Allowance for Credit Losses, Allocation of The Allowance For Credit Losses by Portfolio Segment and By Impairment Methodology (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Allowance for Credit Losses [Roll Forward]
Beginning Balance	$ 60,229,000	$ 55,058,000	$ 58,862,000	$ 55,012,000	$ 55,012,000
Charge-Offs	(17,000)	(25,000)	(33,000)	(487,000)	(1,174,000)
Recoveries	91,000	65,000	224,000	273,000	524,000
Provision	0	1,700,000	1,250,000	2,000,000	4,500,000
Ending Balance	60,303,000	56,798,000	60,303,000	56,798,000	58,862,000
Ending Balance Individually Evaluated for Impairment	140,000	287,000	140,000	287,000	289,000
Ending Balance Collectively Evaluated for Impairment	60,163,000	56,511,000	60,163,000	56,511,000	58,573,000
Loans & Leases [Abstract]
Ending Balance	3,139,801,000	3,111,931,000	3,139,801,000	3,111,931,000	3,099,592,000
Ending Balance Individually Evaluated for Impairment	8,475,000	9,218,000	8,475,000	9,218,000	9,238,000
Ending Balance Collectively Evaluated for Impairment	3,131,326,000	3,102,713,000	3,131,326,000	3,102,713,000	3,090,354,000
Commercial Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	28,890,000	21,423,000	27,679,000	11,053,000	11,053,000
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	(11,000)	2,866,000	1,200,000	13,236,000	16,626,000
Ending Balance	28,879,000	24,289,000	28,879,000	24,289,000	27,679,000
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	28,879,000	24,289,000	28,879,000	24,289,000	27,679,000
Loans & Leases [Abstract]
Ending Balance	1,114,149,000	871,623,000	1,114,149,000	871,623,000	958,980,000
Ending Balance Individually Evaluated for Impairment	74,000	108,000	74,000	108,000	104,000
Ending Balance Collectively Evaluated for Impairment	1,114,075,000	871,515,000	1,114,075,000	871,515,000	958,876,000
Agricultural Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	9,107,000	9,021,000	8,633,000	15,128,000	15,128,000
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	320,000	(229,000)	794,000	(6,336,000)	(6,495,000)
Ending Balance	9,427,000	8,792,000	9,427,000	8,792,000	8,633,000
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	9,427,000	8,792,000	9,427,000	8,792,000	8,633,000
Loans & Leases [Abstract]
Ending Balance	656,337,000	639,172,000	656,337,000	639,172,000	643,014,000
Ending Balance Individually Evaluated for Impairment	0	5,629,000	0	5,629,000	5,629,000
Ending Balance Collectively Evaluated for Impairment	656,337,000	633,543,000	656,337,000	633,543,000	637,385,000
Real Estate Construction [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,405,000	1,452,000	1,643,000	1,949,000	1,949,000
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	28,000	116,000	(210,000)	(381,000)	(306,000)
Ending Balance	1,433,000	1,568,000	1,433,000	1,568,000	1,643,000
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	1,433,000	1,568,000	1,433,000	1,568,000	1,643,000
Loans & Leases [Abstract]
Ending Balance	178,451,000	186,623,000	178,451,000	186,623,000	185,741,000
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	178,451,000	186,623,000	178,451,000	186,623,000	185,741,000
Residential 1st Mortgages [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	957,000	1,771,000	960,000	855,000	855,000
Charge-Offs	0	0	0	0	0
Recoveries	15,000	3,000	74,000	49,000	52,000
Provision	(8,000)	(825,000)	(70,000)	45,000	53,000
Ending Balance	964,000	949,000	964,000	949,000	960,000
Ending Balance Individually Evaluated for Impairment	88,000	118,000	88,000	118,000	117,000
Ending Balance Collectively Evaluated for Impairment	876,000	831,000	876,000	831,000	843,000
Loans & Leases [Abstract]
Ending Balance	309,728,000	293,489,000	309,728,000	293,489,000	299,379,000
Ending Balance Individually Evaluated for Impairment	1,764,000	2,390,000	1,764,000	2,390,000	2,365,000
Ending Balance Collectively Evaluated for Impairment	307,964,000	291,099,000	307,964,000	291,099,000	297,014,000
Home Equity Lines & Loans [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,899,000	2,239,000	2,024,000	2,675,000	2,675,000
Charge-Offs	0	0	0	(7,000)	(7,000)
Recoveries	6,000	31,000	17,000	65,000	78,000
Provision	7,000	(154,000)	(129,000)	(617,000)	(722,000)
