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	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	$ 2,759,593	$ 2,522,937	$ 2,282,524
Individ. evaluated for impairment	28,140	50,105	62,247
Loans pooled for evaluation	2,706,409	2,432,628	2,167,381
Beginning balance	36,011	36,585	38,245
Charge-offs	(3,230)	(2,816)	(2,558)
Recoveries	5,692	4,452	4,943
(Benefit) provision	(5,970)	(2,210)	(4,045)
Ending balance	32,503	36,011	36,585
Ending balance:
Individ. evaluated for impairment	2,046	2,890	4,267
Loans pooled for evaluation	27,760	30,228	28,891
Mortgage Loans on Real Estate [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	2,057,824	1,811,832
Mortgage Loans on Real Estate [Member] | Residential [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	309,907	314,265	279,420
Individ. evaluated for impairment	3,785	6,767	7,188
Loans pooled for evaluation	304,759	305,353	268,227
Beginning balance	2,507	3,086	3,154
Charge-offs	(321)	(224)	(171)
Recoveries	880	204	2
(Benefit) provision	(679)	(559)	101
Ending balance	2,387	2,507	3,086
Ending balance:
Individ. evaluated for impairment	249	335	974
Loans pooled for evaluation	1,952	2,112	1,915
Mortgage Loans on Real Estate [Member] | Commercial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	1,747,917	1,497,567	1,335,939
Individ. evaluated for impairment	15,748	32,407	41,932
Loans pooled for evaluation	1,718,709	1,442,100	1,263,090
Beginning balance	11,443	9,227	9,700
Charge-offs	(827)		(110)
Recoveries	920	243	540
(Benefit) provision	369	1,973	(903)
Ending balance	11,905	11,443	9,227
Ending balance:
Individ. evaluated for impairment	127	395	410
Loans pooled for evaluation	10,329	9,596	8,408
Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	362,303	395,283
Consumer [Member] | Home Equity Lines of Credit [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	289,715	322,492	352,584
Individ. evaluated for impairment	3,196	5,747	6,968
Loans pooled for evaluation	282,159	309,007	336,595
Beginning balance	11,253	15,676	16,375
Charge-offs	(585)	(694)	(1,094)
Recoveries	2,317	666	960
(Benefit) provision	(5,941)	(4,395)	(565)
Ending balance	7,044	11,253	15,676
Ending balance:
Individ. evaluated for impairment	410	605	1,974
Loans pooled for evaluation	6,618	10,423	13,251
Consumer and Industrial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	217,047	194,913	174,945
Individ. evaluated for impairment	4,096	2,671	1,757
Loans pooled for evaluation	208,960	187,393	165,753
Beginning balance	5,271	4,226	4,331
Charge-offs	(455)	(680)	(479)
Recoveries	404	677	1,268
(Benefit) provision	611	1,048	(894)
Ending balance	5,831	5,271	4,226
Ending balance:
Individ. evaluated for impairment	1,130	1,187	423
Loans pooled for evaluation	3,765	2,983	2,569
Construction [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	122,419	120,909
Construction [Member] | Residential [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	55,429	46,135	38,618
Individ. evaluated for impairment	11	4	2,683
Loans pooled for evaluation	54,743	45,410	35,260
Beginning balance	899	1,434	1,559
Charge-offs			(4)
Recoveries	54	1,728	1,377
(Benefit) provision	464	(2,263)	(1,498)
Ending balance	1,417	899	1,434
Ending balance:
Individ. evaluated for impairment			60
Loans pooled for evaluation	1,371	844	332
Construction [Member] | Commercial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	66,990	74,774	36,518
Individ. evaluated for impairment		490	99
Loans pooled for evaluation	66,990	74,284	36,419
Beginning balance	812	411	1,263
Charge-offs			(69)
Recoveries	78	140	181
(Benefit) provision	(210)	261	(964)
Ending balance	680	812	411
Ending balance:
Loans pooled for evaluation	680	812	322
Home Equity Loans [Member] | Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	41,822	40,362	31,314
Individ. evaluated for impairment	1,150	1,731	1,279
Loans pooled for evaluation	39,542	37,004	29,266
Beginning balance	3,138	1,797	1,208
Charge-offs	(219)	(242)	(29)
Recoveries	590	252	34
(Benefit) provision	(892)	1,331	584
Ending balance	2,617	3,138	1,797
Ending balance:
Individ. evaluated for impairment	102	294	284
Loans pooled for evaluation	2,451	2,844	1,513
Auto Indirect [Member] | Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts			112
Individ. evaluated for impairment			18
Loans pooled for evaluation			94
Beginning balance		9	66
Charge-offs		(4)	(3)
Recoveries		42	86
(Benefit) provision		(47)	(140)
Ending balance			9
Ending balance:
Loans pooled for evaluation			9
Other Consumer [Member] | Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	30,766	32,429	33,074
Individ. evaluated for impairment	154	288	323
Loans pooled for evaluation	30,547	32,077	32,677
Beginning balance	688	719	589
Charge-offs	(823)	(972)	(599)
Recoveries	449	500	495
(Benefit) provision	308	441	234
Ending balance	622	688	719
Ending balance:
Individ. evaluated for impairment	28	74	142
Loans pooled for evaluation	594	614	572
Receivables Acquired with Deteriorated Credit Quality [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	25,044	40,204	52,897
Ending balance:
Loans acquired with deteriorated credit quality	2,697	2,893	3,427
Receivables Acquired with Deteriorated Credit Quality [Member] | Mortgage Loans on Real Estate [Member] | Residential [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	1,363	2,145	4,005
Ending balance:
Loans acquired with deteriorated credit quality	186	60	197
Receivables Acquired with Deteriorated Credit Quality [Member] | Mortgage Loans on Real Estate [Member] | Commercial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	13,460	23,060	30,917
Ending balance:
Loans acquired with deteriorated credit quality	1,449	1,452	409
Receivables Acquired with Deteriorated Credit Quality [Member] | Consumer [Member] | Home Equity Lines of Credit [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	4,360	7,738	9,021
Ending balance:
Loans acquired with deteriorated credit quality	17	225	451
Receivables Acquired with Deteriorated Credit Quality [Member] | Consumer and Industrial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	3,991	4,849	7,435
Ending balance:
Loans acquired with deteriorated credit quality	936	1,101	1,234
Receivables Acquired with Deteriorated Credit Quality [Member] | Construction [Member] | Residential [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	675	721	675
Ending balance:
Loans acquired with deteriorated credit quality	45	55	1,042
Receivables Acquired with Deteriorated Credit Quality [Member] | Construction [Member] | Commercial [Member]
Ending balance:
Loans acquired with deteriorated credit quality			89
Receivables Acquired with Deteriorated Credit Quality [Member] | Home Equity Loans [Member] | Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	1,130	1,627	770
Ending balance:
Loans acquired with deteriorated credit quality	64
Receivables Acquired with Deteriorated Credit Quality [Member] | Other Consumer [Member] | Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total loans, net of unamortized deferred loan fees and discounts	$ 65	$ 64	74
Ending balance:
Loans acquired with deteriorated credit quality			$ 5