Loans & Leases and Allowance for Credit Losses, Allocation of The Allowance For Credit Losses by Portfolio Segment and By Impairment Methodology (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Allowance for Credit Losses [Roll Forward]
Beginning Balance	$ 49,064	$ 44,118	$ 47,919	$ 41,523	$ 41,523
Charge-Offs	(54)	(25)	(230)	(130)	(172)
Recoveries	134	103	205	203	233
Provision	1,600	250	2,850	2,850	6,335
Ending Balance	50,744	44,446	50,744	44,446	47,919
Ending Balance Individually Evaluated for Impairment	768	848	768	848	831
Ending Balance Collectively Evaluated for Impairment	49,976	43,598	49,976	43,598	47,088
Loans & Leases [Abstract]
Ending Balance	2,216,779	2,079,670	2,216,779	2,079,670	2,177,601
Ending Balance Individually Evaluated for Impairment	9,238	12,579	9,238	12,579	10,863
Ending Balance Collectively Evaluated for Impairment	2,207,541	2,067,091	2,207,541	2,067,091	2,166,738
Commercial Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	11,242	10,236	11,110	10,063	10,063
Charge-Offs	0	0	(109)	0	0
Recoveries	99	0	110	2	2
Provision	(244)	(114)	(14)	57	1,045
Ending Balance	11,097	10,122	11,097	10,122	11,110
Ending Balance Individually Evaluated for Impairment	385	0	385	0	0
Ending Balance Collectively Evaluated for Impairment	10,712	10,122	10,712	10,122	11,110
Loans & Leases [Abstract]
Ending Balance	683,037	627,114	683,037	627,114	668,046
Ending Balance Individually Evaluated for Impairment	4,855	4,324	4,855	4,324	1,932
Ending Balance Collectively Evaluated for Impairment	678,182	622,790	678,182	622,790	666,114
Agricultural Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	10,265	9,501	9,450	6,881	6,881
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	1,131	(130)	1,946	2,490	2,569
Ending Balance	11,396	9,371	11,396	9,371	9,450
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	11,396	9,371	11,396	9,371	9,450
Loans & Leases [Abstract]
Ending Balance	470,738	439,972	470,738	439,972	467,685
Ending Balance Individually Evaluated for Impairment	0	513	0	513	1,304
Ending Balance Collectively Evaluated for Impairment	470,738	439,459	470,738	439,459	466,381
Real Estate Construction [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	2,687	2,442	3,223	2,485	2,485
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	63	16	(473)	(27)	738
Ending Balance	2,750	2,458	2,750	2,458	3,223
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	2,750	2,458	2,750	2,458	3,223
Loans & Leases [Abstract]
Ending Balance	162,167	175,045	162,167	175,045	176,462
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	162,167	175,045	162,167	175,045	176,462
Residential 1st Mortgages [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	872	837	865	789	789
Charge-Offs	0	0	0	(7)	(21)
Recoveries	18	4	37	13	26
Provision	107	(12)	95	34	71
Ending Balance	997	829	997	829	865
Ending Balance Individually Evaluated for Impairment	61	74	61	74	70
Ending Balance Collectively Evaluated for Impairment	936	755	936	755	795
Loans & Leases [Abstract]
Ending Balance	257,920	238,376	257,920	238,376	242,247
Ending Balance Individually Evaluated for Impairment	1,887	2,173	1,887	2,173	2,126
Ending Balance Collectively Evaluated for Impairment	256,033	236,203	256,033	236,203	240,121
Home Equity Lines & Loans [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	2,170	2,149	2,140	2,146	2,146
Charge-Offs	0	0	0	(46)	(46)
Recoveries	1	69	6	102	103
Provision	90	(23)	115	(7)	(63)
Ending Balance	2,261	2,195	2,261	2,195	2,140
Ending Balance Individually Evaluated for Impairment	17	18	17	18	18
Ending Balance Collectively Evaluated for Impairment	2,244	2,177	2,244	2,177	2,122
Loans & Leases [Abstract]
Ending Balance	33,350	32,513	33,350	32,513	31,625
Ending Balance Individually Evaluated for Impairment	369	409	369	409	402
Ending Balance Collectively Evaluated for Impairment	32,981	32,104	32,981	32,104	31,223
Agricultural [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	7,236	6,223	7,381	6,308	6,308
Charge-Offs	0	0	(7)	0	0
Recoveries	0	0	0	0	0
Provision	124	(1)	(14)	(86)	1,073
Ending Balance	7,360	6,222	7,360	6,222	7,381
Ending Balance Individually Evaluated for Impairment	69	129	69	129	128
Ending Balance Collectively Evaluated for Impairment	7,291	6,093	7,291	6,093	7,253
Loans & Leases [Abstract]
Ending Balance	259,127	274,704	259,127	274,704	295,325
Ending Balance Individually Evaluated for Impairment	368	640	368	640	625
Ending Balance Collectively Evaluated for Impairment	258,759	274,064	258,759	274,064	294,700
Commercial [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	9,544	7,849	8,515	7,836	7,836
Charge-Offs	0	0	0	0	0
Recoveries	2	16	6	45	47
Provision	(486)	(265)	539	(281)	632
Ending Balance	9,060	7,600	9,060	7,600	8,515
Ending Balance Individually Evaluated for Impairment	231	620	231	620	608
Ending Balance Collectively Evaluated for Impairment	8,829	6,980	8,829	6,980	7,907
Loans & Leases [Abstract]
Ending Balance	257,951	214,086	257,951	214,086	217,577
Ending Balance Individually Evaluated for Impairment	1,752	4,509	1,752	4,509	4,464
Ending Balance Collectively Evaluated for Impairment	256,199	209,577	256,199	209,577	213,113
Consumer & Other [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	205	170	200	175	175
Charge-Offs	(54)	(25)	(114)	(77)	(105)
Recoveries	14	14	46	41	55
Provision	44	20	77	40	75
Ending Balance	209	179	209	179	200
Ending Balance Individually Evaluated for Impairment	5	7	5	7	7
Ending Balance Collectively Evaluated for Impairment	204	172	204	172	193
Loans & Leases [Abstract]
Ending Balance	7,312	6,975	7,312	6,975	6,913
Ending Balance Individually Evaluated for Impairment	7	11	7	11	10
Ending Balance Collectively Evaluated for Impairment	7,305	6,964	7,305	6,964	6,903
Leases [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	2,952	3,442	3,586	3,294	3,294
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	242	102	(392)	250	292
Ending Balance	3,194	3,544	3,194	3,544	3,586
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	3,194	3,544	3,194	3,544	3,586
Loans & Leases [Abstract]
Ending Balance	85,177	70,885	85,177	70,885	71,721
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	85,177	70,885	85,177	70,885	71,721
Unallocated [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,891	1,269	1,449	1,546	1,546
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	529	657	971	380	(97)
Ending Balance	2,420	1,926	2,420	1,926	1,449
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	2,420	1,926	2,420	1,926	1,449
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	$ 3,000	$ 4,900	$ 3,000	$ 4,900	$ 3,300