Deferred Compensation and Retirement Plans - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018	Apr. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Increase in market value of the underlying COLI investments			$ 4,547	$ 6,020
Recognized investment income (expense)	$ 2,200	$ 7,200	1,330	14,022
Executive Capital Accumulation Plan
Defined Benefit Plan Disclosure [Line Items]
Gain (loss) on deferred compensation plan	2,200	7,200	$ 2,000	14,400
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	218,800		$ 218,800		$ 186,800
Outstanding policy loans	94,200		94,200		$ 66,700
Increase in market value of the underlying COLI investments	$ 1,500	$ 1,800	$ 4,500	$ 6,000