Allowance for Credit Losses, Allocation of The Allowance For Credit Losses by Portfolio Segment and By Impairment Methodology (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Allowance for Credit Losses [Roll Forward]
Beginning Balance	$ 34,255	$ 32,942	$ 34,217	$ 33,017	$ 33,017
Charge-Offs	(494)	(312)	(529)	(643)	(1,048)
Recoveries	224	188	297	224	398
Provision	250	280	250	500	1,850
Ending Balance	34,235	33,098	34,235	33,098	34,217
Ending Balance Individually Evaluated for Impairment	1,402	915	1,402	915	1,374
Ending Balance Collectively Evaluated for Impairment	32,833	32,183	32,833	32,183	32,843
Loans [Abstract]
Ending Balance	1,295,056	1,203,994	1,295,056	1,203,994	1,246,902
Ending Balance Individually Evaluated for Impairment	12,002	4,390	12,002	4,390	11,597
Ending Balance Collectively Evaluated for Impairment	1,283,054	1,199,604	1,283,054	1,199,604	1,235,305
Commercial Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	6,671	4,443	6,464	5,823	5,823
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	(939)	(66)	(732)	(1,446)	641
Ending Balance	5,732	4,377	5,732	4,377	6,464
Ending Balance Individually Evaluated for Impairment	6	0	6	0	0
Ending Balance Collectively Evaluated for Impairment	5,726	4,377	5,726	4,377	6,464
Loans [Abstract]
Ending Balance	393,159	324,795	393,159	324,795	350,548
Ending Balance Individually Evaluated for Impairment	2,979	299	2,979	299	289
Ending Balance Collectively Evaluated for Impairment	390,180	324,496	390,180	324,496	350,259
Agricultural Real Estate [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	3,795	2,775	2,877	2,583	2,583
Charge-Offs	(400)	0	(400)	0	0
Recoveries	0	89	0	89	90
Provision	86	(231)	1,004	(39)	204
Ending Balance	3,481	2,633	3,481	2,633	2,877
Ending Balance Individually Evaluated for Impairment	300	0	300	0	0
Ending Balance Collectively Evaluated for Impairment	3,181	2,633	3,181	2,633	2,877
Loans [Abstract]
Ending Balance	312,588	285,630	312,588	285,630	311,992
Ending Balance Individually Evaluated for Impairment	5,817	1,512	5,817	1,512	5,423
Ending Balance Collectively Evaluated for Impairment	306,771	284,118	306,771	284,118	306,569
Real Estate Construction [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	969	2,201	986	1,933	1,933
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	8	(301)	(9)	(33)	(947)
Ending Balance	977	1,900	977	1,900	986
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	977	1,900	977	1,900	986
Loans [Abstract]
Ending Balance	32,718	36,033	32,718	36,033	32,680
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	32,718	36,033	32,718	36,033	32,680
Residential 1st Mortgages [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	1,260	1,295	1,219	1,251	1,251
Charge-Offs	0	(1)	(16)	(1)	(152)
Recoveries	0	0	0	0	53
Provision	(223)	157	(166)	201	67
Ending Balance	1,037	1,451	1,037	1,451	1,219
Ending Balance Individually Evaluated for Impairment	0	51	0	51	0
Ending Balance Collectively Evaluated for Impairment	1,037	1,400	1,037	1,400	1,219
Loans [Abstract]
Ending Balance	136,473	123,053	136,473	123,053	140,257
Ending Balance Individually Evaluated for Impairment	528	495	528	495	657
Ending Balance Collectively Evaluated for Impairment	135,945	122,558	135,945	122,558	139,600
Home Equity Lines and Loans [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	3,209	3,552	3,235	3,746	3,746
Charge-Offs	(21)	(47)	(22)	(116)	(259)
Recoveries	18	2	20	10	14
Provision	(222)	7	(249)	(126)	(266)
Ending Balance	2,984	3,514	2,984	3,514	3,235
Ending Balance Individually Evaluated for Impairment	243	60	243	60	173
Ending Balance Collectively Evaluated for Impairment	2,741	3,454	2,741	3,454	3,062
Loans [Abstract]
Ending Balance	37,498	46,284	37,498	46,284	42,042
Ending Balance Individually Evaluated for Impairment	612	826	612	826	980
Ending Balance Collectively Evaluated for Impairment	36,886	45,458	36,886	45,458	41,062
Agricultural [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	9,412	8,757	10,437	8,127	8,127
Charge-Offs	(23)	(240)	(23)	(240)	(294)
Recoveries	7	59	20	61	61
Provision	1,161	(742)	123	(114)	2,543
Ending Balance	10,557	7,834	10,557	7,834	10,437
Ending Balance Individually Evaluated for Impairment	596	586	596	586	996
Ending Balance Collectively Evaluated for Impairment	9,961	7,248	9,961	7,248	9,441
Loans [Abstract]
Ending Balance	214,760	210,780	214,760	210,780	221,032
Ending Balance Individually Evaluated for Impairment	1,500	874	1,500	874	3,937
Ending Balance Collectively Evaluated for Impairment	213,260	209,906	213,260	209,906	217,095
Commercial [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	7,966	8,637	7,963	8,733	8,733
Charge-Offs	(4)	0	(4)	(198)	(198)
Recoveries	189	24	236	32	117
Provision	924	877	880	971	(689)
Ending Balance	9,075	9,538	9,075	9,538	7,963
Ending Balance Individually Evaluated for Impairment	202	197	202	197	144
Ending Balance Collectively Evaluated for Impairment	8,873	9,341	8,873	9,341	7,819
Loans [Abstract]
Ending Balance	159,647	171,621	159,647	171,621	143,293
Ending Balance Individually Evaluated for Impairment	510	363	510	363	250
Ending Balance Collectively Evaluated for Impairment	159,137	171,258	159,137	171,258	143,043
Consumer & Other [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	163	162	182	207	207
Charge-Offs	(46)	(24)	(64)	(88)	(145)
Recoveries	10	14	21	32	63
Provision	41	(12)	29	(11)	57
Ending Balance	168	140	168	140	182
Ending Balance Individually Evaluated for Impairment	55	21	55	21	61
Ending Balance Collectively Evaluated for Impairment	113	119	113	119	121
Loans [Abstract]
Ending Balance	5,546	5,798	5,546	5,798	5,058
Ending Balance Individually Evaluated for Impairment	56	21	56	21	61
Ending Balance Collectively Evaluated for Impairment	5,490	5,777	5,490	5,777	4,997
Leases [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	0	0	0	0	0
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	0	0	0	0	0
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
Loans [Abstract]
Ending Balance	2,667	0	2,667	0	0
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	2,667	0	2,667	0	0
Unallocated [Member]
Allowance for Credit Losses [Roll Forward]
Beginning Balance	810	1,120	854	614	614
Charge-Offs	0	0	0	0	0
Recoveries	0	0	0	0	0
Provision	(586)	591	(630)	1,097	240
Ending Balance	224	1,711	224	1,711	854
Ending Balance Individually Evaluated for Impairment	0	0	0	0	0
Ending Balance Collectively Evaluated for Impairment	224	1,711	224	1,711	854
Loans [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