Deferred Compensation and Retirement Plans - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2021	Jan. 31, 2020	Jan. 31, 2021	Jan. 31, 2020	Apr. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Increase in market value of the underlying COLI investments			$ 8,575	$ 5,794
Recognized investment income (expense)	$ 15,200	$ 5,200	$ 27,200	8,300
Executive Capital Accumulation Plan
Defined Benefit Plan Disclosure [Line Items]
Deferred compensation arrangement vesting period			5 years
Gain (loss) on deferred compensation plan	14,500	5,000	$ 26,300	8,600
Minimum
Defined Benefit Plan Disclosure [Line Items]
Option to receive employee benefits by quarterly installments periods			1 year
Maximum
Defined Benefit Plan Disclosure [Line Items]
Option to receive employee benefits by quarterly installments periods			15 years
CSV of COLI Contracts
Defined Benefit Plan Disclosure [Line Items]
Gross CSV	247,000		$ 247,000		$ 238,700
Outstanding policy loans	84,400		84,400		$ 92,300
Increase in market value of the underlying COLI investments	$ 4,700	$ 1,600	$ 8,600	$ 5,800