Segment Information (Details) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) segment	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Segment information
Number of reportable segments (segment) | segment				2
Total revenues		$ 398,150	$ 617,614	$ 775,531	$ 1,073,058
Net income before equity in net gain on sale of interest in unconsolidated joint venture/real estate, gain on sale of real estate, net, depreciable real estate reserves, and gain on sale of investment in marketable securities		35,813	(70,463)	87,133	(61,648)
Total assets	[1]	15,309,707		15,309,707		$ 15,857,787
Marketing, general and administrative		24,256	24,484	48,399	48,516
Operating Segments | Real Estate Segment
Segment information
Total revenues		337,528	573,400	674,610	974,107
Net income before equity in net gain on sale of interest in unconsolidated joint venture/real estate, gain on sale of real estate, net, depreciable real estate reserves, and gain on sale of investment in marketable securities		(18,561)	(112,938)	(5,376)	(154,491)
Total assets		13,161,680		13,161,680		13,868,672
Operating Segments | Debt and Preferred Equity Segment
Segment information
Total revenues		60,622	44,214	100,921	98,951
Net income before equity in net gain on sale of interest in unconsolidated joint venture/real estate, gain on sale of real estate, net, depreciable real estate reserves, and gain on sale of investment in marketable securities		54,374	$ 42,475	92,509	$ 92,843
Total assets		$ 2,148,027		$ 2,148,027		$ 1,989,115

[1] The Company's consolidated balance sheets include assets and liabilities of consolidated variable interest entities ("VIEs"). See Note 2. The consolidated balance sheets include the following amounts related to our consolidated VIEs, excluding the Operating Partnership: $384.0 million and $412.3 million of land, $1.4 billion and $1.5 billion of building and improvements, $2.0 million and $2.0 million of building and leasehold improvements, $47.4 million and $47.4 million of properties under capital lease, $311.8 million and $327.2 million of accumulated depreciation, $390.5 million and $289.0 million of other assets included in other line items, $626.7 million and $621.8 million of real estate debt, net, $2.5 million and $2.2 million of accrued interest payable, $42.5 million and $42.1 million of capital lease obligations, and $102.3 million and $118.0 million of other liabilities included in other line items as of June 30, 2017 and December 31, 2016, respectively.