Loans Held for Investment and the Allowance for Credit Losses - Summary of Amortized Cost and Results of Internal Risk Rating Review Performed (Details) $ in Thousands	Jun. 30, 2021 USD ($) Rating	Dec. 31, 2020 USD ($) Rating
Accounts Notes And Loans Receivable [Line Items]
Carrying Value, Gross	$ 4,825,890	$ 4,516,400
Allowance for Credit Losses	(51,941)	(59,940)
Carrying Value	$ 4,773,949	$ 4,456,460
Weighted Average Risk Rating | Rating	3.1	3.1
Rating 2
Accounts Notes And Loans Receivable [Line Items]
Carrying Value, Gross	$ 341,749	$ 337,738
Rating 3
Accounts Notes And Loans Receivable [Line Items]
Carrying Value, Gross	3,872,528	3,340,663
Rating 4
Accounts Notes And Loans Receivable [Line Items]
Carrying Value, Gross	580,413	806,893
Rating 5
Accounts Notes And Loans Receivable [Line Items]
Carrying Value, Gross	$ 31,200	$ 31,106