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		3 Months Ended			12 Months Ended
		Mar. 31, 2020		Mar. 31, 2019	Dec. 31, 2019
Loans past due 90 days or more and still accruing		$ 170	[1]	$ 55	$ 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		0.02%		0.01%	0.03%
Accruing restructured loans		$ 1,592		$ 1,995	$ 1,729
Impaired loans:
Impaired loans with no valuation allowance		4,557	[2]	5,212	4,174	[2]
Impaired loans with a valuation allowance		1,114	[2]	1,125	1,115	[2]
Total impaired loans		5,671	[2]	6,337	5,289	[2]
Valuation allowance		(110)		(132)	(110)
Impaired loans, net of allowance		5,561		6,205	5,179
Average recorded investment in impaired loans(1)	[3],[4],[5]	5,677		6,597	5,359
Interest income recognized on impaired loans, after designation as impaired		26		49	171
Amount of income recognized on a cash basis		$ 0		$ 0

[1] Only classes with past due or nonaccrual loans are presented

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

[3] Only classes with past due or nonaccrual loans are presented

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

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