Commitments and Contingent Liabilities - Notional Amount of Outstanding Commitments (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Commitments to extend credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 1,598,318	$ 1,643,187
Financial standby letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	17,760	17,843
Performance standby letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	28,110	26,497
Commercial letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 1,528	$ 1,672