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		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Allowance for Credit Losses [Roll Forward]
Beginning Balance	$ 47,919	$ 41,523	$ 41,523
Charge-Offs	(151)	(44)	(172)
Recoveries	32	50	233
Provision	600	2,600	6,335
Ending Balance	48,400	44,129	47,919
Ending Balance Individually Evaluated for Impairment	1,162	1,088	831
Ending Balance Collectively Evaluated for Impairment	47,238	43,041	47,088
Loans & Leases [Abstract]
Ending Balance	2,146,032	1,993,071	2,177,601
Ending Balance Individually Evaluated for Impairment	10,759	12,345	10,863
Ending Balance Collectively Evaluated for Impairment	2,135,273	1,980,726	2,166,738
Commercial Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	11,110	10,063	10,063
Charge-Offs	(109)	0	0
Recoveries	7	2	2
Provision	657	34	1,045
Ending Balance	11,665	10,099	11,110
Ending Balance Individually Evaluated for Impairment	471	59	0
Ending Balance Collectively Evaluated for Impairment	11,194	10,040	11,110
Loans & Leases [Abstract]
Ending Balance	676,527	611,511	668,046
Ending Balance Individually Evaluated for Impairment	4,924	3,376	1,932
Ending Balance Collectively Evaluated for Impairment	671,603	608,135	666,114
Agricultural Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	9,450	6,881	6,881
Charge-Offs	0	0	0
Recoveries	0	0	0
Provision	(57)	2,281	2,569
Ending Balance	9,393	9,162	9,450
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	9,393	9,162	9,450
Loans & Leases [Abstract]
Ending Balance	463,645	432,281	467,685
Ending Balance Individually Evaluated for Impairment	975	163	1,304
Ending Balance Collectively Evaluated for Impairment	462,670	432,118	466,381
Real Estate Construction [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	3,223	2,485	2,485
Charge-Offs	0	0	0
Recoveries	0	0	0
Provision	(277)	109	738
Ending Balance	2,946	2,594	3,223
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	2,946	2,594	3,223
Loans & Leases [Abstract]
Ending Balance	164,791	166,455	176,462
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	164,791	166,455	176,462
Residential 1st Mortgages [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	865	789	789
Charge-Offs	0	0	(21)
Recoveries	3	6	26
Provision	12	1	71
Ending Balance	880	796	865
Ending Balance Individually Evaluated for Impairment	69	66	70
Ending Balance Collectively Evaluated for Impairment	811	730	795
Loans & Leases [Abstract]
Ending Balance	249,628	212,205	242,247
Ending Balance Individually Evaluated for Impairment	2,069	1,944	2,126
Ending Balance Collectively Evaluated for Impairment	247,559	210,261	240,121
Home Equity Lines & Loans [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	2,140	2,146	2,146
Charge-Offs	0	(19)	(46)
Recoveries	2	2	103
Provision	(17)	(65)	(63)
Ending Balance	2,125	2,064	2,140
Ending Balance Individually Evaluated for Impairment	17	65	18
Ending Balance Collectively Evaluated for Impairment	2,108	1,999	2,122
Loans & Leases [Abstract]
Ending Balance	31,817	31,639	31,625
Ending Balance Individually Evaluated for Impairment	451	1,513	402
Ending Balance Collectively Evaluated for Impairment	31,366	30,126	31,223
Agricultural [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	7,381	6,308	6,308
Charge-Offs	(7)	0	0
Recoveries	0	0	0
Provision	(863)	(404)	1,073
Ending Balance	6,511	5,904	7,381
Ending Balance Individually Evaluated for Impairment	331	115	128
Ending Balance Collectively Evaluated for Impairment	6,180	5,789	7,253
Loans & Leases [Abstract]
Ending Balance	266,010	253,655	295,325
Ending Balance Individually Evaluated for Impairment	698	605	625
Ending Balance Collectively Evaluated for Impairment	265,312	253,050	294,700
Commercial [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	8,515	7,836	7,836
Charge-Offs	0	0	0
Recoveries	4	27	47
Provision	(40)	(138)	632
Ending Balance	8,479	7,725	8,515
Ending Balance Individually Evaluated for Impairment	268	757	608
Ending Balance Collectively Evaluated for Impairment	8,211	6,968	7,907
Loans & Leases [Abstract]
Ending Balance	209,184	213,479	217,577
Ending Balance Individually Evaluated for Impairment	1,633	4,714	4,464
Ending Balance Collectively Evaluated for Impairment	207,551	208,765	213,113
Consumer & Other [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	200	175	175
Charge-Offs	(35)	(25)	(105)
Recoveries	16	13	55
Provision	17	24	75
Ending Balance	198	187	200
Ending Balance Individually Evaluated for Impairment	6	26	7
Ending Balance Collectively Evaluated for Impairment	192	161	193
Loans & Leases [Abstract]
Ending Balance	7,119	7,066	6,913
Ending Balance Individually Evaluated for Impairment	9	30	10
Ending Balance Collectively Evaluated for Impairment	7,110	7,036	6,903
Leases [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	3,586	3,294	3,294
Charge-Offs	0	0	0
Recoveries	0	0	0
Provision	280	(55)	292
Ending Balance	3,866	3,239	3,586
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	3,866	3,239	3,586
Loans & Leases [Abstract]
Ending Balance	77,311	64,780	71,721
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	77,311	64,780	71,721
Unallocated [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,449	1,546	1,546
Charge-Offs	0	0	0
Recoveries	0	0	0
Provision	888	813	(97)
Ending Balance	2,337	2,359	1,449
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	2,337	2,359	1,449
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	$ 3,400	$ 5,300	$ 3,300