Loans - Schedule of Allowances for Loan Losses by Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 4,945	$ 4,471	$ 4,580	$ 4,082
Provision for possible loan losses	210	206	630	617
Charge-offs	(91)	(39)	(202)	(203)
Recoveries	13	23	69	165
Net charge-offs	(78)	(16)	(133)	(38)
Ending balance	5,077	4,661	5,077	4,661
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,316	896	933	1,024
Provision for possible loan losses	27	94	455	(33)
Charge-offs	(54)		(112)	(15)
Recoveries	5	2	18	16
Net charge-offs	(49)	2	(94)	1
Ending balance	1,294	992	1,294	992
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,815	1,927	1,902	1,673
Provision for possible loan losses	(5)	108	(41)	376
Charge-offs			(51)	(14)
Recoveries
Net charge-offs			(51)	(14)
Ending balance	1,810	2,035	1,810	2,035
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,174	1,051	1,096	894
Provision for possible loan losses	95	(45)	162	127
Charge-offs	(28)		(28)	(104)
Recoveries	3	10	14	99
Net charge-offs	(25)	10	(14)	(5)
Ending balance	1,244	1,016	1,244	1,016
Construction & Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	162	217	253	180
Provision for possible loan losses	18	85	(73)	122
Charge-offs
Recoveries
Net charge-offs
Ending balance	180	302	180	302
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	144	64	76	78
Provision for possible loan losses	(48)	46	(10)	24
Charge-offs	(9)	(39)	(11)	(70)
Recoveries	5	11	37	50
Net charge-offs	(4)	(28)	26	(20)
Ending balance	92	82	92	82
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	334	316	320	233
Provision for possible loan losses	123	(82)	137	1
Charge-offs
Recoveries
Net charge-offs
Ending balance	$ 457	$ 234	$ 457	$ 234