Note 7 - Income Taxes - Change in Unrecognized Tax Benefits (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Balance of unrecognized tax benefits	$ 662,000	$ 589,000
Reductions due to lapse of applicable statute of limitations		(148,000)
Additions based on tax positions of prior years		5,000
Additions based on tax positions related to the current year	188,000	216,000
Reductions due to tax positions of prior years	(7,000)
Balance of unrecognized tax benefits	$ 843,000	$ 662,000