Note 5 - Stock-based Compensation - Stock Option Activity (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Outstanding, shares (in shares)	1,395,000	1,349,000
Outstanding, weighted average exercise price (in dollars per share)	$ 0.31	$ 0.23
Options granted, shares (in shares)	145,000	0
Options granted, weighted average exercise price (in dollars per share)	$ 2.62
Options exercised, shares (in shares)	(25,000)	0
Options exercised, weighted average exercise price (in dollars per share)	$ 0.14
Options expired (in shares)		(129,000)
Options expired, weighted average exercise price (in dollars per share)		$ 0.17
Options forfeited, shares (in shares)
Options forfeited, weighted average exercise price (in dollars per share)
Outstanding, weighted average remaining contractual term (Month)	4 years 150 days	3 years 330 days
Outstanding, aggregate intrinsic value	$ 3,585,623
Exercisable, shares (in shares)	1,135,000	1,201,500
Exercisable, weighted average exercise price (in dollars per share)	$ 0.25	$ 0.24
Exercisable, weighted average remaining contractual term (Month)	3 years 30 days	3 years 300 days
Exercisable, aggregate intrinsic value	$ 3,013,473
Outstanding, shares (in shares)	1,515,000	1,220,000
Outstanding, weighted average exercise price (in dollars per share)	$ 0.53	$ 0.24