Quarterly Data (Unaudited) - Summary of Quarterly Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended	36 Months Ended
Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 7,686	$ 7,899	$ 7,930	$ 7,846	$ 8,340	$ 8,270	$ 8,432	$ 8,594	$ 31,361	$ 33,636
Interest expense	636us-gaap_InterestExpense	642us-gaap_InterestExpense	630us-gaap_InterestExpense	645us-gaap_InterestExpense	677us-gaap_InterestExpense	702us-gaap_InterestExpense	737us-gaap_InterestExpense	789us-gaap_InterestExpense	2,553us-gaap_InterestExpense	2,905us-gaap_InterestExpense
Net interest income	7,050us-gaap_InterestIncomeExpenseNet	7,257us-gaap_InterestIncomeExpenseNet	7,300us-gaap_InterestIncomeExpenseNet	7,201us-gaap_InterestIncomeExpenseNet	7,663us-gaap_InterestIncomeExpenseNet	7,568us-gaap_InterestIncomeExpenseNet	7,695us-gaap_InterestIncomeExpenseNet	7,805us-gaap_InterestIncomeExpenseNet	28,808us-gaap_InterestIncomeExpenseNet	30,731us-gaap_InterestIncomeExpenseNet
Provision (reduction in reserve) for loan losses	(169)us-gaap_ProvisionForLoanAndLeaseLosses	(55)us-gaap_ProvisionForLoanAndLeaseLosses	(264)us-gaap_ProvisionForLoanAndLeaseLosses	414us-gaap_ProvisionForLoanAndLeaseLosses	(1,441)us-gaap_ProvisionForLoanAndLeaseLosses	240us-gaap_ProvisionForLoanAndLeaseLosses	53us-gaap_ProvisionForLoanAndLeaseLosses	506us-gaap_ProvisionForLoanAndLeaseLosses	(74)us-gaap_ProvisionForLoanAndLeaseLosses	(642)us-gaap_ProvisionForLoanAndLeaseLosses	4,300us-gaap_ProvisionForLoanAndLeaseLosses	18,800us-gaap_ProvisionForLoanAndLeaseLosses	22,500us-gaap_ProvisionForLoanAndLeaseLosses
Net interest income after provision (reduction in reserve) for loan losses	7,219	7,312	7,564	6,787	9,104	7,328	7,642	7,299	28,882	31,373
Non-interest:
Income	1,279us-gaap_NoninterestIncome	1,180us-gaap_NoninterestIncome	1,485us-gaap_NoninterestIncome	1,147us-gaap_NoninterestIncome	723us-gaap_NoninterestIncome	1,291us-gaap_NoninterestIncome	1,228us-gaap_NoninterestIncome	1,623us-gaap_NoninterestIncome	5,091us-gaap_NoninterestIncome	4,865us-gaap_NoninterestIncome
Expense	7,246us-gaap_NoninterestExpense	7,242us-gaap_NoninterestExpense	7,223us-gaap_NoninterestExpense	6,884us-gaap_NoninterestExpense	8,569us-gaap_NoninterestExpense	7,365us-gaap_NoninterestExpense	7,176us-gaap_NoninterestExpense	7,692us-gaap_NoninterestExpense	28,595us-gaap_NoninterestExpense	30,802us-gaap_NoninterestExpense
Income before income taxes	1,252	1,250	1,826	1,050	1,258	1,254	1,694	1,230
Provision for income taxes	532us-gaap_IncomeTaxExpenseBenefit	413us-gaap_IncomeTaxExpenseBenefit	608us-gaap_IncomeTaxExpenseBenefit	276us-gaap_IncomeTaxExpenseBenefit	303us-gaap_IncomeTaxExpenseBenefit	350us-gaap_IncomeTaxExpenseBenefit	512us-gaap_IncomeTaxExpenseBenefit	344us-gaap_IncomeTaxExpenseBenefit	1,829us-gaap_IncomeTaxExpenseBenefit	1,509us-gaap_IncomeTaxExpenseBenefit
Net income	$ 720us-gaap_ProfitLoss	$ 837us-gaap_ProfitLoss	$ 1,218us-gaap_ProfitLoss	$ 774us-gaap_ProfitLoss	$ 955us-gaap_ProfitLoss	$ 904us-gaap_ProfitLoss	$ 1,182us-gaap_ProfitLoss	$ 886us-gaap_ProfitLoss	$ 3,549us-gaap_ProfitLoss	$ 3,927us-gaap_ProfitLoss
Earnings per common share:
Basic earnings	$ 0.12us-gaap_EarningsPerShareBasic	$ 0.14us-gaap_EarningsPerShareBasic	$ 0.20us-gaap_EarningsPerShareBasic	$ 0.13us-gaap_EarningsPerShareBasic	$ 0.16us-gaap_EarningsPerShareBasic	$ 0.15us-gaap_EarningsPerShareBasic	$ 0.20us-gaap_EarningsPerShareBasic	$ 0.15us-gaap_EarningsPerShareBasic	$ 0.58us-gaap_EarningsPerShareBasic	$ 0.65us-gaap_EarningsPerShareBasic
Diluted earnings	$ 0.12us-gaap_EarningsPerShareDiluted	$ 0.13us-gaap_EarningsPerShareDiluted	$ 0.20us-gaap_EarningsPerShareDiluted	$ 0.13us-gaap_EarningsPerShareDiluted	$ 0.16us-gaap_EarningsPerShareDiluted	$ 0.15us-gaap_EarningsPerShareDiluted	$ 0.20us-gaap_EarningsPerShareDiluted	$ 0.15us-gaap_EarningsPerShareDiluted	$ 0.57us-gaap_EarningsPerShareDiluted	$ 0.65us-gaap_EarningsPerShareDiluted
Dividends declared	$ 0.02	$ 0.01							$ 0.03

Aggregate dividends declared during the period for each share of common stock outstanding.

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