Loans - Nonaccrual Loans and Loans Past Due over 90 Days Still Accruing Interest by Class of Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	$ 17,239	$ 19,232
Past Due Over 90 Days Still on Accrual	890	664
Commercial, industrial, and agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	2,839	1,869
Past Due Over 90 Days Still on Accrual	489	144
Commercial mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	7,694	11,065
Past Due Over 90 Days Still on Accrual	53	0
Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	6,023	5,470
Past Due Over 90 Days Still on Accrual	299	429
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	683	828
Past Due Over 90 Days Still on Accrual	44	37
Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	0	0
Past Due Over 90 Days Still on Accrual	$ 5	$ 54