Commitments, Guarantees and Other Contingencies - Schedule of Contractual Amounts of Unused Lending Commitments to Extend Credit (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013
Schedule of contractual amounts of unused lending commitments to extend credit
Contractual amounts of unused lending commitments	$ 178,368
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	57,086
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	8,221
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	45,380
Commercial and industrial loan commitments [Member]
Schedule of contractual amounts of unused lending commitments to extend credit
Contractual amounts of unused lending commitments	29,721
Overdraft protection line commitments [Member]
Schedule of contractual amounts of unused lending commitments to extend credit
Contractual amounts of unused lending commitments	30,303
Other [Member]
Schedule of contractual amounts of unused lending commitments to extend credit
Contractual amounts of unused lending commitments	$ 7,657