Fair Value Measurement - Schedule of Assets Measured at Fair Value on Nonrecurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Nonrecurring Fair Value Measurements [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Impaired loans	$ 2,937	$ 3,866
Mortgage servicing rights	1,040	825
Significant Unobservable Inputs (Level 3) [Member] | Nonrecurring Fair Value Measurements [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Impaired loans	2,937	3,866
Other real estate owned and repossessed assets	5,007	5,988
Mortgage servicing rights	$ 1,040	$ 825
Significant Unobservable Inputs (Level 3) [Member] | Minimum [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Weighted Average, Appraisal adjustments	0.00%	0.00%
Impaired loans liquidation expenses	(5.70%)	(3.90%)
Significant Unobservable Inputs (Level 3) [Member] | Minimum [Member] | Discounted Cash Flow [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Discount rate	9.00%	9.00%
Remaining term of mortgage	2 years 9 months 18 days	2 years 9 months 18 days
Significant Unobservable Inputs (Level 3) [Member] | Maximum [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Weighted Average, Appraisal adjustments	(28.40%)	(50.80%)
Impaired loans liquidation expenses	(8.00%)	(8.00%)
Significant Unobservable Inputs (Level 3) [Member] | Maximum [Member] | Discounted Cash Flow [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Discount rate	12.00%	12.00%
Remaining term of mortgage	26 years 6 months 0 days	27 years
Significant Unobservable Inputs (Level 3) [Member] | Weighted Average [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Discount rate	9.90%	9.80%
Weighted Average, Appraisal adjustments	(8.90%)	(13.70%)
Impaired loans liquidation expenses	(6.70%)	(6.80%)
Significant Unobservable Inputs (Level 3) [Member] | Weighted Average [Member] | Discounted Cash Flow [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Weighted average remaining term	15 years 6 months 0 days	15 years 9 months 18 days