Commitments and Contingent Liabilities - Notional Amount of Outstanding Commitments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Commitments to extend credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 1,644,486	$ 1,571,987
Financial standby letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	29,379	38,121
Performance standby letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	26,210	32,441
Commercial letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 2,405	$ 0