Loans (Risk Category of Loans by Class) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 3,012,989	$ 3,091,998		$ 3,081,973
Commercial and Industrial Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	150,627	260,788
Fiscal Year Before Current Fiscal Year	64,865	89,539
Two Years Before Current Fiscal Year	68,334	50,720
Three Years Before Current Fiscal Year	34,653	34,881
Four Years Before Current Fiscal Year	20,972	21,838
Prior	56,721	55,896
Revolving Loans Amortized Cost Basis	114,411	125,111
Total	510,583	638,773	$ 534,692	589,758
Commercial Real Estate Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	330,908	297,148
Fiscal Year Before Current Fiscal Year	271,733	225,718
Two Years Before Current Fiscal Year	188,216	196,096
Three Years Before Current Fiscal Year	162,948	208,884
Four Years Before Current Fiscal Year	170,248	182,886
Prior	385,816	326,784
Revolving Loans Amortized Cost Basis	18,624	29,881
Total	1,528,493	1,467,397	1,500,247	1,495,862
Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	37,769	61,323
Fiscal Year Before Current Fiscal Year	52,031	35,433
Two Years Before Current Fiscal Year	28,832	34,790
Three Years Before Current Fiscal Year	28,880	42,363
Four Years Before Current Fiscal Year	33,014	29,875
Prior	90,278	80,213
Revolving Loans Amortized Cost Basis	78,517	92,189
Total	349,321	376,186	384,654	$ 384,526
Leases
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	15,307	18,258
Fiscal Year Before Current Fiscal Year	13,689	17,517
Two Years Before Current Fiscal Year	14,794	9,176
Three Years Before Current Fiscal Year	6,774	5,415
Four Years Before Current Fiscal Year	3,274	1,605
Prior	2,348	3,693
Revolving Loans Amortized Cost Basis	0	0
Total	56,186	55,664	$ 57,257
Pass | Commercial and Industrial Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	149,411	260,027
Fiscal Year Before Current Fiscal Year	64,297	88,273
Two Years Before Current Fiscal Year	67,633	46,681
Three Years Before Current Fiscal Year	32,264	31,612
Four Years Before Current Fiscal Year	18,335	21,025
Prior	51,778	48,508
Revolving Loans Amortized Cost Basis	101,684	109,228
Total	485,402	605,354
Pass | Commercial Real Estate Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	328,394	296,265
Fiscal Year Before Current Fiscal Year	271,691	215,226
Two Years Before Current Fiscal Year	179,773	179,129
Three Years Before Current Fiscal Year	146,504	183,703
Four Years Before Current Fiscal Year	147,663	171,016
Prior	361,853	295,641
Revolving Loans Amortized Cost Basis	18,524	29,634
Total	1,454,402	1,370,614
Pass | Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	36,115	49,242
Fiscal Year Before Current Fiscal Year	46,365	25,449
Two Years Before Current Fiscal Year	24,474	31,285
Three Years Before Current Fiscal Year	25,349	32,368
Four Years Before Current Fiscal Year	25,461	22,702
Prior	73,419	64,890
Revolving Loans Amortized Cost Basis	70,038	75,871
Total	301,221	301,807
Pass | Leases
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	15,307	18,258
Fiscal Year Before Current Fiscal Year	13,689	17,517
Two Years Before Current Fiscal Year	14,794	9,176
Three Years Before Current Fiscal Year	6,774	5,415
Four Years Before Current Fiscal Year	3,274	1,605
Prior	2,348	3,693
Revolving Loans Amortized Cost Basis	0	0
Total	56,186	55,664
Special Mention | Commercial and Industrial Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	616	618
Fiscal Year Before Current Fiscal Year	25	1,102
Two Years Before Current Fiscal Year	246	2,756
Three Years Before Current Fiscal Year	806	1,739
Four Years Before Current Fiscal Year	1,236	206
Prior	1,844	1,972
Revolving Loans Amortized Cost Basis	2,750	9,948
Total	7,523	18,341
