Allowance for Credit Losses, Allocation of The Allowance For Credit Losses by Portfolio Segment and By Impairment Methodology (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Allowance for Credit Losses [Roll Forward]
Beginning Balance	$ 60,175,000	$ 54,824,000	$ 58,862,000	$ 55,012,000	$ 55,012,000
Charge-Offs	(8,000)	(197,000)	(16,000)	(462,000)	(1,174,000)
Recoveries	62,000	131,000	133,000	208,000	524,000
Provision	0	300,000	1,250,000	300,000	4,500,000
Ending Balance	60,229,000	55,058,000	60,229,000	55,058,000	58,862,000
Ending Balance Individually Evaluated for Impairment	159,000	239,000	159,000	239,000	289,000
Ending Balance Collectively Evaluated for Impairment	60,070,000	54,819,000	60,070,000	54,819,000	58,573,000
Loans & Leases [Abstract]
Ending Balance	3,033,196,000	3,064,512,000	3,033,196,000	3,064,512,000	3,099,592,000
Ending Balance Individually Evaluated for Impairment	8,745,000	10,549,000	8,745,000	10,549,000	9,238,000
Ending Balance Collectively Evaluated for Impairment	3,024,451,000	3,053,963,000	3,024,451,000	3,053,963,000	3,090,354,000
Commercial Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	29,066,000	11,122,000	27,679,000	11,053,000	11,053,000
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	(176,000)	10,301,000	1,211,000	10,370,000	16,626,000
Ending Balance	28,890,000	21,423,000	28,890,000	21,423,000	27,679,000
Ending Balance Individually Evaluated for Impairment	0	6,000	0	6,000	0
Ending Balance Collectively Evaluated for Impairment	28,890,000	21,417,000	28,890,000	21,417,000	27,679,000
Loans & Leases [Abstract]
Ending Balance	1,020,077,000	855,762,000	1,020,077,000	855,762,000	958,980,000
Ending Balance Individually Evaluated for Impairment	93,000	1,663,000	93,000	1,663,000	104,000
Ending Balance Collectively Evaluated for Impairment	1,019,984,000	854,099,000	1,019,984,000	854,099,000	958,876,000
Agricultural Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	9,048,000	14,469,000	8,633,000	15,128,000	15,128,000
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	59,000	(5,448,000)	474,000	(6,107,000)	(6,495,000)
Ending Balance	9,107,000	9,021,000	9,107,000	9,021,000	8,633,000
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	9,107,000	9,021,000	9,107,000	9,021,000	8,633,000
Loans & Leases [Abstract]
Ending Balance	630,515,000	635,077,000	630,515,000	635,077,000	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	630,515,000	629,448,000	630,515,000	629,448,000	637,385,000
Real Estate Construction [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,647,000	1,927,000	1,643,000	1,949,000	1,949,000
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	(242,000)	(475,000)	(238,000)	(497,000)	(306,000)
Ending Balance	1,405,000	1,452,000	1,405,000	1,452,000	1,643,000
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	1,405,000	1,452,000	1,405,000	1,452,000	1,643,000
Loans & Leases [Abstract]
Ending Balance	170,933,000	166,548,000	170,933,000	166,548,000	185,741,000
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	170,933,000	166,548,000	170,933,000	166,548,000	185,741,000
Residential 1st Mortgages [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	967,000	1,037,000	960,000	855,000	855,000
Charge-Offs	0	0	0	0	0
Recoveries	31,000	26,000	59,000	46,000	52,000
Provision	(41,000)	708,000	(62,000)	870,000	53,000
Ending Balance	957,000	1,771,000	957,000	1,771,000	960,000
Ending Balance Individually Evaluated for Impairment	97,000	121,000	97,000	121,000	117,000
Ending Balance Collectively Evaluated for Impairment	860,000	1,650,000	860,000	1,650,000	843,000
Loans & Leases [Abstract]
Ending Balance	304,859,000	272,209,000	304,859,000	272,209,000	299,379,000
Ending Balance Individually Evaluated for Impairment	1,929,000	2,411,000	1,929,000	2,411,000	2,365,000
Ending Balance Collectively Evaluated for Impairment	302,930,000	269,798,000	302,930,000	269,798,000	297,014,000
Home Equity Lines and Loans [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,914,000	2,783,000	2,024,000	2,675,000	2,675,000
Charge-Offs	0	(7,000)	0	(7,000)	(7,000)
Recoveries	7,000	13,000	11,000	34,000	78,000
