Note 10 - Income Taxes (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	$ 8,100	$ 3,800
Operating Loss Carryforwards, Total	86,700	81,900
Operating Loss Carryforwards, Subject to Expiration	4,800
Deferred Tax Assets, Gross, Total	23,642	15,727
Unrecognized Tax Benefits, Ending Balance	209	$ 39	$ 39
Research Tax Credit Carryforward [Member]
Tax Credit Carryforward, Amount	$ 404