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Stockholders' Equity - Additional Information (Detail)
12 Months Ended
Apr. 30, 2018
USD ($)
OptionPlan
shares
Apr. 30, 2017
USD ($)
shares
Apr. 30, 2016
USD ($)
shares
Jun. 30, 2015
USD ($)
Sep. 23, 2013
shares
Sep. 26, 2011
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock repurchase authorization | $       $ 50,000,000    
Repurchase of common stock 0 2,600,000        
Number of stock incentive plans | OptionPlan 2          
Intrinsic value of stock outstanding | $ $ 1,400,000 $ 5,200,000 $ 6,100,000      
Intrinsic value of stock exercisable | $ 1,400,000 5,200,000 6,100,000      
Intrinsic value of stock exercised | $ 116,000 1,300,000 27,200,000      
Unrecognized compensation cost of outstanding options | $ $ 0          
Performance period 3 years          
Percentage of maximum aggregate award granted 200.00%          
Percentage of stock outperform in order for target award to vest 5.00%          
Stock-based compensation expense | $ $ 7,815,000 8,590,000 6,472,000      
Grant date fair value of vested RSUs and PSUs | $ $ 5,000,000 $ 5,000,000 $ 4,600,000      
2011 Employee Stock Purchase Plan            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Option exercise price per share as a percentage of fair market value 85.00%          
Number of shares an employee may purchase under the stock purchase plan 12,500          
Fair market value of shares an employee may purchase under the stock purchase plan | $ $ 25,000          
Shares issued under employee stock purchase plan 203,002 144,102 157,674      
PSUs            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Performance period 3 years          
Stock units, awarded 105,000 118,500 104,000      
Share based payment award percentage of award achieved 115.20% 200.00% 173.30%      
Stock units, forfeited 39,429   19,250      
RSUs            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock units, awarded 388,186 394,909 321,692      
Stock units, forfeited 208,496 19,448 66,185      
RSUs and PSUs            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock units, awarded 561,890 666,509 541,077      
Stock units, vested 300,496 433,966 430,768      
Stock units, forfeited 247,925 19,448 85,435      
Grant date fair value of vested RSUs and PSUs | $ $ 6,200,000 $ 11,700,000 $ 7,800,000      
Unrecognized compensation cost related to unvested RSUs and PSUs | $ $ 9,600,000          
Weighted average remaining contractual term 1 year 9 months 18 days          
Executive Officer | PSUs            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock units, awarded 157,700 153,100 137,775      
Stock units, vested 121,504 237,000 180,231      
Executive Officer | RSUs            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock units, awarded 159,167 168,800 117,100      
Director | RSUs            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock units, awarded 52,826 24,896 36,379      
Non-Executive Employees | PSUs | Without Market Conditions            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock units, awarded     5,379      
Non-Executive Employees | RSUs            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock units, awarded 176,193 201,213 168,213      
Employees And Consultants | RSUs and PSUs            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock-based compensation expense | $ $ 7,100,000 $ 7,800,000 $ 5,900,000      
Employees | RSUs and PSUs            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock units, vested 300,496 433,966 430,768      
2013 Incentive Stock Plan            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Authorized of common stock         3,000,000  
Stock option, exercisable period 10 years          
Shares available for grant under incentive stock option 4,746,149          
Maximum            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock repurchase authorization | $   $ 50,000,000        
Payroll deduction of participant's compensation 20.00%          
Maximum | 2011 Employee Stock Purchase Plan            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Common stock reserved under employee stock purchase plan           6,000,000
Maximum | 2013 Incentive Stock Plan            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Period to award vested and calculate volatility rate 4 years          
Minimum            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Payroll deduction of participant's compensation 1.00%          
Minimum | 2013 Incentive Stock Plan            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Period to award vested and calculate volatility rate 3 years