Allowance for Credit Losses, Loan Portfolio Allocated by Management's Internal Risk Ratings (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 1,297,811,000	$ 1,246,902,000	$ 1,210,027,000
Loans outstanding rated doubtful or loss	0	0	0
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	401,626,000	350,548,000	335,664,000
Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	311,401,000	311,992,000	293,864,000
Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	27,099,000	32,680,000	32,701,000
Residential 1st Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	143,577,000	140,257,000	137,464,000
Home Equity Lines & Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	37,160,000	42,042,000	43,990,000
Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	221,569,000	221,032,000	193,053,000
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	145,793,000	143,293,000	167,777,000
Consumer & Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	5,063,000	5,058,000	5,514,000
Leases [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	4,523,000	0	0
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,265,557,000	1,189,106,000	1,142,846,000
Pass [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	389,137,000	326,037,000	313,441,000
Pass [Member] | Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	307,736,000	299,642,000	273,823,000
Pass [Member] | Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	25,467,000	26,445,000	24,856,000
Pass [Member] | Residential 1st Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	142,036,000	137,998,000	135,473,000
Pass [Member] | Home Equity Lines & Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	36,090,000	40,866,000	41,975,000
Pass [Member] | Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	220,504,000	216,164,000	186,398,000
Pass [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	135,303,000	137,217,000	161,685,000
Pass [Member] | Consumer & Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	4,761,000	4,737,000	5,195,000
Pass [Member] | Leases [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	4,523,000
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	22,096,000	36,314,000	38,159,000
Special Mention [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	7,765,000	15,528,000	15,910,000
Special Mention [Member] | Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	2,497,000	6,605,000	9,887,000
Special Mention [Member] | Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,632,000	6,235,000	3,217,000
Special Mention [Member] | Residential 1st Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	780,000	1,192,000	1,211,000
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	464,000	1,168,000	2,300,000
Special Mention [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	8,958,000	5,586,000	5,634,000
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	10,158,000	21,482,000	29,022,000
Substandard [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	4,724,000	8,983,000	6,313,000
Substandard [Member] | Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,168,000	5,745,000	10,154,000
Substandard [Member] | Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0	4,628,000
Substandard [Member] | Residential 1st Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	761,000	1,067,000	780,000
Substandard [Member] | Home Equity Lines & Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,070,000	1,176,000	2,015,000
Substandard [Member] | Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	601,000	3,700,000	4,355,000
Substandard [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,532,000	490,000	458,000
Substandard [Member] | Consumer & Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	302,000	321,000	319,000
Substandard [Member] | Leases [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 0