Note 9 - Stockholders' Equity - Warrants (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 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)	$ 1.49	$ 0.50	$ 0.50
Outstanding, weighted average remaining life (Year)	2 years 94 days	3 years 310 days	2 years 175 days	4 years 36 days
Outstanding, intrinsic value	$ 6,381,930	$ 460,085	$ 2,784,117	$ 956,012
Issued, number of shares (in shares)
Issued, weighted average exercise price (in dollars per share)
Issued, weighted average remaining life (Year)
Issued, intrinsic value
Exercised, number of shares (in shares)	(1,918,925)	(460,725)
Exercised, weighted average exercise price (in dollars per share)	$ 1.57	$ 0.50
Expired or cancelled (in shares)
Expired or cancelled, weighted average exercise price (in dollars per share)
Outstanding , number of shares (in shares)	4,450,471	613,446	6,369,396	1,074,171
Outstanding , weighted average exercise price (in dollars per share)	$ 2.14	$ 0.50	$ 1.49	$ 0.50