Fair Value of Assets Measured on Nonrecurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Impaired Loans
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis	$ 3,135	$ 5,125
Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis	8,008	4,353
Significant Other Observable Inputs (Level 2) | Impaired Loans
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis	3,135	5,125
Significant Other Observable Inputs (Level 2) | Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis	$ 8,000	$ 4,353