Note 5 - Loans and the Allowance for Loan Losses - Loan Portfolio Allocated by Internal Risk Ratings (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Loans	$ 619,718,000	$ 566,199,000
Commercial Portfolio Segment [Member] | Commercial Loans [Member]
Loans	47,892,000	49,563,000
Commercial Portfolio Segment [Member] | Agricultural Loans [Member]
Loans	78,785,000	69,160,000
Commercial Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	316,986,000	271,710,000
Commercial Portfolio Segment [Member] | Construction Loans [Member]
Loans	31,181,000	40,161,000
Residential Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	14,530,000	15,900,000
Residential Portfolio Segment [Member] | Equity Lines of Credit [Member]
Loans	35,471,000	38,490,000
Commercial and Residential Portfolio Segments [Member]
Loans	524,845,000	484,984,000
Pass [Member] | Commercial Portfolio Segment [Member] | Commercial Loans [Member]
Loans	47,334,000	48,905,000
Pass [Member] | Commercial Portfolio Segment [Member] | Agricultural Loans [Member]
Loans	76,620,000	68,910,000
Pass [Member] | Commercial Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	309,785,000	268,159,000
Pass [Member] | Commercial Portfolio Segment [Member] | Construction Loans [Member]
Loans	31,097,000	40,069,000
Pass [Member] | Residential Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	14,253,000	15,621,000
Pass [Member] | Residential Portfolio Segment [Member] | Equity Lines of Credit [Member]
Loans	34,855,000	38,304,000
Pass [Member] | Commercial and Residential Portfolio Segments [Member]
Loans	513,944,000	479,968,000
Special Mention [Member] | Commercial Portfolio Segment [Member] | Commercial Loans [Member]
Loans	478,000	481,000
Special Mention [Member] | Commercial Portfolio Segment [Member] | Agricultural Loans [Member]
Loans	2,165,000	250,000
Special Mention [Member] | Commercial Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	4,954,000	3,420,000
Special Mention [Member] | Commercial Portfolio Segment [Member] | Construction Loans [Member]
Loans
Special Mention [Member] | Residential Portfolio Segment [Member] | Real Estate Loan [Member]
Loans		124,000
Special Mention [Member] | Residential Portfolio Segment [Member] | Equity Lines of Credit [Member]
Loans
Special Mention [Member] | Commercial and Residential Portfolio Segments [Member]
Loans	7,597,000	4,275,000
Substandard [Member] | Commercial Portfolio Segment [Member] | Commercial Loans [Member]
Loans	80,000	177,000
Substandard [Member] | Commercial Portfolio Segment [Member] | Agricultural Loans [Member]
Loans
Substandard [Member] | Commercial Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	2,247,000	131,000
Substandard [Member] | Commercial Portfolio Segment [Member] | Construction Loans [Member]
Loans	84,000	92,000
Substandard [Member] | Residential Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	277,000	155,000
Substandard [Member] | Residential Portfolio Segment [Member] | Equity Lines of Credit [Member]
Loans	616,000	186,000
Substandard [Member] | Commercial and Residential Portfolio Segments [Member]
Loans	3,304,000	741,000
Doubtful [Member] | Commercial Portfolio Segment [Member] | Commercial Loans [Member]
Loans
Doubtful [Member] | Commercial Portfolio Segment [Member] | Agricultural Loans [Member]
Loans
Doubtful [Member] | Commercial Portfolio Segment [Member] | Real Estate Loan [Member]
Loans
Doubtful [Member] | Commercial Portfolio Segment [Member] | Construction Loans [Member]
Loans
Doubtful [Member] | Residential Portfolio Segment [Member] | Real Estate Loan [Member]
Loans
Doubtful [Member] | Residential Portfolio Segment [Member] | Equity Lines of Credit [Member]
Loans
Doubtful [Member] | Commercial and Residential Portfolio Segments [Member]
Loans