Note 4 - Loans - Weighted Average Risk Grades of Loan Portfolio (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Weighted average risk grade of loans	3.03	3.04
Commercial Real Estate Portfolio Segment [Member] | Construction Loans [Member]
Weighted average risk grade of loans	3	3
Commercial Real Estate Portfolio Segment [Member] | Mortgage Loans [Member]
Weighted average risk grade of loans	3.02	3.02
Commercial Real Estate Portfolio Segment [Member] | Land Loans [Member]
Weighted average risk grade of loans	3.72	3.58
Commercial Real Estate Portfolio Segment [Member] | Farmland Loans [Member]
Weighted average risk grade of loans	3.04	3
Commercial Portfolio Segment [Member]
Weighted average risk grade of loans	3.05	3.08
Consumer Portfolio Segment [Member]
Weighted average risk grade of loans	2.29	2.31
Residential Portfolio Segment [Member]
Weighted average risk grade of loans	3.02	3.01
Agriculture [Member]
Weighted average risk grade of loans	3.17	3.12