CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 107,176	$ 2,069	$ 21,143
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization	266,037	269,450	294,624
Amortization of deferred financing costs	11,188	6,804	2,565
Gain on sale of real estate	(133,989)
Straight-lining of rental income	(54,453)	(82,568)	(69,522)
Amortization of above and below-market leases, net	(19,523)	(9,536)	(9,917)
Loss on early extinguishment of debt	7,877	4,608
Unrealized gain on interest rate swaps	(1,802)	(39,814)	(75,760)
Realized and unrealized (gains) losses on marketable securities	(4,664)	(494)	119
Realized and unrealized gains on real estate fund investments			(21,201)
Distributions of earnings from unconsolidated joint ventures	5,700	8,121	4,985
Income from unconsolidated joint ventures	(20,185)	(7,413)	(6,850)
Distributions of earnings from unconsolidated real estate funds	342	392
Loss from unconsolidated real estate funds	6,143	498
Amortization of stock-based compensation expense	15,922	11,278	7,309
Other non-cash adjustments	452	2,628	5,824
Valuation allowance on preferred equity investment	19,588
Changes in operating assets and liabilities:
Real estate fund investments			(127,743)
Accounts and other receivables	(1,000)	(4,521)	(3,152)
Deferred charges	(33,295)	(15,701)	(40,510)
Other assets	10,243	(12,037)	6,465
Accounts payable and accrued expenses	6,305	11,479	(6,152)
Deferred income taxes	(922)	(1,662)	(328)
Other liabilities	2,971	4,702	1,151
Net cash provided by (used in) operating activities	190,111	148,283	(16,950)
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from sale of real estate	540,333
Acquisitions of real estate	(161,184)	(517,823)
Additions to real estate	(86,434)	(132,686)	(107,859)
Purchases of marketable securities	(29,248)	(2,722)	(8,553)
Sales of marketable securities	27,261	2,353	7,072
Investment in unconsolidated joint ventures	(28,791)
Distributions of capital from unconsolidated joint ventures	20,000
Distributions of capital from unconsolidated real estate funds	14,584
Contributions of capital to unconsolidated real estate funds	(790)	(1,780)
Net cash provided by (used in) by investing activities	295,731	(652,658)	(109,340)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repayments of notes and mortgages payable	(1,044,821)	(689,269)	(927,633)
Proceeds from notes and mortgages payable	991,556	1,362,414	1,013,544
Repayment of borrowings under revolving credit facility	(290,000)	(130,000)
Borrowings under revolving credit facility	60,000	340,000	20,000
Distributions to noncontrolling interests	(119,251)	(3,636)	(56,636)
Contributions from noncontrolling interests	100,777	7,651	167,929
Dividends paid to common stockholders	(89,276)	(82,105)	(68,723)
Distributions paid to common unitholders	(11,504)	(18,412)	(16,735)
Settlement of interest rate swap liabilities	(19,425)	(23,654)	(33,741)
Transfer tax refund in connection with the acquisition of noncontrolling interests	9,555
Loss on early extinguishment of debt	(7,877)	(4,608)
Debt issuance costs	(7,344)	(29,387)	(18,871)
Other	(146)
Purchase of marketable securities in connection with the defeasance of notes and mortgages payable		(210,000)
Acquisition of noncontrolling interest in consolidated joint ventures			(261,464)
Net cash (used in) provided by financing activities	(427,756)	518,994	(182,330)
Net increase (decrease) in cash and cash equivalents and restricted cash	58,086	14,619	(308,620)
Cash and cash equivalents and restricted cash at beginning of period	192,339	185,707	494,327
Decrease in cash due to deconsolidation of real estate fund investments		(7,987)
Cash and cash equivalents and restricted cash at end of period	250,425	192,339	185,707
RECONCILIATION OF CASH AND CASH EQUIVALENTS AND RESTRICTED CASH:
Cash and cash equivalents at beginning of period	162,965	143,884	438,599
Restricted cash at beginning of period	29,374	41,823	55,728
Cash and cash equivalents and restricted cash at beginning of period	192,339	185,707	494,327
Cash and cash equivalents at end of period	219,381	162,965	143,884
Restricted cash at end of period	31,044	29,374	41,823
Cash and cash equivalents and restricted cash at end of period	250,425	192,339	185,707
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash payments for interest	132,361	140,111	159,186
Cash payments for income taxes, net of refunds	5,048	2,095	2,798
NON-CASH TRANSACTIONS:
Common shares issued upon redemption of commons units	172,728	312,257
Dividends and distributions declared but not yet paid	25,211	25,151	25,067
Write-off of fully amortized and/or depreciated assets	9,684	11,431	1,399
Additions to real estate included in accounts payable and accrued expenses	10,413	12,104	32,009
Change in fair value of interest rate swaps	(10,618)	(8,161)	$ 9,241
Consolidation (deconsolidation) of real estate and real estate fund investments	102,512	(396,697)
Assumption of notes and mortgages payable	$ 228,000
Transfer of real estate to assets held for sale		(346,685)
Marketable securities transferred in connection with the defeasance of notes and mortgages payable		214,608
Defeasance of notes and mortgages payable		$ (210,000)