Note 13 - Income Taxes (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Expense (Benefit), Total	$ 0	$ 0
Deferred Tax Liabilities, Net, Total	0	0
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	2,700,000	3,300,000
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	991,000	895,000
Domestic Tax Authority [Member]
Operating Loss Carryforwards, Total		$ 62,400,000
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards, Total	106,100,000
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member] | Research Tax Credit Carryforward [Member]
Tax Credit Carryforward, Amount	3,100,000
State and Local Jurisdiction [Member] | Research Tax Credit Carryforward [Member]
Tax Credit Carryforward, Amount	$ 2,300,000