Schedule III - Real Estate and Accumulated Depreciation and Amortization - Summary (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Real Estate and Accumulated Depreciation [Line Items]
Total cost basis for federal income tax purposes	$ 3,800,000
Reconciliation of real estate owned:
Balance at the beginning of year	3,936,459	$ 3,533,172	$ 3,789,711
Additions during year	310,207	676,355	291,004
Properties sold and impaired during the year	(1,091,956)	(270,241)	(527,597)
Other reclassifications	(64,576)	(2,827)	(19,946)
Balance at end of year	3,090,134	3,936,459	3,533,172
Reconciliation of accumulated depreciation and amortization:
Balance at the beginning of year	890,969	844,931	812,207
Depreciation and amortization expense	136,571	139,493	128,384
Accumulated depreciation and amortization of properties sold, impaired and held for sale during year	(290,938)	(93,455)	(86,428)
Other reclassifications	(13,958)	0	(9,232)
Balance at end of year	$ 722,644	$ 890,969	$ 844,931