Allowance for Credit Losses - Summary of Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Receivables [Abstract]
Allowance for loan losses	$ 114,419	$ 106,178	$ 102,353
Allowance for unfunded letters of credit	2,185	2,189
Total allowance for credit losses	$ 116,604	$ 108,367