Loans - Schedule of Allowances for Loan Losses by Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 4,804	$ 4,246	$ 4,580	$ 4,082
Provision for possible loan losses	210	205	420	411
Charge-offs	(95)	(85)	(111)	(164)
Recoveries	26	105	56	142
Net charge-offs	(69)	20	(55)	(22)
Ending balance	4,945	4,471	4,945	4,471
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,176	976	933	1,024
Provision for possible loan losses	171	(78)	413	(127)
Charge-offs	(32)	(11)	(38)	(15)
Recoveries	1	9	8	14
Net charge-offs	(31)	(2)	(30)	(1)
Ending balance	1,316	896	1,316	896
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,824	1,649	1,902	1,673
Provision for possible loan losses	42	278	(36)	268
Charge-offs	(51)		(51)	(14)
Net charge-offs	(51)		(51)	(14)
Ending balance	1,815	1,927	1,815	1,927
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,282	939	1,096	894
Provision for possible loan losses	(110)	87	67	172
Charge-offs		(59)		(104)
Recoveries	2	84	11	89
Net charge-offs	2	25	11	(15)
Ending balance	1,174	1,051	1,174	1,051
Construction & Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	134	184	253	180
Provision for possible loan losses	28	33	(91)	37
Ending balance	162	217	162	217
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	68	74	76	78
Provision for possible loan losses	65	(7)	53	(22)
Charge-offs	(12)	(15)	(22)	(31)
Recoveries	23	12	37	39
Net charge-offs	11	(3)	15	8
Ending balance	144	64	144	64
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	320	424	320	233
Provision for possible loan losses	14	(108)	14	83
Ending balance	$ 334	$ 316	$ 334	$ 316