Note 4 - Income Taxes (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Unrecognized Tax Benefits, Ending Balance	$ 0	$ 0	$ 0
Income Tax Examination, Penalties and Interest Expense, Total	0	$ 0	$ 0
Domestic Tax Authority [Member]
Operating Loss Carryforwards	420,300
Operating Loss Carryforwards, Subject to Expiration	175,400
Operating Loss Carryforwards, Not Subject to Expiration	244,900
State and Local Jurisdiction [Member]
Operating Loss Carryforwards, Subject to Expiration	312,800
Operating Loss Carryforwards, Not Subject to Expiration	$ 20,700