SEC Schedule, Article 12-29, Mortgage Loans on Real Estate (Roll forward) - Mortgage Loans - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate	$ 1,400,100	$ 1,206,962	$ 692,131
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, New Mortgage Loan	716,241	837,502
Net unrealized gains	11,427	6,717
Net realized gains	0	3,878
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Cost of Mortgage Sold	(28,613)	(28,805)
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Collections of Principal	(496,186)	(275,520)
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Amortization of Premium	(6,317)	(6,363)
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Foreclosure	(3,384)	(22,578)
Net realized loss	$ (30)	$ 0