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, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale	$ 215,290	$ 990,864
Cost Basis
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost Basis	210,116	972,434
Fair Value
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale	$ 215,290	$ 990,864