Note 10 - Income Taxes (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards, Net, Indefinite Lived	$ 30,600
Tax Credit Carryforward, Amount	3,600	$ 3,100
Unrecognized Tax Benefits, Ending Balance	0	0
Domestic Tax Authority [Member]
Operating Loss Carryforwards, Total	41,700	25,700
State and Local Jurisdiction [Member]
Operating Loss Carryforwards, Total	37,200	21,500
Current Year Deferred Tax Assets Activity [Member]
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	$ 2,400	$ 5,400