Schedule III - Schedule of Real Estate and Accumulated Depreciation (Reconciliation of Real Estate Accumulated Depreciation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule III - Schedule of Real Estate and Accumulated Depreciation [Abstract]
Gross amount of accumulated depreciation at beginning	$ (2,627,841)	$ (2,396,587)	$ (2,160,530)
Depreciation	(257,469)	(248,818)	(254,982)
Other	(25)		(5,557)
Total additions	(257,494)	(248,818)	(260,539)
Amount of accumulated depreciation for assets sold or disposed	4,392	17,051	24,482
Other	12,436	513
Total deductions	16,828	17,564	24,482
Balance at end	$ (2,868,507)	$ (2,627,841)	$ (2,396,587)