Fair Value Measurements - Schedule of Quantitative Information of Assets Measured at Fair Value on Nonrecurring Basis (Detail) (Fair Value, Measurements, Nonrecurring [Member], USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Impaired Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value estimate	$ 7,775	$ 9,412
Mortgage Servicing Rights [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value estimate	226	214
Other Real Estate Owned [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value estimate		25
Level III [Member] | Impaired Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value estimate	7,775	9,412
Level III [Member] | Mortgage Servicing Rights [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value estimate	226	214
Level III [Member] | Other Real Estate Owned [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value estimate		25
Level III [Member] | Discounted Cash Flow [Member] | Impaired Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value estimate	6,652	7,260
Level III [Member] | Discounted Cash Flow [Member] | Mortgage Servicing Rights [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value estimate	226	214
Discount rate	1.50%	1.50%
Level III [Member] | Discounted Cash Flow [Member] | Minimum [Member] | Impaired Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Remaining term	9 months	4 months
Discount rate	4.63%	7.50%
Level III [Member] | Discounted Cash Flow [Member] | Minimum [Member] | Mortgage Servicing Rights [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Remaining term	18 months	24 months
Level III [Member] | Discounted Cash Flow [Member] | Maximum [Member] | Impaired Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Remaining term	29 years	29 years
Discount rate	12.00%	12.00%
Level III [Member] | Discounted Cash Flow [Member] | Maximum [Member] | Mortgage Servicing Rights [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Remaining term	30 years	30 years
Level III [Member] | Appraisal of Collateral [Member] | Impaired Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value estimate	1,123	2,152
Liquidation expense	(10.00%)	(10.00%)
Level III [Member] | Appraisal of Collateral [Member] | Other Real Estate Owned [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value estimate		$ 25
Level III [Member] | Appraisal of Collateral [Member] | Minimum [Member] | Impaired Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Appraisal adjustments	(20.00%)	(20.00%)
Level III [Member] | Appraisal of Collateral [Member] | Minimum [Member] | Other Real Estate Owned [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Management discount for property type		0.00%
Level III [Member] | Appraisal of Collateral [Member] | Maximum [Member] | Impaired Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Appraisal adjustments	(25.00%)	(35.00%)
Level III [Member] | Appraisal of Collateral [Member] | Maximum [Member] | Other Real Estate Owned [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Management discount for property type		(67.00%)