Note 5 - Stock-based Compensation - Summary of Stock Options (Details)	3 Months Ended
	Mar. 31, 2020 USD ($) $ / shares shares
Shares outstanding (in shares) | shares	126,500
Shares outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 8.94
Shares outstanding, weighted average remaining contractual life (Year)	4 years 219 days
Shares outstanding, aggregate intrinsic value | $	$ 3,209,875
Shares vested and exercisable (in shares) | shares	94,500
Shares vested and exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 4.09
Shares vested and exercisable, weighted average remaining contractual life (Year)	2 years 328 days
Shares vested and exercisable, aggregate intrinsic value | $	$ 2,825,115