Loans (Aging of Past Due Loans) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Total	$ 3,012,989	$ 3,091,998		$ 3,081,973
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	3,106	5,219
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	668	7,545
Greater Than 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	2,082	7,725
Total Past Due
Financing Receivable, Past Due [Line Items]
Total	5,856	20,489
Loans Not Past Due
Financing Receivable, Past Due [Line Items]
Total	3,007,133	3,071,509
Commercial and Industrial Loans
Financing Receivable, Past Due [Line Items]
Total	510,583	638,773	$ 534,692	589,758
Commercial and Industrial Loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	98	477
Commercial and Industrial Loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total		909
Commercial and Industrial Loans | Greater Than 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	438	2,441
Commercial and Industrial Loans | Total Past Due
Financing Receivable, Past Due [Line Items]
Total	536	3,827
Commercial and Industrial Loans | Loans Not Past Due
Financing Receivable, Past Due [Line Items]
Total	510,047	634,946
Commercial Real Estate Loans
Financing Receivable, Past Due [Line Items]
Total	1,528,493	1,467,397	1,500,247	1,495,862
Commercial Real Estate Loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total		5
Commercial Real Estate Loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	6	4,877
Commercial Real Estate Loans | Greater Than 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	1,232	3,682
Commercial Real Estate Loans | Total Past Due
Financing Receivable, Past Due [Line Items]
Total	1,238	8,564
Commercial Real Estate Loans | Loans Not Past Due
Financing Receivable, Past Due [Line Items]
Total	1,527,255	1,458,833
Agricultural Loans
Financing Receivable, Past Due [Line Items]
Total	349,321	376,186	384,654	384,526
Agricultural Loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	0	0
Agricultural Loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	0	0
Agricultural Loans | Greater Than 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total		651
Agricultural Loans | Total Past Due
Financing Receivable, Past Due [Line Items]
Total		651
Agricultural Loans | Loans Not Past Due
Financing Receivable, Past Due [Line Items]
Total	349,321	375,535
Leases
Financing Receivable, Past Due [Line Items]
Total	56,186	55,664	57,257
Leases | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	0	0
Leases | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	0	0
Leases | Greater Than 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	0	0
Leases | Total Past Due
Financing Receivable, Past Due [Line Items]
Total	0	0
Leases | Loans Not Past Due
Financing Receivable, Past Due [Line Items]
Total	56,186	55,664
Home Equity Loans
Financing Receivable, Past Due [Line Items]
Total	217,994	219,348	225,790	225,755
Home Equity Loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	222	672
Home Equity Loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	111	5
Home Equity Loans | Greater Than 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	23	271
Home Equity Loans | Total Past Due
Financing Receivable, Past Due [Line Items]
Total	356	948
Home Equity Loans | Loans Not Past Due
Financing Receivable, Past Due [Line Items]
Total	217,638	218,400
Consumer Loans
Financing Receivable, Past Due [Line Items]
Total	67,150	66,717	69,264	81,217
Consumer Loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	136	233
Consumer Loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	32	84
Consumer Loans | Greater Than 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total		65
Consumer Loans | Total Past Due
Financing Receivable, Past Due [Line Items]
Total	168	382
Consumer Loans | Loans Not Past Due
Financing Receivable, Past Due [Line Items]
Total	66,982	66,335
Credit Cards
Financing Receivable, Past Due [Line Items]
Total	13,856	11,637	11,953
Credit Cards | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	31	95
Credit Cards | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	15	80
Credit Cards | Greater Than 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	62	86
Credit Cards | Total Past Due
Financing Receivable, Past Due [Line Items]
Total	108	261
Credit Cards | Loans Not Past Due
Financing Receivable, Past Due [Line Items]
Total	13,748	11,376
Residential Mortgage Loans
Financing Receivable, Past Due [Line Items]
Total	269,406	256,276	$ 305,002	$ 304,855
Residential Mortgage Loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	2,619	3,737
Residential Mortgage Loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	504	1,590
Residential Mortgage Loans | Greater Than 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	327	529
Residential Mortgage Loans | Total Past Due
Financing Receivable, Past Due [Line Items]
Total	3,450	5,856
Residential Mortgage Loans | Loans Not Past Due
Financing Receivable, Past Due [Line Items]
Total	$ 265,956	$ 250,420