Commitments and Contingencies - Summary of Financial Instruments Outstanding (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Loss Contingencies
Reserve for unfunded lending commitments	$ 11,990	$ 14,145	$ 14,525	$ 11,801
Credit Risk Contract
Loss Contingencies
Commitments to grant loans	398,754	61,240
Unfunded commitments under lines of credit	4,876,141	4,617,802
Commercial and standby letters of credit	165,365	150,281
Reserve for unfunded lending commitments	$ 11,990	$ 14,145