Fair Value - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loan servicing rights	$ 5		$ 5		$ 9
Amortized cost	6		6		11
Valuation allowance	1		1		2
Increase in earnings with respect to servicing rights	0	0	1	3
Unpaid principal balance of impairment loan	7,966		7,966		10,503
Reduction in valuation allowances of impairment loan		(379)		1,179
Charge-offs amount of loans	536		1,802
Unpaid principal balance of impairment loan at collateral	10,193		10,193		10,069
Total impaired loans	14,404		14,404		15,393
Foreclosed assets, net	1,572		1,572		2,370
Charge against earnings of foreclosed assets		0		1,139
Amount of charge-offs on foreclosed assets	780		962
Period of loan due			90 days
Financial instruments measured at fair value on a non-recurring basis [Member] | Fair Value Measurements Using Significant Other Observable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment loans			7,349
Total impaired loans	7,349		7,349		6,809
Foreclosed assets, net	1,414		1,414		1,209
Outstanding amount of foreclosed assets	3,509		3,509		2,348
Valuation allowance on foreclosed assets	$ 0		$ 0		$ 1,139