Note 10 - Shareholders' Equity - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Options outstanding (in shares)	1,065,000	225,000
Options outstanding (in dollars per share)	$ 2.06	$ 1.52
Granted (in shares)	85,000	855,000
Exercised (in shares)	(111,669)	(15,000)
Exercised (in dollars per share)	$ 1.88	$ 1.15
Canceled/expired/forfeited (in shares)	(153,333)
Canceled/expired/forfeited (in dollars per share)	$ 1.58
Options outstanding (in shares)	884,998	1,065,000
Options outstanding (in dollars per share)	$ 2.26	$ 2.06
Options exercisable (in shares)	333,334
Options exercisable (in dollars per share)	$ 1.98
Non-Employee Directors [Member]
Granted (in shares)	85,000	45,000
Granted (in dollars per share)	$ 3.83	$ 3.45
Employees [Member]
Granted (in shares)		810,000
Granted (in dollars per share)		$ 2.12