Annual report pursuant to Section 13 and 15(d)

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

v3.20.2
Comprehensive Income - Changes in Each Component of Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail) - USD ($)
$ in Millions
12 Months Ended
Apr. 30, 2020
Apr. 30, 2019
Apr. 30, 2018
Deferred Compensation and Pension Plan      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Tax effect on unrealized (losses) gains $ (3.1) $ (2.3) $ 2.5
Tax effect on reclassification of realized net losses (gains) 0.8 0.4 0.8
Unrealized (Losses) Gains on Interest Rate Swap      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Tax effect on unrealized (losses) gains (0.2) (0.3) 0.8
Tax effect on reclassifications of realized net gains (losses) $ (0.1) $ 0.1 $ (0.3)