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, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 1,765,871	$ 1,657,051	$ 1,765,871	$ 1,657,051	$ 1,672,007
Individ. evaluated for impairment	70,046	91,218	70,046	91,218	81,235
Loans pooled for evaluation	1,648,036	1,509,053	1,648,036	1,509,053	1,537,060
Loans acquired with deteriorated credit quality	47,789	56,780	47,789	56,780	53,712
Beginning balance	39,968	39,599	38,245	42,648	42,648
Charge-offs	(345)	(985)	(2,139)	(5,703)	(7,543)
Recoveries	1,274	1,119	4,438	3,282	3,855
(Benefit) provision	(2,977)	(393)	(2,624)	(887)	(715)
Ending balance	37,920	39,340	37,920	39,340	38,245
Ending balance:
Individ. evaluated for impairment	4,091	4,458	4,091	4,458	3,975
Loans pooled for evaluation	30,420	30,649	30,420	30,649	30,230
Loans acquired with deteriorated credit quality	3,409	4,233	3,409	4,233	4,040
RE Mortgage [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	228,407	197,129	228,407	197,129	195,013
Individ. evaluated for impairment	7,142	7,013	7,142	7,013	7,342
Loans pooled for evaluation	217,478	183,769	217,478	183,769	183,015
Loans acquired with deteriorated credit quality	3,787	6,347	3,787	6,347	4,656
Beginning balance	2,832	3,231	3,154	3,523	3,523
Charge-offs	(31)	(4)	(167)	(46)	(46)
Recoveries		154		345	345
(Benefit) provision	51	(190)	(135)	(631)	(668)
Ending balance	2,852	3,191	2,852	3,191	3,154
Ending balance:
Individ. evaluated for impairment	902	623	902	623	775
Loans pooled for evaluation	1,765	2,235	1,765	2,235	2,039
Loans acquired with deteriorated credit quality	185	333	185	333	340
RE Mortgage [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	985,746	894,346	985,746	894,346	912,850
Individ. evaluated for impairment	50,322	69,373	50,322	69,373	59,936
Loans pooled for evaluation	908,725	794,301	908,725	794,301	822,654
Loans acquired with deteriorated credit quality	26,699	30,672	26,699	30,672	30,260
Beginning balance	9,831	8,764	9,700	8,782	8,782
Charge-offs	(49)	(23)	(107)	(1,712)	(2,038)
Recoveries	42	295	513	965	994
(Benefit) provision	(53)	704	(335)	1,705	1,962
Ending balance	9,771	9,740	9,771	9,740	9,700
Ending balance:
Individ. evaluated for impairment	413	1,446	413	1,446	1,198
Loans pooled for evaluation	9,182	7,748	9,182	7,748	7,815
Loans acquired with deteriorated credit quality	176	546	176	546	687
Home equity lines of credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	321,942	346,348	321,942	346,348	339,866
Individ. evaluated for impairment	6,733	7,664	6,733	7,664	6,918
Loans pooled for evaluation	306,006	328,215	306,006	328,215	322,865
Loans acquired with deteriorated credit quality	9,203	10,469	9,203	10,469	10,083
Beginning balance	18,055	18,710	16,375	21,367	21,367
Charge-offs	(136)	(331)	(991)	(1,843)	(2,651)
Recoveries	249	304	758	809	1,053
(Benefit) provision	(1,239)	(871)	787	(2,521)	(3,394)
Ending balance	16,929	17,812	16,929	17,812	16,375
Ending balance:
Individ. evaluated for impairment	2,001	1,554	2,001	1,554	1,140
Loans pooled for evaluation	14,428	15,259	14,428	15,259	14,749
Loans acquired with deteriorated credit quality	500	999	500	999	486
Home equity loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	22,378	13,730	22,378	13,730	14,588
Individ. evaluated for impairment	896	551	896	551	778
Loans pooled for evaluation	20,866	12,575	20,866	12,575	13,324
Loans acquired with deteriorated credit quality	616	604	616	604	486
Beginning balance	1,411	1,109	1,208	1,155	1,155
