Schedule III - Consolidated Real Estate and Accumulated Depreciation - Changes in Investment Properties (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate [Roll Forward]
Balance, beginning of year	$ 3,949,431	$ 3,988,819	$ 3,926,180
Acquisitions	0	0	0
Improvements	68,349	78,947	97,161
Impairment	(73,198)	(10,897)	0
Disposals	(311,206)	(107,438)	(34,522)
Balance, end of year	3,633,376	$ 3,949,431	$ 3,988,819
Federal income tax basis	$ 2,700,000