Note 4 - Loans and the Allowance for Loan Losses - Aging Analysis of the Loan Portfolio (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Loans, past due	$ 3,807,000	$ 5,705,000
Loans, 90 days past due and still accruing	0	0
Financing Receivable, Nonaccrual	2,445,000	2,050,000
Loans, current	744,078,000	614,013,000
Loans	747,885,000	619,718,000
Loans, 90 days past due and still accruing	0	0
Financing Receivables 30 to 89 Days Past Due [Member]
Loans, past due	1,362,000	3,655,000
Commercial Portfolio Segment [Member] | Commercial Loans [Member]
Loans, past due	152,000	391,000
Loans, 90 days past due and still accruing	0	0
Financing Receivable, Nonaccrual	3,000	58,000
Loans, current	167,618,000	47,501,000
Loans	167,770,000	47,892,000
Loans, 90 days past due and still accruing	0	0
Commercial Portfolio Segment [Member] | Commercial Loans [Member] | Financing Receivables 30 to 89 Days Past Due [Member]
Loans, past due	149,000	333,000
Commercial Portfolio Segment [Member] | Agricultural Loans [Member]
Loans, past due	250,000	199,000
Loans, 90 days past due and still accruing	0	0
Financing Receivable, Nonaccrual	0	0
Loans, current	73,959,000	78,586,000
Loans	74,209,000	78,785,000
Loans, 90 days past due and still accruing	0	0
Commercial Portfolio Segment [Member] | Agricultural Loans [Member] | Financing Receivables 30 to 89 Days Past Due [Member]
Loans, past due	250,000	199,000
Commercial Portfolio Segment [Member] | Real Estate Loan [Member]
Loans, past due	908,000	2,297,000
Loans, 90 days past due and still accruing	0	0
Financing Receivable, Nonaccrual	866,000	830,000
Loans, current	332,860,000	314,689,000
Loans	333,768,000	316,986,000
Loans, 90 days past due and still accruing	0	0
Commercial Portfolio Segment [Member] | Real Estate Loan [Member] | Financing Receivables 30 to 89 Days Past Due [Member]
Loans, past due	42,000	1,467,000
Commercial Portfolio Segment [Member] | Construction Loans [Member]
Loans, past due	78,000	83,000
Loans, 90 days past due and still accruing	0	0
Financing Receivable, Nonaccrual	78,000	83,000
Loans, current	27,808,000	31,098,000
Loans	27,886,000	31,181,000
Loans, 90 days past due and still accruing	0	0
Commercial Portfolio Segment [Member] | Construction Loans [Member] | Financing Receivables 30 to 89 Days Past Due [Member]
Loans, past due	0	0
Residential Portfolio Segment [Member] | Real Estate Loan [Member]
Loans, past due	274,000	277,000
Loans, 90 days past due and still accruing	0	0
Financing Receivable, Nonaccrual	204,000	277,000
Loans, current	12,574,000	14,253,000
Loans	12,848,000	14,530,000
Loans, 90 days past due and still accruing	0	0
Residential Portfolio Segment [Member] | Real Estate Loan [Member] | Financing Receivables 30 to 89 Days Past Due [Member]
Loans, past due	70,000	0
Residential Portfolio Segment [Member] | Equity Lines of Credit [Member]
Loans, past due	598,000	904,000
Loans, 90 days past due and still accruing	0	0
Financing Receivable, Nonaccrual	516,000	616,000
Loans, current	34,296,000	34,567,000
Loans	34,894,000	35,471,000
Loans, 90 days past due and still accruing	0	0
Residential Portfolio Segment [Member] | Equity Lines of Credit [Member] | Financing Receivables 30 to 89 Days Past Due [Member]
Loans, past due	82,000	288,000
Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Loans, past due	1,426,000	1,463,000
Loans, 90 days past due and still accruing	0	0
Financing Receivable, Nonaccrual	741,000	182,000
Loans, current	90,822,000	88,847,000
Loans	92,248,000	90,310,000
Loans, 90 days past due and still accruing	0	0
Consumer Portfolio Segment [Member] | Automobile Loan [Member] | Financing Receivables 30 to 89 Days Past Due [Member]
Loans, past due	685,000	1,281,000
Consumer Portfolio Segment [Member] | Other Loans [Member]
Loans, past due	121,000	91,000
Loans, 90 days past due and still accruing	0	0
Financing Receivable, Nonaccrual	37,000	4,000
Loans, current	4,141,000	4,472,000
Loans	4,262,000	4,563,000
Loans, 90 days past due and still accruing	0	0
Consumer Portfolio Segment [Member] | Other Loans [Member] | Financing Receivables 30 to 89 Days Past Due [Member]
Loans, past due	$ 84,000	$ 87,000