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, 2019		Sep. 30, 2018	Dec. 31, 2018
Loans past due 90 days or more and still accruing		$ 212	[1]	$ 63	$ 35	[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%		0.01%	0.00%
Accruing restructured loans		$ 1,880		$ 7,843	$ 2,552
Impaired loans:
Impaired loans with no valuation allowance		5,163	[2]	10,530	5,667	[2]
Impaired loans with a valuation allowance		1,070	[2]	1,404	1,153	[2]
Total impaired loans		6,233	[2]	11,934	6,820	[2]
Valuation allowance		(120)		(156)	(139)
Impaired loans, net of allowance		6,113		11,778	6,681
Average recorded investment in impaired loans(1)	[3],[4]	6,729		12,684	9,788	[5]
Interest income recognized on impaired loans, after designation as impaired		144		414	250	[5]
Amount of income recognized on a cash basis		$ 0		$ 0

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

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

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

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

[5] Only classes with impaired loans are shown.