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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Allowance for Credit Losses [Roll Forward]
Beginning Balance	$ 54,907	$ 50,677	$ 55,266	$ 50,342	$ 50,342
Charge-Offs	(18)	(67)	(418)	(88)	(767)
Recoveries	36	27	77	50	158
Provision	200	500	200	833	5,533
Ending Balance	55,125	51,137	55,125	51,137	55,266
Ending Balance Individually Evaluated for Impairment	598	974	598	974	565
Ending Balance Collectively Evaluated for Impairment	54,527	50,163	54,527	50,163	54,701
Loans & Leases [Abstract]
Ending Balance	2,598,898	2,344,448	2,598,898	2,344,448	2,571,241
Ending Balance Individually Evaluated for Impairment	14,775	9,998	14,775	9,998	16,347
Ending Balance Collectively Evaluated for Impairment	2,584,123	2,334,450	2,584,123	2,334,450	2,554,894
Commercial Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	11,400	11,078	11,609	10,922	10,922
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	2
Provision	(720)	(295)	(929)	(139)	685
Ending Balance	10,680	10,783	10,680	10,783	11,609
Ending Balance Individually Evaluated for Impairment	201	333	201	333	234
Ending Balance Collectively Evaluated for Impairment	10,479	10,450	10,479	10,450	11,375
Loans & Leases [Abstract]
Ending Balance	813,750	752,043	813,750	752,043	826,549
Ending Balance Individually Evaluated for Impairment	4,601	4,749	4,601	4,749	4,676
Ending Balance Collectively Evaluated for Impairment	809,149	747,294	809,149	747,294	821,873
Agricultural Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	14,493	12,242	14,092	12,085	12,085
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	79	1,072	480	1,229	2,007
Ending Balance	14,572	13,314	14,572	13,314	14,092
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	14,572	13,314	14,572	13,314	14,092
Loans & Leases [Abstract]
Ending Balance	605,776	540,852	605,776	540,852	584,625
Ending Balance Individually Evaluated for Impairment	5,702	0	5,702	0	7,238
Ending Balance Collectively Evaluated for Impairment	600,074	540,852	600,074	540,852	577,387
Real Estate Construction [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,207	1,873	1,249	1,846	1,846
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	490	(257)	448	(230)	(597)
Ending Balance	1,697	1,616	1,697	1,616	1,249
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	1,697	1,616	1,697	1,616	1,249
Loans & Leases [Abstract]
Ending Balance	93,539	94,223	93,539	94,223	98,568
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	93,539	94,223	93,539	94,223	98,568
Residential 1st Mortgages [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	863	827	880	815	815
Charge-Offs	0	(12)	0	(12)	(31)
Recoveries	3	3	6	6	15
Provision	(2)	46	(22)	55	81
Ending Balance	864	864	864	864	880
Ending Balance Individually Evaluated for Impairment	122	131	122	131	125
Ending Balance Collectively Evaluated for Impairment	742	733	742	733	755
Loans & Leases [Abstract]
Ending Balance	257,408	261,804	257,408	261,804	259,736
Ending Balance Individually Evaluated for Impairment	2,444	2,628	2,444	2,628	2,491
Ending Balance Collectively Evaluated for Impairment	254,964	259,176	254,964	259,176	257,245
Home Equity Lines & Loans [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	2,738	2,343	2,761	2,324	2,324
Charge-Offs	0	0	0	(4)	(8)
Recoveries	5	1	11	2	6
Provision	0	204	(29)	226	439
Ending Balance	2,743	2,548	2,743	2,548	2,761
Ending Balance Individually Evaluated for Impairment	12	16	12	16	15
Ending Balance Collectively Evaluated for Impairment	2,731	2,532	2,731	2,532	2,746
Loans & Leases [Abstract]
Ending Balance	40,210	37,669	40,210	37,669	40,789
Ending Balance Individually Evaluated for Impairment	247	324	247	324	297
Ending Balance Collectively Evaluated for Impairment	39,963	37,345	39,963	37,345	40,492
Agricultural [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	7,448	7,868	8,242	8,159	8,159
Charge-Offs	0	0	0	0	0
Recoveries	4	7	11	13	61
Provision	29	(217)	(772)	(514)	22
Ending Balance	7,481	7,658	7,481	7,658	8,242
Ending Balance Individually Evaluated for Impairment	99	0	99	0	0
Ending Balance Collectively Evaluated for Impairment	7,382	7,658	7,382	7,658	8,242
Loans & Leases [Abstract]
Ending Balance	284,858	273,170	284,858	273,170	290,463
Ending Balance Individually Evaluated for Impairment	196	0	196	0	0
Ending Balance Collectively Evaluated for Impairment	284,662	273,170	284,662	273,170	290,463
Commercial [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	11,933	9,374	11,656	9,197	9,197
Charge-Offs	0	(14)	(379)	(14)	(613)
Recoveries	12	1	23	3	20
Provision	322	75	967	250	3,052
Ending Balance	12,267	9,436	12,267	9,436	11,656
Ending Balance Individually Evaluated for Impairment	158	487	158	487	185
Ending Balance Collectively Evaluated for Impairment	12,109	8,949	12,109	8,949	11,471
Loans & Leases [Abstract]
Ending Balance	382,192	286,651	382,192	286,651	343,834
Ending Balance Individually Evaluated for Impairment	1,579	2,290	1,579	2,290	1,639
Ending Balance Collectively Evaluated for Impairment	380,613	284,361	380,613	284,361	342,195
Consumer & Other [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	467	239	494	209	209
Charge-Offs	(18)	(41)	(39)	(58)	(115)
Recoveries	12	15	26	26	54
Provision	3	57	(17)	93	346
Ending Balance	464	270	464	270	494
Ending Balance Individually Evaluated for Impairment	6	7	6	7	6
Ending Balance Collectively Evaluated for Impairment	458	263	458	263	488
Loans & Leases [Abstract]
Ending Balance	17,844	7,390	17,844	7,390	19,412
Ending Balance Individually Evaluated for Impairment	6	7	6	7	6
Ending Balance Collectively Evaluated for Impairment	17,838	7,383	17,838	7,383	19,406
Leases [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	4,008	3,390	4,022	3,363	3,363
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	(908)	10	(922)	37	659
Ending Balance	3,100	3,400	3,100	3,400	4,022
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	3,100	3,400	3,100	3,400	4,022
Loans & Leases [Abstract]
Ending Balance	103,321	90,646	103,321	90,646	107,265
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	103,321	90,646	103,321	90,646	107,265
Unallocated [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	350	1,443	261	1,422	1,422
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	907	(195)	996	(174)	(1,161)
Ending Balance	1,257	1,248	1,257	1,248	261
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	1,257	1,248	1,257	1,248	261
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	$ 2,700	$ 2,900	$ 2,700	$ 2,900	$ 2,800