Deferred Compensation and Retirement Plans - Additional Information (Detail)	12 Months Ended
	Apr. 30, 2021 USD ($) Person Jurisdiction	Apr. 30, 2020 USD ($) Person	Apr. 30, 2019 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Recognized investment income(expense)	$ 38,500,000	$ (1,800,000)	$ 8,100,000
Increase in market value of the underlying COLI investments	13,017,000	6,551,000	6,160,000
Net CSV	161,295,000	146,408,000
CSV of COLI Contracts
Defined Benefit Plan Disclosure [Line Items]
Outstanding policy loans	80,000,000.0	92,300,000
Total death benefits payable, net of loans	443,900,000	451,700,000
Increase in market value of the underlying COLI investments	13,000,000.0	6,600,000	6,200,000
Net CSV	$ 161,300,000	146,400,000
Equity Securities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation range	50.00%
Equity Securities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation range	70.00%
Debt Securities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation range	30.00%
Debt Securities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation range	50.00%
Long Term Performance Unit Plan
Defined Benefit Plan Disclosure [Line Items]
Value per unit award	$ 50,000
Annual Benefit Payments per vested unit after anniversary period	$ 25,000
Number of payments after the seventh anniversary of the grant date	5 years
Vesting percentage on each anniversary date	25.00%
Enhanced Wealth Accumulation Plan
Defined Benefit Plan Disclosure [Line Items]
Participant contribution period towards deferred compensation plans (in years)	8 years
Participant after tax contribution period towards deferred compensation plans (in years)	15 years
Additional deferred units to acquire (in years)	5 years
Medical and Life Insurance plan | Hay Group
Defined Benefit Plan Disclosure [Line Items]
Benefit plan, number of participants | Person	118
Total benefit obligation	$ 6,584,000	7,527,000	7,310,000
International Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Number of foreign jurisdictions | Jurisdiction	24
Total benefit obligation	$ 15,600,000	$ 14,900,000
Long-term benefit obligation accrued, number of participants | Person	2,557	2,991
Company's contributions	$ 12,700,000	$ 14,400,000
Executive Capital Accumulation Plan
Defined Benefit Plan Disclosure [Line Items]
Total benefit obligation	163,582,000	129,315,000	130,161,000
Company's contributions	$ 8,200,000	9,000,000.0	8,500,000
Deferred compensation arrangement vesting period	5 years
Gain (loss) on deferred compensation plan	$ 37,300,000	(800,000)	8,700,000
Company's contributions, unamortized portion	$ 20,200,000	17,000,000.0
Defined Contribution Plan
Defined Benefit Plan Disclosure [Line Items]
Company's matching contributions		3,000,000.0
Percentage contribution by the participants to defined contribution plan	50.00%
Deferred Compensation Plan
Defined Benefit Plan Disclosure [Line Items]
Total benefit obligation	$ 205,740,000	180,821,000	$ 148,369,000
Deferred Compensation Plan | CSV of COLI Contracts
Defined Benefit Plan Disclosure [Line Items]
Gross CSV	241,300,000	238,700,000
Outstanding policy loans	80,000,000.0	$ 92,300,000
Company Owned Life Insurance Held In Trust | CSV of COLI Contracts
Defined Benefit Plan Disclosure [Line Items]
Net CSV	145,100,000
Total death benefits, net of loans held in trust	$ 398,900,000