Deferred Compensation and Retirement Plans - Components of Net Periodic Benefits Costs (Detail) - Deferred Compensation Plan - USD ($) $ in Thousands		3 Months Ended
		Jul. 31, 2018	Jul. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 3,646	$ 2,065
Interest cost		1,296	1,020
Amortization of actuarial loss		446	577
Expected return on plan assets	[1]	(392)	(399)
Net periodic service credit amortization		(77)
Net periodic benefit costs	[2]	$ 4,919	$ 3,263

[1] The expected long-term rate of return on plan assets is 6.25% and 6.50% for July 31, 2018 and 2017, 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.