Commercial and Retail Credit Exposure Credit Risk Profile by Internal Rating (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 990,569	$ 920,209
Residential Mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans	502,619	434,976
Residential Mortgage | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	486,027	417,772
Residential Mortgage | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	2,012	2,473
Residential Mortgage | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	14,580	14,731
Consumer loans
Financing Receivable, Recorded Investment [Line Items]
Loans	199,102	202,384
Consumer loans | Real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	100,516	96,864
Consumer loans | Auto
Financing Receivable, Recorded Investment [Line Items]
Loans	15,572	15,203
Consumer loans | Boat/RV
Financing Receivable, Recorded Investment [Line Items]
Loans	76,416	83,557
Consumer loans | Other
Financing Receivable, Recorded Investment [Line Items]
Loans	6,598	6,760
Consumer loans | Pass | Real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	97,972	94,066
Consumer loans | Pass | Auto
Financing Receivable, Recorded Investment [Line Items]
Loans	15,533	15,135
Consumer loans | Pass | Boat/RV
Financing Receivable, Recorded Investment [Line Items]
Loans	75,026	82,639
Consumer loans | Pass | Other
Financing Receivable, Recorded Investment [Line Items]
Loans	6,434	6,680
Consumer loans | Substandard | Real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	2,544	2,798
Consumer loans | Substandard | Auto
Financing Receivable, Recorded Investment [Line Items]
Loans	39	68
Consumer loans | Substandard | Boat/RV
Financing Receivable, Recorded Investment [Line Items]
Loans	1,390	918
Consumer loans | Substandard | Other
Financing Receivable, Recorded Investment [Line Items]
Loans	164	80
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	288,848	282,849
Commercial | Real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	203,613	197,390
Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Loans	67,773	64,628
Commercial | Construction and development
Financing Receivable, Recorded Investment [Line Items]
Loans	17,462	20,831
Commercial | Pass | Real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	185,794	167,991
Commercial | Pass | Other
Financing Receivable, Recorded Investment [Line Items]
Loans	63,413	56,691
Commercial | Pass | Construction and development
Financing Receivable, Recorded Investment [Line Items]
Loans	9,314	8,093
Commercial | Special Mention | Real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	6,692	11,940
Commercial | Special Mention | Other
Financing Receivable, Recorded Investment [Line Items]
Loans	255	880
Commercial | Special Mention | Construction and development
Financing Receivable, Recorded Investment [Line Items]
Loans	172	538
Commercial | Substandard | Real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	11,127	16,488
Commercial | Substandard | Other
Financing Receivable, Recorded Investment [Line Items]
Loans	3,281	6,260
Commercial | Substandard | Construction and development
Financing Receivable, Recorded Investment [Line Items]
Loans	7,976	12,105
Commercial | Doubtful | Real estate
Financing Receivable, Recorded Investment [Line Items]
Loans		971
Commercial | Doubtful | Other
Financing Receivable, Recorded Investment [Line Items]
Loans	824	797
Commercial | Doubtful | Construction and development
Financing Receivable, Recorded Investment [Line Items]
Loans		$ 95