Financial Instruments - Financial Instruments and Balance Sheet Classification (Detail) - USD ($) $ in Thousands		Oct. 31, 2020	Apr. 30, 2020
Investment Holdings [Line Items]
Cash and cash equivalents		$ 553,109	$ 689,244
Marketable Securities, Current		47,719	41,951
Marketable securities, non-current		146,625	132,134
Other Accrued Liabilities		(113)
Income Taxes & Other Receivables			2,634
Fair Value		747,340	865,963
Fair Value, Inputs, Level 2
Investment Holdings [Line Items]
Cost		40,251	38,313
Unrealized Gains		10	65
Unrealized Losses		(10)	(19)
Fair Value		40,251	38,359
Cash and cash equivalents			5,686
Marketable Securities, Current		40,251	32,673
Fair Value, Inputs, Level 2 | Commercial Paper
Investment Holdings [Line Items]
Cost		21,386	19,132
Unrealized Gains		3	39
Unrealized Losses		(3)
Fair Value		21,386	19,171
Cash and cash equivalents			4,785
Marketable Securities, Current		21,386	14,386
Fair Value, Inputs, Level 2 | Corporate Notes/Bonds
Investment Holdings [Line Items]
Cost		16,890	19,181
Unrealized Gains		7	26
Unrealized Losses		(6)	(19)
Fair Value		16,891	19,188
Cash and cash equivalents			901
Marketable Securities, Current		16,891	18,287
Fair Value, Inputs, Level 2 | U.S. Treasury and Agency Securities
Investment Holdings [Line Items]
Cost		1,975
Unrealized Losses		(1)
Fair Value		1,974
Marketable Securities, Current		1,974
Fair Value, Inputs, Level 2 | Foreign Exchange Forward Contracts
Investment Holdings [Line Items]
Other Accrued Liabilities		(113)
Income Taxes & Other Receivables			2,634
Fair Value		(113)	2,634
Fair Value, Inputs, Level 1 | Mutual Funds
Investment Holdings [Line Items]
Marketable Securities, Current	[1]	7,468	9,278
Marketable securities, non-current	[1]	146,625	132,134
Fair Value	[1]	154,093	141,412
Fair Value, Inputs, Level 1 | Equity Securities
Investment Holdings [Line Items]
Marketable Securities, Current		7,468	9,278
Marketable securities, non-current		146,625	132,134
Fair Value		154,093	141,412
Fair Value, Inputs, Level 1 | Cash
Investment Holdings [Line Items]
Cash and cash equivalents		463,916	611,795
Fair Value		463,916	611,795
Fair Value, Inputs, Level 1 | Money Market Funds
Investment Holdings [Line Items]
Cash and cash equivalents		89,193	71,763
Fair Value		$ 89,193	$ 71,763

[1] These investments are held in trust for settlement of the Company’s vested obligations of $133.8 million and $124.6 million as of October 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 $24.4 million and $21.7 million as of October 31, 2020 and April 30, 2020, respectively. During the three and six months ended October 31, 2020, the fair value of the investments increased; therefore, the Company recognized a gain of $0.6 million and $12.0 million, respectively, which was recorded in other income, net. During the three and six months ended October 31, 2019, the fair value of the investments increased; therefore, the Company recognized a gain of $1.2 million and $3.1 million, respectively, which was recorded in other income, net.