Allowance for Credit Losses, Allocation of The Allowance For Credit Losses by Portfolio Segment and By Impairment Methodology (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Allowance for Credit Losses [Roll Forward]
Beginning Balance	$ 58,862,000	$ 55,012,000	$ 55,012,000
Charge-Offs	(8,000)	(265,000)	(1,174,000)
Recoveries	71,000	77,000	524,000
Provision	1,250,000	0	4,500,000
Ending Balance	60,175,000	54,824,000	58,862,000
Ending Balance Individually Evaluated for Impairment	178,000	595,000	289,000
Ending Balance Collectively Evaluated for Impairment	59,997,000	54,229,000	58,573,000
Loans & Leases [Abstract]
Ending Balance	3,111,011,000	2,670,109,000	3,099,592,000
Ending Balance Individually Evaluated for Impairment	8,939,000	15,071,000	9,238,000
Ending Balance Collectively Evaluated for Impairment	3,102,072,000	2,655,038,000	3,090,354,000
Commercial Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	27,679,000	11,053,000	11,053,000
Charge-Offs	0	0	0
Recoveries	0	0	0
Provision	1,387,000	69,000	16,626,000
Ending Balance	29,066,000	11,122,000	27,679,000
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	29,066,000	11,122,000	27,679,000
Loans & Leases [Abstract]
Ending Balance	1,008,032,000	861,311,000	958,980,000
Ending Balance Individually Evaluated for Impairment	99,000	4,486,000	104,000
Ending Balance Collectively Evaluated for Impairment	1,007,933,000	856,825,000	958,876,000
Agricultural Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	8,633,000	15,128,000	15,128,000
Charge-Offs	0	0	0
Recoveries	0	0	0
Provision	415,000	(659,000)	(6,495,000)
Ending Balance	9,048,000	14,469,000	8,633,000
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	9,048,000	14,469,000	8,633,000
Loans & Leases [Abstract]
Ending Balance	634,244,000	594,154,000	643,014,000
Ending Balance Individually Evaluated for Impairment	0	5,629,000	5,629,000
Ending Balance Collectively Evaluated for Impairment	634,244,000	588,525,000	637,385,000
Real Estate Construction [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,643,000	1,949,000	1,949,000
Charge-Offs	0	0	0
Recoveries	0	0	0
Provision	4,000	(22,000)	(306,000)
Ending Balance	1,647,000	1,927,000	1,643,000
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	1,647,000	1,927,000	1,643,000
Loans & Leases [Abstract]
Ending Balance	208,573,000	126,956,000	185,741,000
Ending Balance Individually Evaluated for Impairment	2,149,000	0	0
Ending Balance Collectively Evaluated for Impairment	206,424,000	126,956,000	185,741,000
Residential 1st Mortgages [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	960,000	855,000	855,000
Charge-Offs	0	0	0
Recoveries	28,000	19,000	52,000
Provision	(21,000)	163,000	53,000
Ending Balance	967,000	1,037,000	960,000
Ending Balance Individually Evaluated for Impairment	107,000	116,000	117,000
Ending Balance Collectively Evaluated for Impairment	860,000	921,000	843,000
Loans & Leases [Abstract]
Ending Balance	305,085,000	256,732,000	299,379,000
Ending Balance Individually Evaluated for Impairment	2,000	2,310,000	2,365,000
Ending Balance Collectively Evaluated for Impairment	305,083,000	254,422,000	297,014,000
Home Equity Lines and Loans [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	2,024,000	2,675,000	2,675,000
Charge-Offs	0	0	(7,000)
Recoveries	4,000	20,000	78,000
Provision	(114,000)	88,000	(722,000)
Ending Balance	1,914,000	2,783,000	2,024,000
Ending Balance Individually Evaluated for Impairment	8,000	10,000	8,000
Ending Balance Collectively Evaluated for Impairment	1,906,000	2,773,000	2,016,000
Loans & Leases [Abstract]
Ending Balance	32,407,000	40,747,000	34,239,000
Ending Balance Individually Evaluated for Impairment	153,000	200,000	158,000
Ending Balance Collectively Evaluated for Impairment	32,254,000	40,547,000	34,081,000
Agricultural [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	4,814,000	8,076,000	8,076,000
Charge-Offs	0	0	0
Recoveries	3,000	28,000	81,000
Provision	(570,000)	(1,145,000)	(3,343,000)
Ending Balance	4,247,000	6,959,000	4,814,000
Ending Balance Individually Evaluated for Impairment	0	398,000	92,000
Ending Balance Collectively Evaluated for Impairment	4,247,000	6,561,000	4,722,000
Loans & Leases [Abstract]
Ending Balance	221,152,000	264,771,000	264,372,000
Ending Balance Individually Evaluated for Impairment	6,122,000	733,000	495,000
Ending Balance Collectively Evaluated for Impairment	215,030,000	264,038,000	263,877,000
Commercial [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	9,961,000	11,466,000	11,466,000
Charge-Offs	0	(244,000)	(1,101,000)
Recoveries	29,000	2,000	280,000
Provision	(14,000)	990,000	(684,000)
Ending Balance	9,976,000	12,214,000	9,961,000
Ending Balance Individually Evaluated for Impairment	15,000	11,000	20,000
Ending Balance Collectively Evaluated for Impairment	9,961,000	12,203,000	9,941,000
Loans & Leases [Abstract]
Ending Balance	367,875,000	404,329,000	374,816,000
Ending Balance Individually Evaluated for Impairment	228,000	1,517,000	233,000
Ending Balance Collectively Evaluated for Impairment	367,647,000	402,812,000	374,583,000
Consumer & Other [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	333,000	456,000	456,000
Charge-Offs	(8,000)	(21,000)	(66,000)
Recoveries	7,000	8,000	33,000
Provision	(36,000)	(61,000)	(90,000)
Ending Balance	296,000	382,000	333,000
Ending Balance Individually Evaluated for Impairment	48,000	60,000	52,000
Ending Balance Collectively Evaluated for Impairment	248,000	322,000	281,000
Loans & Leases [Abstract]
Ending Balance	232,209,000	14,839,000	235,529,000
Ending Balance Individually Evaluated for Impairment	186,000	196,000	254,000
Ending Balance Collectively Evaluated for Impairment	232,023,000	14,643,000	235,275,000
Leases [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,731,000	3,162,000	3,162,000
Charge-Offs	0	0	0
Recoveries	0	0	0
Provision	(57,000)	26,000	(1,431,000)
Ending Balance	1,674,000	3,188,000	1,731,000
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	1,674,000	3,188,000	1,731,000
Loans & Leases [Abstract]
Ending Balance	101,434,000	106,270,000	103,522,000
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	101,434,000	106,270,000	103,522,000
Unallocated [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,084,000	192,000	192,000
Charge-Offs	0	0	0
Recoveries	0	0	0
Provision	256,000	551,000	892,000
Ending Balance	1,340,000	743,000	1,084,000
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	1,340,000	743,000	1,084,000
Loans & Leases [Abstract]
Ending Balance	0	0	0
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	0	0	0
Restructured Loans [Member]
Loans & Leases [Abstract]
Ending Balance Individually Evaluated for Impairment	$ 601,000	$ 2,500,000	$ 876,000