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Stockholders' Equity - Summary of Stock Options (Details)
12 Months Ended
Apr. 30, 2017
$ / shares
shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Stock option plans, exercise price range, lower limit $ 1.83
Stock option plans, exercise price range, upper limit $ 18.67
Number of outstanding options | shares 5,548
Weighted average exercise price of outstanding options $ 5.82
Weighted average remaining contractual term of outstanding options 6 years 5 months 3 days
Number of exercisable options | shares 3,310
Weighted average exercise price of exercisable options $ 6.46
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 1.83
Stock option plans, exercise price range, upper limit $ 3.03
Number of outstanding options | shares 260
Weighted average exercise price of outstanding options $ 2.46
Weighted average remaining contractual term of outstanding options 3 years
Number of exercisable options | shares 219
Weighted average exercise price of exercisable options $ 2.36
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 838
Weighted average exercise price of outstanding options $ 3.15
Weighted average remaining contractual term of outstanding options 5 years 10 months 2 days
Number of exercisable options | shares 415
Weighted average exercise price of exercisable options $ 3.15
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 $ 3.65
Number of outstanding options | shares 91
Weighted average exercise price of outstanding options $ 3.55
Weighted average remaining contractual term of outstanding options 5 years
Number of exercisable options | shares 23
Weighted average exercise price of exercisable options $ 3.42
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 3.94
Stock option plans, exercise price range, upper limit $ 3.94
Number of outstanding options | shares 300
Weighted average exercise price of outstanding options $ 3.94
Weighted average remaining contractual term of outstanding options 6 years 1 month 7 days
Number of exercisable options | shares 0
Weighted average exercise price of exercisable options $ 0.00
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 4.00
Stock option plans, exercise price range, upper limit $ 4.36
Number of outstanding options | shares 675
Weighted average exercise price of outstanding options $ 4.27
Weighted average remaining contractual term of outstanding options 7 years 4 months 25 days
Number of exercisable options | shares 175
Weighted average exercise price of exercisable options $ 4.31
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 4.70
Stock option plans, exercise price range, upper limit $ 6.28
Number of outstanding options | shares 547
Weighted average exercise price of outstanding options $ 5.26
Weighted average remaining contractual term of outstanding options 6 years 1 month 7 days
Number of exercisable options | shares 378
Weighted average exercise price of exercisable options $ 5.18
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 6.42
Stock option plans, exercise price range, upper limit $ 6.42
Number of outstanding options | shares 1,036
Weighted average exercise price of outstanding options $ 6.42
Weighted average remaining contractual term of outstanding options 8 years 1 month 18 days
Number of exercisable options | shares 475
Weighted average exercise price of exercisable options $ 6.42
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 6.54
Stock option plans, exercise price range, upper limit $ 7.39
Number of outstanding options | shares 662
Weighted average exercise price of outstanding options $ 6.90
Weighted average remaining contractual term of outstanding options 5 years 7 months 4 days
Number of exercisable options | shares 621
Weighted average exercise price of exercisable options $ 6.88
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 7.53
Stock option plans, exercise price range, upper limit $ 9.51
Number of outstanding options | shares 1,016
Weighted average exercise price of outstanding options $ 8.71
Weighted average remaining contractual term of outstanding options 6 years 5 months 12 days
Number of exercisable options | shares 883
Weighted average exercise price of exercisable options $ 8.84
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 9.52
Stock option plans, exercise price range, upper limit $ 18.67
Number of outstanding options | shares 123
Weighted average exercise price of outstanding options $ 13.59
Weighted average remaining contractual term of outstanding options 5 years 1 month
Number of exercisable options | shares 121
Weighted average exercise price of exercisable options $ 13.63