Provision	(22,000)	(550,000)	(136,000)	(463,000)	(722,000)
Ending Balance	1,899,000	2,239,000	1,899,000	2,239,000	2,024,000
Ending Balance Individually Evaluated for Impairment	7,000	8,000	7,000	8,000	8,000
Ending Balance Collectively Evaluated for Impairment	1,892,000	2,231,000	1,892,000	2,231,000	2,016,000
Loans & Leases [Abstract]
Ending Balance	32,026,000	37,966,000	32,026,000	37,966,000	34,239,000
Ending Balance Individually Evaluated for Impairment	140,000	168,000	140,000	168,000	158,000
Ending Balance Collectively Evaluated for Impairment	31,886,000	37,798,000	31,886,000	37,798,000	34,081,000
Agricultural [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	4,247,000	6,959,000	4,814,000	8,076,000	8,076,000
Charge-Offs	0	0	0	0	0
Recoveries	2,000	3,000	5,000	30,000	81,000
Provision	303,000	(2,172,000)	(267,000)	(3,316,000)	(3,343,000)
Ending Balance	4,552,000	4,790,000	4,552,000	4,790,000	4,814,000
Ending Balance Individually Evaluated for Impairment	0	79,000	0	79,000	92,000
Ending Balance Collectively Evaluated for Impairment	4,552,000	4,711,000	4,552,000	4,711,000	4,722,000
Loans & Leases [Abstract]
Ending Balance	236,436,000	261,986,000	236,436,000	261,986,000	264,372,000
Ending Balance Individually Evaluated for Impairment	6,177,000	473,000	6,177,000	473,000	495,000
Ending Balance Collectively Evaluated for Impairment	230,259,000	261,513,000	230,259,000	261,513,000	263,877,000
Commercial [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	9,976,000	12,214,000	9,961,000	11,466,000	11,466,000
Charge-Offs	0	(182,000)	0	(426,000)	(1,101,000)
Recoveries	16,000	79,000	45,000	80,000	280,000
Provision	(72,000)	(2,068,000)	(86,000)	(1,077,000)	(684,000)
Ending Balance	9,920,000	10,043,000	9,920,000	10,043,000	9,961,000
Ending Balance Individually Evaluated for Impairment	11,000	0	11,000	0	20,000
Ending Balance Collectively Evaluated for Impairment	9,909,000	10,043,000	9,909,000	10,043,000	9,941,000
Loans & Leases [Abstract]
Ending Balance	361,432,000	369,817,000	361,432,000	369,817,000	374,816,000
Ending Balance Individually Evaluated for Impairment	224,000	10,000	224,000	10,000	233,000
Ending Balance Collectively Evaluated for Impairment	361,208,000	369,807,000	361,208,000	369,807,000	374,583,000
Consumer & Other [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	296,000	382,000	333,000	456,000	456,000
Charge-Offs	(8,000)	(8,000)	(16,000)	(29,000)	(66,000)
Recoveries	6,000	10,000	13,000	18,000	33,000
Provision	(13,000)	(25,000)	(49,000)	(86,000)	(90,000)
Ending Balance	281,000	359,000	281,000	359,000	333,000
Ending Balance Individually Evaluated for Impairment	44,000	25,000	44,000	25,000	52,000
Ending Balance Collectively Evaluated for Impairment	237,000	334,000	237,000	334,000	281,000
Loans & Leases [Abstract]
Ending Balance	177,042,000	361,035,000	177,042,000	361,035,000	235,529,000
Ending Balance Individually Evaluated for Impairment	182,000	195,000	182,000	195,000	254,000
Ending Balance Collectively Evaluated for Impairment	176,860,000	360,840,000	176,860,000	360,840,000	235,275,000
Leases [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,674,000	3,188,000	1,731,000	3,162,000	3,162,000
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	(35,000)	(388,000)	(92,000)	(362,000)	(1,431,000)
Ending Balance	1,639,000	2,800,000	1,639,000	2,800,000	1,731,000
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	1,639,000	2,800,000	1,639,000	2,800,000	1,731,000
Loans & Leases [Abstract]
Ending Balance	99,876,000	104,112,000	99,876,000	104,112,000	103,522,000
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	99,876,000	104,112,000	99,876,000	104,112,000	103,522,000
Unallocated [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,340,000	743,000	1,084,000	192,000	192,000
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	239,000	417,000	495,000	968,000	892,000
Ending Balance	1,579,000	1,160,000	1,579,000	1,160,000	1,084,000
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	1,579,000	1,160,000	1,579,000	1,160,000	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	$ 361,000	$ 3,100,000	$ 361,000	$ 3,100,000	$ 876,000