Quarterly report pursuant to Section 13 or 15(d)

Note 4 - Stockholders' Equity - Stock Options by Exercise Price Range (Details)

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Note 4 - Stockholders' Equity - Stock Options by Exercise Price Range (Details) - USD ($)
3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Number of options outstanding (in shares) 2,432,662  
Weighted- average exercise price (in dollars per share) $ 7.37  
Weighted- average remaining contractual life (Year) 6 years 146 days 5 years 36 days
Aggregate intrinsic value $ 19,040  
Range One [Member]    
Range of exercise prices, lower limit (in dollars per share)  
Range of exercise prices, upper limit (in dollars per share) $ 0.50  
Number of options outstanding (in shares) 800,000  
Weighted- average exercise price (in dollars per share) $ 0.43  
Weighted- average remaining contractual life (Year) 9 years 255 days  
Aggregate intrinsic value $ 19,040  
Range Two [Member]    
Range of exercise prices, lower limit (in dollars per share) $ 1  
Range of exercise prices, upper limit (in dollars per share) $ 3.50  
Number of options outstanding (in shares) 588,640  
Weighted- average exercise price (in dollars per share) $ 1.15  
Weighted- average remaining contractual life (Year) 7 years 36 days  
Aggregate intrinsic value  
Range Three [Member]    
Range of exercise prices, lower limit (in dollars per share) $ 3.51  
Range of exercise prices, upper limit (in dollars per share) $ 13  
Number of options outstanding (in shares) 532,236  
Weighted- average exercise price (in dollars per share) $ 9.76  
Weighted- average remaining contractual life (Year) 4 years 36 days  
Aggregate intrinsic value  
Range Four [Member]    
Range of exercise prices, lower limit (in dollars per share) $ 13.01  
Range of exercise prices, upper limit (in dollars per share) $ 26  
Number of options outstanding (in shares) 343,782  
Weighted- average exercise price (in dollars per share) $ 14.79  
Weighted- average remaining contractual life (Year) 2 years 292 days  
Aggregate intrinsic value  
Range Five [Member]    
Range of exercise prices, lower limit (in dollars per share) $ 26.01  
Range of exercise prices, upper limit (in dollars per share) $ 39  
Number of options outstanding (in shares) 65,504  
Weighted- average exercise price (in dollars per share) $ 30.85  
Weighted- average remaining contractual life (Year) 2 years 73 days  
Aggregate intrinsic value  
Range Six [Member]    
Range of exercise prices, lower limit (in dollars per share) $ 39.01  
Range of exercise prices, upper limit (in dollars per share) $ 56  
Number of options outstanding (in shares) 102,500  
Weighted- average exercise price (in dollars per share) $ 45.03  
Weighted- average remaining contractual life (Year) 4 years 109 days  
Aggregate intrinsic value