Allowance for Credit Losses, Aging Analysis of Loan Portfolio by the Time Past Due (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 89 Days Past Due	$ 1,710	$ 547	$ 872
90 Days or More and Still Accruing	0	0	0
Nonaccrual	9,478	9,298	3,760
Total Past Due	11,188	9,845	4,632
Current	1,215,507	1,237,057	1,153,651
Total Loans	1,226,695	1,246,902	1,158,283
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 89 Days Past Due	364	150	0
90 Days or More and Still Accruing	0	0	0
Nonaccrual	0	0	831
Total Past Due	364	150	831
Current	360,529	350,398	320,330
Total Loans	360,893	350,548	321,161
Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 89 Days Past Due	893	0	594
90 Days or More and Still Accruing	0	0	0
Nonaccrual	5,335	5,423	934
Total Past Due	6,228	5,423	1,528
Current	312,595	306,569	276,103
Total Loans	318,823	311,992	277,631
Real Estate Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 89 Days Past Due	0	0	0
90 Days or More and Still Accruing	0	0	0
Nonaccrual	0	0	0
Total Past Due	0	0	0
Current	32,681	32,680	32,036
Total Loans	32,681	32,680	32,036
Residential 1st Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 89 Days Past Due	0	23	0
90 Days or More and Still Accruing	0	0	0
Nonaccrual	405	445	391
Total Past Due	405	468	391
Current	145,014	139,789	111,269
Total Loans	145,419	140,257	111,660
Home Equity Lines & Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 89 Days Past Due	275	70	221
90 Days or More and Still Accruing	0	0	0
Nonaccrual	195	213	523
Total Past Due	470	283	744
Current	39,671	41,759	48,350
Total Loans	40,141	42,042	49,094
Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 89 Days Past Due	0	0	0
90 Days or More and Still Accruing	0	0	0
Nonaccrual	3,237	3,198	846
Total Past Due	3,237	3,198	846
Current	178,488	217,834	199,188
Total Loans	181,725	221,032	200,034
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 89 Days Past Due	0	293	0
90 Days or More and Still Accruing	0	0	0
Nonaccrual	287	0	213
Total Past Due	287	293	213
Current	141,828	143,000	159,853
Total Loans	142,115	143,293	160,066
Consumer & Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 89 Days Past Due	178	11	57
90 Days or More and Still Accruing	0	0	0
Nonaccrual	19	19	22
Total Past Due	197	30	79
Current	4,701	5,028	6,522
Total Loans	$ 4,898	$ 5,058	$ 6,601