Segment Information - Additional Information (Details) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) segment	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Segment information
Number of reportable segments (segment) | segment				2
Total revenues		$ 374,600	$ 416,681	$ 1,150,131	$ 1,489,739
Net income (loss) 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		44,765	42,721	131,898	(18,927)
Total assets	[1]	15,109,870		15,109,870		$ 15,857,787
Marketing, general and administrative		23,963	25,458	72,362	73,974
Operating Segments | Real Estate Segment
Segment information
Total revenues		326,780	341,285	1,001,390	1,315,392
Net income (loss) 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		4,873	(32,731)	(504)	(187,222)
Total assets		12,939,363		12,939,363		13,868,672
Operating Segments | Debt and Preferred Equity Segment
Segment information
Total revenues		47,820	75,396	148,741	174,347
Net income (loss) 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		39,892	$ 75,452	132,402	$ 168,295
Total assets		$ 2,170,507		$ 2,170,507		$ 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: $384.3 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, $323.3 million and $327.2 million of accumulated depreciation, $235.4 million and $244.2 million of other assets included in other line items, $627.8 million and $621.8 million of real estate debt, net, $2.5 million and $2.2 million of accrued interest payable, $42.7 million and $42.1 million of capital lease obligations, and $58.5 million and $73.3 million of other liabilities included in other line items as of September 30, 2017 and December 31, 2016, respectively.