Loans - Nonaccrual Loans and Loans Past Due over 90 Days Still Accruing Interest by Class of Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	$ 15,325	$ 12,159
Past Due Over 90 Days Still on Accrual	70	105
Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	2,830	3,560
Past Due Over 90 Days Still on Accrual	0	3
Commercial Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	5,592	3,651
Past Due Over 90 Days Still on Accrual	0	0
Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	5,733	3,671
Past Due Over 90 Days Still on Accrual	27	87
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	1,170	1,277
Past Due Over 90 Days Still on Accrual	15	15
Credit Cards [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	0	0
Past Due Over 90 Days Still on Accrual	$ 28	$ 0