Financial Instruments - Financial Instruments and Balance Sheet Classification (Detail) - USD ($) $ in Thousands		Jul. 31, 2018	Apr. 30, 2018	Jul. 31, 2017	Apr. 30, 2017
Investment Holdings [Line Items]
Cash and cash equivalents		$ 365,729	$ 520,848	$ 282,019	$ 410,882
Marketable Securities, Current		10,952	14,293
Marketable securities, non-current		123,124	122,792
Income Taxes & Other Receivables		36,999	29,089
Other Accrued Liabilities		(150,534)	(170,339)
Fair Value, Inputs, Level 1
Investment Holdings [Line Items]
Cost		490,318	647,925
Unrealized Gains		10,395	11,040
Unrealized Losses		(908)	(1,032)
Fair Value		499,805	657,933
Cash and cash equivalents		365,729	520,848
Marketable Securities, Current		10,952	14,293
Marketable securities, non-current		123,124	122,792
Fair Value, Inputs, Level 1 | Cash
Investment Holdings [Line Items]
Cost		344,684	519,818
Fair Value		344,684	519,818
Cash and cash equivalents		344,684	519,818
Fair Value, Inputs, Level 1 | Money Market Funds
Investment Holdings [Line Items]
Cost		21,045	1,030
Fair Value		21,045	1,030
Cash and cash equivalents		21,045	1,030
Fair Value, Inputs, Level 1 | Mutual Funds
Investment Holdings [Line Items]
Cost	[1]	124,589	127,077
Unrealized Gains	[1]	10,395	11,040
Unrealized Losses	[1]	(908)	(1,032)
Fair Value	[1]	134,076	137,085
Marketable Securities, Current	[1]	10,952	14,293
Marketable securities, non-current	[1]	123,124	122,792
Fair Value, Inputs, Level 2 | Foreign Exchange Forward Contracts
Investment Holdings [Line Items]
Unrealized Gains		603	1,778
Unrealized Losses		(621)	(1,025)
Fair Value		(18)	753
Income Taxes & Other Receivables			753
Other Accrued Liabilities		(18)
Fair Value, Inputs, Level 2 | Interest Rate Swap
Investment Holdings [Line Items]
Fair Value		2,256	2,076
Income Taxes & Other Receivables		2,256	2,076
Unrealized Gains		$ 2,256	$ 2,076

[1] These investments are held in trust for settlement of the Company’s vested obligations of $125.4 million and $118.2 million as of July 31, 2018 and April 30, 2018, respectively, under the ECAP (see Note 6 — Deferred Compensation and Retirement Plans). During the three months ended July 31, 2018 and 2017, the fair value of the investments increased; therefore, the Company recognized income of $4.0 million and $3.4 million, respectively, which was recorded in other income, net.