Commitments and Contingent Liabilities - Notional Amount of Outstanding Commitments (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Commitments to extend credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 1,643,908	$ 1,643,187
Financial standby letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	17,805	17,843
Performance standby letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	27,352	26,497
Commercial letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 1,718	$ 1,672