Note 5 - Allowance for Loan Losses (Details Textual)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Loan Balance For Reviewing High Risk Loans Minimum	$ 250,000
Impaired Financing Receivable, Number of Loans Below Review Threshold	134		144
Impaired Financing Receivable Recorded Investment Below Review Threshold	$ 3,900,000		$ 3,500,000
Loans and Leases Receivable, Gross, Total	779,991,000	$ 782,027,000	768,497,000
Loans and Leases Receivable, Allowance, Ending Balance	6,589,000	7,277,000	7,467,000	$ 7,508,000
Substandard [Member]
Loans and Leases Receivable, Gross, Total	22,622,000	$ 22,788,000
Loans Not Classified as Impaired [Member] | Substandard [Member]
Loans and Leases Receivable, Gross, Total	10,280,000		12,700,000
Loans and Leases Receivable, Allowance, Ending Balance	$ 1,860,000		$ 1,220,000