Deferred Compensation and Retirement Plans - Components of Net Periodic Benefits Costs (Detail) - Deferred Compensation Plan - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 4,538	$ 3,148	$ 12,716	$ 8,292
Interest cost		1,330	1,045	3,956	3,110
Amortization of actuarial loss		446	577	1,338	1,731
Expected return on plan assets	[1]	(392)	(398)	(1,176)	(1,195)
Net periodic service credit amortization		(77)		(231)
Net periodic benefit costs	[2]	$ 5,845	$ 4,372	$ 16,603	$ 11,938

[1] The expected long-term rate of return on plan assets is 6.25% and 6.50% for January 31, 2019 and 2018, 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 income.