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Advertising Costs - Additional Information (Detail) (Selling and Marketing Expense, USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Oct. 31, 2013
Oct. 31, 2012
Oct. 31, 2013
Oct. 31, 2012
Selling and Marketing Expense
       
Advertising Costs [Line Items]        
Advertising expense for continuing operations $ 4.1 $ 4.0 $ 8.4 $ 7.1