Comprehensive Income - Changes in Each Component of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands		12 Months Ended
		Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		$ 1,221,381
Ending balance		1,366,389	$ 1,221,381
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(83,652)	(60,270)	$ (32,399)
Unrealized (losses) gains arising during the period		49,986	(23,382)	(27,871)
Ending balance		(33,666)	(83,652)	(60,270)
Deferred Compensation and Pension Plan
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	[1]	(23,554)	(16,838)	(9,073)
Unrealized (losses) gains arising during the period	[1]	2,660	(8,883)	(6,461)
Reclassification of realized net losses (gains) to net income	[1]	2,759	2,167	1,092
Effect of adoption of accounting standard	[1]			(2,396)
Ending balance	[1]	(18,135)	(23,554)	(16,838)
Unrealized Gains (Losses) on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		34
Unrealized (losses) gains arising during the period		(53)	37
Reclassification of realized net losses (gains) to net income			(3)
Ending balance		(19)	34
Unrealized Gains on Interest Rate Swap
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	[2]		456	1,337
Unrealized (losses) gains arising during the period	[2]		(678)	(800)
Reclassification of realized net losses (gains) to net income	[2]		222	(280)
Effect of adoption of accounting standard	[2]			199
Ending balance	[2]			456
Accumulated Other Comprehensive Loss, Net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(107,172)	(76,652)	(40,135)
Unrealized (losses) gains arising during the period		52,593	(32,906)	(35,132)
Reclassification of realized net losses (gains) to net income		2,759	2,386	812
Effect of adoption of accounting standard				(2,197)
Ending balance		$ (51,820)	$ (107,172)	$ (76,652)

[1] The tax effects on unrealized gains (losses) were $1.1 million, $(3.1) million and $(2.3) million as of April 30, 2021, 2020 and 2019, respectively. The tax effects on reclassifications of realized net losses were $1.0 million, $0.8 million and $0.4 million as of April 30, 2021, 2020 and 2019, respectively.

[2] The tax effects on unrealized (losses) gains were $(0.2) million and $(0.3) million as of 2020 and 2019, respectively. The tax effects on the reclassification of realized net (losses) gains to net income was $(0.1) million and $0.1 million as of 2020 and 2019, respectively.