Note 4 - Loans and the Allowance for Loan Losses - Aging Analysis of the Loan Portfolio (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Loans, past due	$ 5,233,000	$ 5,705,000
Loans, 90 days past due and still accruing
Financing Receivable, Nonaccrual	2,310,000	2,050,000
Loans, current	618,510,000	614,013,000
Loans	623,743,000	619,718,000
Loans, 90 days past due and still accruing
Financing Receivables 30 to 89 Days Past Due [Member]
Loans, past due	2,923,000	3,655,000
Commercial Portfolio Segment [Member] | Commercial Loans [Member]
Loans, past due	260,000	391,000
Loans, 90 days past due and still accruing
Financing Receivable, Nonaccrual	47,000	58,000
Loans, current	48,986,000	47,501,000
Loans	49,246,000	47,892,000
Loans, 90 days past due and still accruing
Commercial Portfolio Segment [Member] | Commercial Loans [Member] | Financing Receivables 30 to 89 Days Past Due [Member]
Loans, past due	213,000	333,000
Commercial Portfolio Segment [Member] | Agricultural Loans [Member]
Loans, past due	130,000	199,000
Loans, 90 days past due and still accruing
Financing Receivable, Nonaccrual
Loans, current	75,914,000	78,586,000
Loans	76,044,000	78,785,000
Loans, 90 days past due and still accruing
Commercial Portfolio Segment [Member] | Agricultural Loans [Member] | Financing Receivables 30 to 89 Days Past Due [Member]
Loans, past due	130,000	199,000
Commercial Portfolio Segment [Member] | Real Estate Loan [Member]
Loans, past due	1,719,000	2,297,000
Loans, 90 days past due and still accruing
Financing Receivable, Nonaccrual	891,000	830,000
Loans, current	330,575,000	314,689,000
Loans	332,294,000	316,986,000
Loans, 90 days past due and still accruing
Commercial Portfolio Segment [Member] | Real Estate Loan [Member] | Financing Receivables 30 to 89 Days Past Due [Member]
Loans, past due	828,000	1,467,000
Commercial Portfolio Segment [Member] | Construction Loans [Member]
Loans, past due	82,000	83,000
Loans, 90 days past due and still accruing
Financing Receivable, Nonaccrual	82,000	83,000
Loans, current	19,592,000	31,098,000
Loans	19,674,000	31,181,000
Loans, 90 days past due and still accruing
Commercial Portfolio Segment [Member] | Construction Loans [Member] | Financing Receivables 30 to 89 Days Past Due [Member]
Loans, past due
Residential Portfolio Segment [Member] | Real Estate Loan [Member]
Loans, past due	378,000	277,000
Loans, 90 days past due and still accruing
Financing Receivable, Nonaccrual	267,000	277,000
Loans, current	13,442,000	14,253,000
Loans	13,820,000	14,530,000
Loans, 90 days past due and still accruing
Residential Portfolio Segment [Member] | Real Estate Loan [Member] | Financing Receivables 30 to 89 Days Past Due [Member]
Loans, past due	111,000
Residential Portfolio Segment [Member] | Equity Lines of Credit [Member]
Loans, past due	900,000	904,000
Loans, 90 days past due and still accruing
Financing Receivable, Nonaccrual	574,000	616,000
Loans, current	34,362,000	34,567,000
Loans	35,262,000	35,471,000
Loans, 90 days past due and still accruing
Residential Portfolio Segment [Member] | Equity Lines of Credit [Member] | Financing Receivables 30 to 89 Days Past Due [Member]
Loans, past due	326,000	288,000
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Loans, past due	1,689,000	1,463,000
Loans, 90 days past due and still accruing
Financing Receivable, Nonaccrual	414,000	182,000
Loans, current	91,173,000	88,847,000
Loans	92,862,000	90,310,000
Loans, 90 days past due and still accruing
Consumer Portfolio Segment [Member] | Automobile Loan [Member] | Financing Receivables 30 to 89 Days Past Due [Member]
Loans, past due	1,275,000	1,281,000
Consumer Portfolio Segment [Member] | Other Loans [Member]
Loans, past due	75,000	91,000
Loans, 90 days past due and still accruing
Financing Receivable, Nonaccrual	35,000	4,000
Loans, current	4,466,000	4,472,000
Loans	4,541,000	4,563,000
Loans, 90 days past due and still accruing
Consumer Portfolio Segment [Member] | Other Loans [Member] | Financing Receivables 30 to 89 Days Past Due [Member]
Loans, past due	$ 40,000	$ 87,000