Annual report pursuant to Section 13 and 15(d)

Summary of Marketable Securities (Parenthetical) (Detail)

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Summary of Marketable Securities (Parenthetical) (Detail) (USD $)
In Millions, unless otherwise specified
Apr. 30, 2013
Apr. 30, 2012
Schedule Of Marketable Securities [Line Items]    
Obligations for which assets are held in trust $ 99.2 $ 82.6
Cash equivalents 93.6 60.5
Restricted cash $ 2.9 $ 10.0