Schedule III - REAL ESTATE ASSETS AND ACCUMULATED DEPRECIATION Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of Carrying Amount of Real Estate Investments and Accumulated Depreciation [Roll Forward]
Balance at beginning of period	$ 8,240,521	$ 8,187,183	$ 8,123,514
Additions and improvements	263,265	230,990	282,282
Acquisitions of real estate assets	0	182,747	0
Disposals, deconsolidations and accumulated depreciation on impairments	(435,331)	(249,716)	(189,372)
Transfers from real estate assets	(3,986)	(4,738)	(11,383)
Impairment of real estate assets	(116,822)	(105,945)	(17,858)
Balance at end of period	7,947,647	8,240,521	8,187,183
Accumulated depreciation, beginning of period	2,382,568	2,240,007	2,056,357
Depreciation expense	272,697	274,544	269,602
Accumulated depreciation on real estate assets sold, retired, deconsolidated or impaired	(228,157)	(131,983)	(85,952)
Accumulated depreciation, end of period	$ 2,427,108	$ 2,382,568	$ 2,240,007