Commitments and Contingent Liabilities - Notional Amount of Outstanding Commitments (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Commitments to extend credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 1,576,245	$ 1,635,948
Financial standby letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	20,089	36,075
Performance standby letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	26,317	25,915
Commercial letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 2,023	$ 2,611