Note 12 - Income Taxes (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Tax Expense (Benefit), Total	$ 0	$ 0
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	5,100	4,700
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued, Total	0	0
State and Local Jurisdiction [Member]
Income Tax Expense (Benefit), Total	0	0
Operating Loss Carryforwards	208,000
Domestic Tax Authority [Member]
Operating Loss Carryforwards	344,300
Operating Loss Carryforwards, Not Subject to Expiration	86,800
Domestic Tax Authority [Member] | Research Tax Credit Carryforward [Member]
Tax Credit Carryforward, Amount	$ 4,300	$ 4,200