CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid in Capital [Member]	Earnings (Less than) In Excess of Distributions [Member]	Accumulated Other Comprehensive Loss [Member]	Noncontrolling Interest [Member] Consolidated Real Estate Funds [Member]	Noncontrolling Interest [Member] Consolidated Joint Ventures [Member]	Noncontrolling Interest [Member] Operating Partnership [Member]
Beginning balance at Dec. 31, 2014	$ 5,554,953	$ 2,122	$ 3,851,432	$ 57,308		$ 338,070	$ 347,818	$ 958,203
Common stock, shares outstanding at Dec. 31, 2014		212,107,000
Net (loss) income	(11,427)			(9,731)		2,209	(1,541)	(2,364)
Dividends and distributions	(35,325)			(28,422)				(6,903)
Contributions from noncontrolling interests in joint ventures and funds	2,430					(100)	2,530
Distributions to noncontrolling interests in joint ventures and funds	(3,488)					(2,772)	(716)
Adjustments to noncontrolling interests			(43,409)					43,409
Amortization of equity awards	3,035		581					2,454
Other	(830)		(411)	(97)		(322)
Ending balance at Mar. 31, 2015	5,509,348	$ 2,122	3,808,193	19,058		337,085	348,091	994,799
Common stock, shares outstanding at Mar. 31, 2015		212,107,000
Beginning balance at Dec. 31, 2015	$ 5,310,550	$ 2,122	3,802,858	(36,120)	$ (7,843)	414,637	236,849	898,047
Common stock, shares outstanding at Dec. 31, 2015	212,112,137	212,112,000
Deconsolidation of real estate fund investments at Dec. 31, 2015	$ (351,035)					(351,035)
Beginning balance, after adjustment at Dec. 31, 2015	4,959,515	$ 2,122	3,802,858	(36,120)	(7,843)	63,602	236,849	898,047
Net (loss) income	(7,487)			(6,494)		(674)	1,252	(1,571)
Common shares issued upon redemption of common units		$ 8	14,419					(14,427)
Common shares issued upon redemption of common units		830,000
Common units issued under Omnibus share plan		95,000
Dividends and distributions	(25,147)			(20,239)				(4,908)
Change in value of interest rate swaps	(29,867)				(24,058)			(5,809)
Pro rata share of other comprehensive income of unconsolidated joint ventures	107				86			21
Amortization of equity awards	3,845		747					3,098
Other	345		320	18		7
Ending balance at Mar. 31, 2016	$ 4,901,311	$ 2,130	$ 3,818,344	$ (62,835)	$ (31,815)	$ 62,935	$ 238,101	$ 874,451
Common stock, shares outstanding at Mar. 31, 2016	213,036,508	213,037,000