Loans & Leases and Allowance for Credit Losses, Allocation of Allowance For Credit Losses by Portfolio Segment and By Impairment Methodology (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Allowance for Credit Losses [Roll Forward]
Beginning Balance	$ 54,824	$ 54,907	$ 55,012	$ 55,266	$ 55,266
Charge-Offs	(197)	(18)	(462)	(418)	(675)
Recoveries	131	36	208	77	221
Provision	300	200	300	200	200
Ending Balance	55,058	55,125	55,058	55,125	55,012
Ending Balance Individually Evaluated for Impairment	239	598	239	598	661
Ending Balance Collectively Evaluated for Impairment	54,819	54,527	54,819	54,527	54,351
Loans & Leases [Abstract]
Ending Balance	3,064,512	2,598,898	3,064,512	2,598,898	2,673,027
Ending Balance Individually Evaluated for Impairment	10,549	14,775	10,549	14,775	14,691
Ending Balance Collectively Evaluated for Impairment	3,053,963	2,584,123	3,053,963	2,584,123	2,658,336
Commercial Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	11,122	11,400	11,053	11,609	11,609
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	10,301	(720)	10,370	(929)	(556)
Ending Balance	21,423	10,680	21,423	10,680	11,053
Ending Balance Individually Evaluated for Impairment	6	201	6	201	234
Ending Balance Collectively Evaluated for Impairment	21,417	10,479	21,417	10,479	10,819
Loans & Leases [Abstract]
Ending Balance	855,762	813,750	855,762	813,750	838,570
Ending Balance Individually Evaluated for Impairment	1,663	4,601	1,663	4,601	4,524
Ending Balance Collectively Evaluated for Impairment	854,099	809,149	854,099	809,149	834,046
Agricultural Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	14,469	14,493	15,128	14,092	14,092
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	(5,448)	79	(6,107)	480	1,036
Ending Balance	9,021	14,572	9,021	14,572	15,128
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	9,021	14,572	9,021	14,572	15,128
Loans & Leases [Abstract]
Ending Balance	635,077	605,776	635,077	605,776	625,767
Ending Balance Individually Evaluated for Impairment	5,629	5,702	5,629	5,702	5,654
Ending Balance Collectively Evaluated for Impairment	629,448	600,074	629,448	600,074	620,113
Real Estate Construction [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,927	1,207	1,949	1,249	1,249
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	(475)	490	(497)	448	700
Ending Balance	1,452	1,697	1,452	1,697	1,949
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	1,452	1,697	1,452	1,697	1,949
Loans & Leases [Abstract]
Ending Balance	166,548	93,539	166,548	93,539	115,644
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	166,548	93,539	166,548	93,539	115,644
Residential 1st Mortgages [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,037	863	855	880	880
Charge-Offs	0	0	0	0	0
Recoveries	26	3	46	6	13
Provision	708	(2)	870	(22)	(38)
Ending Balance	1,771	864	1,771	864	855
Ending Balance Individually Evaluated for Impairment	121	122	121	122	118
Ending Balance Collectively Evaluated for Impairment	1,650	742	1,650	742	737
Loans & Leases [Abstract]
Ending Balance	272,209	257,408	272,209	257,408	255,253
Ending Balance Individually Evaluated for Impairment	2,411	2,444	2,411	2,444	2,368
Ending Balance Collectively Evaluated for Impairment	269,798	254,964	269,798	254,964	252,885
Home Equity Lines & Loans [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	2,783	2,738	2,675	2,761	2,761
Charge-Offs	(7)	0	(7)	0	0
Recoveries	13	5	34	11	28
Provision	(550)	0	(463)	(29)	(114)
Ending Balance	2,239	2,743	2,239	2,743	2,675
Ending Balance Individually Evaluated for Impairment	8	12	8	12	12
Ending Balance Collectively Evaluated for Impairment	2,231	2,731	2,231	2,731	2,663
Loans & Leases [Abstract]
Ending Balance	37,966	40,210	37,966	40,210	39,270
Ending Balance Individually Evaluated for Impairment	168	247	168	247	229
Ending Balance Collectively Evaluated for Impairment	37,798	39,963	37,798	39,963	39,041
Agricultural [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	6,959	7,448	8,076	8,242	8,242
Charge-Offs	0	0	0	0	0
Recoveries	3	4	30	11	38
Provision	(2,172)	29	(3,316)	(772)	(204)
Ending Balance	4,790	7,481	4,790	7,481	8,076
Ending Balance Individually Evaluated for Impairment	79	99	79	99	99
Ending Balance Collectively Evaluated for Impairment	4,711	7,382	4,711	7,382	7,977
Loans & Leases [Abstract]
Ending Balance	261,986	284,858	261,986	284,858	292,904
Ending Balance Individually Evaluated for Impairment	473	196	473	196	188
Ending Balance Collectively Evaluated for Impairment	261,513	284,662	261,513	284,662	292,716
Commercial [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	12,214	11,933	11,466	11,656	11,656
Charge-Offs	(182)	0	(426)	(379)	(592)
Recoveries	79	12	80	23	90
Provision	(2,068)	322	(1,077)	967	312
Ending Balance	10,043	12,267	10,043	12,267	11,466
Ending Balance Individually Evaluated for Impairment	0	158	0	158	137
Ending Balance Collectively Evaluated for Impairment	10,043	12,109	10,043	12,109	11,329
Loans & Leases [Abstract]
Ending Balance	369,817	382,192	369,817	382,192	384,795
Ending Balance Individually Evaluated for Impairment	10	1,579	10	1,579	1,528
Ending Balance Collectively Evaluated for Impairment	369,807	380,613	369,807	380,613	383,267
Consumer & Other [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	382	467	456	494	494
Charge-Offs	(8)	(18)	(29)	(39)	(83)
Recoveries	10	12	18	26	52
Provision	(25)	3	(86)	(17)	(7)
Ending Balance	359	464	359	464	456
Ending Balance Individually Evaluated for Impairment	25	6	25	6	61
Ending Balance Collectively Evaluated for Impairment	334	458	334	458	395
Loans & Leases [Abstract]
Ending Balance	361,035	17,844	361,035	17,844	15,422
Ending Balance Individually Evaluated for Impairment	195	6	195	6	200
Ending Balance Collectively Evaluated for Impairment	360,840	17,838	360,840	17,838	15,222
Leases [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	3,188	4,008	3,162	4,022	4,022
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	(388)	(908)	(362)	(922)	(860)
Ending Balance	2,800	3,100	2,800	3,100	3,162
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	2,800	3,100	2,800	3,100	3,162
Loans & Leases [Abstract]
Ending Balance	104,112	103,321	104,112	103,321	105,402
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	104,112	103,321	104,112	103,321	105,402
Unallocated [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	743	350	192	261	261
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	417	907	968	996	(69)
Ending Balance	1,160	1,257	1,160	1,257	192
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	1,160	1,257	1,160	1,257	192
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	$ 3,100	$ 2,600	$ 3,100	$ 2,600	$ 2,600