Categories of Loans (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 975,557	$ 990,569
Undisbursed loans in process	(6,015)	(7,418)
Unamortized deferred loan costs, net	2,325	2,432
Allowance for loan losses	(15,991)	(16,038)	(16,634)	(16,815)
Net loans	955,876	969,545
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	287,383	288,848
Allowance for loan losses	(9,873)	(9,908)	(10,244)	(10,602)
Commercial | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	202,046	203,613
Commercial | Construction and development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	17,061	17,462
Commercial | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	68,276	67,773
Residential Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	491,133	502,619
Allowance for loan losses	(3,534)	(3,394)	(3,471)	(3,444)
Residential Mortgage | One- to four- family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	491,133	502,619
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	197,041	199,102
Allowance for loan losses	(2,584)	(2,736)	(2,919)	(2,769)
Consumer loans | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	100,461	100,516
Consumer loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	6,293	6,598
Consumer loans | Auto
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	15,082	15,572
Consumer loans | Boat/RV
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 75,205	$ 76,416