Special Mention | Commercial Real Estate Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	2,440	883
Fiscal Year Before Current Fiscal Year	42	9,361
Two Years Before Current Fiscal Year	755	15,232
Three Years Before Current Fiscal Year	14,876	23,489
Four Years Before Current Fiscal Year	22,585	7,578
Prior	16,149	20,294
Revolving Loans Amortized Cost Basis	0	147
Total	56,847	76,984
Special Mention | Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	1,654	11,503
Fiscal Year Before Current Fiscal Year	5,666	9,911
Two Years Before Current Fiscal Year	4,292	3,111
Three Years Before Current Fiscal Year	3,146	8,767
Four Years Before Current Fiscal Year	6,473	2,707
Prior	7,512	10,125
Revolving Loans Amortized Cost Basis	8,249	16,318
Total	36,992	62,442
Special Mention | Leases
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	0	0
Fiscal Year Before Current Fiscal Year	0	0
Two Years Before Current Fiscal Year	0	0
Three Years Before Current Fiscal Year	0	0
Four Years Before Current Fiscal Year	0	0
Prior	0	0
Revolving Loans Amortized Cost Basis	0	0
Total	0	0
Substandard | Commercial and Industrial Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	600	143
Fiscal Year Before Current Fiscal Year	543	164
Two Years Before Current Fiscal Year	455	1,283
Three Years Before Current Fiscal Year	1,583	1,530
Four Years Before Current Fiscal Year	1,401	607
Prior	3,099	5,416
Revolving Loans Amortized Cost Basis	9,977	5,935
Total	17,658	15,078
Substandard | Commercial Real Estate Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	74	0
Fiscal Year Before Current Fiscal Year	0	1,131
Two Years Before Current Fiscal Year	7,688	1,735
Three Years Before Current Fiscal Year	1,568	1,692
Four Years Before Current Fiscal Year	0	4,292
Prior	7,814	10,849
Revolving Loans Amortized Cost Basis	100	100
Total	17,244	19,799
Substandard | Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	0	578
Fiscal Year Before Current Fiscal Year	0	73
Two Years Before Current Fiscal Year	66	394
Three Years Before Current Fiscal Year	385	1,228
Four Years Before Current Fiscal Year	1,080	4,466
Prior	9,347	5,198
Revolving Loans Amortized Cost Basis	230	0
Total	11,108	11,937
Substandard | Leases
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	0	0
Fiscal Year Before Current Fiscal Year	0	0
Two Years Before Current Fiscal Year	0	0
Three Years Before Current Fiscal Year	0	0
Four Years Before Current Fiscal Year	0	0
Prior	0	0
Revolving Loans Amortized Cost Basis	0	0
Total	0	0
Doubtful | Commercial and Industrial Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	0	0
Fiscal Year Before Current Fiscal Year	0	0
Two Years Before Current Fiscal Year	0	0
Three Years Before Current Fiscal Year	0	0
Four Years Before Current Fiscal Year	0	0
Prior	0	0
Revolving Loans Amortized Cost Basis	0	0
Total	0	0
Doubtful | Commercial Real Estate Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	0	0
Fiscal Year Before Current Fiscal Year	0	0
Two Years Before Current Fiscal Year	0	0
Three Years Before Current Fiscal Year	0	0
Four Years Before Current Fiscal Year	0	0
Prior	0	0
Revolving Loans Amortized Cost Basis	0	0
Total	0	0
Doubtful | Agricultural Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	0	0
Fiscal Year Before Current Fiscal Year	0	0
Two Years Before Current Fiscal Year	0	0
Three Years Before Current Fiscal Year	0	0
Four Years Before Current Fiscal Year	0	0
Prior	0	0
Revolving Loans Amortized Cost Basis	0	0
Total	0	0
Doubtful | Leases
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	0	0
Fiscal Year Before Current Fiscal Year	0	0
Two Years Before Current Fiscal Year	0	0
Three Years Before Current Fiscal Year	0	0
Four Years Before Current Fiscal Year	0	0
Prior	0	0
Revolving Loans Amortized Cost Basis	0	0
Total	$ 0	$ 0