Deferred Compensation and Retirement Plans - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2019	Jul. 31, 2018	Apr. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Increase in market value of the underlying COLI investments	$ 2,338	$ 1,347
Recognized investment income (expense)	1,945	4,001
Executive Capital Accumulation Plan
Defined Benefit Plan Disclosure [Line Items]
Gain (loss) on deferred compensation plan	$ 2,300	4,200
Minimum
Defined Benefit Plan Disclosure [Line Items]
Option to receive employee benefits by quarterly installments periods	1 year
Minimum | Executive Capital Accumulation Plan
Defined Benefit Plan Disclosure [Line Items]
Deferred compensation arrangement vesting period	4 years
Maximum
Defined Benefit Plan Disclosure [Line Items]
Option to receive employee benefits by quarterly installments periods	15 years
Maximum | Executive Capital Accumulation Plan
Defined Benefit Plan Disclosure [Line Items]
Deferred compensation arrangement vesting period	5 years
CSV of COLI Contracts
Defined Benefit Plan Disclosure [Line Items]
Gross CSV	$ 219,100		$ 219,200
Outstanding policy loans	92,300		$ 93,200
Increase in market value of the underlying COLI investments	$ 2,300	$ 1,300