Note 11 - Subsequent Events (Details Textual) - USD ($)	1 Months Ended	2 Months Ended		12 Months Ended
	Feb. 28, 2021	Mar. 15, 2021	Mar. 12, 2021	Dec. 31, 2020	Dec. 31, 2019
Class of Warrant or Right, Exercised During Period (in shares)				19,106,504	17,415,859
Proceeds from Warrant Exercises				$ 8,046,103	$ 3,888,425
Proceeds from Issuance of Common Stock				$ 10,827,100
Subsequent Event [Member]
Class of Warrant or Right, Exercised During Period (in shares)		4,230,000
Proceeds from Warrant Exercises		$ 2,200,000	$ 2,000,000
Proceeds from Issuance of Common Stock	$ 1,000,000
Subsequent Event [Member] | Underwriter Warrants in Connection with the February 2021 Common Stock Offering [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)	1,682,927
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)	$ 1.28125
Warrants and Rights Outstanding, Term (Year)	5 years
Subsequent Event [Member] | Public Offering, Inclusive of Underwriter Shares [Member]
Stock Issued During Period, Shares, New Issues (in shares)	33,658,538
Shares Issued, Price Per Share (in dollars per share)	$ 1.025
Underwriter Option to Purchase Additional Shares, Term (Day)	30 days
Proceeds from Issuance of Common Stock	$ 31,200,000