Note 9 - Stockholders' Equity - Warrants (Details) - USD ($)	9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Outstanding, number of shares (in shares)	6,369,396	1,074,171	1,074,171
Outstanding, weighted average exercise price (in dollars per share)	$ 1.97	$ 0.50	$ 0.50
Outstanding, weighted average remaining life (Year)	1 year 9 months 3 days	2 years 8 months 23 days	2 years 5 months 23 days	4 years 1 month 6 days
Outstanding, intrinsic value	$ 1,088,192	$ 880,449	$ 2,784,117	$ 956,012
Issued, number of shares (in shares)	0	6,459,000
Issued, weighted average exercise price (in dollars per share)		$ 2.01
Exercised, number of shares (in shares)	(2,004,926)	(1,133,975)
Exercised, weighted average exercise price (in dollars per share)	$ 1.57	$ 0.87
Expired or cancelled (in shares)	0	0
Expired or cancelled, weighted average exercise price (in dollars per share)	$ 0	$ 0
Issued, weighted average remaining life (Year)		3 years
Outstanding , number of shares (in shares)	4,364,470	6,399,196	6,369,396	1,074,171
Outstanding , weighted average exercise price (in dollars per share)	$ 2.15	$ 1.95	$ 1.97	$ 0.50