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		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 2,653,630	$ 2,393,762	$ 2,653,630	$ 2,393,762	$ 2,522,937
Individ. evaluated for impairment	27,927	65,025	27,927	65,025	50,105
Loans pooled for evaluation	2,595,359	2,282,497	2,595,359	2,282,497	2,432,628
Loans acquired with deteriorated credit quality	30,344	46,240	30,344	46,240	40,204
Beginning balance	36,388	36,055	36,011	36,585	36,585
Charge-offs	(641)	(514)	(1,930)	(1,749)	(2,816)
Recoveries	535	547	1,992	1,055	4,452
(Benefit) provision	(773)	(633)	(564)	(436)	(2,210)
Ending balance	35,509	35,455	35,509	35,455	36,011
Ending balance:
Individ. evaluated for impairment	2,170	4,245	2,170	4,245	2,890
Loans pooled for evaluation	30,531	27,988	30,531	27,988	30,228
Home Equity Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	306,678	344,115	306,678	344,115	322,492
Individ. evaluated for impairment	4,984	6,135	4,984	6,135	5,747
Loans pooled for evaluation	295,444	329,788	295,444	329,788	309,007
Loans acquired with deteriorated credit quality	6,250	8,192	6,250	8,192	7,738
Beginning balance	9,907	15,233	11,253	15,676	15,676
Charge-offs	(114)	(84)	(328)	(425)	(694)
Recoveries	60	230	341	349	666
(Benefit) provision	(651)	(1,386)	(2,064)	(1,607)	(4,395)
Ending balance	9,202	13,993	9,202	13,993	11,253
Ending balance:
Individ. evaluated for impairment	506	1,779	506	1,779	605
Loans pooled for evaluation	8,680	11,798	8,680	11,798	10,423
Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	32,434	33,101	32,434	33,101	32,429
Individ. evaluated for impairment	277	403	277	403	288
Loans pooled for evaluation	32,094	32,631	32,094	32,631	32,077
Loans acquired with deteriorated credit quality	63	67	63	67	64
Beginning balance	687	644	688	719	719
Charge-offs	(233)	(176)	(440)	(444)	(972)
Recoveries	101	107	231	259	500
(Benefit) provision	141	130	217	171	441
Ending balance	696	705	696	705	688
Ending balance:
Individ. evaluated for impairment	87	128	87	128	74
Loans pooled for evaluation	609	577	609	577	614
Construction [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	62,331	41,958	62,331	41,958	46,135
Individ. evaluated for impairment	11	328	11	328	4
Loans pooled for evaluation	61,771	40,907	61,771	40,907	45,410
Loans acquired with deteriorated credit quality	549	723	549	723	721
Beginning balance	1,066	750	899	1,434	1,434
Recoveries				11	1,728
(Benefit) provision	255	92	422	(603)	(2,263)
Ending balance	1,321	842	1,321	842	899
Ending balance:
Loans pooled for evaluation	1,271	653	1,271	653	844
Construction [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	87,321	57,658	87,321	57,658	74,774
Individ. evaluated for impairment		88		88	490
Loans pooled for evaluation	87,321	57,570	87,321	57,570	74,284
Beginning balance	818	250	812	411	411
Recoveries		14	1	33	140
(Benefit) provision	134	145	139	(35)	261
Ending balance	952	409	952	409	812
Ending balance:
Loans pooled for evaluation	952	409	952	409	812
C&I [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	209,840	195,791	209,840	195,791	194,913
Individ. evaluated for impairment	1,930	2,048	1,930	2,048	2,671
Loans pooled for evaluation	203,626	188,642	203,626	188,642	187,393
Loans acquired with deteriorated credit quality	4,284	5,101	4,284	5,101	4,849
Beginning balance	6,139	3,976	5,271	4,226	4,226
Charge-offs	(76)	(5)	(114)	(539)	(680)
Recoveries	61	121	238	208	677
(Benefit) provision	(859)	310	(130)	507	1,048
