Note 9 - Stockholders' Equity - Outstanding Warrants (Details)	Sep. 30, 2021 $ / shares shares
Outstanding Warrants to Purchase Shares (in shares)	22,276,844
The 2018 Warrants [Member]
Outstanding Warrants to Purchase Shares (in shares)	762,344
Exercise Price (in dollars per share) | $ / shares	$ 4.05
Expiration date	May 30, 2022
The 2020 Warrants [Member]
Outstanding Warrants to Purchase Shares (in shares)	6,489,500
Exercise Price (in dollars per share) | $ / shares	$ 1.00
The 2020 Warrants [Member] | Minimum [Member]
Expiration date	Dec. 11, 2024
The 2020 Warrants [Member] | Maximum [Member]
Expiration date	Jun. 21, 2025
January 2021 Warrants [Member]
Outstanding Warrants to Purchase Shares (in shares)	4,500,000
Exercise Price (in dollars per share) | $ / shares	$ 1.055
Expiration date	Jul. 08, 2025
March 2021 Warrants [Member]
Outstanding Warrants to Purchase Shares (in shares)	10,525,000
Exercise Price (in dollars per share) | $ / shares	$ 2.88
Expiration date	Sep. 22, 2025