Loans and Leases - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Loans and Leases Receivable, Net of Deferred Income, Acquired	$ 295,450
Carrying amount	$ 1,253	$ 0
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 term.
Other accruing impaired loans	$ 30,000	33,800
Specific reserves for other accruing impaired loans	$ 186	$ 476
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
Amount of loan relationship with risk ratings of grade 1-5 reviewed annually	500
Amount of loan relationship due for review after 60 or more past due days	$ 500
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
Amount of loan relationship with risk ratings of grade six reviewed annually	$ 500
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
Amount of loan relationship due for review after 60 or more past due days	500
Amount of loan relationship with risk ratings of grade six reviewed annually	$ 2,000
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%
Valley Green Bank [Member]
Financing Receivable, Recorded Investment [Line Items]
Carrying amount	$ 1,253