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 income (loss)	1,078			(13,324)		16,677	964	(3,239)
Common shares issued under Omnibus share plan		5,000
Common units issued under Omnibus share plan			(2,131)					2,131
Dividends and distributions	(85,462)			(68,724)				(16,738)
Contributions from noncontrolling interests	133,111					130,586	2,525
Distributions to noncontrolling interests	(54,975)					(54,259)	(716)
Change in value of interest rate swaps	(18,602)				$ (14,959)			(3,643)
Pro rata share of other comprehensive loss of unconsolidated joint ventures	(535)				(430)			(105)
Adjustments to noncontrolling interests			43,981					(43,981)
Amortization of equity awards	6,224		1,172					5,052
Other	(926)		(470)	(134)		(327)	5
Ending balance at Sep. 30, 2015	5,534,866	$ 2,122	3,893,984	(24,874)	(15,389)	430,747	350,596	897,680
Common stock, shares outstanding at Sep. 30, 2015		212,112,000
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 fundinvestments upon adoption of ASU 2015-02 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 income (loss)	4,892			(3,445)		(819)	10,062	(906)
Common shares issued upon redemption of common units		$ 74	126,068					(126,142)
Common shares issued upon redemption of common units		7,403,000
Common shares issued under Omnibus share plan		97,000
Dividends and distributions	(75,449)			(61,953)				(13,496)
Distributions to noncontrolling interests	(2,692)						(2,692)
Change in value of interest rate swaps	(33,812)				(27,231)			(6,581)
Pro rata share of other comprehensive loss of unconsolidated joint ventures	(19)				(18)			(1)
Amortization of equity awards	9,624		1,605					8,019
Other	231		18	191		7	15
Ending balance at Sep. 30, 2016	$ 4,862,290	$ 2,196	$ 3,930,549	$ (101,327)	$ (35,092)	$ 62,790	$ 244,234	$ 758,940
Common stock, shares outstanding at Sep. 30, 2016	219,611,535	219,612,000