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		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Year-To-Date Allowance for Loan Losses [Roll Forward]
Beginning Balance	$ 34,217	$ 33,017	$ 33,017
Charge-Offs	(35)	(331)	(1,048)
Recoveries	73	36	398
Provision	0	220	1,850
Ending Balance	34,255	32,942	34,217
Ending Balance Individually Evaluated for Impairment	1,706	1,081	1,374
Ending Balance Collectively Evaluated for Impairment	32,549	31,861	32,843
Loans [Abstract]
Ending Balance	1,226,695	1,158,283	1,246,902
Ending Balance Individually Evaluated for Impairment	10,906	4,999	11,597
Ending Balance Collectively Evaluated for Impairment	1,215,789	1,153,284	1,235,305
Commercial Real Estate [Member]
Year-To-Date Allowance for Loan Losses [Roll Forward]
Beginning Balance	6,464	5,823	5,823
Charge-Offs	0	0	0
Recoveries	0	0	0
Provision	207	(1,380)	641
Ending Balance	6,671	4,443	6,464
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	6,671	4,443	6,464
Loans [Abstract]
Ending Balance	360,893	321,161	350,548
Ending Balance Individually Evaluated for Impairment	107	1,137	289
Ending Balance Collectively Evaluated for Impairment	360,786	320,024	350,259
Agricultural Real Estate [Member]
Year-To-Date Allowance for Loan Losses [Roll Forward]
Beginning Balance	2,877	2,583	2,583
Charge-Offs	0	0	0
Recoveries	0	0	90
Provision	918	192	204
Ending Balance	3,795	2,775	2,877
Ending Balance Individually Evaluated for Impairment	263	0	0
Ending Balance Collectively Evaluated for Impairment	3,532	2,775	2,877
Loans [Abstract]
Ending Balance	318,823	277,631	311,992
Ending Balance Individually Evaluated for Impairment	5,335	933	5,423
Ending Balance Collectively Evaluated for Impairment	313,488	276,698	306,569
Real Estate Construction [Member]
Year-To-Date Allowance for Loan Losses [Roll Forward]
Beginning Balance	986	1,933	1,933
Charge-Offs	0	0	0
Recoveries	0	0	0
Provision	(17)	268	(947)
Ending Balance	969	2,201	986
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	969	2,201	986
Loans [Abstract]
Ending Balance	32,681	32,036	32,680
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	32,681	32,036	32,680
Residential 1st Mortgages [Member]
Year-To-Date Allowance for Loan Losses [Roll Forward]
Beginning Balance	1,219	1,251	1,251
Charge-Offs	(16)	0	(152)
Recoveries	0	0	53
Provision	57	44	67
Ending Balance	1,260	1,295	1,219
Ending Balance Individually Evaluated for Impairment	0	48	0
Ending Balance Collectively Evaluated for Impairment	1,260	1,247	1,219
Loans [Abstract]
Ending Balance	145,419	111,660	140,257
Ending Balance Individually Evaluated for Impairment	735	406	657
Ending Balance Collectively Evaluated for Impairment	144,684	111,254	139,600
Home Equity Lines and Loans [Member]
Year-To-Date Allowance for Loan Losses [Roll Forward]
Beginning Balance	3,235	3,746	3,746
Charge-Offs	(1)	(69)	(259)
Recoveries	2	8	14
Provision	(27)	(133)	(266)
Ending Balance	3,209	3,552	3,235
Ending Balance Individually Evaluated for Impairment	153	114	173
Ending Balance Collectively Evaluated for Impairment	3,056	3,438	3,062
Loans [Abstract]
Ending Balance	40,141	49,094	42,042
Ending Balance Individually Evaluated for Impairment	398	1,007	980
Ending Balance Collectively Evaluated for Impairment	39,743	48,087	41,062
Agricultural [Member]
Year-To-Date Allowance for Loan Losses [Roll Forward]
Beginning Balance	10,437	8,127	8,127
Charge-Offs	0	0	(294)
Recoveries	13	2	61
Provision	(1,038)	628	2,543
Ending Balance	9,412	8,757	10,437
Ending Balance Individually Evaluated for Impairment	1,022	846	996
Ending Balance Collectively Evaluated for Impairment	8,390	7,911	9,441
Loans [Abstract]
Ending Balance	181,725	200,034	221,032
Ending Balance Individually Evaluated for Impairment	3,740	1,155	3,937
Ending Balance Collectively Evaluated for Impairment	177,985	198,879	217,095
Commercial [Member]
Year-To-Date Allowance for Loan Losses [Roll Forward]
Beginning Balance	7,963	8,733	8,733
Charge-Offs	0	(198)	(198)
Recoveries	47	8	117
Provision	(44)	94	(689)
Ending Balance	7,966	8,637	7,963
Ending Balance Individually Evaluated for Impairment	210	51	144
Ending Balance Collectively Evaluated for Impairment	7,756	8,586	7,819
Loans [Abstract]
Ending Balance	142,115	160,066	143,293
Ending Balance Individually Evaluated for Impairment	533	339	250
Ending Balance Collectively Evaluated for Impairment	141,582	159,727	143,043
Consumer & Other [Member]
Year-To-Date Allowance for Loan Losses [Roll Forward]
Beginning Balance	182	207	207
Charge-Offs	(18)	(64)	(145)
Recoveries	11	18	63
Provision	(12)	1	57
Ending Balance	163	162	182
Ending Balance Individually Evaluated for Impairment	58	22	61
Ending Balance Collectively Evaluated for Impairment	105	140	121
Loans [Abstract]
Ending Balance	4,898	6,601	5,058
Ending Balance Individually Evaluated for Impairment	58	22	61
Ending Balance Collectively Evaluated for Impairment	4,840	6,579	4,997
Unallocated [Member]
Year-To-Date Allowance for Loan Losses [Roll Forward]
Beginning Balance	854	614	614
Charge-Offs	0	0	0
Recoveries	0	0	0
Provision	(44)	506	240
Ending Balance	810	1,120	854
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	810	1,120	854
Loans [Abstract]
Ending Balance	0	0	0
Ending Balance Individually Evaluated for Impairment	0	0	0
Ending Balance Collectively Evaluated for Impairment	$ 0	$ 0	$ 0