Comprehensive (Loss) Income - Changes in Each Component of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands		3 Months Ended
		Jul. 31, 2020	Jul. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		$ 1,221,381
Ending balance		1,215,658
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(83,652)	$ (60,270)
Unrealized gains (losses) arising during the period		24,947	(5,362)
Ending balance		(58,705)	(65,632)
Deferred Compensation and Pension Plan
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(23,554)	(16,838)	[1]
Reclassification of realized net losses (gains) to net income		642	495	[1]
Ending balance		(22,912)	(16,343)	[1]
Unrealized Gains (Losses) on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		34
Unrealized gains (losses) arising during the period		(9)
Ending balance		25
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(107,172)	(76,652)
Unrealized gains (losses) arising during the period		24,938	(5,853)
Reclassification of realized net losses (gains) to net income		642	391
Ending balance		$ (81,592)	(82,114)
Unrealized (Losses) Gains on Interest Rate Swap
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	[2]		456
Unrealized gains (losses) arising during the period	[2]		(491)
Reclassification of realized net losses (gains) to net income	[2]		(104)
Ending balance	[2]		$ (139)

[1] The tax effect on the reclassifications of realized net losses was $0.2 million and $0.2 million for the three months ended July 31, 2020 and 2019, respectively.

[2] The tax effect on unrealized losses was $0.2 million for the three months ended July 31, 2019.