Note 5 - Stock-based Compensation - Summary of Stock Options (Details)	3 Months Ended
	Mar. 31, 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)	5 years 36 days
Shares outstanding, aggregate intrinsic value | $	$ 1,411,515
Shares vested and exercisable (in shares) | shares	186,500
Shares vested and exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 1.90
Shares vested and exercisable, weighted average remaining contractual life (Year)	4 years 109 days
Shares vested and exercisable, aggregate intrinsic value | $	$ 1,262,185