Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRs - TDRs By Class (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Modifications [Line Items]
Accruing	$ 813	$ 1,233
Non-accrual	11,703	20,514
Total	12,516	21,747	$ 8,478
Commercial, industrial, and agricultural | Commercial and industrial
Financing Receivable, Modifications [Line Items]
Accruing	0	227
Non-accrual	8,859	16,420
Total	8,859	16,647
Commercial, industrial, and agricultural | Agricultural
Financing Receivable, Modifications [Line Items]
Accruing	0	0
Non-accrual	0	0
Total	0	0
Commercial real estate loans
Financing Receivable, Modifications [Line Items]
Accruing	184	333
Non-accrual	2,500	3,600
Total	2,684	3,933
Commercial real estate loans | Office, retail, and industrial
Financing Receivable, Modifications [Line Items]
Accruing	0	0
Non-accrual	2,340	3,600
Total	2,340	3,600
Commercial real estate loans | Multi-family
Financing Receivable, Modifications [Line Items]
Accruing	0	163
Non-accrual	160	0
Total	160	163
Commercial real estate loans | Construction
Financing Receivable, Modifications [Line Items]
Accruing	0	0
Non-accrual	0	0
Total	0	0
Commercial real estate loans | Other commercial real estate
Financing Receivable, Modifications [Line Items]
Accruing	184	170
Non-accrual	0	0
Total	184	170
Total corporate loans
Financing Receivable, Modifications [Line Items]
Accruing	184	560
Non-accrual	11,359	20,020
Total	11,543	20,580
Consumer loans
Financing Receivable, Modifications [Line Items]
Accruing	629	673
Non-accrual	344	494
Total	973	1,167
Consumer loans | Home equity
Financing Receivable, Modifications [Line Items]
Accruing	31	36
Non-accrual	116	240
Total	147	276
Consumer loans | 1-4 family mortgages
Financing Receivable, Modifications [Line Items]
Accruing	598	637
Non-accrual	228	0
Total	826	637
Consumer loans | Installment
Financing Receivable, Modifications [Line Items]
Accruing	0	0
Non-accrual	0	254
Total	$ 0	$ 254