Note 3 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans - Loans Past Due 90 Days or More and Impaired Loans (Details) - USD ($) $ in Thousands		9 Months Ended			12 Months Ended
		Sep. 30, 2020		Sep. 30, 2019	Dec. 31, 2019
Loans past due 90 days or more and still accruing		$ 236	[1]	$ 212	$ 231	[1]
Ratio of loans past due 90 days or more and still accruing to loans, net of unearned income and deferred fees and costs		0.03%		0.03%	0.03%
Accruing restructured loans		$ 1,426		$ 1,880	$ 1,729
Impaired loans:
Impaired loans with no valuation allowance		3,939	[2]	5,163	4,174	[2]
Impaired loans with a valuation allowance		1,056	[2]	1,070	1,115	[2]
Total impaired loans		4,995	[2]	6,233	5,289	[2]
Valuation allowance		(104)		(120)	(110)
Impaired loans, net of allowance		4,891		6,113	5,179
Average recorded investment in impaired loans(1)	[2]	5,227		6,729	5,359	[3]
Interest income recognized on impaired loans, after designation as impaired		$ 49		$ 144	$ 171

[1] Only classes with past-due or nonaccrual loans are shown.

[2] Only classes with impaired loans are shown.

[3] Recorded investment is net of charge-offs and interest paid while a loan is in nonaccrual status.