Allowance for Loan Losses - Summary of Activity in Allowance for Loan Losses, and Ending Balance of Loans, Net of Unearned Fees for Periods Indicated (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 2,712,226	$ 2,469,566	$ 2,712,226	$ 2,469,566	$ 2,522,937
Individ. evaluated for impairment	29,603	63,474	29,603	63,474	50,105
Loans pooled for evaluation	2,655,740	2,361,149	2,655,740	2,361,149	2,432,628
Loans acquired with deteriorated credit quality	26,883	44,943	26,883	44,943	40,204
Beginning balance	35,509	35,455	36,011	36,585	36,585
Charge-offs	(664)	(687)	(2,594)	(2,436)	(2,816)
Recoveries	2,612	2,616	4,604	3,671	4,452
(Benefit) provision	(3,973)	(866)	(4,537)	(1,302)	(2,210)
Ending balance	33,484	36,518	33,484	36,518	36,011
Ending balance:
Individ. evaluated for impairment	2,821	2,534	2,821	2,534	2,890
Loans pooled for evaluation	27,903	30,145	27,903	30,145	30,228
Home Equity Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	301,884	331,689	301,884	331,689	322,492
Individ. evaluated for impairment	3,820	6,212	3,820	6,212	5,747
Loans pooled for evaluation	292,833	316,910	292,833	316,910	309,007
Loans acquired with deteriorated credit quality	5,231	8,567	5,231	8,567	7,738
Beginning balance	9,202	13,993	11,253	15,676	15,676
Charge-offs	(122)	(199)	(450)	(624)	(694)
Recoveries	1,580	197	1,921	546	666
(Benefit) provision	(2,258)	(1,202)	(4,322)	(2,809)	(4,395)
Ending balance	8,402	12,789	8,402	12,789	11,253
Ending balance:
Individ. evaluated for impairment	511	937	511	937	605
Loans pooled for evaluation	7,866	11,438	7,866	11,438	10,423
Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	31,611	33,027	31,611	33,027	32,429
Individ. evaluated for impairment	278	293	278	293	288
Loans pooled for evaluation	31,272	32,670	31,272	32,670	32,077
Loans acquired with deteriorated credit quality	61	64	61	64	64
Beginning balance	696	705	688	719	719
Charge-offs	(160)	(348)	(600)	(792)	(972)
Recoveries	107	122	338	381	500
(Benefit) provision	24	189	241	360	441
Ending balance	667	668	667	668	688
Ending balance:
Individ. evaluated for impairment	72	85	72	85	74
Loans pooled for evaluation	595	583	595	583	614
Construction [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	57,892	46,067	57,892	46,067	46,135
Individ. evaluated for impairment	11	318	11	318	4
Loans pooled for evaluation	57,338	45,019	57,338	45,019	45,410
Loans acquired with deteriorated credit quality	543	730	543	730	721
Beginning balance	1,321	842	899	1,434	1,434
Recoveries		1,717		1,728	1,728
(Benefit) provision	(16)	(1,523)	406	(2,126)	(2,263)
Ending balance	1,305	1,036	1,305	1,036	899
Ending balance:
Loans pooled for evaluation	1,257	859	1,257	859	844
Construction [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	61,295	64,006	61,295	64,006	74,774
Individ. evaluated for impairment		80		80	490
Loans pooled for evaluation	61,295	63,926	61,295	63,926	74,284
Beginning balance	952	409	812	411	411
Recoveries		19	1	52	140
(Benefit) provision	(528)	235	(389)	200	261
Ending balance	424	663	424	663	812
Ending balance:
Loans pooled for evaluation	424	663	424	663	812
C&I [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	217,110	199,330	217,110	199,330	194,913
Individ. evaluated for impairment	2,397	1,589	2,397	1,589	2,671
Loans pooled for evaluation	210,565	192,748	210,565	192,748	187,393
Loans acquired with deteriorated credit quality	4,148	4,993	4,148	4,993	4,849
Beginning balance	5,265	4,402	5,271	4,226	4,226
Charge-offs	(307)	(52)	(421)	(591)	(680)
Recoveries	85	186	323	394	677
(Benefit) provision	199	174	69	681	1,048
