Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Net income	$ 269,397	$ 875,726
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	360,403	349,282
Amortization of right of use assets - operating leases	2,963	1,128
Non-cash compensation expense	34,370	27,899
(Income) Loss from unconsolidated joint ventures	(3,852)	(1,463)
Distributions of net cash flow from operations of unconsolidated joint ventures	14,387	13,382
(Gains) losses from investments in securities	(3,934)	893
Allowance for current expected credit losses	(418)	484
Non-cash portion of interest expense	11,784	11,483
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	(7,756)	(613,932)
Change in assets and liabilities:
Tenant and other receivables, net	17,110	18,516
Notes receivable, net	(277)	(258)
Accrued rental income, net	(39,434)	(43,399)
Prepaid expenses and other assets	(14,122)	(12,057)
Lease liabilities - operating leases	(1,566)	799
Accounts payable and accrued expenses	6,100	(20,493)
Accrued interest payable	1,741	5,262
Other liabilities	(53,919)	(21,912)
Tenant leasing costs	(27,109)	(37,068)
Total adjustments	291,079	(321,454)
Net cash provided by operating activities	560,476	554,272
Cash flows from investing activities:
Acquisitions of real estate	(100,176)	(133,406)
Construction in progress	(235,577)	(247,615)
Building and other capital improvements	(66,033)	(68,386)
Tenant improvements	(161,619)	(118,903)
Proceeds from sales of real estate	0	506,337
Capital contributions to unconsolidated joint ventures	(20,032)	(106,168)
Capital distributions from unconsolidated joint ventures	122	54,413
Proceeds from sale of investment in unconsolidated joint venture	17,789	0
Issuance of notes receivable, net	0	(9,800)
Investments in securities, net	1,915	3,006
Net cash used in investing activities	(563,611)	(120,522)
Cash flows from financing activities:
Repayments of mortgage notes payable	(9,294)	(8,477)
Proceeds from unsecured senior notes	846,345	1,248,125
Redemption of unsecured senior notes	(843,710)	0
Borrowings on unsecured line of credit	0	265,000
Repayments of unsecured line of credit	0	(265,000)
Repayment of unsecured term loan	500,000	0
Preferred Stock, Redemption Amount	(200,000)	0
Finance Lease, Principal Payments	(618)	0
Deferred financing costs	(13,642)	(9,465)
Debt prepayment and extinguishment costs	(185)	0
Net proceeds from equity transactions	19,580	3,183
Dividends and distributions	(343,117)	(344,239)
Contributions from noncontrolling interests in property partnerships	2,420	5,957
Distributions to noncontrolling interests in property partnerships	(37,929)	(29,065)
Net cash provided by (used in) financing activities	(1,078,914)	866,019
Net increase (decrease) in cash and cash equivalents and cash held in escrows	(1,082,049)	1,299,769
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	637,280	1,991,655
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	557,307	1,691,047
Cash held in escrows,end of period	79,973	300,608
Supplemental disclosures:
Cash paid for interest	226,367	213,754
Interest capitalized	25,046	27,866
Non-cash investing and financing activities:
Write-off of fully depreciated real estate	(98,672)	(50,141)
Change in real estate included in accounts payable and accrued expenses	(22,822)	(25,461)
Right-of-use assets obtained in exchange for operating lease liability	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	169,718	171,077
Conversions of noncontrolling interests to stockholders’ equity	6,285	26,344
Issuance of restricted securities to employees and non-employee directors	42,515	43,462
Boston Properties Limited Partnership
Net income	274,222	892,277
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	355,578	345,694
Amortization of right of use assets - operating leases	2,963	1,128
Non-cash compensation expense	34,370	27,899
(Income) Loss from unconsolidated joint ventures	(3,852)	(1,463)
Distributions of net cash flow from operations of unconsolidated joint ventures	14,387	13,382
(Gains) losses from investments in securities	(3,934)	893
Allowance for current expected credit losses	(418)	484
Non-cash portion of interest expense	11,784	11,483
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	(7,756)	(626,895)
Change in assets and liabilities:
Tenant and other receivables, net	17,110	18,516
Notes receivable, net	(277)	(258)
Accrued rental income, net	(39,434)	(43,399)
Prepaid expenses and other assets	(14,122)	(12,057)
Lease liabilities - operating leases	(1,566)	799
Accounts payable and accrued expenses	6,100	(20,493)
Accrued interest payable	1,741	5,262
Other liabilities	(53,919)	(21,912)
Tenant leasing costs	(27,109)	(37,068)
Total adjustments	286,254	(338,005)
Net cash provided by operating activities	560,476	554,272
Cash flows from investing activities:
Acquisitions of real estate	(100,176)	(133,406)
Construction in progress	(235,577)	(247,615)
Building and other capital improvements	(66,033)	(68,386)
Tenant improvements	(161,619)	(118,903)
Proceeds from sales of real estate	0	506,337
Capital contributions to unconsolidated joint ventures	(20,032)	(106,168)
Capital distributions from unconsolidated joint ventures	122	54,413
Proceeds from sale of investment in unconsolidated joint venture	17,789	0
Issuance of notes receivable, net	0	(9,800)
Investments in securities, net	1,915	3,006
Net cash used in investing activities	(563,611)	(120,522)
Cash flows from financing activities:
Repayments of mortgage notes payable	(9,294)	(8,477)
Proceeds from unsecured senior notes	846,345	1,248,125
Redemption of unsecured senior notes	(843,710)	0
Borrowings on unsecured line of credit	0	265,000
Repayments of unsecured line of credit	0	(265,000)
Repayment of unsecured term loan	(500,000)	0
Preferred Stock, Redemption Amount	(200,000)	0
Finance Lease, Principal Payments	618	0
Deferred financing costs	(13,642)	(9,465)
Debt prepayment and extinguishment costs	(185)	0
Net proceeds from equity transactions	19,580	3,183
Dividends and distributions	(343,117)	(344,239)
Contributions from noncontrolling interests in property partnerships	2,420	5,957
Distributions to noncontrolling interests in property partnerships	(37,929)	(29,065)
Net cash provided by (used in) financing activities	(1,078,914)	866,019
Net increase (decrease) in cash and cash equivalents and cash held in escrows	(1,082,049)	1,299,769
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	637,280	1,991,655
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	557,307	1,691,047
Cash held in escrows,end of period	79,973	300,608
Supplemental disclosures:
Cash paid for interest	226,367	213,754
Interest capitalized	25,046	27,866
Non-cash investing and financing activities:
Write-off of fully depreciated real estate	(97,358)	(50,141)
Change in real estate included in accounts payable and accrued expenses	(22,822)	(25,461)
Right-of-use assets obtained in exchange for operating lease liability	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	169,718	171,077
Conversions of noncontrolling interests to stockholders’ equity	6,285	26,344
Issuance of restricted securities to employees and non-employee directors	$ 42,515	$ 43,462