Classes of Loans (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 990,569	$ 920,209
Undisbursed loans in process	(7,418)	(5,352)
Unamortized deferred loan costs, net	2,432	2,418
Allowance for loan losses	(16,038)	(16,815)	(16,372)	(16,414)
Net loans	969,545	900,460
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	288,848	282,849
Allowance for loan losses	(9,908)	(10,602)	(10,124)	(10,003)
Commercial | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	203,613	197,390
Commercial | Construction and development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	17,462	20,831
Commercial | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	67,773	64,628
Residential Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	502,619	434,976
Allowance for loan losses	(3,394)	(3,444)	(2,212)	(2,359)
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	199,102	202,384
Allowance for loan losses	(2,736)	(2,769)	(4,036)	(4,052)
Consumer loans | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	100,516	96,864
Consumer loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	6,598	6,760
Consumer loans | Auto
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	15,572	15,203
Consumer loans | Boat/RV
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 76,416	$ 83,557