Segment Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) segment	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Segment information
Number of reportable segments (segment) | segment	2
Total revenues	$ 1,863,981	$ 1,662,829	$ 1,519,978
Income from continuing operations before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price fair value adjustment, gain on sale of real estate, depreciable real estate reserves, loss on early extinguishment of debt, and (loss) gain on sale of marketable securities	7,256	90,289	201,500
Total assets	15,857,787	19,727,646
Marketing, general and administrative	99,759	94,873	92,488
Operating Segments | Real Estate Segment
Segment information
Total revenues	1,629,919	1,465,881	1,320,777
Income from continuing operations before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price fair value adjustment, gain on sale of real estate, depreciable real estate reserves, loss on early extinguishment of debt, and (loss) gain on sale of marketable securities	(203,988)	(78,681)	31,805
Total assets	13,868,085	17,765,854
Operating Segments | Debt and Preferred Equity Segment
Segment information
Total revenues	234,062	196,948	199,201
Income from continuing operations before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price fair value adjustment, gain on sale of real estate, depreciable real estate reserves, loss on early extinguishment of debt, and (loss) gain on sale of marketable securities	211,244	168,970	$ 169,695
Total assets	$ 1,989,702	$ 1,961,792