Schedule III - REAL ESTATE ASSETS AND ACCUMULATED DEPRECIATION - Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Carrying Amount of Real Estate Investments and Accumulated Depreciation [Roll Forward]
Balance at beginning of period	$ 6,411,400	$ 7,278,608	$ 7,621,930
Additions and improvements	36,337	129,923	144,256
Acquisitions of real estate assets		5,700	3,301
Disposals, deconsolidations and accumulated depreciation on impairments	(377,165)	(786,889)	(305,813)
Transfers to (from) real estate assets	332	22,573	(11,531)
Impairment of real estate assets	(211,791)	(238,515)	(173,535)
Balance at end of period	5,859,113	6,411,400	7,278,608
Accumulated depreciation, beginning of period	2,349,404	2,493,082	2,465,095
Depreciation expense	205,671	241,631	261,838
Accumulated depreciation on real estate assets sold, retired, deconsolidated or impaired	(313,654)	(385,309)	(233,851)
Accumulated depreciation, end of period	$ 2,241,421	$ 2,349,404	$ 2,493,082