Debt - Collateralized Loan Obligation (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Jan. 01, 2020	Mar. 31, 2019
Variable Interest Entity [Line Items]
Cash	$ 88,960	$ 87,246		$ 79,698
Commercial mortgage loans, held for investment, net	2,640,979	2,762,042	$ 2,762,042
Accrued interest receivable	15,877	16,308
Total assets	3,501,885	3,540,620		$ 3,540,620
Notes payable	40,167	29,167
Accrued interest payable	2,886	4,958
Total liabilities	2,571,423	2,514,705
Allowance for loan losses	21,702	921
Collateralized loan obligations	1,739,009	1,803,185
Collaterized loan obligation
Variable Interest Entity [Line Items]
Cash	28,680	89,946
Commercial mortgage loans, held for investment, net	2,235,406	2,294,663
Accrued interest receivable	10,522	6,254
Total assets	2,274,608	2,390,863
Notes payable	2,006,137	2,064,601
Accrued interest payable	1,659	2,576
Total liabilities	2,007,796	2,067,177
Restricted cash	28,200	89,300
Allowance for loan losses	10,500	800
Collateralized loan obligations	267,100	261,400
Deferred financing cost and discount	$ 14,400	$ 19,200