Loans Held for Sale, at Fair Value - Summary of Loans Held for Sale at Cost Basis and Fair Value (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair Value	$ 739,383	$ 215,290
Cost Basis
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost Basis	703,321	210,116
Fair Value
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair Value	$ 739,383	$ 215,290