Note 7 - Income Taxes - Change in Unrecognized Tax Benefits (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Balance of unrecognized tax benefits	$ 768,000	$ 592,000
Reductions due to lapse of applicable statute of limitations	(38,000)	(34,000)
Reductions due to tax positions of prior years		4,000
Additions based on tax positions related to the current year	345,000	206,000
Balance of unrecognized tax benefits	$ 1,075,000	$ 768,000