Allowance for Credit Losses, Impaired Loans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
With no related allowance recorded [Abstract]
Recorded Investment	$ 6,456	$ 3,743	$ 9,214
Unpaid Principal Balance	6,553	4,102	9,435
Average Recorded Investment	7,837	4,196	5,653
Interest Income Recognized	8	11	71
With an allowance recorded [Abstract]
Recorded Investment	4,470	1,264	2,405
Unpaid Principal Balance	4,532	2,005	2,463
Related Allowance	1,706	1,081	1,374
Average Recorded Investment	3,439	2,799	1,423
Interest Income Recognized	11	1	9
Recorded Investment, Total	10,926	5,007	11,619
Unpaid Principal Balance, Total	11,085	6,107	11,898
Related Allowance	1,706	1,081	1,374
Average Recorded Investment, Total	11,276	6,995	7,076
Interest Income Recognized, Total	19	12	80
Commercial Real Estate [Member]
With no related allowance recorded [Abstract]
Recorded Investment	107	1,142	289
Unpaid Principal Balance	110	1,136	289
Average Recorded Investment	198	1,349	506
Interest Income Recognized	2	3	20
With an allowance recorded [Abstract]
Recorded Investment		0
Unpaid Principal Balance		0
Related Allowance		0
Average Recorded Investment		1,509
Interest Income Recognized		0
Related Allowance		0
Agricultural Real Estate [Member]
With no related allowance recorded [Abstract]
Recorded Investment	3,508	934	5,437
Unpaid Principal Balance	3,500	1,183	5,454
Average Recorded Investment	4,473	945	2,611
Interest Income Recognized	0	0	0
With an allowance recorded [Abstract]
Recorded Investment	1,841
Unpaid Principal Balance	1,834
Related Allowance	263
Average Recorded Investment	921
Interest Income Recognized	0
Related Allowance	263
Residential 1st Mortgages [Member]
With no related allowance recorded [Abstract]
Recorded Investment	736	297	658
Unpaid Principal Balance	782	309	761
Average Recorded Investment	697	758	458
Interest Income Recognized	3	0	3
With an allowance recorded [Abstract]
Recorded Investment		108	0
Unpaid Principal Balance		109	0
Related Allowance		48	0
Average Recorded Investment		54	54
Interest Income Recognized		0	0
Related Allowance		48	0
Home Equity Lines & Loans [Member]
With no related allowance recorded [Abstract]
Recorded Investment	249	822	792
Unpaid Principal Balance	268	850	871
Average Recorded Investment	521	646	775
Interest Income Recognized	1	4	23
With an allowance recorded [Abstract]
Recorded Investment	153	187	194
Unpaid Principal Balance	196	190	237
Related Allowance	153	114	173
Average Recorded Investment	174	150	182
Interest Income Recognized	0	1	4
Related Allowance	153	114	173
Agricultural [Member]
With no related allowance recorded [Abstract]
Recorded Investment	1,753	309	1,932
Unpaid Principal Balance	1,783	309	1,954
Average Recorded Investment	1,843	286	1,159
Interest Income Recognized	0	4	19
With an allowance recorded [Abstract]
Recorded Investment	1,988	847	2,006
Unpaid Principal Balance	2,004	1,577	2,019
Related Allowance	1,022	846	996
Average Recorded Investment	1,997	962	997
Interest Income Recognized	8	0	1
Related Allowance	1,022	846	996
Commercial [Member]
With no related allowance recorded [Abstract]
Recorded Investment	103	239	106
Unpaid Principal Balance	110	315	106
Average Recorded Investment	105	214	144
Interest Income Recognized	2	0	6
With an allowance recorded [Abstract]
Recorded Investment	143	100	144
Unpaid Principal Balance	144	106	144
Related Allowance	210	51	144
Average Recorded Investment	144	102	159
Interest Income Recognized	2	0	4
Related Allowance	210	51	144
Consumer & Other [Member]
With an allowance recorded [Abstract]
Recorded Investment	345	22	61
Unpaid Principal Balance	354	23	63
Related Allowance	58	22	61
Average Recorded Investment	203	23	31
Interest Income Recognized	1	0	0
Related Allowance	$ 58	$ 22	$ 61