Aging of Corporation's Loan and Lease Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 Days Past Due	$ 914		$ 1,627
60 - 89 Days Past Due	314		425
Over 89 Days Past Due			728
Total Past Due	1,228		2,780
Current	1,488,174		1,381,636
Total Accruing Loans and Leases	1,489,402		1,384,416
Nonaccrual Loans and Leases	10,613	[1]	14,040	[1]
Total	1,500,015		1,398,456
Commercial mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 Days Past Due			704
60 - 89 Days Past Due	147		130
Total Past Due	147		834
Current	622,113		544,893
Total Accruing Loans and Leases	622,260		545,727
Nonaccrual Loans and Leases	511	[1]	631	[1]
Total	622,771		546,358
Home equity lines and loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 Days Past Due			107
60 - 89 Days Past Due			84
Total Past Due			191
Current	186,090		191,878
Total Accruing Loans and Leases	186,090		192,069
Nonaccrual Loans and Leases	1,544	[1]	2,792	[1]
Total	187,634		194,861
Residential mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 Days Past Due	849		399
60 - 89 Days Past Due	105		141
Total Past Due	954		540
Current	286,853		283,924
Total Accruing Loans and Leases	287,807		284,464
Nonaccrual Loans and Leases	3,838	[1]	3,748	[1]
Total	291,645		288,212
Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Over 89 Days Past Due			728
Total Past Due			728
Current	37,394		22,866
Total Accruing Loans and Leases	37,394		23,594
Nonaccrual Loans and Leases	1,661	[1]	3,314	[1]
Total	39,055		26,908
Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 Days Past Due	34		376
60 - 89 Days Past Due			50
Total Past Due	34		426
Current	300,231		287,688
Total Accruing Loans and Leases	300,265		288,114
Nonaccrual Loans and Leases	2,994	[1]	3,506	[1]
Total	303,259		291,620
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 Days Past Due	4		8
60 - 89 Days Past Due			7
Total Past Due	4		15
Current	17,519		17,644
Total Accruing Loans and Leases	17,523		17,659
Nonaccrual Loans and Leases	49	[1]	7	[1]
Total	17,572		17,666
Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 Days Past Due	27		33
60 - 89 Days Past Due	62		13
Total Past Due	89		46
Current	37,974		32,743
Total Accruing Loans and Leases	38,063		32,789
Nonaccrual Loans and Leases	16	[1]	42	[1]
Total	$ 38,079		$ 32,831

[1] Purchased credit-impaired loans, which have been recorded at their fair values at acquisition, and which are performing, are excluded from this table, with the exception of $90 thousand of purchased credit-impaired loans as of both September 30, 2013 and December 31, 2012, which became non-performing subsequent to acquisition.