Commitments and Contingent Liabilities - Notional Amount of Outstanding Commitments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Commitments to extend credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 1,568,438	$ 1,506,618
Financial standby letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	40,245	47,185
Performance standby letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	34,084	69,240
Commercial letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 0	$ 685