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
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	$ 41,244	$ 43,922
Charge-offs	(3,155)	(3,707)
Recoveries	609	502
Provision (credit) for loan losses	2,630	2,231
Ending balance	41,328	42,948
Loans individually evaluated for impairment	5,068	3,849
Loans collectively evaluated for impairment	36,260	39,099
Ending balance	41,328	42,948
Loans individually evaluated for impairment	51,707	56,498	43,282
Loans collectively evaluated for impairment	2,952,965	2,730,939
Ending balance	3,004,672	2,787,437
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	12,751	13,663
Charge-offs	(1,113)	(256)
Recoveries	324	226
Provision (credit) for loan losses	442	(865)
Ending balance	12,404	12,768
Loans individually evaluated for impairment	1,865	868
Loans collectively evaluated for impairment	10,539	11,900
Ending balance	12,404	12,768
Loans individually evaluated for impairment	4,583	4,991	5,003
Loans collectively evaluated for impairment	833,598	727,831
Ending balance	838,181	732,822
Owner-Occupied Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	7,638	6,108
Charge-offs	(197)	(1)
Recoveries	6	12
Provision (credit) for loan losses	1,342	219
Ending balance	8,789	6,338
Loans individually evaluated for impairment	1,191	47
Loans collectively evaluated for impairment	7,598	6,291
Ending balance	8,789	6,338
Loans individually evaluated for impairment	6,318	13,263	5,197
Loans collectively evaluated for impairment	792,895	752,961
Ending balance	799,213	766,224
Commercial Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	6,932	8,079
Charge-offs	(160)	(1,697)
Recoveries	37	3
Provision (credit) for loan losses	554	808
Ending balance	7,363	7,193
Loans individually evaluated for impairment	1,019	2,000
Loans collectively evaluated for impairment	6,344	5,193
Ending balance	7,363	7,193
Loans individually evaluated for impairment	15,786	11,240	8,661
Loans collectively evaluated for impairment	730,543	622,510
Ending balance	746,329	633,750
Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	3,326	6,456
Charge-offs	(88)	(19)
Recoveries	7	15
Provision (credit) for loan losses	(529)	333
Ending balance	2,716	6,785
Loans individually evaluated for impairment
Loans collectively evaluated for impairment	2,716	6,785
Ending balance	2,716	6,785
Loans individually evaluated for impairment	1,070	1,216	1,158
Loans collectively evaluated for impairment	100,415	132,265
Ending balance	101,485	133,481
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	3,078	3,124
Charge-offs	(364)	(440)
Recoveries	18	18
Provision (credit) for loan losses	33	579
Ending balance	2,765	3,281
Loans individually evaluated for impairment	807	922
Loans collectively evaluated for impairment	1,958	2,359
Ending balance	2,765	3,281
Loans individually evaluated for impairment	18,413	19,578	17,852
Loans collectively evaluated for impairment	199,740	218,276
Ending balance	218,153	237,854
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	6,494	5,631
Charge-offs	(1,233)	(1,294)
Recoveries	217	228
Provision (credit) for loan losses	771	1,176
Ending balance	6,249	5,741
Loans individually evaluated for impairment	186	12
Loans collectively evaluated for impairment	6,063	5,729
Ending balance	6,249	5,741
Loans individually evaluated for impairment	5,537	6,210	5,411
Loans collectively evaluated for impairment	295,774	277,096
Ending balance	301,311	283,306
Estimation/Complexity Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	1,025	861
Charge-offs
Recoveries
Provision (credit) for loan losses	17	(19)
Ending balance	1,042	842
Loans individually evaluated for impairment
Loans collectively evaluated for impairment	1,042	842
Ending balance	1,042	842
Loans individually evaluated for impairment
Loans collectively evaluated for impairment
Ending balance