Segments - Schedule of Reconciliation of NOI to Net Income (Loss) Income Attributable to Common Stockholders (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
NOI									$ 448,262	$ 433,565	$ 423,986
Fee income									24,212	16,931	10,248
Depreciation and amortization expense									(266,037)	(269,450)	(294,624)
General and administrative expenses									(61,577)	(53,510)	(42,056)
Transaction related costs and transfer taxes due in connection with the sale of shares by a former joint venture partner									(2,027)	(2,404)	(10,355)
NOI from unconsolidated joint ventures									(19,643)	(17,195)	(16,580)
Income from unconsolidated joint ventures									20,185	7,413	6,850
Income from real estate fund investments											37,975
Loss from unconsolidated real estate funds									(6,143)	(498)
Interest and other (loss) income, net									(9,031)	6,934	871
Interest and debt expense									(143,762)	(153,138)	(168,366)
Loss on early extinguishment of debt									(7,877)	(4,608)
Gain on sale of real estate									133,989
Unrealized gain on interest rate swaps									1,802	39,814	75,760
Net income before income taxes									112,353	3,854	23,709
Income tax expense									(5,177)	(1,785)	(2,566)
Net income									107,176	2,069	21,143
Consolidated joint ventures									10,365	(15,423)	(5,459)
Consolidated real estate funds									(19,797)	1,316	(21,173)
Operating Partnership									(11,363)	2,104	1,070
Net income (loss) attributable to common stockholders	$ (6,793)	$ (10,214)	$ 103,016	$ 372	$ (6,489)	$ (139)	$ 3,188	$ (6,494)	86,381	(9,934)	(4,419)
Deal Cost [Member]
Segment Reporting Information [Line Items]
Transaction related costs and transfer taxes due in connection with the sale of shares by a former joint venture partner									$ (2,027)	$ (2,404)	(4,483)
Transfer Taxes [Member]
Segment Reporting Information [Line Items]
Transaction related costs and transfer taxes due in connection with the sale of shares by a former joint venture partner											$ (5,872)