Segment Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) segment	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Segment information
Number of reportable segments (segment) | segment			2
Total revenues	$ 432,066	$ 390,274	$ 1,237,439	$ 1,133,351
(Loss) income from continuing operations before equity in net gain on sale of interest in unconsolidated joint venture/real estate and purchase price fair value adjustment	20,994	27,556	33,272	130,821
Total assets	19,490,569		$ 19,490,569		$ 17,096,587
Leverage rate assumption (as a percent)			100.00%
Marketing, general and administrative expenses and transaction related costs	23,500	22,600	$ 72,100	69,800
Operating Segments | Real Estate Segment
Segment information
Total revenues	382,738	346,305	1,100,851	995,584
(Loss) income from continuing operations before equity in net gain on sale of interest in unconsolidated joint venture/real estate and purchase price fair value adjustment	(22,486)	(10,542)	(81,405)	13,148
Total assets	17,966,608		17,966,608		15,671,662
Operating Segments | Debt and Preferred Equity Segment
Segment information
Total revenues	49,328	43,969	136,588	137,767
(Loss) income from continuing operations before equity in net gain on sale of interest in unconsolidated joint venture/real estate and purchase price fair value adjustment	43,480	$ 38,098	114,677	$ 117,673
Total assets	$ 1,523,961		$ 1,523,961		$ 1,424,925