Note 6 - Stock-based Compensation - Summary of Stock Options (Details)	3 Months Ended
	Mar. 31, 2021 USD ($) $ / shares shares
Shares outstanding (in shares) | shares	59,000
Shares outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 17.35
Shares outstanding, weighted average remaining contractual life (Year)	7 years 146 days
Shares outstanding, aggregate intrinsic value | $	$ 1,389,970
Shares vested and exercisable (in shares) | shares	45,000
Shares vested and exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 14.83
Shares vested and exercisable, weighted average remaining contractual life (Year)	7 years 73 days
Shares vested and exercisable, aggregate intrinsic value | $	$ 1,173,570