Note 10 - Shareholders' Equity - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Options outstanding (in shares)	568,740	1,326,414
Options outstanding (in dollars per share)	$ 3.42	$ 2.86
Exercised (in shares)	(134,494)	(757,674)
Exercised (in dollars per share)	$ 3.17	$ 2.64
Canceled/expired/forfeited (in shares)	(6,666)	0
Canceled/expired/forfeited (in dollars per share)	$ 3.62	$ 0
Options outstanding (in shares)	427,580	568,740
Options outstanding (in dollars per share)	$ 3.50	$ 3.42
Options exercisable (in shares)	315,583
Options exercisable (in dollars per share)	$ 3.47
Employees and Directors [Member]
Granted to employees and directors (in shares)	0	0
Granted to employees and directors (in dollars per share)	$ 0	$ 0