Note 3 - Stock-based Compensation - Stock Option Activity (Details) - $ / shares	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Options outstanding (in shares)	1,065,000
Options outstanding, weighted average exercise price (in dollars per share)	$ 2.06
Granted to employees and non-employee directors (in shares)	25,000	810,000
Granted to employees and non-employee directors, weighted average exercise price (in dollars per share)	$ 3.66
Exercised (in shares)	(70,001)
Exercised, weighted average exercise price (in dollars per share)	$ 1.78
Canceled/expired/forfeited (in shares)	(20,000)
Canceled/expired/forfeited, weighted average exercise price (in dollars per share)	$ 1.58
Options outstanding, Septermber 30, 2017 (in shares)	999,999
Options outstanding, Septermber 30, 2017 (in dollars per share)	$ 2.13
Options exercisable (in shares)	330,000
Options exercisable, weighted average exercise price (in dollars per share)	$ 1.96