Fair Value - Assets Measured at Fair Value on Nonrecurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans measured for impairment (net of guarantees and specific reserve)	$ 5,877	$ 22,969
Other real estate owned	17,972	11,000
Assets, Fair Value Disclosure, Nonrecurring, Total	23,849	33,969
Loans measured for impairment (net of guarantees and specific reserve), Total Loss	2	455
Other real estate owned, Total Loss	1,416	2,427
Assets at fair value on a nonrecurring basis, Total Loss	1,418	2,882
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans measured for impairment (net of guarantees and specific reserve)
Other real estate owned
Assets, Fair Value Disclosure, Nonrecurring, Total
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans measured for impairment (net of guarantees and specific reserve)
Other real estate owned
Assets, Fair Value Disclosure, Nonrecurring, Total
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans measured for impairment (net of guarantees and specific reserve)	5,877	22,969
Other real estate owned	17,972	11,000
Assets, Fair Value Disclosure, Nonrecurring, Total	$ 23,849	$ 33,969