Allowance for Loan Losses - Summary of Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Allowance for loan losses:
Allowance for loan losses, beginning of period	$ 23,863	$ 22,245	$ 23,075	$ 22,318
Charge-offs	(118)	(129)	(298)	(613)
Recoveries	93	214	345	425
Provision	375		1,175	200
Reclassification to other liabilities	(5)		(89)
Allowance for loan losses, end of period	24,208	22,330	24,208	22,330
Amount of allowance for loan losses for loans deemed to be impaired	163	261	163	261
Amount of allowance for loan losses for loans not deemed to be impaired	24,045	22,069	24,045	22,069
Loans:
Total loans, net	1,841,093	1,640,830	1,841,093	1,640,830	$ 1,731,536
Loans deemed to be impaired	4,409	3,349	4,409	3,349
Loans not deemed to be impaired	1,836,684	1,637,481	1,836,684	1,637,481
Construction and Land Development [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	2,234	1,733	2,041	1,592
Provision	(3)	126	193	267
Reclassification to other liabilities			(3)
Allowance for loan losses, end of period	2,231	1,859	2,231	1,859
Amount of allowance for loan losses for loans deemed to be impaired	4	11	4	11
Amount of allowance for loan losses for loans not deemed to be impaired	2,227	1,848	2,227	1,848
Loans:
Total loans, net	19,522	27,308	19,522	27,308	27,421
Loans deemed to be impaired	95	100	95	100
Loans not deemed to be impaired	19,427	27,208	19,427	27,208
Commercial and Industrial [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	5,842	4,428	5,899	4,757
Charge-offs		(43)		(95)
Recoveries	24	75	115	147
Provision	307	995	188	646
Reclassification to other liabilities			(29)
Allowance for loan losses, end of period	6,173	5,455	6,173	5,455
Amount of allowance for loan losses for loans deemed to be impaired	9	25	9	25
Amount of allowance for loan losses for loans not deemed to be impaired	6,164	5,430	6,164	5,430
Loans:
Total loans, net	549,290	378,154	549,290	378,154	452,235
Loans deemed to be impaired	399	539	399	539
Loans not deemed to be impaired	548,891	377,615	548,891	377,615
Municipal [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	1,801	1,000	994	1,488
Provision	(29)	117	778	(371)
Allowance for loan losses, end of period	1,772	1,117	1,772	1,117
Amount of allowance for loan losses for loans not deemed to be impaired	1,772	1,117	1,772	1,117
Loans:
Total loans, net	145,063	87,016	145,063	87,016	85,685
Loans not deemed to be impaired	145,063	87,016	145,063	87,016
Commercial Real Estate [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	10,650	11,723	10,589	11,199
Charge-offs				(298)
Recoveries		80		84
Provision	(752)	(1,086)	(680)	(268)
Reclassification to other liabilities			(11)
Allowance for loan losses, end of period	9,898	10,717	9,898	10,717
Amount of allowance for loan losses for loans deemed to be impaired	143	98	143	98
Amount of allowance for loan losses for loans not deemed to be impaired	9,755	10,619	9,755	10,619
Loans:
Total loans, net	692,778	701,523	692,778	701,523	721,506
Loans deemed to be impaired	3,707	1,692	3,707	1,692
Loans not deemed to be impaired	689,071	699,831	689,071	699,831
Residential Real Estate [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	1,302	722	1,320	776
Recoveries	2	1	5	5
Provision	624	115	605	57
Reclassification to other liabilities			(2)
Allowance for loan losses, end of period	1,928	838	1,928	838
Amount of allowance for loan losses for loans deemed to be impaired	7	36	7	36
Amount of allowance for loan losses for loans not deemed to be impaired	1,921	802	1,921	802
Loans:
Total loans, net	222,881	264,105	222,881	264,105	255,346
Loans deemed to be impaired	208	927	208	927
Loans not deemed to be impaired	222,673	263,178	222,673	263,178
Consumer [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	608	709	644	810
Charge-offs	(91)	(86)	(271)	(220)
Recoveries	67	58	225	189
Provision	5	(2)	(6)	(100)
Reclassification to other liabilities			(3)
Allowance for loan losses, end of period	589	679	589	679
Amount of allowance for loan losses for loans not deemed to be impaired	589	679	589	679
Loans:
Total loans, net	11,474	10,633	11,474	10,633	11,323
Loans not deemed to be impaired	11,474	10,633	11,474	10,633
Home Equity [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	1,158	650	1,077	599
Charge-offs	(27)		(27)
Provision	155	51	272	102
Reclassification to other liabilities	(5)		(41)
Allowance for loan losses, end of period	1,281	701	1,281	701
Amount of allowance for loan losses for loans deemed to be impaired		91		91
Amount of allowance for loan losses for loans not deemed to be impaired	1,281	610	1,281	610
Loans:
Total loans, net	200,085	172,091	200,085	172,091	$ 178,020
Loans deemed to be impaired		91		91
Loans not deemed to be impaired	200,085	172,000	200,085	172,000
Unallocated [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	268	1,280	511	1,097
Provision	68	(316)	(175)	(133)
Allowance for loan losses, end of period	336	964	336	964
Amount of allowance for loan losses for loans not deemed to be impaired	$ 336	$ 964	$ 336	$ 964