Annual report pursuant to Section 13 and 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
 12 Months Ended
Apr. 30, 2017
Apr. 30, 2016
Apr. 30, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]      
Total stock-based compensation expense, pre-tax $ 18,958 $ 18,895 $ 13,899
Tax benefit from stock-based compensation expense (4,756) (7,347) (3,893)
Total stock-based compensation expense, net of tax 14,202 11,548 10,006
Restricted Stock      
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]      
Total stock-based compensation expense, pre-tax 18,045 18,288 13,602
Stock Options      
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]      
Total stock-based compensation expense, pre-tax   17 135
ESPP      
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]      
Total stock-based compensation expense, pre-tax $ 913 $ 590 $ 162