Estimated Fair Value of Financial Instruments - Balances of Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Fair Value Of Other Financial Instrument [Line Items]
Impaired and nonaccrual loans	$ 27,796	$ 34,471
Other real estate	1,366	1,687
Total assets at fair value on a nonrecurring basis	29,162	36,158
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value Of Other Financial Instrument [Line Items]
Impaired and nonaccrual loans	0	0
Other real estate	0	0
Total assets at fair value on a nonrecurring basis	0	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value Of Other Financial Instrument [Line Items]
Impaired and nonaccrual loans	0	0
Other real estate	0	0
Total assets at fair value on a nonrecurring basis	0	0
Significant Unobservable Inputs (Level 3) [Member]
Fair Value Of Other Financial Instrument [Line Items]
Impaired and nonaccrual loans	27,796	34,471
Other real estate	1,366	1,687
Total assets at fair value on a nonrecurring basis	$ 29,162	$ 36,158