Off-Balance Sheet Commitments - Distribution of Undisbursed Loan Commitments (Detail)

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Off-Balance Sheet Commitments - Distribution of Undisbursed Loan Commitments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Loss Contingencies [Line Items]
Total undisbursed loan commitments	$ 250,479	$ 212,885
Commitments to extend credit [Member]
Loss Contingencies [Line Items]
Total undisbursed loan commitments	225,070	182,746
Standby letters of credit [Member]
Loss Contingencies [Line Items]
Total undisbursed loan commitments	9,326	10,588
Commercial letters of credit [Member]
Loss Contingencies [Line Items]
Total undisbursed loan commitments	4,149	6,092
Unused credit card lines [Member]
Loss Contingencies [Line Items]
Total undisbursed loan commitments	$ 11,934	$ 13,459