Note 5 - Stock-based Compensation - Summary of Stock Options (Details)	9 Months Ended
	Sep. 30, 2018 USD ($) $ / shares shares
Shares outstanding (in shares) | shares	227,500
Shares outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 2.47
Shares outstanding, weighted average remaining contractual life (Year)	4 years 328 days
Shares outstanding, aggregate intrinsic value | $	$ 1,843,765
Shares vested and exercisable (in shares) | shares	199,000
Shares vested and exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 2.03
Shares vested and exercisable, weighted average remaining contractual life (Year)	4 years 109 days
Shares vested and exercisable, aggregate intrinsic value | $	$ 1,700,110