Note 10 - Shareholders' Equity - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Options outstanding (in shares)	1,326,414	1,022,913
Options outstanding (in dollars per share)	$ 2.86	$ 2.69
Granted to employees and directors (in shares)	370,000
Exercised (in shares)	(757,674)	(66,499)
Exercised (in dollars per share)	$ 2.64	$ 1.96
Canceled/expired/forfeited (in shares)
Canceled/expired/forfeited (in dollars per share)
Options outstanding (in shares)	568,740	1,326,414
Options outstanding (in dollars per share)	$ 3.37	$ 2.86
Options exercisable (in shares)	200,500
Options exercisable (in dollars per share)	$ 3.48
Employees and Directors [Member]
Granted to employees and directors (in shares)		370,000
Granted to employees and directors (in dollars per share)		$ 3.59