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		6 Months Ended			12 Months Ended
		Jun. 30, 2019		Jun. 30, 2018	Dec. 31, 2018
Loans past due 90 days or more and still accruing		$ 50	[1]	$ 61	$ 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		0.01%		0.01%	0.00%
Accruing restructured loans		$ 1,954		$ 8,337	$ 2,552
Impaired loans with no valuation allowance		5,167	[2]	10,607	5,667	[2]
Impaired loans with a valuation allowance		1,484	[2]	1,435	1,153	[2]
Total impaired loans		6,651	[2]	12,042	6,820	[2]
Valuation allowance		(129)		(162)	(139)
Impaired loans, net of allowance		6,522		11,880	6,681
Average recorded investment in impaired loans(1)	[3],[4]	6,703		12,326	9,788	[5]
Interest income recognized on impaired loans, after designation as impaired		52		239	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.