Commitments, Credit Risk, and Contingencies - Summary of The Contractual Amount of Commitments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Summary of the contractual amount of commitments
Contractual amount of commitments, Total	$ 156,416	$ 178,683
Commitments to extend credit [Member]
Summary of the contractual amount of commitments
Contractual amount of commitments, Total	67,248	92,128
Home Equity Loans [Member]
Summary of the contractual amount of commitments
Contractual amount of commitments, Total	80,832	78,410
Standby letters of credit [Member]
Summary of the contractual amount of commitments
Contractual amount of commitments, Total	$ 8,336	$ 8,145