Assets Measured at Fair Value on Non-recurring Basis (Detail) (Fair Value, Measurements, Nonrecurring, USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Impaired loan on non-recurring basis	$ 19,823	[1]	$ 20,225	[1]
Other real estate owned	6,258		7,575
Mortgage servicing rights	665		3,484
Residential Real Estate - Owner Occupied
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Impaired loan on non-recurring basis	787		782
Other real estate owned	798		1,195
Residential Real Estate - Non Owner Occupied
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Impaired loan on non-recurring basis	1,887		1,788
Commercial Real Estate
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Impaired loan on non-recurring basis	15,443		15,618
Other real estate owned	460		1,219
Real Estate Construction
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Impaired loan on non-recurring basis	1,505		1,552
Other real estate owned	5,000		5,161
Commercial
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Impaired loan on non-recurring basis	201		182
Home Equity
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Impaired loan on non-recurring basis			303
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Impaired loan on non-recurring basis	19,823	[1]	20,225	[1]
Other real estate owned	6,258		7,575
Mortgage servicing rights	665		3,484
Fair Value, Inputs, Level 3 | Residential Real Estate - Owner Occupied
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Impaired loan on non-recurring basis	787		782
Other real estate owned	798		1,195
Fair Value, Inputs, Level 3 | Residential Real Estate - Non Owner Occupied
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Impaired loan on non-recurring basis	1,887		1,788
Fair Value, Inputs, Level 3 | Commercial Real Estate
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Impaired loan on non-recurring basis	15,443		15,618
Other real estate owned	460		1,219
Fair Value, Inputs, Level 3 | Real Estate Construction
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Impaired loan on non-recurring basis	1,505		1,552
Other real estate owned	5,000		5,161
Fair Value, Inputs, Level 3 | Commercial
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Impaired loan on non-recurring basis	201		182
Fair Value, Inputs, Level 3 | Home Equity
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Impaired loan on non-recurring basis			$ 303

[1] The impaired loan balances exclude non-collateral dependent TDRs.