Allowance for Loan Losses - Summary of Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Allowance for loan losses:
Allowance for loan losses, beginning of period	$ 24,827	$ 23,544	$ 24,406	$ 23,075
Charge-offs	(100)	(111)	(197)	(180)
Recoveries	72	164	190	252
Provision	490	350	890	800
Reclassification to other liabilities		(84)		(84)
Allowance for loan losses, end of period	25,289	23,863	25,289	23,863
Amount of allowance for loan losses for loans deemed to be impaired	200	174	200	174
Amount of allowance for loan losses for loans not deemed to be impaired	25,089	23,689	25,089	23,689
Loans:
Total loans, net	2,033,799	1,801,904	2,033,799	1,801,904	$ 1,923,933
Loans deemed to be impaired	7,311	4,457	7,311	4,457
Loans not deemed to be impaired	2,026,488	1,797,447	2,026,488	1,797,447
Construction and Land Development [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	873	1,973	1,012	2,041
Provision	264	264	125	196
Reclassification to other liabilities		(3)		(3)
Allowance for loan losses, end of period	1,137	2,234	1,137	2,234
Amount of allowance for loan losses for loans deemed to be impaired		6		6
Amount of allowance for loan losses for loans not deemed to be impaired	1,137	2,228	1,137	2,228
Loans:
Total loans, net	14,159	31,178	14,159	31,178	14,928
Loans deemed to be impaired		96		96
Loans not deemed to be impaired	14,159	31,082	14,159	31,082
Commercial and Industrial [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	7,369	6,693	6,972	5,899
Charge-offs	(29)		(29)
Recoveries	34	56	54	91
Provision	189	(878)	566	(119)
Reclassification to other liabilities		(29)		(29)
Allowance for loan losses, end of period	7,563	5,842	7,563	5,842
Amount of allowance for loan losses for loans deemed to be impaired	11	10	11	10
Amount of allowance for loan losses for loans not deemed to be impaired	7,552	5,832	7,552	5,832
Loans:
Total loans, net	650,542	493,033	650,542	493,033	612,503
Loans deemed to be impaired	365	410	365	410
Loans not deemed to be impaired	650,177	492,623	650,177	492,623
Municipal [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	1,899	990	1,612	994
Provision	(40)	811	247	807
Allowance for loan losses, end of period	1,859	1,801	1,859	1,801
Amount of allowance for loan losses for loans not deemed to be impaired	1,859	1,801	1,859	1,801
Loans:
Total loans, net	127,259	134,386	127,259	134,386	135,418
Loans not deemed to be impaired	127,259	134,386	127,259	134,386
Commercial Real Estate [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	11,216	10,533	11,135	10,589
Provision	(188)	128	(107)	72
Reclassification to other liabilities		(11)		(11)
Allowance for loan losses, end of period	11,028	10,650	11,028	10,650
Amount of allowance for loan losses for loans deemed to be impaired	120	151	120	151
Amount of allowance for loan losses for loans not deemed to be impaired	10,908	10,499	10,908	10,499
Loans:
Total loans, net	736,603	728,658	736,603	728,658	696,173
Loans deemed to be impaired	2,603	3,736	2,603	3,736
Loans not deemed to be impaired	734,000	724,922	734,000	724,922
Residential Real Estate [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	1,671	1,249	1,698	1,320
Recoveries		2	2	3
Provision	447	53	418	(19)
Reclassification to other liabilities		(2)		(2)
Allowance for loan losses, end of period	2,118	1,302	2,118	1,302
Amount of allowance for loan losses for loans deemed to be impaired	69	7	69	7
Amount of allowance for loan losses for loans not deemed to be impaired	2,049	1,295	2,049	1,295
Loans:
Total loans, net	264,744	219,494	264,744	219,494	241,357
Loans deemed to be impaired	4,343	215	4,343	215
Loans not deemed to be impaired	260,401	219,279	260,401	219,279
Consumer [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	452	693	582	644
Charge-offs	(71)	(111)	(168)	(180)
Recoveries	38	106	134	158
Provision	(224)	(77)	(353)	(11)
Reclassification to other liabilities		(3)		(3)
Allowance for loan losses, end of period	195	608	195	608
Amount of allowance for loan losses for loans not deemed to be impaired	195	608	195	608
Loans:
Total loans, net	11,218	11,339	11,218	11,339	11,697
Loans not deemed to be impaired	11,218	11,339	11,218	11,339
Home Equity [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	1,050	1,185	1,102	1,077
Provision	96	9	44	117
Reclassification to other liabilities		(36)		(36)
Allowance for loan losses, end of period	1,146	1,158	1,146	1,158
Amount of allowance for loan losses for loans not deemed to be impaired	1,146	1,158	1,146	1,158
Loans:
Total loans, net	229,274	183,816	229,274	183,816	$ 211,857
Loans not deemed to be impaired	229,274	183,816	229,274	183,816
Unallocated [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	297	228	293	511
Provision	(54)	40	(50)	(243)
Allowance for loan losses, end of period	243	268	243	268
Amount of allowance for loan losses for loans not deemed to be impaired	$ 243	$ 268	$ 243	$ 268