Financial Instruments - Financial Instruments and Balance Sheet Classification (Detail) - USD ($) $ in Thousands		Oct. 31, 2018	Apr. 30, 2018	Oct. 31, 2017	Apr. 30, 2017
Investment Holdings [Line Items]
Cash and cash equivalents		$ 387,679	$ 520,848	$ 282,625	$ 410,882
Marketable Securities, Current		6,686	14,293
Marketable securities, non-current		128,913	122,792
Income Taxes & Other Receivables		29,009	29,089
Other Accrued Liabilities		(153,088)	(170,339)
Fair Value, Inputs, Level 1
Investment Holdings [Line Items]
Cost		520,881	647,925
Unrealized Gains		5,061	11,040
Unrealized Losses		(2,664)	(1,032)
Fair Value		523,278	657,933
Cash and cash equivalents		387,679	520,848
Marketable Securities, Current		6,686	14,293
Marketable securities, non-current		128,913	122,792
Fair Value, Inputs, Level 1 | Cash
Investment Holdings [Line Items]
Cost		366,549	519,818
Fair Value		366,549	519,818
Cash and cash equivalents		366,549	519,818
Fair Value, Inputs, Level 1 | Money Market Funds
Investment Holdings [Line Items]
Cost		21,130	1,030
Fair Value		21,130	1,030
Cash and cash equivalents		21,130	1,030
Fair Value, Inputs, Level 1 | Mutual Funds
Investment Holdings [Line Items]
Cost	[1]	133,202	127,077
Unrealized Gains	[1]	5,061	11,040
Unrealized Losses	[1]	(2,664)	(1,032)
Fair Value	[1]	135,599	137,085
Marketable Securities, Current	[1]	6,686	14,293
Marketable securities, non-current	[1]	128,913	122,792
Fair Value, Inputs, Level 2 | Foreign Exchange Forward Contracts
Investment Holdings [Line Items]
Unrealized Gains		1,436	1,778
Unrealized Losses		(2,150)	(1,025)
Fair Value		(714)	753
Income Taxes & Other Receivables			753
Other Accrued Liabilities		(714)
Fair Value, Inputs, Level 2 | Interest Rate Swap
Investment Holdings [Line Items]
Fair Value		2,452	2,076
Income Taxes & Other Receivables		2,452	2,076
Unrealized Gains		$ 2,452	$ 2,076

[1] These investments are held in trust for settlement of the Company’s vested obligations of $115.9 million and $118.2 million as of October 31, 2018 and April 30, 2018, respectively, under the ECAP (see Note 6 — Deferred Compensation and Retirement Plans). Unvested obligations under the deferred compensation plans totaled $24.2 million and $29.5 million as of October 31, 2018 and April 30, 2018, respectively. During the three and six months ended October 31, 2018, the fair value of the investments decreased; therefore, the Company recognized a loss of $4.8 million and $0.8 million, respectively, which was recorded in other (loss) income, net. During the three and six months ended October 31, 2017, the fair value of the investments increased; therefore, the Company recognized income of $3.4 million and $6.8 million, respectively, which was recorded in other (loss) income, net.