Note 6 - Stock-based Compensation - Stock Option Activity (Details) - USD ($)	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Outstanding, shares (in shares)	1,515,000	1,395,000	1,220,000	1,349,000	1,395,000	1,349,000
Outstanding, weighted average exercise price (in dollars per share)	$ 0.53	$ 0.31	$ 0.24	$ 0.23	$ 0.31	$ 0.23
Options granted, shares (in shares)	127,500	145,000	10,000	0	272,500	10,000
Options granted, weighted average exercise price (in dollars per share)	$ 2.85	$ 2.62	$ 0.15
Options exercised, shares (in shares)	(360,000)	(25,000)	0		(385,000)	0
Options exercised, weighted average exercise price (in dollars per share)	$ 0.22	$ 0.14
Options expired, shares (in shares)	(20,000)		(10,000)	(129,000)
Options expired, weighted average exercise price (in dollars per share)	$ 0.17		$ 0.19	$ 0.17
Outstanding, weighted average remaining contractual term (Month)	6 years		3 years 9 months
Outstanding, aggregate intrinsic value	$ 2,876,868		$ 37,353		$ 2,876,868	$ 37,353
Exercisable, shares (in shares)	780,000		1,207,000		780,000	1,207,000
Exercisable, weighted average exercise price (in dollars per share)	$ 0.33		$ 0.24		$ 0.33	$ 0.24
Exercisable, weighted average remaining contractual term (Month)	3 years 2 months		3 years 8 months
Exercisable, aggregate intrinsic value	$ 2,194,843		$ 36,703		$ 2,194,843	$ 36,703
Outstanding, weighted average exercise price (in dollars per share)	$ 0.86	$ 0.53	$ 0.24	$ 0.24	$ 0.86	$ 0.24
Outstanding, shares (in shares)	1,262,500	1,515,000	1,220,000	1,220,000	1,262,500	1,220,000
Outstanding, weighted average exercise price (in dollars per share)	$ 0.86	$ 0.53	$ 0.24	$ 0.24	$ 0.86	$ 0.24