44,257	$ 43,244