Note 10 - Shareholders' Equity - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Options outstanding (in shares)	1,022,913	884,998
Options outstanding (in dollars per share)	$ 2.69	$ 2.26
Granted to employees and directors (in shares)	370,000	349,750
Exercised (in shares)	(66,499)	(211,835)
Exercised (in dollars per share)	$ 1.96	$ 1.86
Canceled/expired/forfeited (in shares)
Canceled/expired/forfeited (in dollars per share)
Options outstanding (in shares)	1,326,414	1,022,913
Options outstanding (in dollars per share)	$ 2.97	$ 2.69
Options exercisable (in shares)	694,914
Options exercisable (in dollars per share)	$ 2.51
Employees and Directors [Member]
Granted to employees and directors (in shares)	370,000	349,750
Granted to employees and directors (in dollars per share)	$ 3.59	$ 3.27