Segment Information - Additional Information (Details) $ in Thousands		3 Months Ended
		Mar. 31, 2018 USD ($) segment	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Segment information
Number of reportable segments (segment) | segment		2
Total revenues		$ 301,695	$ 377,381
Net income before equity in net (loss) gain on sale of interest in unconsolidated joint venture/real estate, purchase price and other fair value adjustments, gain on sale of real estate, net, depreciable real estate reserves, and gain on sale of investment in marketable securities		47,449	51,320
Total assets	[1]	13,380,870		$ 13,982,904
Marketing, general and administrative		23,528	24,143
Operating Segments | Real Estate Segment
Segment information
Total revenues		256,405	337,082
Net income before equity in net (loss) gain on sale of interest in unconsolidated joint venture/real estate, purchase price and other fair value adjustments, gain on sale of real estate, net, depreciable real estate reserves, and gain on sale of investment in marketable securities		14,024	13,807
Total assets		11,144,740		11,643,261
Operating Segments | Debt and Preferred Equity Segment
Segment information
Total revenues		45,290	40,299
Net income before equity in net (loss) gain on sale of interest in unconsolidated joint venture/real estate, purchase price and other fair value adjustments, gain on sale of real estate, net, depreciable real estate reserves, and gain on sale of investment in marketable securities		33,425	$ 37,513
Total assets		$ 2,236,130		$ 2,339,643

[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: $174.8 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, $29.8 million and $330.9 million of accumulated depreciation, $706.0 million and $221.0 million of other assets included in other line items, $134.4 million and $628.9 million of real estate debt, net, $0.4 million and $2.5 million of accrued interest payable, $43.0 million and $42.8 million of capital lease obligations, and $17.7 million and $56.8 million of other liabilities included in other line items as of September 30, 2017 and December 31, 2016, respectively.