Deferred Compensation and Retirement Plans - Reconciliation of Fair Value of Plan Assets (Detail) - USD ($) $ in Thousands		12 Months Ended
		Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Current liability	[1]	$ 18,338	$ 19,143
Non-current liability		346,455	289,136
Total benefit obligation		364,793	308,279
Medical and Life Insurance plan | Hay Group
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation, beginning of year		7,527	7,310
Interest cost		140	227	$ 243
Actuarial (gain) loss		(549)	458
Benefits paid		(534)	(468)
Benefit obligation, end of year		6,584	7,527	$ 7,310
Current liability		601	666
Non-current liability		5,983	6,861
Total benefit obligation		$ 6,584	$ 7,527

[1] Current portion of benefit obligation is included in Compensation and benefits payable in the consolidated balance sheet