Quarterly report pursuant to Section 13 or 15(d)

Changes in Each Component of Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail)

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Changes in Each Component of Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail) - USD ($)
$ in Millions
3 Months Ended
Jul. 31, 2015
Jul. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]    
Tax effects on reclassifications of realized net losses $ 0.3 $ 0.3