Retirement Benefits - Summary of Fair Value Assets in Defined Benefit Pension Plans (Detail) - USD ($) $ in Thousands	Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 21,459	$ 17,316	$ 19,035
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14,814	10,797
Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,314	5,377
Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	331	1,142
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	21,459	17,316
Level 1 | Large Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,726	5,831
Level 1 | Small/Mid Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,128	2,121
Level 1 | International
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,173	1,850
Level 1 | Emerging Markets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	862	483
Level 1 | Liquid Alternatives
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	925	512
Level 1 | Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,314	5,377
Level 1 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	331	1,142
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 | Large Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 | Small/Mid Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 | International
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 | Emerging Markets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 | Liquid Alternatives
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 | Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 | Large Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 | Small/Mid Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 | International
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 | Emerging Markets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 | Liquid Alternatives
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 | Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0