Commitments and Letters of Credit - Notional Amount of Commitments and Letter of Credit Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Commitments to extend credit
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 1,733,820	$ 1,643,187
Financial standby letters of credit
Loss Contingencies [Line Items]
Financial instrument of credit risk	18,108	17,843
Performance standby letters of credit
Loss Contingencies [Line Items]
Financial instrument of credit risk	26,630	26,497
Commercial letters of credit
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 1,301	$ 1,672