Comprehensive Income - Changes in Each Component of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands		3 Months Ended				6 Months Ended
		Oct. 31, 2020		Oct. 31, 2019		Oct. 31, 2020		Oct. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance						$ 1,221,381
Ending balance		$ 1,219,972				1,219,972
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(58,705)		$ (65,632)		(83,652)		$ (60,270)
Unrealized gains (losses) arising during the period		(2,721)		1,329		22,226		(4,033)
Ending balance		(61,426)		(64,303)		(61,426)		(64,303)
Deferred Compensation and Pension Plan
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(22,912)	[1]	(16,343)	[2]	(23,554)	[1]	(16,838)	[2]
Reclassification of realized net losses (gains) to net income		683	[1]	495	[2]	1,325	[1]	990	[2]
Ending balance		(22,229)	[1]	(15,848)	[2]	(22,229)	[1]	(15,848)	[2]
Unrealized Gains (Losses) on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		25				34
Unrealized gains (losses) arising during the period		(25)				(34)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(81,592)		(82,114)		(107,172)		(76,652)
Unrealized gains (losses) arising during the period		(2,746)		1,014		22,192		(4,839)
Reclassification of realized net losses (gains) to net income		683		454		1,325		845
Ending balance		$ (83,655)		(80,646)		$ (83,655)		(80,646)
Unrealized (Losses) Gains on Interest Rate Swap
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	[3]			(139)				456
Unrealized gains (losses) arising during the period	[3]			(315)				(806)
Reclassification of realized net losses (gains) to net income	[3]			(41)				(145)
Ending balance	[3]			$ (495)				$ (495)

[1] The tax effect on the reclassifications of realized net losses was $0.2 million and $0.5 million for the three and six months ended October 31, 2020, respectively.

[2] The tax effect on the reclassifications of realized net losses was $0.2 million and $0.3 million for the three and six months ended October 31, 2019, respectively.

[3] The tax effect on unrealized losses was $0.1 million and $0.3 million for the three and six months ended October 31, 2019, respectively.