Loans and Leases - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Measure taken to reduce the risk of difference in actual value and residual value of the leased assets at maturity	The Corporation greatly reduces this risk primarily by using $1.00 buyout leases, in which the entire cost of the leased equipment is included in the contractual payments, leaving no residual payment at the end of the lease terms.
Other accruing impaired loans	$ 35,100,000	$ 27,500,000
Specific reserves for other accruing impaired loans	1,000,000	1,600,000
Maximum modification period on short-term basis	up to one year
Restructured loan past due period	less than ninety days past due
Minimum [Member]
Financing Receivable, Recorded Investment [Line Items]
Amount of loan relationship with risk ratings of grade 1-5 reviewed quarterly	2,500,000
Amount of loan relationship with risk ratings of grade 1-5 reviewed annually	500,000
Amount of loan relationship due for review after 60 or more past due days	500,000
Aging period due of reviewing loans rated 1 through 6	60 days
Amount of loan relationship with risk ratings of grade six reviewed quarterly	2,000,000
Amount of loan relationship with risk ratings of grade six reviewed annually	500,000
Loan-to-value ratio for residential mortgage loans with private mortgage insurance	80.00%
Maximum [Member]
Financing Receivable, Recorded Investment [Line Items]
Amount of loan relationship with risk ratings of grade 1-5 reviewed annually	2,500,000
Amount of loan relationship due for review after 60 or more past due days	500,000
Amount of loan relationship with risk ratings of grade six reviewed annually	$ 2,000,000
Loan-to-value ratio for residential mortgage loans without private mortgage insurance	80.00%
Combined loan-to-value ratio for home equity loans without private mortgage insurance	80.00%
Combined loan-to-value ratio for home equity loans without private mortgage insurance for corporations strongest profile borrower	85.00%