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Note 8 - Stock-Based Compensation - Stock Options Under the Plans (Details) - $ / shares
3 Months Ended 12 Months Ended
Jul. 31, 2015
Apr. 30, 2015
Outstanding as of April 30, 2015 (in shares) 1,062,603 1,083,952
Outstanding April 30, 2013. (in dollars per share) $ 4 $ 4.32
Outstanding as of April 30, 2015 5 years 219 days 5 years 255 days
Forfeited (in shares) (72,737)  
Forfeited. (in dollars per share) $ 6.34  
Exercised (in shares)    
Exercised. (in dollars per share)    
Granted (in shares) 51,388  
Granted. (in dollars per share) $ 0.58  
Exercisable as of July 31, 2015 (in shares) 819,481  
Exercisable as of July 31, 2015 (in dollars per share) $ 4.86  
Exercisable as of July 31, 2015 4 years 255 days