Deferred Compensation and Retirement Plans - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2020	Oct. 31, 2019	Apr. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Increase in market value of the underlying COLI investments			$ 3,899	$ 4,209
Recognized investment income (expense)	$ 600	$ 1,200	$ 12,000	3,100
Executive Capital Accumulation Plan
Defined Benefit Plan Disclosure [Line Items]
Deferred compensation arrangement vesting period			5 years
Gain (loss) on deferred compensation plan	600	1,300	$ 11,800	3,500
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	241,900		$ 241,900		$ 238,700
Outstanding policy loans	91,700		91,700		$ 92,300
Increase in market value of the underlying COLI investments	$ 1,800	$ 1,900	$ 3,900	$ 4,200