Quarterly report pursuant to Section 13 or 15(d)

Note 10 - Common Stock - Summary of Outstanding Warrants (Details)

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Note 10 - Common Stock - Summary of Outstanding Warrants (Details) - $ / shares
3 Months Ended
Mar. 31, 2020
Nov. 30, 2019
Nov. 26, 2019
Nov. 12, 2019
May 22, 2017
Shares Outstanding Under Warrants (in shares) 23,665,905        
Employee Performance Bonus Warrants, February 2015 Issuance [Member]          
Expiration Date Feb. 17, 2025        
Exercise Price (in dollars per share) $ 400        
Shares Outstanding Under Warrants (in shares) 754        
Contractor Warrants, March 2015 Issuance [Member]          
Expiration Date Mar. 26, 2025        
Exercise Price (in dollars per share) $ 272        
Shares Outstanding Under Warrants (in shares) 14        
Contractor Warrants, May 2015 Issuance [Member]          
Expiration Date May 12, 2025        
Exercise Price (in dollars per share) $ 424        
Shares Outstanding Under Warrants (in shares) 362        
May 2015 Issuance Second Contractor [Member]          
Expiration Date May 17, 2020        
Exercise Price (in dollars per share) $ 424        
Shares Outstanding Under Warrants (in shares) 215        
Performance Bonus Warrants, December 2015 Issuance [Member]          
Expiration Date Dec. 16, 2025        
Exercise Price (in dollars per share) $ 560        
Shares Outstanding Under Warrants (in shares) 267        
Distributor Warrants, April 2016 Issuance [Member]          
Expiration Date Apr. 01, 2026        
Exercise Price (in dollars per share) $ 608        
Shares Outstanding Under Warrants (in shares) 250        
Contractor Warrants, May 2016 Issuance [Member]          
Expiration Date May 11, 2021        
Exercise Price (in dollars per share) $ 774        
Shares Outstanding Under Warrants (in shares) 50        
June 2016 Issuance Related to 2016 Loan Agreement [Member]          
Expiration Date Jun. 20, 2026        
Exercise Price (in dollars per share) $ 498        
Shares Outstanding Under Warrants (in shares) 1,004        
May 2017 Issuance Related to 2017 Loan Agreement [Member]          
Expiration Date May 25, 2027        
Exercise Price (in dollars per share) $ 950       $ 950
Shares Outstanding Under Warrants (in shares) 2,220       2,220
Series A Warrants [Member]          
Expiration Date Nov. 26, 2020        
Exercise Price (in dollars per share) $ 1.55 $ 1.55      
Shares Outstanding Under Warrants (in shares) 6,393,113 7,419,353      
Series B Warrants [Member]          
Expiration Date Nov. 26, 2024        
Exercise Price (in dollars per share) $ 1.55 $ 1.55      
Shares Outstanding Under Warrants (in shares) 7,373,880 7,419,353      
Warrants Issued Upon Conversion of Term Loan with CRG [Member]          
Expiration Date Nov. 26, 2024        
Exercise Price (in dollars per share) $ 1.84        
Shares Outstanding Under Warrants (in shares) 9,893,776   9,893,776 9,893,776