Quarterly report pursuant to Section 13 or 15(d)

Note 5 - Stockholders' Equity - Stock Options by Exercise Price Range (Details)

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Note 5 - Stockholders' Equity - Stock Options by Exercise Price Range (Details) - USD ($)
6 Months Ended 12 Months Ended
Jun. 30, 2017
Dec. 31, 2016
Number of options outstanding (in shares) 1,710,009  
Weighted-average exercise price (in dollars per share) $ 22.14  
Weighted-average remaining contractual life (Year) 4 years 255 days 5 years 36 days
Aggregate intrinsic value $ 287,704  
Range One [Member]    
Minimum range of exercise prices (in dollars per share) $ 3.50  
Maximum range of exercise prices (in dollars per share) $ 13  
Number of options outstanding (in shares) 751,480  
Weighted-average exercise price (in dollars per share) $ 9.51  
Weighted-average remaining contractual life (Year) 6 years 292 days  
Aggregate intrinsic value $ 287,704  
Range Two [Member]    
Minimum range of exercise prices (in dollars per share) $ 13.01  
Maximum range of exercise prices (in dollars per share) $ 26  
Number of options outstanding (in shares) 379,774  
Weighted-average exercise price (in dollars per share) $ 15.30  
Weighted-average remaining contractual life (Year) 4 years 219 days  
Aggregate intrinsic value  
Range Three [Member]    
Minimum range of exercise prices (in dollars per share) $ 26.01  
Maximum range of exercise prices (in dollars per share) $ 39  
Number of options outstanding (in shares) 155,339  
Weighted-average exercise price (in dollars per share) $ 32.52  
Weighted-average remaining contractual life (Year) 2 years 73 days  
Aggregate intrinsic value  
Range Four [Member]    
Minimum range of exercise prices (in dollars per share) $ 39.01  
Maximum range of exercise prices (in dollars per share) $ 65  
Number of options outstanding (in shares) 423,416  
Weighted-average exercise price (in dollars per share) $ 46.86  
Weighted-average remaining contractual life (Year) 1 year 328 days  
Aggregate intrinsic value