Loans Held for Sale, at Fair Value - Summary of Loans Held for Sale at Cost Basis and Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable
Loans held for sale, at fair value	$ 1,086,805	$ 215,290
Cost Basis
Accounts, Notes, Loans and Financing Receivable
Loans held for sale, at fair value	1,062,511	210,116
Fair Value
Accounts, Notes, Loans and Financing Receivable
Loans held for sale, at fair value	$ 1,086,805	$ 215,290