Note 5 - Income Taxes (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Unrecognized Tax Benefits, Ending Balance	$ 4,100,000	$ 4,100,000
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	4,000,000.0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense, Total	$ 10,000	$ 12,000
Domestic Tax Authority [Member]
Open Tax Year	2018 2019 2020 2021