Commitments and Contingencies - Summary of Commitments to Extend Credit and Standby Letters of Credit (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Commitments And Contingencies Disclosure [Abstract]
Commitments to extend credit	$ 190,813	$ 180,733	$ 156,330
Standby letters of credit	$ 6,747	$ 6,788	$ 8,349