Quarterly report pursuant to Section 13 or 15(d)

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

v3.3.1.900
Changes in Each Component of Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Oct. 31, 2015
Oct. 31, 2014
Oct. 31, 2015
Oct. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Tax effects on reclassifications of realized net losses $ 0.3 $ 0.3 $ 0.6 $ 0.6