Allowance for Loan Losses and Credit Quality Information - Schedule of Allowance for Loan Losses and Loan Balances (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	$ 41,328	$ 42,948	$ 41,244	$ 43,922
Charge-offs	(1,159)	(4,035)	(4,314)	(7,742)
Recoveries	1,162	901	1,771	1,403
Provision (credit)	50	1,680	2,680	3,911
Ending balance	41,381	41,494	41,381	41,494
Loans individually evaluated for impairment	4,401	6,161	4,401	6,161
Loans collectively evaluated for impairment	36,980	35,333	36,980	35,333
Ending balance	41,381	41,494	41,381	41,494
Loans individually evaluated for impairment	45,840	52,052	45,840	52,052	43,282
Loans collectively evaluated for impairment	2,995,637	2,788,245	2,995,637	2,788,245
Ending balance	3,041,477	2,840,297	3,041,477	2,840,297
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	12,404	12,768	12,751	13,663
Charge-offs	(382)	(883)	(1,495)	(1,139)
Recoveries	483	401	807	627
Provision (credit)	841	681	1,283	(184)
Ending balance	13,346	12,967	13,346	12,967
Loans individually evaluated for impairment	1,881	2,171	1,881	2,171
Loans collectively evaluated for impairment	11,465	10,796	11,465	10,796
Ending balance	13,346	12,967	13,346	12,967
Loans individually evaluated for impairment	4,109	6,048	4,109	6,048	5,003
Loans collectively evaluated for impairment	853,245	733,581	853,245	733,581
Ending balance	857,354	739,629	857,354	739,629
Owner-Occupied Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	8,789	6,338	7,638	6,108
Charge-offs	(124)	(36)	(321)	(37)
Recoveries	161	33	167	45
Provision (credit)	(840)	1,714	502	1,933
Ending balance	7,986	8,049	7,986	8,049
Loans individually evaluated for impairment	1,157	977	1,157	977
Loans collectively evaluated for impairment	6,829	7,072	6,829	7,072
Ending balance	7,986	8,049	7,986	8,049
Loans individually evaluated for impairment	4,928	12,681	4,928	12,681	5,197
Loans collectively evaluated for impairment	773,329	755,261	773,329	755,261
Ending balance	778,257	767,942	778,257	767,942
Commercial Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	7,363	7,193	6,932	8,079
Charge-offs		(24)	(160)	(1,721)
Recoveries	2	106	39	109
Provision (credit)	252	(930)	806	(122)
Ending balance	7,617	6,345	7,617	6,345
Loans individually evaluated for impairment	307	1,995	307	1,995
Loans collectively evaluated for impairment	7,310	4,350	7,310	4,350
Ending balance	7,617	6,345	7,617	6,345
Loans individually evaluated for impairment	13,483	10,791	13,483	10,791	8,661
Loans collectively evaluated for impairment	749,607	677,442	749,607	677,442
Ending balance	763,090	688,233	763,090	688,233
Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	2,716	6,785	3,326	6,456
Charge-offs		(1,321)	(88)	(1,340)
Recoveries	177	70	184	85
Provision (credit)	(574)	(1,582)	(1,103)	(1,249)
Ending balance	2,319	3,952	2,319	3,952
Loans individually evaluated for impairment
Loans collectively evaluated for impairment	2,319	3,952	2,319	3,952
Ending balance	2,319	3,952	2,319	3,952
Loans individually evaluated for impairment		646		646
Loans collectively evaluated for impairment	119,333	124,892	119,333	124,892
Ending balance	119,333	125,538	119,333	125,538
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	2,765	3,281	3,078	3,124
Charge-offs	(163)	(255)	(527)	(695)
Recoveries	25	23	43	41
Provision (credit)	132	181	165	760
Ending balance	2,759	3,230	2,759	3,230
Loans individually evaluated for impairment	872	1,006	872	1,006
Loans collectively evaluated for impairment	1,887	2,224	1,887	2,224
Ending balance	2,759	3,230	2,759	3,230
Loans individually evaluated for impairment	17,743	16,961	17,743	16,961	17,852
Loans collectively evaluated for impairment	193,180	216,755	193,180	216,755
Ending balance	210,923	233,716	210,923	233,716
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	6,249	5,741	6,494	5,631
Charge-offs	(490)	(1,516)	(1,723)	(2,810)
Recoveries	314	268	531	496
Provision (credit)	226	1,644	997	2,820
Ending balance	6,299	6,137	6,299	6,137
Loans individually evaluated for impairment	184	12	184	12
Loans collectively evaluated for impairment	6,115	6,125	6,115	6,125
Ending balance	6,299	6,137	6,299	6,137
Loans individually evaluated for impairment	5,577	4,925	5,577	4,925	5,411
Loans collectively evaluated for impairment	306,943	280,314	306,943	280,314
Ending balance	312,520	285,239	312,520	285,239
Estimation/Complexity Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	1,042	842	1,025	861
Charge-offs
Recoveries
Provision (credit)	13	(28)	30	(47)
Ending balance	1,055	814	1,055	814
Loans individually evaluated for impairment
Loans collectively evaluated for impairment	1,055	814	1,055	814
Ending balance	1,055	814	1,055	814
Loans individually evaluated for impairment
Loans collectively evaluated for impairment
Ending balance