Note 7 - Income Taxes - Change in Unrecognized Tax Benefits (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Balance of unrecognized tax benefits	$ 592,000	$ 554,000
Reductions due to lapse of applicable statute of limitations	(34,000)	(43,000)
Reductions due to settlement with taxing authorities		(300,000)
Additions based on tax positions related to the current year	206,000	381,000
Additions due to tax positions of prior years	4,000
Balance of unrecognized tax benefits	$ 768,000	$ 592,000