Annual report pursuant to Section 13 and 15(d)

Goodwill And Intangible Assets - Additional Information (Detail)

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Goodwill And Intangible Assets - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Apr. 30, 2013
Apr. 30, 2012
Apr. 30, 2011
Schedule Of Goodwill And Intangible Assets [Line Items]      
Amortization expense $ 5.0 $ 2.2 $ 2.4