Commitments - Summary of Commitments to Extend Credit and Standby Letters of Credit (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Commitments And Contingencies Disclosure [Abstract]
Commitments to extend credit	$ 193,515	$ 180,733	$ 143,890
Standby letters of credit	$ 7,142	$ 6,788	$ 9,039