Ending balance	5,265	4,402	5,265	4,402	5,271
Ending balance:
Individ. evaluated for impairment	647	676	647	676	1,187
Loans pooled for evaluation	3,545	2,536	3,545	2,536	2,983
Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	42,002	34,572	42,002	34,572	40,362
Individ. evaluated for impairment	1,944	1,438	1,944	1,438	1,731
Loans pooled for evaluation	38,427	32,372	38,427	32,372	37,004
Loans acquired with deteriorated credit quality	1,631	762	1,631	762	1,627
Beginning balance	3,111	1,980	3,138	1,797	1,797
Charge-offs	(93)	(117)	(93)	(128)	(242)
Recoveries	23	6	72	9	252
(Benefit) provision	(20)	259	(96)	450	1,331
Ending balance	3,021	2,128	3,021	2,128	3,138
Ending balance:
Individ. evaluated for impairment	203	387	203	387	294
Loans pooled for evaluation	2,818	1,741	2,818	1,741	2,844
Auto Indirect [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Beginning balance		6		9	9
Charge-offs		(4)		(4)	(4)
Recoveries		16		36	42
(Benefit) provision		(18)		(41)	(47)
RE Mortgage [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	318,206	291,488	318,206	291,488	314,265
Individ. evaluated for impairment	6,629	7,467	6,629	7,467	6,767
Loans pooled for evaluation	309,952	280,147	309,952	280,147	305,353
Loans acquired with deteriorated credit quality	1,625	3,874	1,625	3,874	2,145
Beginning balance	2,765	2,765	2,507	3,086	3,086
Charge-offs	(125)	(128)	(162)	(209)	(224)
Recoveries	225		227	1	204
(Benefit) provision	(173)	198	120	(43)	(559)
Ending balance	2,692	2,835	2,692	2,835	2,507
Ending balance:
Individ. evaluated for impairment	474	857	474	857	335
Loans pooled for evaluation	2,008	1,884	2,008	1,884	2,112
RE Mortgage [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,594,818	1,395,079	1,594,818	1,395,079	1,497,567
Individ. evaluated for impairment	12,152	47,118	12,152	47,118	32,407
Loans pooled for evaluation	1,566,724	1,320,440	1,566,724	1,320,440	1,442,100
Loans acquired with deteriorated credit quality	15,942	27,521	15,942	27,521	23,060
Beginning balance	11,895	10,451	11,443	9,227	9,227
Charge-offs			(793)
Recoveries	65	53	882	149	243
(Benefit) provision	400	(363)	828	765	1,973
Ending balance	12,360	10,141	12,360	10,141	11,443
Ending balance:
Individ. evaluated for impairment	253	418	253	418	395
Loans pooled for evaluation	10,648	8,390	10,648	8,390	9,596
Receivables Acquired with Deteriorated Credit Quality [Member]
Ending balance:
Loans acquired with deteriorated credit quality	2,808	3,222	2,808	3,222	2,893
Receivables Acquired with Deteriorated Credit Quality [Member] | Home Equity Lines of Credit [Member]
Ending balance:
Loans acquired with deteriorated credit quality	16	416	16	416	225
Receivables Acquired with Deteriorated Credit Quality [Member] | Construction [Member] | Residential [Member]
Ending balance:
Loans acquired with deteriorated credit quality	50	189	50	189	55
Receivables Acquired with Deteriorated Credit Quality [Member] | C&I [Member]
Ending balance:
Loans acquired with deteriorated credit quality	1,073	1,190	1,073	1,190	1,101
Receivables Acquired with Deteriorated Credit Quality [Member] | RE Mortgage [Member] | Residential [Member]
Ending balance:
Loans acquired with deteriorated credit quality	210	94	210	94	60
Receivables Acquired with Deteriorated Credit Quality [Member] | RE Mortgage [Member] | Commercial [Member]
Ending balance:
Loans acquired with deteriorated credit quality	$ 1,459	$ 1,333	$ 1,459	$ 1,333	$ 1,452