Deferred Compensation and Retirement Plans - Components of Net Periodic Benefits Costs (Detail) - Deferred Compensation Plan - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2020	Oct. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 8,197	$ 6,474	$ 15,480	$ 11,930
Interest cost		1,047	1,422	2,080	2,815
Amortization of actuarial loss		996	745	1,993	1,490
Expected return on plan assets	[1]	(351)	(363)	(702)	(726)
Net periodic service credit amortization		(102)	(77)	(203)	(154)
Net periodic benefit costs	[2]	$ 9,787	$ 8,201	$ 18,648	$ 15,355

[1] The expected long-term rate of return on plan assets was 6.00% and 6.00% for October 31, 2020 and 2019, respectively.

[2] The service cost, interest cost and the 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 operations.