Note 6 - Income Taxes (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)
Unrecognized Tax Benefits, Ending Balance	$ 0
Income Tax Examination, Penalties and Interest Expense, Total	0
Domestic Tax Authority [Member]
Operating Loss Carryforwards, Total	239,800
Operating Loss Carryforwards, Subject to Expiration	175,000
Operating Loss Carryforwards, Not Subject to Expiration	64,400
State and Local Jurisdiction [Member]
Operating Loss Carryforwards, Subject to Expiration	189,800
Operating Loss Carryforwards, Not Subject to Expiration	$ 10,000