CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($)	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash Flows from Operating Activities:
Net income (loss)	$ (3,612,000)	$ (6,581,000)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	175,752,000	176,722,000
Loss from unconsolidated joint ventures	20,810,000	14,444,000
Amortization of stock-based compensation expense	14,421,000	14,141,000
Straight-lining of rental revenue	(7,925,000)	(24,170,000)
Amortization of deferred financing costs	7,306,000	6,957,000
Distributions of earnings from unconsolidated joint ventures	3,950,000	1,688,000
Amortization of above and below-market leases, net	(2,335,000)	(4,653,000)
Realized and unrealized gains on marketable securities	(1,271,000)	(129,000)
Income from unconsolidated real estate funds	(604,000)	(85,000)
Distributions of earnings from unconsolidated real estate funds	535,000	480,000
Other non-cash adjustments	2,330,000	231,000
Changes in operating assets and liabilities:
Accounts and other receivables	6,118,000	3,942,000
Deferred charges	(12,664,000)	(10,116,000)
Other assets	(30,014,000)	(36,068,000)
Accounts payable and accrued expenses	12,830,000	2,827,000
Other liabilities	2,433,000	(61,000)
Net cash provided by operating activities	188,060,000	139,569,000
Cash Flows from Investing Activities:
Additions to real estate	(74,134,000)	(60,348,000)
Purchases of marketable securities	(21,562,000)	(12,207,000)
Sales of marketable securities	18,305,000	19,049,000
Contributions of capital to unconsolidated joint ventures	(11,750,000)
Distributions of capital from unconsolidated real estate funds	3,959,000
Contributions of capital to unconsolidated real estate funds	(3,198,000)	(2,945,000)
Repayment of amounts due from affiliates		36,918,000
Net cash used in investing activities	(88,380,000)	(19,533,000)
Cash Flows from Financing Activities:
Proceeds from notes and mortgages payable	888,566,000	9,791,000
Repayment of notes and mortgages payable	(850,000,000)
Dividends paid to common stockholders	(45,970,000)	(67,165,000)
Distributions to noncontrolling interests	(19,616,000)	(9,530,000)
Debt issuance costs	(10,593,000)
Distributions paid to common unitholders	(4,612,000)	(6,724,000)
Repurchase of shares related to stock compensation agreements and related tax withholdings	(214,000)	(318,000)
Purchase of interest rate caps	(140,000)
Contributions from noncontrolling interests	121,000	11,555,000
Borrowings under revolving credit facility		163,082,000
Proceeds from the sale of a 10.0% interest in 1633 Broadway		111,984,000
Repurchases of common shares		(108,520,000)
Repayment of note payable issued in connection with the acquisition of noncontrolling interest in consolidated real estate fund		(8,771,000)
Net cash (used in) provided by financing activities	(42,458,000)	95,384,000
Net increase in cash and cash equivalents and restricted cash	57,222,000	215,420,000
Cash and cash equivalents and restricted cash at beginning of period	465,324,000	331,487,000
Cash and cash equivalents and restricted cash at end of period	522,546,000	546,907,000
Reconciliation of Cash and Cash Equivalents and Restricted Cash:
Cash and cash equivalents at beginning of period	434,530,000	306,215,000
Restricted cash at beginning of period	30,794,000	25,272,000
Cash and cash equivalents and restricted cash at beginning of period	465,324,000	331,487,000
Cash and cash equivalents at end of period	494,569,000	515,942,000
Restricted cash at end of period	27,977,000	30,965,000
Cash and cash equivalents and restricted cash at end of period	522,546,000	546,907,000
Supplemental Disclosure of Cash Flow Information:
Cash payments for interest	98,917,000	102,379,000
Cash payments for income taxes, net of refunds	970,000	1,440,000
Non-Cash Transactions:
Dividends and distributions declared but not yet paid	16,897,000	24,173,000
Additions to real estate included in accounts payable and accrued expenses	17,842,000	14,644,000
Write-off of fully amortized and/or depreciated assets	43,232,000	8,677,000
Common shares issued upon redemption of common units	165,000	$ 85,710,000
Change in value of interest rate swaps and interest rate caps	$ 995,000