Deferred Compensation and Retirement Plans - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017	Apr. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Increase in market value of the underlying COLI investments			$ 3,003	$ 4,227
Recognized investment income (expense)	$ (4,800)	$ 3,400	(836)	6,797
Executive Capital Accumulation Plan
Defined Benefit Plan Disclosure [Line Items]
Gain (loss) on deferred compensation plan	(4,300)	3,500	$ (200)	7,200
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	219,200		$ 219,200		$ 186,800
Outstanding policy loans	96,000		96,000		$ 66,700
Increase in market value of the underlying COLI investments	$ 1,700	$ 1,700	$ 3,000	$ 4,200