Allowance for Loan Losses - Summary of Allowance for Loan Losses (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
Allowance for loan losses:
Allowance for loan losses, beginning of period	$ 19,759	$ 17,434	$ 19,197	$ 16,574
Loans charged off	(160)	(635)	(533)	(1,059)
Recoveries	151	280	336	464
Provision	750	900	1,500	2,000
Allowance for loan losses, end of period	20,500	17,979	20,500	17,979
Amount of allowance for loan losses for loans deemed to be impaired	1,539	2,413	1,539	2,413
Amount of allowance for loan losses for loans not deemed to be impaired	18,961	15,566	18,961	15,566
Loans:
Ending balance	1,163,732	1,028,830	1,163,732	1,028,830
Loans deemed to be impaired	6,234	6,662	6,234	6,662
Loans not deemed to be impaired	1,157,498	1,022,168	1,157,498	1,022,168
Construction and Land Development [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	3,199	2,920	3,041	2,893
Provision	42	(31)	200	(4)
Allowance for loan losses, end of period	3,241	2,889	3,241	2,889
Amount of allowance for loan losses for loans deemed to be impaired	1,000	1,000	1,000	1,000
Amount of allowance for loan losses for loans not deemed to be impaired	2,241	1,889	2,241	1,889
Loans:
Ending balance	34,919	36,422	34,919	36,422
Loans deemed to be impaired	1,500	1,500	1,500	1,500
Loans not deemed to be impaired	33,419	34,922	33,419	34,922
Commercial and Industrial [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	3,523	3,220	3,118	3,139
Loans charged off	(6)	(289)	(234)	(399)
Recoveries	56	164	121	206
Provision	(358)	371	210	520
Allowance for loan losses, end of period	3,215	3,466	3,215	3,466
Amount of allowance for loan losses for loans deemed to be impaired	92	871	92	871
Amount of allowance for loan losses for loans not deemed to be impaired	3,123	2,595	3,123	2,595
Loans:
Ending balance	101,918	78,971	101,918	78,971
Loans deemed to be impaired	1,102	2,328	1,102	2,328
Loans not deemed to be impaired	100,816	76,643	100,816	76,643
Commercial Real Estate [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	8,779	7,341	9,065	6,566
Recoveries	1	2	4	3
Provision	644	411	355	1,185
Allowance for loan losses, end of period	9,424	7,754	9,424	7,754
Amount of allowance for loan losses for loans deemed to be impaired	204	450	204	450
Amount of allowance for loan losses for loans not deemed to be impaired	9,220	7,304	9,220	7,304
Loans:
Ending balance	609,462	535,232	609,462	535,232
Loans deemed to be impaired	2,365	2,321	2,365	2,321
Loans not deemed to be impaired	607,097	532,911	607,097	532,911
Residential Real Estate [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	2,071	1,784	1,994	1,886
Loans charged off		(59)		(219)
Recoveries	1	3	4	9
Provision	(42)	65	32	117
Allowance for loan losses, end of period	2,030	1,793	2,030	1,793
Amount of allowance for loan losses for loans deemed to be impaired	147	92	147	92
Amount of allowance for loan losses for loans not deemed to be impaired	1,883	1,701	1,883	1,701
Loans:
Ending balance	283,392	259,006	283,392	259,006
Loans deemed to be impaired	1,171	513	1,171	513
Loans not deemed to be impaired	282,221	258,493	282,221	258,493
Consumer [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	357	317	333	356
Loans charged off	(154)	(287)	(299)	(441)
Recoveries	92	111	206	246
Provision	68	152	123	132
Allowance for loan losses, end of period	363	293	363	293
Amount of allowance for loan losses for loans deemed to be impaired
Amount of allowance for loan losses for loans not deemed to be impaired	363	293	363	293
Loans:
Ending balance	8,123	6,597	8,123	6,597
Loans not deemed to be impaired	8,123	6,597	8,123	6,597
Home Equity [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	833	741	886	704
Recoveries	1		1
Provision	98	(60)	45	(23)
Allowance for loan losses, end of period	932	681	932	681
Amount of allowance for loan losses for loans deemed to be impaired	96		96
Amount of allowance for loan losses for loans not deemed to be impaired	836	681	836	681
Loans:
Ending balance	125,918	112,602	125,918	112,602
Loans deemed to be impaired	96		96
Loans not deemed to be impaired	125,822	112,602	125,822	112,602
Unallocated [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	997	1,111	760	1,030
Provision	298	(8)	535	73
Allowance for loan losses, end of period	1,295	1,103	1,295	1,103
Amount of allowance for loan losses for loans not deemed to be impaired	$ 1,295	$ 1,103	$ 1,295	$ 1,103