Ending balance	5,242	4,710	5,242	4,710	5,271
Ending balance:
Individ. evaluated for impairment	822	447	822	447	1,187
Loans pooled for evaluation	3,426	3,071	3,426	3,071	2,983
RE Mortgage [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	313,069	302,105	313,069	302,105	314,265
Individ. evaluated for impairment	5,415	7,286	5,415	7,286	6,767
Loans pooled for evaluation	306,289	292,607	306,289	292,607	305,353
Loans acquired with deteriorated credit quality	1,365	2,212	1,365	2,212	2,145
Beginning balance	2,692	2,835	2,507	3,086	3,086
Charge-offs	(50)	(15)	(212)	(224)	(224)
Recoveries	391	60	618	61	204
(Benefit) provision	(631)	(241)	(511)	(284)	(559)
Ending balance	2,402	2,639	2,402	2,639	2,507
Ending balance:
Individ. evaluated for impairment	423	345	423	345	335
Loans pooled for evaluation	1,798	2,178	1,798	2,178	2,112
RE Mortgage [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,685,844	1,454,977	1,685,844	1,454,977	1,497,567
Individ. evaluated for impairment	15,571	46,237	15,571	46,237	32,407
Loans pooled for evaluation	1,656,292	1,381,982	1,656,292	1,381,982	1,442,100
Loans acquired with deteriorated credit quality	13,981	26,758	13,981	26,758	23,060
Beginning balance	12,360	10,141	11,443	9,227	9,227
Charge-offs			(793)
Recoveries	20	78	902	227	243
(Benefit) provision	(406)	882	422	1,647	1,973
Ending balance	11,974	11,101	11,974	11,101	11,443
Ending balance:
Individ. evaluated for impairment	841	502	841	502	395
Loans pooled for evaluation	9,680	8,659	9,680	8,659	9,596
Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	43,521	38,365	43,521	38,365	40,362
Individ. evaluated for impairment	2,111	1,459	2,111	1,459	1,731
Loans pooled for evaluation	39,856	35,287	39,856	35,287	37,004
Loans acquired with deteriorated credit quality	1,554	1,619	1,554	1,619	1,627
Beginning balance	3,021	2,128	3,138	1,797	1,797
Charge-offs	(25)	(73)	(118)	(201)	(242)
Recoveries	429	235	501	244	252
(Benefit) provision	(357)	622	(453)	1,072	1,331
Ending balance	3,068	2,912	3,068	2,912	3,138
Ending balance:
Individ. evaluated for impairment	152	218	152	218	294
Loans pooled for evaluation	2,857	2,694	2,857	2,694	2,844
Auto Indirect [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Beginning balance				9	9
Charge-offs				(4)	(4)
Recoveries		2		38	42
(Benefit) provision		(2)		(43)	(47)
Receivables Acquired with Deteriorated Credit Quality [Member]
Ending balance:
Loans acquired with deteriorated credit quality	2,760	3,839	2,760	3,839	2,893
Receivables Acquired with Deteriorated Credit Quality [Member] | Home Equity Lines of Credit [Member]
Ending balance:
Loans acquired with deteriorated credit quality	25	413	25	413	225
Receivables Acquired with Deteriorated Credit Quality [Member] | Construction [Member] | Residential [Member]
Ending balance:
Loans acquired with deteriorated credit quality	48	177	48	177	55
Receivables Acquired with Deteriorated Credit Quality [Member] | C&I [Member]
Ending balance:
Loans acquired with deteriorated credit quality	994	1,192	994	1,192	1,101
Receivables Acquired with Deteriorated Credit Quality [Member] | RE Mortgage [Member] | Residential [Member]
Ending balance:
Loans acquired with deteriorated credit quality	181	115	181	115	60
Receivables Acquired with Deteriorated Credit Quality [Member] | RE Mortgage [Member] | Commercial [Member]
Ending balance:
Loans acquired with deteriorated credit quality	1,453	$ 1,942	1,453	$ 1,942	$ 1,452
Receivables Acquired with Deteriorated Credit Quality [Member] | Home Equity Loans [Member]
Ending balance:
Loans acquired with deteriorated credit quality	$ 59		$ 59