Comprehensive Income (Loss) - Changes in Each Component of Accumulated Other Comprehensive Loss (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended
Jul. 31, 2021	Jul. 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

Amount of tax (expense) benefit for reclassification adjustment from accumulated other comprehensive (income) loss of defined benefit plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=123454820&loc=SL4569616-111683

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=124509347&loc=d3e640-108580

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Balance Type:	debit
Period Type:	duration