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Stockholders Equity - Summary of Stock Options (Details)
12 Months Ended
Apr. 30, 2016
$ / shares
shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Stock option plans, exercise price range, lower limit $ 0.16
Stock option plans, exercise price range, upper limit $ 18.67
Number of outstanding options | shares 6,688,200
Weighted average exercise price of outstanding options $ 6.64
Weighted average remaining contractual term of outstanding options 6 years 5 months 5 days
Number of exercisable options | shares 3,004,111
Weighted average exercise price of exercisable options $ 8.04
Range One [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Stock option plans, exercise price range, lower limit 0.16
Stock option plans, exercise price range, upper limit $ 3.03
Number of outstanding options | shares 392,937
Weighted average exercise price of outstanding options $ 2.35
Weighted average remaining contractual term of outstanding options 3 years 2 months 24 days
Number of exercisable options | shares 332,937
Weighted average exercise price of exercisable options $ 2.23
Range Two [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Stock option plans, exercise price range, lower limit 3.15
Stock option plans, exercise price range, upper limit $ 3.15
Number of outstanding options | shares 990,000
Weighted average exercise price of outstanding options $ 3.15
Weighted average remaining contractual term of outstanding options 6 years 10 months 3 days
Number of exercisable options | shares 0
Weighted average exercise price of exercisable options $ 0.00
Range Three [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Stock option plans, exercise price range, lower limit 3.42
Stock option plans, exercise price range, upper limit $ 4.86
Number of outstanding options | shares 734,387
Weighted average exercise price of outstanding options $ 4.36
Weighted average remaining contractual term of outstanding options 7 years 2 months 24 days
Number of exercisable options | shares 254,387
Weighted average exercise price of exercisable options $ 4.69
Range Four [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Stock option plans, exercise price range, lower limit 4.87
Stock option plans, exercise price range, upper limit $ 6.28
Number of outstanding options | shares 261,911
Weighted average exercise price of outstanding options $ 5.49
Weighted average remaining contractual term of outstanding options 8 years 5 months 27 days
Number of exercisable options | shares 112,327
Weighted average exercise price of exercisable options $ 5.44
Range Five [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Stock option plans, exercise price range, lower limit 6.42
Stock option plans, exercise price range, upper limit $ 6.42
Number of outstanding options | shares 1,196,400
Weighted average exercise price of outstanding options $ 6.42
Weighted average remaining contractual term of outstanding options 8 years 9 months 7 days
Number of exercisable options | shares 0
Weighted average exercise price of exercisable options $ 0.00
Range Six [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Stock option plans, exercise price range, lower limit 6.54
Stock option plans, exercise price range, upper limit $ 7.36
Number of outstanding options | shares 788,373
Weighted average exercise price of outstanding options $ 6.96
Weighted average remaining contractual term of outstanding options 7 years 4 months 3 days
Number of exercisable options | shares 523,263
Weighted average exercise price of exercisable options $ 6.89
Range Seven [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Stock option plans, exercise price range, lower limit 7.39
Stock option plans, exercise price range, upper limit $ 7.53
Number of outstanding options | shares 756,475
Weighted average exercise price of outstanding options $ 7.47
Weighted average remaining contractual term of outstanding options 4 years 3 months 7 days
Number of exercisable options | shares 489,204
Weighted average exercise price of exercisable options $ 7.46
Range Eight [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Stock option plans, exercise price range, lower limit 7.6
Stock option plans, exercise price range, upper limit $ 9.51
Number of outstanding options | shares 892,709
Weighted average exercise price of outstanding options $ 9.18
Weighted average remaining contractual term of outstanding options 6 years 9 months 11 days
Number of exercisable options | shares 635,401
Weighted average exercise price of exercisable options $ 9.21
Range Nine [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Stock option plans, exercise price range, lower limit 9.52
Stock option plans, exercise price range, upper limit $ 15.12
Number of outstanding options | shares 639,808
Weighted average exercise price of outstanding options $ 12.60
Weighted average remaining contractual term of outstanding options 2 years 7 months 10 days
Number of exercisable options | shares 621,392
Weighted average exercise price of exercisable options $ 12.61
Range Ten [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Stock option plans, exercise price range, lower limit 18.67
Stock option plans, exercise price range, upper limit $ 18.67
Number of outstanding options | shares 35,200
Weighted average exercise price of outstanding options $ 18.67
Weighted average remaining contractual term of outstanding options 5 years 11 months 5 days
Number of exercisable options | shares 35,200
Weighted average exercise price of exercisable options $ 18.67