Schedule IV - Mortgage Loans On Real Estate - Rollforward of mortgage loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Balance at beginning of period	$ 9,540,598	$ 5,115,210	$ 3,890,751
Additions during period:
Originations/acquisitions	12,911,261	10,607,896	5,741,427
Deductions during period:
Sales	(5,218,797)	(5,426,304)	(3,982,683)
Principal repayments	(1,851,278)	(843,984)	(576,620)
Transfers to REO	(7,552)	(4,104)	(4,219)
Changes in fair value, net	255,885	91,884	46,554
Balance at end of period	$ 15,630,117	$ 9,540,598	$ 5,115,210