Note 3 - Loans and Allowance for Loan Losses (Details Textual)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Loans Charge-off Period			90 days
Performance Period			180 days
Financing Receivable, Allowance for Credit Losses, Write-downs	$ 195,000	$ 206,000	$ 617,000	$ 694,000
Collateral Dependent Loans, Value of Significant Properties	200,000		200,000
Mortgage Loans in Process of Foreclosure, Amount	634,000		634,000		$ 588,000
Impaired Financing Receivable, Interest Income, Cash Basis Method, Total	0	0	0	0
Loans and Leases Receivable, Impaired, Commitment to Lend	0		0		0
Troubled Debt Restructuring, Principal Charge-offs	0	0	0	0
Troubled Debt Restructuring, Specific Allowance	0	0	$ 0	0
Financing Receivable, Modifications, Subsequent Default, Number of Contracts			0
Financial Receivable, Trouble Debt Restructure, Defaulted, Provisions Loan Losses or Net Charge-offs			$ 0
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Outstanding Balance, Total	530,000		530,000		625,000
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Allowance for Loan Losses	0		0		2,000
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Allowance for Loan Losses, Decreases	$ 0	$ 4,000	2,000	$ 4,000
Classified Loans [Member]
Allowance for Loan and Lease Losses, Period Increase (Decrease), Total			479,000		506,000
Overall Qualitative Factor [Member]
Allowance for Loan and Lease Losses, Period Increase (Decrease), Total			$ 2,400,000		$ 2,600,000
Bank Overdrafts [Member]
Loans Charge-off Period			45 days
Other than Consumer Portfolio Segment [Member]
Number of Loans	5		5
Financing Receivable, Allowance for Credit Losses, Write-downs			$ 97,000