Annual report pursuant to Section 13 and 15(d)

Employee Stock Plans - Additional Information (Detail)

v2.4.0.6
Employee Stock Plans - Additional Information (Detail) (USD $)
12 Months Ended
Apr. 30, 2013
Apr. 30, 2012
Apr. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected volatility   47.07% 47.67%
Risk-free interest rate   1.47% 1.83%
Expected option life (in years)   5 years 5 years
Expected dividend yield   0.00% 0.00%
Aggregate intrinsic value of options outstanding $ 3,300,000    
Aggregate intrinsic value of options exercisable 2,400,000    
Common stock repurchased, value 2,838,000 4,215,000 13,844,000
Cash proceeds from exercise of stock options 2,100,000 2,900,000  
Proceeds from exercise of warrants     2,983,000
Common Stock
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares repurchased during the period 197,000 190,000 934,000
Common stock repurchased, value 2,838,000 4,215,000 13,844,000
Stock issued for stock options exercised 237,856 228,835  
Open Market Repurchase | Common Stock
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares repurchased during the period     724,064
Common stock repurchased, value     10,600,000
Employee Stock Purchase Plan
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Authorized payroll deductions 15.00%    
Authorized payroll deductions, value 25,000    
Fair market price of common stock 85.00%    
Employees stock purchased   76,909 153,913
Employees stock purchased, per share value   $ 18.69 $ 14.13
Shares reserved for issuance 1,500,000    
Amended shares reserved for issuance 3,000,000    
Shares available for future issuance 1,600,000    
Stock Incentive Plan 2008
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock incentive plan, maximum number of shares issuable 5,700,000    
Issuance of full-value stock awards limitation, required ratio to stock option and stock appreciation rights 1.91    
Time Based Restricted Stock | Minimum
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 3 years    
Time Based Restricted Stock | Maximum
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 4 years    
Market Based Restricted Stock
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 3 years    
Stock Options
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total unrecognized compensation cost related to non-vested awards 700,000    
Expected cost recognized over weighted-average period 9 months 18 days    
Stock issued for stock options exercised 238,000 235,000 625,000
Stock Options | Minimum
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 3 years    
Expiration period 7 years    
Stock Options | Maximum
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 4 years    
Expiration period 10 years    
Restricted Stock
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total unrecognized compensation cost related to non-vested awards 17,700,000    
Expected cost recognized over weighted-average period 2 years 4 months 24 days    
Shares repurchased during the period 197,456 190,141  
Common stock repurchased, value 2,800,000 4,200,000  
Warrant
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Warrant date issued   Jun. 30, 2002  
Warrants issued   274,207  
Common stock at an exercise price   11.94  
Common stock issued in exchange for warrants     274,207
Proceeds from exercise of warrants     $ 3,000,000