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Comprehensive Income (Loss) - Changes in Each Component of Accumulated Other Comprehensive Loss (Parenthetical) (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Oct. 31, 2021
Oct. 31, 2020
Oct. 31, 2021
Oct. 31, 2020
Deferred Compensation and Pension Plan        
Accumulated Other Comprehensive Income Loss [Line Items]        
Tax effect on reclassification of realized net losses $ 0.1 $ 0.2 $ 0.2 $ 0.5