Deferred Compensation And Retirement Plans - Components of Net Periodic Benefits Costs (Detail) - Deferred Compensation Plan - USD ($) $ in Thousands		12 Months Ended
		Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 17,281	$ 11,373	$ 5,402
Interest cost		5,044	3,787	3,925
Amortization of actuarial loss (gain)		1,798	2,308	3,051
Expected return on plan assets		(1,568)	(1,594)	(1,559)
Net periodic benefit cost	[1]	$ 22,555	$ 15,874	$ 10,819

[1] The service cost, interest cost and other components of net periodic benefit costs are included in compensation and benefits expense, interest expense, net and other income, net, respectively, on the consolidated statements of income.