Note 9 - Income Taxes (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Taxes Paid	$ 0	$ 0
Research Tax Credit Carryforward [Member]
Tax Credit Carryforward, Amount	1,100
Domestic Tax Authority [Member]
Operating Loss Carryforwards, Total	65,700
Operating Loss Carryforwards, Subject to Expiration	$ 62,600