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, unless otherwise specified
12 Months Ended
Apr. 30, 2013
Apr. 30, 2012
Apr. 30, 2011
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]      
Total stock-based compensation expense, pre-tax $ 11,906 $ 13,399 $ 15,547
Tax benefit from stock-based compensation expense (4,142) (4,701) (5,675)
Total stock-based compensation expense, net of tax 7,764 8,698 9,872
Restricted Stock
     
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]      
Total stock-based compensation expense, pre-tax 11,001 12,381 14,090
Stock Options
     
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]      
Total stock-based compensation expense, pre-tax 905 933 1,028
Employee Stock Purchase Plan
     
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]      
Total stock-based compensation expense, pre-tax   $ 85 $ 429