Note 4 - Loans - Weighted Average Risk Grades of Loan Portfolio (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Weighted average risk grade of loans	3.04	3.05
Commercial Real Estate Portfolio Segment [Member] | Construction Loans [Member]
Weighted average risk grade of loans	3	3.08
Commercial Real Estate Portfolio Segment [Member] | Mortgage Loans [Member]
Weighted average risk grade of loans	3.02	3.01
Commercial Real Estate Portfolio Segment [Member] | Land Loans [Member]
Weighted average risk grade of loans	3.58	3.71
Commercial Real Estate Portfolio Segment [Member] | Farmland Loans [Member]
Weighted average risk grade of loans	3	3.14
Commercial Portfolio Segment [Member]
Weighted average risk grade of loans	3.08	3.09
Consumer Portfolio Segment [Member]
Weighted average risk grade of loans	2.31	2.34
Residential Portfolio Segment [Member]
Weighted average risk grade of loans	3.01	3.01
Agriculture [Member]
Weighted average risk grade of loans	3.12	3.19