Loans Held for Sale, at Fair Value - Summary of Loans Held for Sale at Cost Basis and Fair Value (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable
Loans held for sale, at fair value	$ 1,537,734	$ 215,290
Cost Basis
Accounts, Notes, Loans and Financing Receivable
Loans held for sale, at fair value	1,510,598	210,116
Fair Value
Accounts, Notes, Loans and Financing Receivable
Loans held for sale, at fair value	$ 1,537,734	$ 215,290