Note 4 - Allowance for Loan Losses and Impaired Loans (Details Textual)		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Loans and Leases Receivable, Allowance, Ending Balance		$ 5,550,000	$ 4,794,000	$ 5,550,000	$ 4,794,000	$ 4,900,000	$ 5,342,000	$ 4,654,000	$ 3,893,000
Provision for Loan and Lease Losses, Total		219,000	$ 291,000	576,000	$ 1,027,000
Loans and Leases Receivable, Gross, Total		686,117,000		686,117,000		664,095,000
Impaired Financing Receivable, Recorded Investment, Total	[1]	5,883,000		5,883,000		6,169,000
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	[1]	2,775,000		2,775,000		2,580,000
Financing Receivable, Troubled Debt Restructuring		3,400,000		3,400,000		3,900,000
Financing Receivable, Troubled Debt Restructuring, Collectively Evaluated for impairment		2,800,000		2,800,000		3,600,000
Financing Receivable, Troubled Debt Restructuring, Related Allowance		$ 152,000		$ 152,000		192,000
Financing Receivable, Modifications, Number of Contracts		0	1	1	5
Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts		0	0	0	0
Financing Receivable, Outstanding Loan Payments Approved for Deferment				$ 66,500,000
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Ending Balance		$ 0		0		0
Purchase Credit Impaired Loans				0		0
Maximum [Member]
Financing Receivable, Troubled Debt Restructuring							$ 250,000
Collateral Pledged [Member]
Impaired Financing Receivable, Recorded Investment, Total		3,100,000		3,100,000		3,200,000
Doubtful [Member]
Loans and Leases Receivable, Gross, Total		0		0
Unallocated Financing Receivables [Member]
Provision for Loan and Lease Losses, Total				0
SBA PPP Loans [Member]
Loans and Leases Receivable, Gross, Total		37,762,000		37,762,000		$ 51,118,000
SBA PPP Loans [Member] | SBA CARES Act Paycheck Protection Program [Member]
Loans and Leases Receivable, Allowance, Ending Balance		$ 0		$ 0

[1] Recorded investment is the loan balance, net of any charge-offs