Segment Information - Additional Information (Details) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) segment	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Segment information
Number of reportable segments (segment) | segment				2
Total revenues		$ 307,545	$ 374,600	$ 910,356	$ 1,150,131
Net income		99,454	45,795	329,176	62,734
Total assets	[1]	13,455,004		13,455,004		$ 13,982,904
Marketing, general and administrative		20,594	23,963	66,601	72,362
Operating Segments | Real Estate Segment
Segment information
Total revenues		258,568	326,780	766,816	1,001,390
Net income		62,587	6,073	224,609	(68,379)
Total assets		11,256,296		11,256,296		11,631,290
Operating Segments | Debt and Preferred Equity Segment
Segment information
Total revenues		48,977	47,820	143,540	148,741
Net income		36,867	$ 39,722	104,567	$ 131,113
Total assets		$ 2,198,708		$ 2,198,708		$ 2,351,614

[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: $110.0 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, $34.6 million and $330.9 million of accumulated depreciation, $991.3 million and $221.0 million of other assets included in other line items, $141.0 million and $628.9 million of real estate debt, net, $0.4 million and $2.5 million of accrued interest payable, $43.4 million and $42.8 million of capital lease obligations, and $203.4 million and $56.8 million of other liabilities included in other line items as of September 30, 2018 and December 31, 2017, respectively.