Quarterly report pursuant to Section 13 or 15(d)

Note 9 - Common Stock - Summary of Outstanding Warrants (Details)

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Note 9 - Common Stock - Summary of Outstanding Warrants (Details) - $ / shares
3 Months Ended
Mar. 31, 2019
May 22, 2017
Shares Outstanding Under Warrants (in shares) 642,622  
September 2014 Issuance Through Private Offering [Member]    
Expiration Date Sep. 23, 2019  
Exercise Price (in dollars per share) $ 4.24  
Shares Outstanding Under Warrants (in shares) 86,831  
Vendors and Contractor Warrants, October 2014 Issuance [Member]    
Expiration Date Oct. 13, 2019  
Exercise Price (in dollars per share) $ 4.24  
Shares Outstanding Under Warrants (in shares) 29,000  
Vendors and Contractor Warrants, November 2014 Issuance [Member]    
Expiration Date Nov. 12, 2019  
Exercise Price (in dollars per share) $ 4.24  
Shares Outstanding Under Warrants (in shares) 12,500  
Employee Performance Bonus Warrants, February 2015 Issuance [Member]    
Expiration Date Feb. 17, 2025  
Exercise Price (in dollars per share) $ 4  
Shares Outstanding Under Warrants (in shares) 75,697  
Contractor Warrants, March 2015 Issuance [Member]    
Expiration Date Mar. 26, 2025  
Exercise Price (in dollars per share) $ 2.72  
Shares Outstanding Under Warrants (in shares) 1,454  
Contractor Warrants, May 2015 Issuance [Member]    
Expiration Date May 12, 2025  
Exercise Price (in dollars per share) $ 4.24  
Shares Outstanding Under Warrants (in shares) 36,229  
May 2015 Issuance Second Contractor [Member]    
Expiration Date May 17, 2020  
Exercise Price (in dollars per share) $ 4.24  
Shares Outstanding Under Warrants (in shares) 21,585  
Performance Bonus Warrants, December 2015 Issuance [Member]    
Expiration Date Dec. 16, 2025  
Exercise Price (in dollars per share) $ 5.60  
Shares Outstanding Under Warrants (in shares) 26,875  
Distributor Warrants, April 2016 Issuance [Member]    
Expiration Date Apr. 01, 2026  
Exercise Price (in dollars per share) $ 6.08  
Shares Outstanding Under Warrants (in shares) 25,000  
Contractor Warrants, May 2016 Issuance [Member]    
Expiration Date May 11, 2021  
Exercise Price (in dollars per share) $ 7.74  
Shares Outstanding Under Warrants (in shares) 5,000  
June 2016 Issuance Related to 2016 Loan Agreement [Member]    
Expiration Date Jun. 20, 2026  
Exercise Price (in dollars per share) $ 4.98  
Shares Outstanding Under Warrants (in shares) 100,402  
May 2017 Issuance Related to 2017 Loan Agreement [Member]    
Expiration Date May 25, 2027  
Exercise Price (in dollars per share) $ 9.50 $ 9.50
Shares Outstanding Under Warrants (in shares) 222,049 222,049