Comprehensive Income (Loss) - Changes in Each Component of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands		3 Months Ended
		Jul. 31, 2019	Jul. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		$ 1,240,656
Ending balance		1,260,900
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(60,270)	$ (32,399)
Unrealized (losses) gains arising during the period		(5,362)	(14,562)
Ending balance		(65,632)	(46,961)
Deferred Compensation and Pension Plan
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	[1]	(16,838)	(9,073)
Reclassification of realized net losses (gains) to net income	[1]	495	273
Effect of adoption of accounting standard	[1]		(2,396)
Ending balance	[1]	(16,343)	(11,196)
Unrealized (Losses) 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]	(491)	149
Reclassification of realized net losses (gains) to net income	[2]	(104)	(16)
Effect of adoption of accounting standard	[2]		199
Ending balance	[2]	(139)	1,669
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(76,652)	(40,135)
Unrealized (losses) gains arising during the period		(5,853)	(14,413)
Reclassification of realized net losses (gains) to net income		391	257
Effect of adoption of accounting standard			(2,197)
Ending balance		$ (82,114)	$ (56,488)

[1] The tax effect on the reclassifications of realized net losses was $0.2 million and $0.1 million for the three months ended July 31, 2019 and 2018, respectively.

[2] The tax effect on unrealized (losses) gains was $(0.2) million and $0.1 million for the three months ended July 31, 2019 and 2018, respectively.