Note 10 - Shareholders' Equity - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Options outstanding (in shares)	884,998	1,065,000
Options outstanding (in dollars per share)	$ 2.26	$ 2.06
Granted (in shares)	349,750	85,000
Exercised (in shares)	(211,835)	(111,669)
Exercised (in dollars per share)	$ 1.86	$ 1.88
Canceled/expired/forfeited (in shares)		(153,333)
Canceled/expired/forfeited (in dollars per share)		$ 1.58
Options outstanding (in shares)	1,022,913	884,998
Options outstanding (in dollars per share)	$ 2.69	$ 2.26
Options exercisable (in shares)	406,835
Options exercisable (in dollars per share)	$ 2.30
Non-Employee Directors [Member]
Granted (in shares)		85,000
Granted (in dollars per share)		$ 3.83
Employees and Directors [Member]
Granted (in shares)	349,750
Granted (in dollars per share)	$ 3.27