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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Allowance for Credit Losses [Roll Forward]
Beginning Balance	$ 44,118	$ 39,037	$ 41,523	$ 35,401	$ 35,401
Charge-Offs	(25)	(21)	(130)	(67)	(96)
Recoveries	103	74	203	3,106	5,468
Provision	250	0	2,850	650	750
Ending Balance	44,446	39,090	44,446	39,090	41,523
Ending Balance Individually Evaluated for Impairment	848	1,196	848	1,196	1,213
Ending Balance Collectively Evaluated for Impairment	43,598	37,894	43,598	37,894	40,310
Loans & Leases [Abstract]
Ending Balance	2,079,670	1,910,270	2,079,670	1,910,270	1,996,359
Ending Balance Individually Evaluated for Impairment	12,579	17,191	12,579	17,191	12,044
Ending Balance Collectively Evaluated for Impairment	2,067,091	1,893,079	2,067,091	1,893,079	1,984,315
Commercial Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	10,236	8,591	10,063	7,842	7,842
Charge-Offs	0	0	0	0	0
Recoveries	0	0	2	2,939	2,939
Provision	(114)	654	57	(1,536)	(718)
Ending Balance	10,122	9,245	10,122	9,245	10,063
Ending Balance Individually Evaluated for Impairment	0	61	0	61	61
Ending Balance Collectively Evaluated for Impairment	10,122	9,184	10,122	9,184	10,002
Loans & Leases [Abstract]
Ending Balance	627,114	558,743	627,114	558,743	603,650
Ending Balance Individually Evaluated for Impairment	4,324	4,120	4,324	4,120	3,420
Ending Balance Collectively Evaluated for Impairment	622,790	554,623	622,790	554,623	600,230
Agricultural Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	9,501	7,272	6,881	4,185	4,185
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	(130)	208	2,490	3,295	2,696
Ending Balance	9,371	7,480	9,371	7,480	6,881
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	9,371	7,480	9,371	7,480	6,881
Loans & Leases [Abstract]
Ending Balance	439,972	432,610	439,972	432,610	424,034
Ending Balance Individually Evaluated for Impairment	513	0	513	0	0
Ending Balance Collectively Evaluated for Impairment	439,459	432,610	439,459	432,610	424,034
Real Estate Construction [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	2,442	2,177	2,485	1,669	1,669
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	2,225
Provision	16	211	(27)	719	(1,409)
Ending Balance	2,458	2,388	2,458	2,388	2,485
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	2,458	2,388	2,458	2,388	2,485
Loans & Leases [Abstract]
Ending Balance	175,045	161,762	175,045	161,762	151,974
Ending Balance Individually Evaluated for Impairment	0	4,307	0	4,307	0
Ending Balance Collectively Evaluated for Impairment	175,045	157,455	175,045	157,455	151,974
Residential 1st Mortgages [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	837	731	789	1,022	1,022
Charge-Offs	0	0	(7)	0	0
Recoveries	4	3	13	4	8
Provision	(12)	18	34	(274)	(241)
Ending Balance	829	752	829	752	789
Ending Balance Individually Evaluated for Impairment	74	70	74	70	69
Ending Balance Collectively Evaluated for Impairment	755	682	755	682	720
Loans & Leases [Abstract]
Ending Balance	238,376	196,893	238,376	196,893	206,405
Ending Balance Individually Evaluated for Impairment	2,173	2,036	2,173	2,036	2,010
Ending Balance Collectively Evaluated for Impairment	236,203	194,857	236,203	194,857	204,395
Home Equity Lines & Loans [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	2,149	2,073	2,146	2,426	2,426
Charge-Offs	0	0	(46)	0	0
Recoveries	69	37	102	85	87
Provision	(23)	45	(7)	(356)	(367)
Ending Balance	2,195	2,155	2,195	2,155	2,146
Ending Balance Individually Evaluated for Impairment	18	35	18	35	35
Ending Balance Collectively Evaluated for Impairment	2,177	2,120	2,177	2,120	2,111
Loans & Leases [Abstract]
Ending Balance	32,513	31,833	32,513	31,833	33,056
Ending Balance Individually Evaluated for Impairment	409	1,264	409	1,264	1,214
Ending Balance Collectively Evaluated for Impairment	32,104	30,569	32,104	30,569	31,842
Agricultural [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	6,223	5,046	6,308	6,104	6,104
Charge-Offs	0	0	0	0	0
Recoveries	0	1	0	3	4
Provision	(1)	91	(86)	(969)	200
Ending Balance	6,222	5,138	6,222	5,138	6,308
Ending Balance Individually Evaluated for Impairment	129	120	129	120	115
Ending Balance Collectively Evaluated for Impairment	6,093	5,018	6,093	5,018	6,193
Loans & Leases [Abstract]
Ending Balance	274,704	249,783	274,704	249,783	293,966
Ending Balance Individually Evaluated for Impairment	640	630	640	630	606
Ending Balance Collectively Evaluated for Impairment	274,064	249,153	274,064	249,153	293,360
Commercial [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	7,849	8,878	7,836	8,195	8,195
Charge-Offs	0	0	0	(12)	(12)
Recoveries	16	20	45	24	136
Provision	(265)	(653)	(281)	38	(483)
Ending Balance	7,600	8,245	7,600	8,245	7,836
Ending Balance Individually Evaluated for Impairment	620	879	620	879	905
Ending Balance Collectively Evaluated for Impairment	6,980	7,366	6,980	7,366	6,931
Loans & Leases [Abstract]
Ending Balance	214,086	210,491	214,086	210,491	210,804
Ending Balance Individually Evaluated for Impairment	4,509	4,797	4,509	4,797	4,760
Ending Balance Collectively Evaluated for Impairment	209,577	205,694	209,577	205,694	206,044
Consumer & Other [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	170	217	175	218	218
Charge-Offs	(25)	(21)	(77)	(55)	(84)
Recoveries	14	13	41	51	69
Provision	20	7	40	2	(28)
Ending Balance	179	216	179	216	175
Ending Balance Individually Evaluated for Impairment	7	31	7	31	28
Ending Balance Collectively Evaluated for Impairment	172	185	172	185	147
Loans & Leases [Abstract]
Ending Balance	6,975	6,735	6,975	6,735	6,592
Ending Balance Individually Evaluated for Impairment	11	37	11	37	34
Ending Balance Collectively Evaluated for Impairment	6,964	6,698	6,964	6,698	6,558
Leases [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	3,442	2,532	3,294	2,211	2,211
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	102	539	250	860	1,083
Ending Balance	3,544	3,071	3,544	3,071	3,294
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	3,544	3,071	3,544	3,071	3,294
Loans & Leases [Abstract]
Ending Balance	70,885	61,420	70,885	61,420	65,878
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	70,885	61,420	70,885	61,420	65,878
Unallocated [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,269	1,520	1,546	1,529	1,529
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	657	(1,120)	380	(1,129)	17
Ending Balance	1,926	400	1,926	400	1,546
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	1,926	400	1,926	400	1,546
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	$ 4,900	$ 9,300	$ 4,900	$ 9,300	$ 4,900