Loans - Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, Beginning Balance	$ 19,704	$ 19,693
Charge-offs	(818)	(726)
Recoveries	154	158
Provision (benefit) for loan losses	1,306	1,631
Allowance for loan losses, Ending Balance	20,346	20,756
Commercial, industrial, and agricultural
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, Beginning Balance	7,341	6,160
Charge-offs	0	(31)
Recoveries	4	68
Provision (benefit) for loan losses	442	85
Allowance for loan losses, Ending Balance	7,787	6,282
Commercial Mortgages
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, Beginning Balance	7,490	9,007
Charge-offs	(17)	0
Recoveries	0	0
Provision (benefit) for loan losses	1,373	1,013
Allowance for loan losses, Ending Balance	8,846	10,020
Residential real estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, Beginning Balance	2,156	2,033
Charge-offs	(98)	0
Recoveries	65	3
Provision (benefit) for loan losses	(740)	16
Allowance for loan losses, Ending Balance	1,383	2,052
Consumer
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, Beginning Balance	2,377	2,179
Charge-offs	(549)	(590)
Recoveries	46	49
Provision (benefit) for loan losses	166	427
Allowance for loan losses, Ending Balance	2,040	2,065
Credit cards
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, Beginning Balance	103	120
Charge-offs	(26)	(19)
Recoveries	5	7
Provision (benefit) for loan losses	23	15
Allowance for loan losses, Ending Balance	105	123
Overdrafts
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses, Beginning Balance	237	194
Charge-offs	(128)	(86)
Recoveries	34	31
Provision (benefit) for loan losses	42	75
Allowance for loan losses, Ending Balance	$ 185	$ 214