Allowance for Credit Losses, Loan Portfolio Allocated by Management's Internal Risk Ratings (Details) (USD $)	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 1,295,056,000	$ 1,246,902,000	$ 1,203,994,000
Loans outstanding rated doubtful or loss	0	0	0
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	393,159,000	350,548,000	324,795,000
Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	312,588,000	311,992,000	285,630,000
Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	32,718,000	32,680,000	36,033,000
Residential 1st Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	136,473,000	140,257,000	123,053,000
Home Equity Lines & Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	37,498,000	42,042,000	46,284,000
Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	214,760,000	221,032,000	210,780,000
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	159,647,000	143,293,000	171,621,000
Consumer & Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	5,546,000	5,058,000	5,798,000
Leases [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	2,667,000
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,255,088,000	1,189,106,000	1,114,784,000
Pass [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	378,570,000	326,037,000	287,439,000
Pass [Member] | Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	304,516,000	299,642,000	261,347,000
Pass [Member] | Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	26,534,000	26,445,000	28,169,000
Pass [Member] | Residential 1st Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	134,766,000	137,998,000	120,787,000
Pass [Member] | Home Equity Lines & Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	36,407,000	40,866,000	43,895,000
Pass [Member] | Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	212,923,000	216,164,000	202,469,000
Pass [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	153,445,000	137,217,000	165,113,000
Pass [Member] | Consumer & Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	5,260,000	4,737,000	5,565,000
Pass [Member] | Leases [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	2,667,000
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	23,110,000	36,314,000	66,710,000
Special Mention [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	7,817,000	15,528,000	30,475,000
Special Mention [Member] | Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,936,000	6,605,000	20,362,000
Special Mention [Member] | Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	6,184,000	6,235,000	3,217,000
Special Mention [Member] | Residential 1st Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	786,000	1,192,000	1,235,000
Special Mention [Member] | Home Equity Lines & Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0	0
Special Mention [Member] | Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	526,000	1,168,000	5,515,000
Special Mention [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	5,861,000	5,586,000	5,906,000
Special Mention [Member] | Consumer & Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0	0
Special Mention [Member] | Leases [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	0
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	16,858,000	21,482,000	22,500,000
Substandard [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	6,772,000	8,983,000	6,881,000
Substandard [Member] | Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	6,136,000	5,745,000	3,921,000
Substandard [Member] | Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0	4,647,000
Substandard [Member] | Residential 1st Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	921,000	1,067,000	1,031,000
Substandard [Member] | Home Equity Lines & Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,091,000	1,176,000	2,389,000
Substandard [Member] | Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,311,000	3,700,000	2,796,000
Substandard [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	341,000	490,000	602,000
Substandard [Member] | Consumer & Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	286,000	321,000	233,000
Substandard [Member] | Leases [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 0