Comprehensive Income (Loss) - Changes in Each Component of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2019	Oct. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance				$ 1,240,656
Ending balance		$ 1,255,931		1,255,931
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(65,632)	$ (46,961)	(60,270)	$ (32,399)
Unrealized gains (losses) arising during the period		1,329	(12,511)	(4,033)	(27,073)
Ending balance		(64,303)	(59,472)	(64,303)	(59,472)
Deferred Compensation and Pension Plan
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	[1]	(16,343)	(11,196)	(16,838)	(9,073)
Reclassification of realized net losses (gains) to net income	[1]	495	273	990	546
Effect of adoption of accounting standard	[1]				(2,396)
Ending balance	[1]	(15,848)	(10,923)	(15,848)	(10,923)
Unrealized (Losses) Gains on Interest Rate Swap
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	[2]	(139)	1,669	456	1,337
Unrealized gains (losses) arising during the period	[2]	(315)	193	(806)	342
Reclassification of realized net losses (gains) to net income	[2]	(41)	(48)	(145)	(64)
Effect of adoption of accounting standard	[2]				199
Ending balance	[2]	(495)	1,814	(495)	1,814
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(82,114)	(56,488)	(76,652)	(40,135)
Unrealized gains (losses) arising during the period		1,014	(12,318)	(4,839)	(26,731)
Reclassification of realized net losses (gains) to net income		454	225	845	482
Effect of adoption of accounting standard					(2,197)
Ending balance		$ (80,646)	$ (68,581)	$ (80,646)	$ (68,581)

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

[2] The tax effect on unrealized gains was $0.1 million for both the three and six months ended October 31, 2018, respectively.