Note 4 - Loans and the Allowance for Loan Losses - Loan Portfolio Allocated by Internal Risk Ratings (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Loans	$ 623,743	$ 619,718
Commercial Portfolio Segment [Member] | Commercial Loans [Member]
Loans	49,246	47,892
Commercial Portfolio Segment [Member] | Agricultural Loans [Member]
Loans	76,044	78,785
Commercial Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	332,294	316,986
Commercial Portfolio Segment [Member] | Construction Loans [Member]
Loans	19,674	31,181
Residential Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	13,820	14,530
Residential Portfolio Segment [Member] | Equity Lines of Credit [Member]
Loans	35,262	35,471
Commercial and Residential Portfolio Segments [Member]
Loans	526,340	524,845
Pass [Member] | Commercial Portfolio Segment [Member] | Commercial Loans [Member]
Loans	48,784	47,334
Pass [Member] | Commercial Portfolio Segment [Member] | Agricultural Loans [Member]
Loans	73,909	76,620
Pass [Member] | Commercial Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	326,468	309,785
Pass [Member] | Commercial Portfolio Segment [Member] | Construction Loans [Member]
Loans	19,592	31,097
Pass [Member] | Residential Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	13,553	14,253
Pass [Member] | Residential Portfolio Segment [Member] | Equity Lines of Credit [Member]
Loans	34,688	34,855
Pass [Member] | Commercial and Residential Portfolio Segments [Member]
Loans	516,994	513,944
Special Mention [Member] | Commercial Portfolio Segment [Member] | Commercial Loans [Member]
Loans	415	478
Special Mention [Member] | Commercial Portfolio Segment [Member] | Agricultural Loans [Member]
Loans	2,135	2,165
Special Mention [Member] | Commercial Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	4,935	4,954
Special Mention [Member] | Commercial Portfolio Segment [Member] | Construction Loans [Member]
Loans
Special Mention [Member] | Residential Portfolio Segment [Member] | Real Estate Loan [Member]
Loans
Special Mention [Member] | Residential Portfolio Segment [Member] | Equity Lines of Credit [Member]
Loans
Special Mention [Member] | Commercial and Residential Portfolio Segments [Member]
Loans	7,485	7,597
Substandard [Member] | Commercial Portfolio Segment [Member] | Commercial Loans [Member]
Loans	47	80
Substandard [Member] | Commercial Portfolio Segment [Member] | Agricultural Loans [Member]
Loans
Substandard [Member] | Commercial Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	891	2,247
Substandard [Member] | Commercial Portfolio Segment [Member] | Construction Loans [Member]
Loans	82	84
Substandard [Member] | Residential Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	267	277
Substandard [Member] | Residential Portfolio Segment [Member] | Equity Lines of Credit [Member]
Loans	574	616
Substandard [Member] | Commercial and Residential Portfolio Segments [Member]
Loans	1,861	3,304
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