Commitments, Guarantees and Other Contingencies - Schedule of Contractual Amounts of Unused Lending Commitments to Extend Credit (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012
Schedule of contractual amounts of unused lending commitments to extend credit
Contractual amounts of unused lending commitments	$ 162,767
Revolving, open-end lines secured by single-family residential properties [Member]
Schedule of contractual amounts of unused lending commitments to extend credit
Contractual amounts of unused lending commitments	53,381
Commercial real estate, construction, and land development loans secured by real estate [Member]
Schedule of contractual amounts of unused lending commitments to extend credit
Contractual amounts of unused lending commitments
Single family residential construction loan commitments [Member]
Schedule of contractual amounts of unused lending commitments to extend credit
Contractual amounts of unused lending commitments	4,505
Commercial real estate, other construction loan, and land development loan commitments [Member]
Schedule of contractual amounts of unused lending commitments to extend credit
Contractual amounts of unused lending commitments	49,095
Commercial and industrial loan commitments [Member]
Schedule of contractual amounts of unused lending commitments to extend credit
Contractual amounts of unused lending commitments	21,843
Overdraft Protection Line [Member]
Schedule of contractual amounts of unused lending commitments to extend credit
Contractual amounts of unused lending commitments	25,650
Other [Member]
Schedule of contractual amounts of unused lending commitments to extend credit
Contractual amounts of unused lending commitments	$ 8,293