Schedule IV - Mortgage Loans On Real Estate - Rollforward of mortgage loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Balance at beginning of period	$ 15,630,117	$ 9,540,598	$ 5,115,210
Additions during period:
Originations/acquisitions	5,914,728	12,911,261	10,607,896
Deductions during period:
Sales	(6,398,690)	(5,218,797)	(5,426,304)
Principal repayments	(2,313,143)	(1,851,278)	(843,984)
Transfers to REO	(14,104)	(7,552)	(4,104)
Deconsolidation adjustments	(3,849,779)	0	0
Changes in fair value, net	(91,503)	255,885	91,884
Balance at end of period	$ 8,877,626	$ 15,630,117	$ 9,540,598