Schedule III-Real Estate and Accumulated Depreciation - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Changes in total real estate assets
Balances, beginning of year	$ 9,127,533	$ 9,209,211	$ 10,689,656
Additions	246,719	202,280	254,604
Dispositions and retirements	(495,432)	(283,958)	(1,735,049)
Balances, end of year	8,878,820	9,127,533	9,209,211
Aggregate gross cost of the property for federal income tax purposes	8,363,296
Changes in accumulated depreciation
Balances, beginning of year	2,018,303	1,851,901	1,892,744
Additions	275,236	277,917	277,270
Dispositions and retirements	(200,495)	(111,515)	(318,113)
Balances, end of year	$ 2,093,044	$ 2,018,303	$ 1,851,901
Buildings and improvements | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Estimated useful lives of assets	5 years
Buildings and improvements | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Estimated useful lives of assets	40 years
Tenant improvements | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Estimated useful lives of assets	5 years
Tenant improvements | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Estimated useful lives of assets	7 years
Equipment and furnishings | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Estimated useful lives of assets	5 years
Equipment and furnishings | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
Estimated useful lives of assets	7 years