Loans Held for Investment and the Allowance for Credit Losses - Summary of Loan Portfolio Activity (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2021 USD ($)
Loans And Leases Receivable Disclosure [Abstract]
Balance as of December 31, 2020	$ 4,456,460
Loans originated and acquired	631,408
Additional fundings	74,312
Amortization of origination fees	3,775
Collection of principal	(339,315)
Loan sale	(60,690)
Change in allowance for credit losses	7,999
Balance as of June 30, 2021	$ 4,773,949