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, 2016	Mar. 31, 2015	Dec. 31, 2015
Allowance for Credit Losses [Roll Forward]
Beginning Balance	$ 41,523	$ 35,401	$ 35,401
Charge-Offs	(44)	(29)	(96)
Recoveries	50	2,968	5,468
Provision	2,600	600	750
Ending Balance	44,129	38,940	41,523
Ending Balance Individually Evaluated for Impairment	1,088	1,470	1,213
Ending Balance Collectively Evaluated for Impairment	43,041	37,470	40,310
Loans & Leases [Abstract]
Ending Balance	1,993,071	1,705,320	1,996,359
Ending Balance Individually Evaluated for Impairment	12,345	17,025	12,044
Ending Balance Collectively Evaluated for Impairment	1,980,726	1,688,295	1,984,315
Commercial Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	10,063	7,842	7,842
Charge-Offs	0	0	0
Recoveries	2	2,938	2,939
Provision	34	(2,826)	(718)
Ending Balance	10,099	7,954	10,063
Ending Balance Individually Evaluated for Impairment	59	61	61
Ending Balance Collectively Evaluated for Impairment	10,040	7,893	10,002
Loans & Leases [Abstract]
Ending Balance	611,511	529,550	603,650
Ending Balance Individually Evaluated for Impairment	3,376	3,573	3,420
Ending Balance Collectively Evaluated for Impairment	608,135	525,977	600,230
Agricultural Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	6,881	4,185	4,185
Charge-Offs	0	0	0
Recoveries	0	0	0
Provision	2,281	2,716	2,696
Ending Balance	9,162	6,901	6,881
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	9,162	6,901	6,881
Loans & Leases [Abstract]
Ending Balance	432,281	351,866	424,034
Ending Balance Individually Evaluated for Impairment	163	0	0
Ending Balance Collectively Evaluated for Impairment	432,118	351,866	424,034
Real Estate Construction [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	2,485	1,669	1,669
Charge-Offs	0	0	0
Recoveries	0	0	2,225
Provision	109	247	(1,409)
Ending Balance	2,594	1,916	2,485
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	2,594	1,916	2,485
Loans & Leases [Abstract]
Ending Balance	166,455	101,616	151,974
Ending Balance Individually Evaluated for Impairment	0	4,363	0
Ending Balance Collectively Evaluated for Impairment	166,455	97,253	151,974
Residential 1st Mortgages [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	789	1,022	1,022
Charge-Offs	0	0	0
Recoveries	6	0	8
Provision	1	(349)	(241)
Ending Balance	796	673	789
Ending Balance Individually Evaluated for Impairment	66	72	69
Ending Balance Collectively Evaluated for Impairment	730	601	720
Loans & Leases [Abstract]
Ending Balance	212,205	182,431	206,405
Ending Balance Individually Evaluated for Impairment	1,944	2,080	2,010
Ending Balance Collectively Evaluated for Impairment	210,261	180,351	204,395
Home Equity Lines and Loans [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	2,146	2,426	2,426
Charge-Offs	(19)	0	0
Recoveries	2	5	87
Provision	(65)	(335)	(367)
Ending Balance	2,064	2,096	2,146
Ending Balance Individually Evaluated for Impairment	65	53	35
Ending Balance Collectively Evaluated for Impairment	1,999	2,043	2,111
Loans & Leases [Abstract]
Ending Balance	31,639	31,724	33,056
Ending Balance Individually Evaluated for Impairment	1,513	1,668	1,214
Ending Balance Collectively Evaluated for Impairment	30,126	30,056	31,842
Agricultural [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	6,308	6,104	6,104
Charge-Offs	0	0	0
Recoveries	0	1	4
Provision	(404)	(1,503)	200
Ending Balance	5,904	4,602	6,308
Ending Balance Individually Evaluated for Impairment	115	129	115
Ending Balance Collectively Evaluated for Impairment	5,789	4,473	6,193
Loans & Leases [Abstract]
Ending Balance	253,655	216,231	293,966
Ending Balance Individually Evaluated for Impairment	605	457	606
Ending Balance Collectively Evaluated for Impairment	253,050	215,774	293,360
Commercial [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	7,836	8,195	8,195
Charge-Offs	0	(12)	(12)
Recoveries	27	2	136
Provision	(138)	756	(483)
Ending Balance	7,725	8,941	7,836
Ending Balance Individually Evaluated for Impairment	757	1,118	905
Ending Balance Collectively Evaluated for Impairment	6,968	7,823	6,931
Loans & Leases [Abstract]
Ending Balance	213,479	236,141	210,804
Ending Balance Individually Evaluated for Impairment	4,714	4,840	4,760
Ending Balance Collectively Evaluated for Impairment	208,765	231,301	206,044
Consumer & Other [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	175	218	218
Charge-Offs	(25)	(17)	(84)
Recoveries	13	22	69
Provision	24	(11)	(28)
Ending Balance	187	212	175
Ending Balance Individually Evaluated for Impairment	26	37	28
Ending Balance Collectively Evaluated for Impairment	161	175	147
Loans & Leases [Abstract]
Ending Balance	7,066	4,915	6,592
Ending Balance Individually Evaluated for Impairment	30	44	34
Ending Balance Collectively Evaluated for Impairment	7,036	4,871	6,558
Leases [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	3,294	2,211	2,211
Charge-Offs	0	0	0
Recoveries	0	0	0
Provision	(55)	288	1,083
Ending Balance	3,239	2,499	3,294
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	3,239	2,499	3,294
Loans & Leases [Abstract]
Ending Balance	64,780	50,846	65,878
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	64,780	50,846	65,878
Unallocated [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,546	1,529	1,529
Charge-Offs	0	0	0
Recoveries	0	0	0
Provision	813	1,617	17
Ending Balance	2,359	3,146	1,546
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	2,359	3,146	1,546
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	$ 5,300	$ 9,800	$ 4,900