Fair Value Measurements - Schedule of Quantitative Information of Assets Measured at Fair Value on Nonrecurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Level III [Member] | Discounted Cash Flow [Member] | Impaired Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value estimate	$ 7,080	$ 7,260
Level III [Member] | Discounted Cash Flow [Member] | Mortgage Servicing Rights [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value estimate	228	214
Level III [Member] | Appraisal of Collateral [Member] | Impaired Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value estimate	1,191	2,152
Level III [Member] | Appraisal of Collateral [Member] | Other Real Estate Owned [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value estimate		25
Fair Value, Measurements, Nonrecurring [Member] | Impaired Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value estimate	8,271	9,412
Fair Value, Measurements, Nonrecurring [Member] | Mortgage Servicing Rights [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value estimate	228	214
Fair Value, Measurements, Nonrecurring [Member] | Other Real Estate Owned [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value estimate		25
Fair Value, Measurements, Nonrecurring [Member] | Level III [Member] | Impaired Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value estimate	8,271	9,412
Fair Value, Measurements, Nonrecurring [Member] | Level III [Member] | Mortgage Servicing Rights [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value estimate	228	214
Fair Value, Measurements, Nonrecurring [Member] | Level III [Member] | Other Real Estate Owned [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value estimate		$ 25
Fair Value, Measurements, Nonrecurring [Member] | Level III [Member] | Discounted Cash Flow [Member] | Mortgage Servicing Rights [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	1.50%	1.50%
Fair Value, Measurements, Nonrecurring [Member] | Level III [Member] | Discounted Cash Flow [Member] | Minimum [Member] | Impaired Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Remaining term	6 months	4 months
Discount rate	4.63%	7.50%
Fair Value, Measurements, Nonrecurring [Member] | Level III [Member] | Discounted Cash Flow [Member] | Minimum [Member] | Mortgage Servicing Rights [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Remaining term	15 months	24 months
Fair Value, Measurements, Nonrecurring [Member] | 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%
Fair Value, Measurements, Nonrecurring [Member] | 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
Fair Value, Measurements, Nonrecurring [Member] | Level III [Member] | Appraisal of Collateral [Member] | Impaired Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Liquidation expense	(10.00%)	(10.00%)
Fair Value, Measurements, Nonrecurring [Member] | 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%)
Fair Value, Measurements, Nonrecurring [Member] | 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%
Fair Value, Measurements, Nonrecurring [Member] | 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%)
Fair Value, Measurements, Nonrecurring [Member] | 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%)