Loans (Collateral-dependent Loans by Class) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 3,012,989	$ 3,091,998		$ 3,081,973
Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	10,429	21,121
Equipment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	2,487	3,018
Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	579	669
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	8,744	1,687
Total
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	22,239	26,495
Commercial and Industrial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	510,583	638,773	$ 534,692	589,758
Commercial and Industrial Loans | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	2,618	4,943
Commercial and Industrial Loans | Equipment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	2,487	3,014
Commercial and Industrial Loans | Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	579	669
Commercial and Industrial Loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	8,719	154
Commercial and Industrial Loans | Total
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	14,403	8,780
Commercial Real Estate Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,528,493	1,467,397	1,500,247	1,495,862
Commercial Real Estate Loans | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	5,170	11,877
Commercial Real Estate Loans | Equipment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Commercial Real Estate Loans | Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Commercial Real Estate Loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	25	1,530
Commercial Real Estate Loans | Total
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	5,195	13,407
Agricultural Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	349,321	376,186	384,654	384,526
Agricultural Loans | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,560	3,064
Agricultural Loans | Equipment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Agricultural Loans | Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Agricultural Loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Agricultural Loans | Total
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,560	3,064
Leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	56,186	55,664	57,257
Leases | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Leases | Equipment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Leases | Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Leases | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Leases | Total
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Home Equity Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	217,994	219,348	225,790	225,755
Home Equity Loans | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	412	416
Home Equity Loans | Equipment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Home Equity Loans | Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Home Equity Loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Home Equity Loans | Total
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	412	416
Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	67,150	66,717	69,264	81,217
Consumer Loans | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	5	4
Consumer Loans | Equipment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	4
Consumer Loans | Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Consumer Loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	3
Consumer Loans | Total
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	5	11
Credit Cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	13,856	11,637	11,953
Credit Cards | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Credit Cards | Equipment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Credit Cards | Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Credit Cards | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Credit Cards | Total
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Residential Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	269,406	256,276	$ 305,002	$ 304,855
Residential Mortgage Loans | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	664	817
Residential Mortgage Loans | Equipment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Residential Mortgage Loans | Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Residential Mortgage Loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	0	0
Residential Mortgage Loans | Total
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 664	$ 817