Quarterly report pursuant to Section 13 or 15(d)

Components of Stock-Based Compensation Expense Recognized (Detail)

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Components of Stock-Based Compensation Expense Recognized (Detail) - USD ($)
$ in Thousands
 3 Months Ended
Jul. 31, 2015
Jul. 31, 2014
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]    
Total stock-based compensation expense, pre-tax $ 3,691 $ 3,319
Tax benefit from stock-based compensation expense (1,154) (982)
Total stock-based compensation expense, net of tax 2,537 2,337
Restricted Stock    
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]    
Total stock-based compensation expense, pre-tax 3,554 3,252
Stock Options    
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]    
Total stock-based compensation expense, pre-tax 17 $ 67
ESPP    
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]    
Total stock-based compensation expense, pre-tax $ 120