Quarterly report pursuant to Section 13 or 15(d)

Note 4 - Stockholders' Equity - Summary of Warrant Activity (Details)

v3.19.1
Note 4 - Stockholders' Equity - Summary of Warrant Activity (Details) - Stock Purchase Warrants [Member]
3 Months Ended
Mar. 31, 2019
$ / shares
shares
Number of warrants outstanding (in shares) | shares 7,203,494
Range One [Member]  
Lower exercise price range (in dollars per share) $ 0.30
Upper range of exercise prices (in dollars per share) $ 0.875
Number of warrants outstanding (in shares) | shares 6,662,709
Range One [Member] | Minimum [Member]  
Expiration dates May 31, 2021
Range One [Member] | Maximum [Member]  
Expiration dates Aug. 31, 2024
Range Two [Member]  
Lower exercise price range (in dollars per share) $ 1.11
Upper range of exercise prices (in dollars per share) $ 5.79
Number of warrants outstanding (in shares) | shares 34,617
Range Two [Member] | Minimum [Member]  
Expiration dates May 31, 2021
Range Two [Member] | Maximum [Member]  
Expiration dates May 31, 2023
Range Three [Member]  
Expiration dates Jan. 31, 2022
Lower exercise price range (in dollars per share) $ 12.80
Upper range of exercise prices (in dollars per share) $ 12.90
Number of warrants outstanding (in shares) | shares 39,296
Range Four [Member]  
Expiration dates Mar. 31, 2020
Lower exercise price range (in dollars per share) $ 16.20
Upper range of exercise prices (in dollars per share) $ 16.30
Number of warrants outstanding (in shares) | shares 174,544
Range Five [Member]  
Expiration dates Dec. 31, 2019
Lower exercise price range (in dollars per share) $ 22.10
Upper range of exercise prices (in dollars per share) $ 27.90
Number of warrants outstanding (in shares) | shares 44,233
Range Five [Member] | Maximum [Member]  
Expiration dates Jan. 31, 2021
Range Six [Member]  
Lower exercise price range (in dollars per share) $ 34.50
Upper range of exercise prices (in dollars per share) $ 39.20
Number of warrants outstanding (in shares) | shares 236,556
Range Six [Member] | Minimum [Member]  
Expiration dates Oct. 31, 2019
Range Six [Member] | Maximum [Member]  
Expiration dates Oct. 31, 2021
Range Seven [Member]  
Expiration dates Jul. 31, 2019
Lower exercise price range (in dollars per share) $ 52.31
Upper range of exercise prices (in dollars per share) $ 52.31
Number of warrants outstanding (in shares) | shares 11,539