Schedule IV - Reconciliation of Activity Regarding Mortgage Loans on Real Estate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Mortgage Loans On Real Estate [Abstract]
Balance at January 1	$ 4,980,389	$ 4,293,787	$ 3,175,672
Additions during period:
Loans originated	430,050	2,341,692	2,071,391
Additional fundings	237,856	268,356	258,308
Amortization of deferred fees and expenses	11,345	16,345	16,907
Deductions during period:
Collection of principal	(885,565)	(1,880,222)	(1,150,241)
Loan sales	(145,675)	(59,569)	(78,250)
Loan extinguishment on conversion to REO	(112,000)
Allowance for credit losses	(59,940)
Balance at December 31	$ 4,456,460	$ 4,980,389	$ 4,293,787