Note 10 - Shareholders' Equity - Information About Stock Options (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) $ / shares shares
Range of Exercise Prices, Lower Limit (in dollars per share)	$ 1.58
Range of Exercise Prices, Upper Limit (in dollars per share)	$ 3.90
Options Outstanding, Options (in shares) | shares	568,710
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 3.37
Options Outstanding, Weighted Average Remaining Contract Life (Year)	2 years 306 days
Options Outstanding, Aggregate Intrinsic Value | $	$ 4,473,000
Options Exercisable, Options (in shares) | shares	200,500
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 3.48
Options Exercisable, Weighted Average Remaining Contract Life (Year)	2 years 229 days
Options Exercisable, Aggregate Intrinsic Value | $	$ 1,601,000