Comprehensive Income - Changes in Each Component of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands		3 Months Ended				9 Months Ended
		Jan. 31, 2021		Jan. 31, 2020		Jan. 31, 2021		Jan. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance						$ 1,221,381
Ending balance		$ 1,293,187				1,293,187
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(61,426)		$ (64,303)		(83,652)		$ (60,270)
Unrealized gains (losses) arising during the period		25,083		403		47,309		(3,630)
Ending balance		(36,343)		(63,900)		(36,343)		(63,900)
Deferred Compensation and Pension Plan
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(22,229)	[1]	(15,848)	[2]	(23,554)	[1]	(16,838)	[2]
Unrealized gains (losses) arising during the period	[2]			450				450
Reclassification of realized net losses to net income		663	[1]	493	[2]	1,988	[1]	1,483	[2]
Ending balance		(21,566)	[1]	(14,905)	[2]	(21,566)	[1]	(14,905)	[2]
Unrealized Gains (Losses) on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance						34
Unrealized gains (losses) arising during the period		(5)		(5)		(39)		(5)
Ending balance		(5)		(5)		(5)		(5)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(83,655)		(80,646)		(107,172)		(76,652)
Unrealized gains (losses) arising during the period		25,078		976		47,270		(3,863)
Reclassification of realized net losses to net income		663		860		1,988		1,705
Ending balance		$ (57,914)		(78,810)		$ (57,914)		(78,810)
Unrealized (Losses) Gains on Interest Rate Swap
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	[3]			(495)				456
Unrealized gains (losses) arising during the period	[3]			128				(678)
Reclassification of realized net losses to net income	[3]			$ 367				$ 222

[1] The tax effect on the reclassifications of realized net losses to net income was $0.2 million and $0.7 million for the three and nine months ended January 31, 2021, respectively.

[2] The tax effect on unrealized gains was $0.2 million for both the three and nine months ended January 31, 2020. The tax effect on the reclassifications of realized net losses to net income was $0.2 million and $0.5 million for the three and nine months ended January 31, 2020, respectively.

[3] The tax effect on unrealized gains (losses) was $0.1 million and) ($0.2) million for the three and nine months ended January 31, 2020, respectively. The tax effect on the reclassification of realized net losses to net income was $0.1 million for both the three and nine months ended January 31, 2020.