Commitments and Contingencies - Summary of Financial Instruments Outstanding (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Loss Contingencies
Reserve for unfunded lending commitments	$ 14,525	$ 11,801	$ 12,099	$ 11,147
Credit Risk Contract
Loss Contingencies
Commitments to grant loans	140,139	161,350
Unfunded commitments under lines of credit	4,602,464	4,007,954
Commercial and standby letters of credit	147,208	134,882
Reserve for unfunded lending commitments	$ 14,525	$ 11,801