CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 18,993,000	$ 107,176,000	$ 2,069,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	258,225,000	266,037,000	269,450,000
Straight-lining of rental income	(59,061,000)	(54,453,000)	(82,568,000)
Real estate impairment loss	46,000,000
Gain on sale of real estate	(36,845,000)	(133,989,000)
Amortization of stock-based compensation expense	19,646,000	15,922,000	11,278,000
Amortization of above and below-market leases, net	(16,059,000)	(19,523,000)	(9,536,000)
Amortization of deferred financing costs	11,023,000	11,188,000	6,804,000
Distributions of earnings from unconsolidated joint ventures	6,207,000	5,700,000	8,121,000
Income from unconsolidated joint ventures	(3,468,000)	(20,185,000)	(7,413,000)
Realized and unrealized losses (gains) on marketable securities	1,604,000	(4,664,000)	(494,000)
Distributions of earnings from unconsolidated real estate funds	330,000	342,000	392,000
Loss from unconsolidated real estate funds	269,000	6,143,000	498,000
Valuation allowance on preferred equity investment		19,588,000
Loss on early extinguishment of debt		7,877,000	4,608,000
Unrealized gain on interest rate swaps		(1,802,000)	(39,814,000)
Other non-cash adjustments	288,000	(470,000)	966,000
Changes in operating assets and liabilities:
Accounts and other receivables	(2,994,000)	(1,000,000)	(4,521,000)
Deferred charges	(31,861,000)	(33,295,000)	(15,701,000)
Other assets	(57,216,000)	10,243,000	(12,037,000)
Accounts payable and accrued expenses	4,200,000	6,305,000	11,479,000
Other liabilities	(2,758,000)	2,971,000	4,702,000
Net cash provided by operating activities	156,523,000	190,111,000	148,283,000
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from sale of real estate	349,013,000	540,333,000
Additions to real estate	(137,915,000)	(86,434,000)	(132,686,000)
Investment in and contributions of capital to unconsolidated joint ventures	(29,883,000)	(28,791,000)
Sales of marketable securities	24,794,000	27,261,000	2,353,000
Purchases of marketable securities	(20,019,000)	(29,248,000)	(2,722,000)
Escrow deposits and loans receivable for Residential Development Fund	(15,680,000)
Deposit on real estate	(10,000,000)
Contributions of capital to unconsolidated real estate funds	(3,779,000)	(790,000)	(1,780,000)
Distributions of capital from unconsolidated real estate funds	79,000	14,584,000
Acquisitions of real estate		(161,184,000)	(517,823,000)
Distributions of capital from unconsolidated joint ventures		20,000,000
Net cash provided by (used in) by investing activities	156,610,000	295,731,000	(652,658,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repurchases of common shares	(102,863,000)
Dividends paid to common stockholders	(94,991,000)	(89,276,000)	(82,105,000)
Contributions from noncontrolling interests	45,116,000	100,777,000	7,651,000
Repayment of loans to affiliates	(27,299,000)
Distributions to noncontrolling interests	(18,184,000)	(119,251,000)	(3,636,000)
Proceeds from notes and mortgages payable	16,700,000	991,556,000	1,362,414,000
Distributions paid to common unitholders	(10,064,000)	(11,504,000)	(18,412,000)
Debt issuance costs and other	(6,564,000)	(7,490,000)	(29,387,000)
Repayments of notes and mortgages payable		(1,044,821,000)	(689,269,000)
Repayment of borrowings under revolving credit facility		(290,000,000)	(130,000,000)
Borrowings under revolving credit facility		60,000,000	340,000,000
Settlement of interest rate swap liabilities		(19,425,000)	(23,654,000)
Transfer tax refund in connection with the acquisition of noncontrolling interests		9,555,000
Loss on early extinguishment of debt		(7,877,000)	(4,608,000)
Purchase of marketable securities in connection with the defeasance of notes and mortgages payable			(210,000,000)
Net cash (used in) provided by financing activities	(198,149,000)	(427,756,000)	518,994,000
Net increase in cash and cash equivalents and restricted cash	114,984,000	58,086,000	14,619,000
Cash and cash equivalents and restricted cash at beginning of period	250,425,000	192,339,000	185,707,000
Decrease in cash due to deconsolidation of real estate fund investments			(7,987,000)
Cash and cash equivalents and restricted cash at end of period	365,409,000	250,425,000	192,339,000
RECONCILIATION OF CASH AND CASH EQUIVALENTS AND RESTRICTED CASH:
Cash and cash equivalents at beginning of period	219,381,000	162,965,000	143,884,000
Restricted cash at beginning of period	31,044,000	29,374,000	41,823,000
Cash and cash equivalents and restricted cash at beginning of period	250,425,000	192,339,000	185,707,000
Cash and cash equivalents at end of period	339,653,000	219,381,000	162,965,000
Restricted cash at end of period	25,756,000	31,044,000	29,374,000
Cash and cash equivalents and restricted cash at end of period	365,409,000	250,425,000	192,339,000
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash payments for interest	136,452,000	132,361,000	140,111,000
Cash payments for income taxes, net of refunds	4,049,000	5,048,000	2,095,000
NON-CASH TRANSACTIONS:
Common shares issued upon redemption of commons units	3,461,000	172,728,000	312,257,000
Dividends and distributions declared but not yet paid	25,902,000	25,211,000	25,151,000
Write-off of fully amortized and/or depreciated assets	4,158,000	9,684,000	11,431,000
Basis adjustment to investment in unconsolidated joint ventures upon adoption of ASU 2017-05	7,086,000
Additions to real estate included in accounts payable and accrued expenses	19,872,000	10,413,000	12,104,000
Change in value of interest rate swaps	$ (7,273,000)	(10,618,000)	(8,161,000)
Consolidation (deconsolidation) of real estate and real estate fund investments		102,512,000	(396,697,000)
Assumption of notes and mortgages payable		$ 228,000,000
Transfer of real estate to assets held for sale			(346,685,000)
Marketable securities transferred in connection with the defeasance of notes and mortgages payable			214,608,000
Defeasance of notes and mortgages payable			$ (210,000,000)