Loans - Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Balance	$ 19,473	$ 19,704
Charge-offs	(910)	(818)
Recoveries	273	154
Provision (benefit) for loan losses	3,079	1,306
Allowance for loan losses, Ending Balance	21,915	20,346
Commercial, industrial and agricultural
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Balance	8,287	7,341
Charge-offs	(25)	0
Recoveries	18	4
Provision (benefit) for loan losses	2,252	442
Allowance for loan losses, Ending Balance	10,532	7,787
Commercial Mortgages
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Balance	6,952	7,490
Charge-offs	0	(17)
Recoveries	172	0
Provision (benefit) for loan losses	368	1,373
Allowance for loan losses, Ending Balance	7,492	8,846
Residential real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Balance	1,499	2,156
Charge-offs	(143)	(98)
Recoveries	3	65
Provision (benefit) for loan losses	99	(740)
Allowance for loan losses, Ending Balance	1,458	1,383
Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Balance	2,411	2,377
Charge-offs	(592)	(549)
Recoveries	43	46
Provision (benefit) for loan losses	276	166
Allowance for loan losses, Ending Balance	2,138	2,040
Credit cards
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Balance	84	103
Charge-offs	(31)	(26)
Recoveries	1	5
Provision (benefit) for loan losses	58	23
Allowance for loan losses, Ending Balance	112	105
Overdrafts
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Balance	240	237
Charge-offs	(119)	(128)
Recoveries	36	34
Provision (benefit) for loan losses	26	42
Allowance for loan losses, Ending Balance	$ 183	$ 185