Schedule III - Schedule of Real Estate and Accumulated Depreciation (Reconciliation of Real Estate Accumulated Depreciation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule III - Schedule of Real Estate and Accumulated Depreciation [Abstract]
Gross amount of accumulated depreciation at beginning	$ (3,133,061)	$ (2,868,507)	$ (2,627,841)
Depreciation	(275,947)	(269,606)	(257,469)
Other	(38)	(83)	(25)
Total additions	(275,985)	(269,689)	(257,494)
Amount of accumulated depreciation for assets sold or disposed	4,244	2,887	4,392
Other	21,432	2,248	12,436
Total deductions	25,676	5,135	16,828
Balance at end	$ (3,383,370)	$ (3,133,061)	$ (2,868,507)