Financial Instruments - Financial Instruments and Balance Sheet Classification (Detail) - USD ($) $ in Thousands		Jul. 31, 2020	Apr. 30, 2020
Investment Holdings [Line Items]
Cash and cash equivalents		$ 542,786	$ 689,244
Marketable Securities, Current		49,870	41,951
Marketable securities, non-current		140,330	132,134
Income Taxes & Other Receivables		42,243	38,755
Income Taxes & Other Receivables		406	2,634
Fair Value		733,392	865,963
Fair Value, Inputs, Level 2
Investment Holdings [Line Items]
Cost		40,125	38,313
Unrealized Gains		41	65
Unrealized Losses		(8)	(19)
Fair Value		40,158	38,359
Cash and cash equivalents		1,800	5,686
Marketable Securities, Current		38,358	32,673
Fair Value, Inputs, Level 2 | Commercial Paper
Investment Holdings [Line Items]
Cost		20,879	19,132
Unrealized Gains		12	39
Unrealized Losses		(5)
Fair Value		20,886	19,171
Cash and cash equivalents		1,800	4,785
Marketable Securities, Current		19,086	14,386
Fair Value, Inputs, Level 2 | Corporate Notes/Bonds
Investment Holdings [Line Items]
Cost		19,246	19,181
Unrealized Gains		29	26
Unrealized Losses		(3)	(19)
Fair Value		19,272	19,188
Cash and cash equivalents			901
Marketable Securities, Current		19,272	18,287
Fair Value, Inputs, Level 2 | Foreign Exchange Forward Contracts
Investment Holdings [Line Items]
Income Taxes & Other Receivables		406	2,634
Fair Value		406	2,634
Fair Value, Inputs, Level 1 | Mutual Funds
Investment Holdings [Line Items]
Marketable Securities, Current	[1]	11,512	9,278
Marketable securities, non-current	[1]	140,330	132,134
Fair Value	[1]	151,842	141,412
Fair Value, Inputs, Level 1 | Equity Securities
Investment Holdings [Line Items]
Marketable Securities, Current		11,512	9,278
Marketable securities, non-current		140,330	132,134
Fair Value		151,842	141,412
Fair Value, Inputs, Level 1 | Cash
Investment Holdings [Line Items]
Cash and cash equivalents		451,359	611,795
Fair Value		451,359	611,795
Fair Value, Inputs, Level 1 | Money Market Funds
Investment Holdings [Line Items]
Cash and cash equivalents		89,627	71,763
Fair Value		$ 89,627	$ 71,763

[1] These investments are held in trust for settlement of the Company’s vested obligations of $137.4 million and $124.6 million as of July 31, 2020 and April 30, 2020, respectively, under the ECAP (see Note 6 — Deferred Compensation and Retirement Plans). Unvested obligations under the deferred compensation plans totaled $24.1 million and $21.7 million as of July 31, 2020 and April 30, 2020, respectively. During the three months ended July 31, 2020 and 2019, the fair value of the investments increased; therefore, the Company recognized a gain of $11.5 million and $1.9 million, respectively, which was recorded in other income, net.