Note 12 - Income Taxes (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Income Tax Expense (Benefit), Total	$ 0
Unrecognized Tax Benefits, Ending Balance	0
Domestic Tax Authority [Member]
Operating Loss Carryforwards, Total	400,300
Domestic Tax Authority [Member] | Research Tax Credit Carryforward [Member]
Operating Loss Carryforwards, Total	3,500
State and Local Jurisdiction [Member]
Operating Loss Carryforwards, Total	$ 375,700