Segment Information - Additional Information (Details) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) segment	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Segment information
Number of reportable segments (segment) | segment				2
Total revenues		$ 301,116	$ 398,150	$ 602,811	$ 775,531
Net income (loss) before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price and other fair value adjustments, (loss) gain on sale of real estate net, depreciable real estate reserves, and gain on sale of marketable securities		47,515	35,813	94,964	87,133
Total assets	[1]	13,713,928		13,713,928		$ 13,982,904
Marketing, general and administrative		22,479	24,256	46,007	48,399
Operating Segments | Real Estate Segment
Segment information
Total revenues		251,843	337,528	508,248	674,610
Net income (loss) before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price and other fair value adjustments, (loss) gain on sale of real estate net, depreciable real estate reserves, and gain on sale of marketable securities		13,239	(16,232)	27,263	(2,425)
Total assets		11,249,972		11,249,972		11,631,700
Operating Segments | Debt and Preferred Equity Segment
Segment information
Total revenues		49,273	60,622	94,563	100,921
Net income (loss) before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price and other fair value adjustments, (loss) gain on sale of real estate net, depreciable real estate reserves, and gain on sale of marketable securities		34,276	$ 52,045	67,701	$ 89,558
Total assets		$ 2,463,956		$ 2,463,956		$ 2,351,204

[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: $175.0 million and $398.0 million of land, $0.3 billion and $1.4 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, $32.2 million and $330.9 million of accumulated depreciation, $860.2 million and $221.0 million of other assets included in other line items, $136.2 million and $628.9 million of real estate debt, net, $0.4 million and $2.5 million of accrued interest payable, $43.2 million and $42.8 million of capital lease obligations, and $155.6 million and $56.8 million of other liabilities included in other line items as of June 30, 2018 and December 31, 2017, respectively.