Allowance for Credit Losses, Allocation of The Allowance For Loan Losses by Portfolio Segment and By Impairment Methodology (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for Credit Losses [Roll Forward]
Beginning Balance				$ 50,342				$ 47,919	$ 50,342	$ 47,919
Charge-Offs									(767)	(685)
Recoveries									158	258
Provision	$ 2,200	$ 2,500	$ 500	333	$ 0	$ 1,600	$ 650	600	5,533	2,850	$ 6,335
Ending Balance	55,266				50,342				55,266	50,342	47,919
Ending Balance Individually Evaluated for Impairment	565				684				565	684
Ending Balance Collectively Evaluated for Impairment	54,701				49,658				54,701	49,658
Loans & Leases [Abstract]
Ending Balance	2,571,241				2,215,295				2,571,241	2,215,295
Ending Balance Individually Evaluated for Impairment	16,347				9,279				16,347	9,279
Ending Balance Collectively Evaluated for Impairment	2,554,894				2,206,016				2,554,894	2,206,016
Commercial Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance				10,922				11,110	10,922	11,110
Charge-Offs									0	(109)
Recoveries									2	109
Provision									685	(188)
Ending Balance	11,609				10,922				11,609	10,922	11,110
Ending Balance Individually Evaluated for Impairment	234				366				234	366
Ending Balance Collectively Evaluated for Impairment	11,375				10,556				11,375	10,556
Loans & Leases [Abstract]
Ending Balance	826,549				684,961				826,549	684,961
Ending Balance Individually Evaluated for Impairment	4,676				4,822				4,676	4,822
Ending Balance Collectively Evaluated for Impairment	821,873				680,139				821,873	680,139
Agricultural Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance				12,085				9,450	12,085	9,450
Charge-Offs									0	0
Recoveries									0	0
Provision									2,007	2,635
Ending Balance	14,092				12,085				14,092	12,085	9,450
Ending Balance Individually Evaluated for Impairment	0				0				0	0
Ending Balance Collectively Evaluated for Impairment	14,092				12,085				14,092	12,085
Loans & Leases [Abstract]
Ending Balance	584,625				499,231				584,625	499,231
Ending Balance Individually Evaluated for Impairment	7,238				0				7,238	0
Ending Balance Collectively Evaluated for Impairment	577,387				499,231				577,387	499,231
Real Estate Construction [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance				1,846				3,223	1,846	3,223
Charge-Offs									0	0
Recoveries									0	0
Provision									(597)	(1,377)
Ending Balance	1,249				1,846				1,249	1,846	3,223
Ending Balance Individually Evaluated for Impairment	0				0				0	0
Ending Balance Collectively Evaluated for Impairment	1,249				1,846				1,249	1,846
Loans & Leases [Abstract]
Ending Balance	98,568				100,206				98,568	100,206
Ending Balance Individually Evaluated for Impairment	0				0				0	0
Ending Balance Collectively Evaluated for Impairment	98,568				100,206				98,568	100,206
Residential 1st Mortgages [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance				815				865	815	865
Charge-Offs									(31)	(53)
Recoveries									15	40
Provision									81	(37)
Ending Balance	880				815				880	815	865
Ending Balance Individually Evaluated for Impairment	125				73				125	73
Ending Balance Collectively Evaluated for Impairment	755				742				755	742
Loans & Leases [Abstract]
Ending Balance	259,736				260,751				259,736	260,751
Ending Balance Individually Evaluated for Impairment	2,491				2,373				2,491	2,373
Ending Balance Collectively Evaluated for Impairment	257,245				258,378				257,245	258,378
Home Equity Lines and Loans [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance				2,324				2,140	2,324	2,140
Charge-Offs									(8)	(3)
Recoveries									6	8
Provision									439	179
Ending Balance	2,761				2,324				2,761	2,324	2,140
Ending Balance Individually Evaluated for Impairment	15				17				15	17
Ending Balance Collectively Evaluated for Impairment	2,746				2,307				2,746	2,307
Loans & Leases [Abstract]
Ending Balance	40,789				34,525				40,789	34,525
Ending Balance Individually Evaluated for Impairment	297				340				297	340
Ending Balance Collectively Evaluated for Impairment	40,492				34,185				40,492	34,185
Agricultural [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance				8,159				7,381	8,159	7,381
Charge-Offs									0	(374)
Recoveries									61	17
Provision									22	1,135
Ending Balance	8,242				8,159				8,242	8,159	7,381
Ending Balance Individually Evaluated for Impairment	0				0				0	0
Ending Balance Collectively Evaluated for Impairment	8,242				8,159				8,242	8,159
Loans & Leases [Abstract]
Ending Balance	290,463				273,582				290,463	273,582
Ending Balance Individually Evaluated for Impairment	0				0				0	0
Ending Balance Collectively Evaluated for Impairment	290,463				273,582				290,463	273,582
Commercial [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance				9,197				8,515	9,197	8,515
Charge-Offs									(613)	0
Recoveries									20	8
Provision									3,052	674
Ending Balance	11,656				9,197				11,656	9,197	8,515
Ending Balance Individually Evaluated for Impairment	185				220				185	220
Ending Balance Collectively Evaluated for Impairment	11,471				8,977				11,471	8,977
Loans & Leases [Abstract]
Ending Balance	343,834				265,703				343,834	265,703
Ending Balance Individually Evaluated for Impairment	1,639				1,734				1,639	1,734
Ending Balance Collectively Evaluated for Impairment	342,195				263,969				342,195	263,969
Consumer & Other [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance				209				200	209	200
Charge-Offs									(115)	(146)
Recoveries									54	76
Provision									346	79
Ending Balance	494				209				494	209	200
Ending Balance Individually Evaluated for Impairment	6				8				6	8
Ending Balance Collectively Evaluated for Impairment	488				201				488	201
Loans & Leases [Abstract]
Ending Balance	19,412				6,656				19,412	6,656
Ending Balance Individually Evaluated for Impairment	6				10				6	10
Ending Balance Collectively Evaluated for Impairment	19,406				6,646				19,406	6,646
Leases [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance				3,363				3,586	3,363	3,586
Charge-Offs									0	0
Recoveries									0	0
Provision									659	(223)
Ending Balance	4,022				3,363				4,022	3,363	3,586
Ending Balance Individually Evaluated for Impairment	0				0				0	0
Ending Balance Collectively Evaluated for Impairment	4,022				3,363				4,022	3,363
Loans & Leases [Abstract]
Ending Balance	107,265				89,680				107,265	89,680
Ending Balance Individually Evaluated for Impairment	0				0				0	0
Ending Balance Collectively Evaluated for Impairment	107,265				89,680				107,265	89,680
Unallocated [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance				$ 1,422				$ 1,449	1,422	1,449
Charge-Offs									0	0
Recoveries									0	0
Provision									(1,161)	(27)
Ending Balance	261				1,422				261	1,422	$ 1,449
Ending Balance Individually Evaluated for Impairment	0				0				0	0
Ending Balance Collectively Evaluated for Impairment	261				1,422				261	1,422
Loans & Leases [Abstract]
Ending Balance	0				0				0	0
Ending Balance Individually Evaluated for Impairment	0				0				0	0
Ending Balance Collectively Evaluated for Impairment	0				0				0	0
Restructured Loans [Member]
Loans & Leases [Abstract]
Ending Balance Individually Evaluated for Impairment	$ 2,800				$ 3,000				$ 2,800	$ 3,000