Ending Balance	1,912,000	2,116,000	1,912,000	2,116,000	2,024,000
Ending Balance Individually Evaluated for Impairment	6,000	8,000	6,000	8,000	8,000
Ending Balance Collectively Evaluated for Impairment	1,906,000	2,108,000	1,906,000	2,108,000	2,016,000
Loans & Leases [Abstract]
Ending Balance	31,664,000	35,875,000	31,664,000	35,875,000	34,239,000
Ending Balance Individually Evaluated for Impairment	112,000	164,000	112,000	164,000	158,000
Ending Balance Collectively Evaluated for Impairment	31,552,000	35,711,000	31,552,000	35,711,000	34,081,000
Agricultural [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	4,552,000	4,790,000	4,814,000	8,076,000	8,076,000
Charge-Offs	0	0	0	0	0
Recoveries	24,000	24,000	29,000	54,000	81,000
Provision	29,000	(142,000)	(238,000)	(3,458,000)	(3,343,000)
Ending Balance	4,605,000	4,672,000	4,605,000	4,672,000	4,814,000
Ending Balance Individually Evaluated for Impairment	0	92,000	0	92,000	92,000
Ending Balance Collectively Evaluated for Impairment	4,605,000	4,580,000	4,605,000	4,580,000	4,722,000
Loans & Leases [Abstract]
Ending Balance	235,085,000	252,031,000	235,085,000	252,031,000	264,372,000
Ending Balance Individually Evaluated for Impairment	6,129,000	498,000	6,129,000	498,000	495,000
Ending Balance Collectively Evaluated for Impairment	228,956,000	251,533,000	228,956,000	251,533,000	263,877,000
Commercial [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	9,920,000	10,043,000	9,961,000	11,466,000	11,466,000
Charge-Offs	0	0	0	(426,000)	(1,101,000)
Recoveries	38,000	0	83,000	80,000	280,000
Provision	824,000	(50,000)	738,000	(1,127,000)	(684,000)
Ending Balance	10,782,000	9,993,000	10,782,000	9,993,000	9,961,000
Ending Balance Individually Evaluated for Impairment	6,000	13,000	6,000	13,000	20,000
Ending Balance Collectively Evaluated for Impairment	10,776,000	9,980,000	10,776,000	9,980,000	9,941,000
Loans & Leases [Abstract]
Ending Balance	394,326,000	367,052,000	394,326,000	367,052,000	374,816,000
Ending Balance Individually Evaluated for Impairment	218,000	235,000	218,000	235,000	233,000
Ending Balance Collectively Evaluated for Impairment	394,108,000	366,817,000	394,108,000	366,817,000	374,583,000
Consumer & Other [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	281,000	359,000	333,000	456,000	456,000
Charge-Offs	(17,000)	(25,000)	(33,000)	(54,000)	(66,000)
Recoveries	8,000	7,000	21,000	25,000	33,000
Provision	26,000	23,000	(23,000)	(63,000)	(90,000)
Ending Balance	298,000	364,000	298,000	364,000	333,000
Ending Balance Individually Evaluated for Impairment	40,000	56,000	40,000	56,000	52,000
Ending Balance Collectively Evaluated for Impairment	258,000	308,000	258,000	308,000	281,000
Loans & Leases [Abstract]
Ending Balance	129,665,000	359,697,000	129,665,000	359,697,000	235,529,000
Ending Balance Individually Evaluated for Impairment	178,000	194,000	178,000	194,000	254,000
Ending Balance Collectively Evaluated for Impairment	129,487,000	359,503,000	129,487,000	359,503,000	235,275,000
Leases [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,639,000	2,800,000	1,731,000	3,162,000	3,162,000
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	(780,000)	114,000	(872,000)	(248,000)	(1,431,000)
Ending Balance	859,000	2,914,000	859,000	2,914,000	1,731,000
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	859,000	2,914,000	859,000	2,914,000	1,731,000
Loans & Leases [Abstract]
Ending Balance	90,396,000	106,369,000	90,396,000	106,369,000	103,522,000
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	90,396,000	106,369,000	90,396,000	106,369,000	103,522,000
Unallocated [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,579,000	1,160,000	1,084,000	192,000	192,000
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	(435,000)	(19,000)	60,000	949,000	892,000
Ending Balance	1,144,000	1,141,000	1,144,000	1,141,000	1,084,000
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	1,144,000	1,141,000	1,144,000	1,141,000	1,084,000
Loans & Leases [Abstract]
Ending Balance	0	0	0	0	0
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	0	0	0	0	0
Restructured Loans [Member]
Loans & Leases [Abstract]
Ending Balance Individually Evaluated for Impairment	$ 327,200	$ 828,500	$ 327,200	$ 828,500	$ 876,000