Loans Held for Sale - Summary of Loans Held for Sale at Cost Basis and Fair Value (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Loans Receivable Held For Sale Net [Abstract]
Cost basis	$ 659,825	$ 1,074,429
Fair Value	$ 660,332	$ 1,071,836