Schedule III - Real Estate and Accumulated Depreciation and Amortization - Summary (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation Disclosure [Abstract]
Total cost basis for federal income tax purposes	$ 4,000,000
Reconciliation of real estate owned:
Balance at the beginning of year	3,320,574	$ 3,090,134	$ 3,936,459
Additions during year	580,861	663,742	310,207
Properties sold and impaired during the year	(354,218)	(496,730)	(1,091,956)
Other reclassifications	(32,653)	63,428	(64,576)
Balance at end of year	3,514,564	3,320,574	3,090,134
Reconciliation of accumulated depreciation and amortization:
Balance at the beginning of year	675,596	722,644	890,969
Depreciation and amortization expense	127,504	118,525	136,571
Accumulated depreciation and amortization of properties sold, impaired and held for sale during year	(102,261)	(177,709)	(290,938)
Other reclassifications	(16,371)	12,136	(13,958)
Balance at end of year	$ 684,468	$ 675,596	$ 722,644