Summary of Significant Accounting Policies - Impact of Adoption of New Accounting Policy (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Commercial mortgage loans, held for investment, net	$ 2,640,979	$ 2,762,042	$ 2,762,042
Accounts payable and accrued expenses	10,008	10,925	10,925
Accumulated deficit	$ (121,500)	(85,968)	$ (85,968)
Transition Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Commercial mortgage loans, held for investment, net		(7,211)
Accounts payable and accrued expenses		(550)
Accumulated deficit		(7,761)
Post-adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Commercial mortgage loans, held for investment, net		2,754,831
Accounts payable and accrued expenses		10,375
Accumulated deficit		$ (93,729)