Charge-offs		(30)	(11)	(56)	(94)
Recoveries	4	3	31	29	41
(Benefit) provision	229	(50)	416	(96)	106
Ending balance	1,644	1,032	1,644	1,032	1,208
Ending balance:
Individ. evaluated for impairment	213	49	213	49	169
Loans pooled for evaluation	1,431	983	1,431	983	1,039
Auto Indirect [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	212	1,351	212	1,351	946
Individ. evaluated for impairment	23	66	23	66	60
Loans pooled for evaluation	189	1,285	189	1,285	886
Beginning balance	28	114	66	243	243
Charge-offs		(9)		(67)	(68)
Recoveries	19	34	70	180	195
(Benefit) provision	(31)	(58)	(120)	(275)	(304)
Ending balance	16	81	16	81	66
Ending balance:
Individ. evaluated for impairment		2		2	1
Loans pooled for evaluation	16	79	16	79	65
Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	29,088	28,282	29,088	28,282	27,763
Individ. evaluated for impairment	194	94	194	94	90
Loans pooled for evaluation	28,830	28,113	28,830	28,113	27,592
Loans acquired with deteriorated credit quality	64	75	64	75	81
Beginning balance	556	567	589	696	696
Charge-offs	(118)	(239)	(389)	(724)	(887)
Recoveries	71	199	373	601	759
(Benefit) provision	160	7	96	(39)	21
Ending balance	669	534	669	534	589
Ending balance:
Individ. evaluated for impairment	69	6	69	6	8
Loans pooled for evaluation	600	521	600	521	581
Loans acquired with deteriorated credit quality		7		7
C&I [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	135,085	133,616	135,085	133,616	131,878
Individ. evaluated for impairment	1,902	3,333	1,902	3,333	3,177
Loans pooled for evaluation	127,363	123,476	127,363	123,476	122,166
Loans acquired with deteriorated credit quality	5,820	6,807	5,820	6,807	6,535
Beginning balance	4,407	4,929	4,331	4,703	4,703
Charge-offs	(11)	(318)	(401)	(1,143)	(1,599)
Recoveries	94	108	1,155	244	340
(Benefit) provision	(428)	(234)	(1,023)	681	887
Ending balance	4,062	4,485	4,062	4,485	4,331
Ending balance:
Individ. evaluated for impairment	433	678	433	678	585
Loans pooled for evaluation	2,354	2,448	2,354	2,448	2,402
Loans acquired with deteriorated credit quality	1,275	1,359	1,275	1,359	1,344
Construction [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	24,386	27,601	24,386	27,601	31,933
Individ. evaluated for impairment	2,720	2,872	2,720	2,872	2,756
Loans pooled for evaluation	20,140	23,497	20,140	23,497	27,611
Loans acquired with deteriorated credit quality	1,526	1,232	1,526	1,232	1,566
Beginning balance	1,511	1,288	1,559	1,400	1,400
Charge-offs			(4)	(20)	(20)
Recoveries	769	2	1,377	63	63
(Benefit) provision	(702)	157	(1,354)	4	116
Ending balance	1,578	1,447	1,578	1,447	1,559
Ending balance:
Individ. evaluated for impairment	60	91	60	91	91
Loans pooled for evaluation	349	723	349	723	751
Loans acquired with deteriorated credit quality	1,169	633	1,169	633	717
Construction [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	18,627	14,648	18,627	14,648	17,170
Individ. evaluated for impairment	114	252	114	252	178
Loans pooled for evaluation	18,439	13,822	18,439	13,822	16,947
Loans acquired with deteriorated credit quality	74	574	74	574	45
Beginning balance	1,337	887	1,263	779	779
Charge-offs		(31)	(69)	(92)	(140)
Recoveries	26	20	161	46	65
(Benefit) provision	(964)	142	(956)	285	559
Ending balance	399	1,018	399	1,018	1,263
Ending balance:
Individ. evaluated for impairment		9		9	8
Loans pooled for evaluation	295	653	295	653	789
Loans acquired with deteriorated credit quality	$ 104	$ 356	$ 104	$ 356	$ 466