Allowance for Loan Losses - Summary of Allowance for Loan Losses (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	Dec. 31, 2012
Allowance for loan losses:
Allowance for loan losses, beginning of period	$ 20,500	$ 17,979	$ 19,197	$ 16,574
Charge-offs	(149)	(728)	(682)	(1,787)
Recoveries	149	157	485	621
Provision	750	1,250	2,250	3,250
Allowance for loan losses, end of period	21,250	18,658	21,250	18,658
Amount of allowance for loan losses for loans deemed to be impaired	1,769	2,113	1,769	2,113
Amount of allowance for loan losses for loans not deemed to be impaired	19,481	16,545	19,481	16,545
Loans:
Total loans, net	1,231,048	1,064,923	1,231,048	1,064,923	1,111,788
Loans deemed to be impaired	8,566	6,558	8,566	6,558
Loans not deemed to be impaired	1,222,482	1,058,365	1,222,482	1,058,365
Construction and Land Development [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	3,241	2,889	3,041	2,893
Provision	(114)	140	86	136
Allowance for loan losses, end of period	3,127	3,029	3,127	3,029
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	2,127	2,029	2,127	2,029
Loans:
Total loans, net	32,750	38,318	32,750	38,318	38,618
Loans deemed to be impaired	1,500	1,500	1,500	1,500
Loans not deemed to be impaired	31,250	36,818	31,250	36,818
Commercial and Industrial [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	3,215	3,466	3,118	3,139
Charge-offs		(532)	(234)	(931)
Recoveries	42	38	163	243
Provision	(534)	133	(324)	654
Allowance for loan losses, end of period	2,723	3,105	2,723	3,105
Amount of allowance for loan losses for loans deemed to be impaired	90	455	90	455
Amount of allowance for loan losses for loans not deemed to be impaired	2,633	2,650	2,633	2,649
Loans:
Total loans, net	87,468	78,567	87,468	78,567	88,475
Loans deemed to be impaired	1,132	1,882	1,132	1,882
Loans not deemed to be impaired	86,336	76,685	86,336	76,685
Commercial Real Estate [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	9,424	7,754	9,065	6,566
Recoveries	2	2	5	5
Provision	1,162	967	1,518	2,152
Allowance for loan losses, end of period	10,588	8,723	10,588	8,723
Amount of allowance for loan losses for loans deemed to be impaired	445	434	445	434
Amount of allowance for loan losses for loans not deemed to be impaired	10,143	8,289	10,143	8,289
Loans:
Total loans, net	666,166	562,252	666,166	562,252	576,465
Loans deemed to be impaired	4,688	2,302	4,688	2,302
Loans not deemed to be impaired	661,478	559,950	661,478	559,950
Residential Real Estate [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	2,030	1,793	1,994	1,886
Charge-offs		(49)		(110)
Recoveries	4	2	9	11
Provision	176	240	207	199
Allowance for loan losses, end of period	2,210	1,986	2,210	1,986
Amount of allowance for loan losses for loans deemed to be impaired	139	127	139	127
Amount of allowance for loan losses for loans not deemed to be impaired	2,071	1,859	2,071	1,859
Loans:
Total loans, net	309,291	262,426	309,291	262,426	281,857
Loans deemed to be impaired	1,151	777	1,151	777
Loans not deemed to be impaired	308,140	261,649	308,140	261,649
Consumer [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	363	293	333	356
Charge-offs	(149)	(147)	(448)	(587)
Recoveries	101	99	307	346
Provision	76	52	199	182
Allowance for loan losses, end of period	391	297	391	297
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	391	297	391	297
Loans:
Total loans, net	8,728	6,661	8,728	6,661	7,450
Loans not deemed to be impaired	8,728	6,661	8,728	6,661
Home Equity [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	932	681	886	704
Charge-offs				(159)
Recoveries		16	1	16
Provision	17	176	62	312
Allowance for loan losses, end of period	949	873	949	873
Amount of allowance for loan losses for loans deemed to be impaired	95	97	95	97
Amount of allowance for loan losses for loans not deemed to be impaired	854	776	854	776
Loans:
Total loans, net	126,645	116,699	126,645	116,699	118,923
Loans deemed to be impaired	95	97	95	97
Loans not deemed to be impaired	126,550	116,602	126,550	116,602
Unallocated [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	1,295	1,103	760	1,030
Provision	(33)	(458)	502	(385)
Allowance for loan losses, end of period	1,262	645	1,262	645
Amount of allowance for loan losses for loans not deemed to be impaired	$ 1,262	$ 645	$ 1,262	$ 645