Retirement Benefits - Additional Information (Detail) - USD ($)	12 Months Ended
Apr. 30, 2021	Apr. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Defined pension benefit plan, net periodic benefit cost	$ 560,000
Anticipated contribution in the next fiscal year related to pension plans	0
Employer contributions	$ 30,000	$ 0
Increase decrease in the discount rate	1.00%	1.00%
Decrease increase pension expense	$ 165,000	$ 183,000
Age limit of employees to be eligible for contribution (in years)	21 years
Minimum service period of employees to be eligible for contribution (in months)	3 months
Employee's compensation (as a percent)	3.00%
Employer matching contributions	$ 997,000	$ 974,000
Maximum
Defined Benefit Plan Disclosure [Line Items]
Matching contributions by company (as a percent)	100.00%
Contributions by employer per employee's compensation (as a percent)	3.00%
Employee's compensation (as a percent)	4.00%
Minimum
Defined Benefit Plan Disclosure [Line Items]
Matching contributions by company (as a percent)	50.00%
Contributions by employer per employee's compensation (as a percent)	5.00%
Equity Securities \| Maximum
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, Plan asset percentage	75.00%	75.00%
Fixed Income \| Maximum
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, Plan asset percentage	25.00%	25.00%
Yield Curve Technique
Defined Benefit Plan Disclosure [Line Items]
Increase decrease in the discount rate	1.00%	1.00%
Decrease increase pension expense	$ 286,000	$ 236,000
Yield Curve Technique \| Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Par amount outstanding	$ 250,000,000

Defined benefit plan percentage changes in discount rate.

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Amount of contribution received by defined benefit plan from employer which increases plan assets.

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Amount of cost (credit) included in accumulated other comprehensive (income) loss expected to be recognized in net periodic benefit cost (credit) for fiscal year following most recent annual statement of financial position.

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Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

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Amount of increase (decrease) in obligation for pension and other postretirement benefits. Includes, but is not limited to, defined benefit and defined contribution plans.

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