Note 4 - Loans and the Allowance for Loan Losses - Loan Portfolio Allocated by Internal Risk Ratings (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Loans	$ 573,446	$ 566,199
Commercial Portfolio Segment [Member] | Commercial Loans [Member]
Loans	42,707	49,563
Commercial Portfolio Segment [Member] | Agricultural Loans [Member]
Loans	70,041	69,160
Commercial Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	282,533	271,710
Commercial Portfolio Segment [Member] | Construction Loans [Member]
Loans	37,637	40,161
Residential Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	16,413	15,900
Residential Portfolio Segment [Member] | Equity Lines of Credit [Member]
Loans	37,519	38,490
Commercial and Residential Portfolio Segments [Member]
Loans	486,850	484,984
Pass [Member] | Commercial Portfolio Segment [Member] | Commercial Loans [Member]
Loans	42,011	48,905
Pass [Member] | Commercial Portfolio Segment [Member] | Agricultural Loans [Member]
Loans	69,791	68,910
Pass [Member] | Commercial Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	278,359	268,159
Pass [Member] | Commercial Portfolio Segment [Member] | Construction Loans [Member]
Loans	37,547	40,069
Pass [Member] | Residential Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	16,144	15,621
Pass [Member] | Residential Portfolio Segment [Member] | Equity Lines of Credit [Member]
Loans	37,341	38,304
Pass [Member] | Commercial and Residential Portfolio Segments [Member]
Loans	481,193	479,968
Special Mention [Member] | Commercial Portfolio Segment [Member] | Commercial Loans [Member]
Loans	540	481
Special Mention [Member] | Commercial Portfolio Segment [Member] | Agricultural Loans [Member]
Loans	250	250
Special Mention [Member] | Commercial Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	3,564	3,420
Special Mention [Member] | Commercial Portfolio Segment [Member] | Construction Loans [Member]
Loans
Special Mention [Member] | Residential Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	120	124
Special Mention [Member] | Residential Portfolio Segment [Member] | Equity Lines of Credit [Member]
Loans
Special Mention [Member] | Commercial and Residential Portfolio Segments [Member]
Loans	4,474	4,275
Substandard [Member] | Commercial Portfolio Segment [Member] | Commercial Loans [Member]
Loans	156	177
Substandard [Member] | Commercial Portfolio Segment [Member] | Agricultural Loans [Member]
Loans
Substandard [Member] | Commercial Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	610	131
Substandard [Member] | Commercial Portfolio Segment [Member] | Construction Loans [Member]
Loans	90	92
Substandard [Member] | Residential Portfolio Segment [Member] | Real Estate Loan [Member]
Loans	149	155
Substandard [Member] | Residential Portfolio Segment [Member] | Equity Lines of Credit [Member]
Loans	178	186
Substandard [Member] | Commercial and Residential Portfolio Segments [Member]
Loans	1,183	741
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