Loans Held for Investment and the Allowance for Credit Losses - Summary of Loans Held for Investment Portfolio Activity (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2022 USD ($)
Loans And Leases Receivable Disclosure [Abstract]
Balance as of January 1, 2022	$ 4,867,203
Loans originated	223,871
Additional fundings	29,235
Amortization of origination fees	1,491
Collection of principal	(47,698)
Collection of accrued PIK interest	(313)
(Increase) of allowance for credit losses	(4,308)
Balance as of March 31, 2022	$ 5,069,481