Financial Instruments - Fair Value of Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Feb. 02, 2020	Jan. 31, 2019	Jan. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 932,260	$ 793,932
Gross Unrealized Gains	7,263	900
Gross Unrealized Losses	(4)	(1,238)
Fair Value	965,874	836,632
Cash Equivalents	14,069	71,327
Marketable securities	936,518	749,482
Restricted cash	15,287	15,823	$ 14,763
Restricted Cash	15,287	15,823
Corporate Debt Securities \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	452,318	363,860
Gross Unrealized Gains	3,954	534
Gross Unrealized Losses	(1)	(757)
Fair Value	456,271	363,637
Cash Equivalents	3,001	0
Marketable securities	453,270	363,637
Restricted Cash	0	0
Foreign Government Debt [Member] \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	14,994	7,965
Gross Unrealized Gains	147	36
Gross Unrealized Losses	0	0
Fair Value	15,141	8,001
Cash Equivalents	0	0
Marketable securities	15,141	8,001
Restricted Cash	0	0
US Government Agencies Debt Securities \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	53,930	69,114
Gross Unrealized Gains	317	17
Gross Unrealized Losses	(3)	(154)
Fair Value	54,244	68,977
Cash Equivalents	0	9,983
Marketable securities	54,244	58,994
Restricted Cash	0	0
US Government Debt Securities \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	323,751	315,329
Gross Unrealized Gains	2,146	208
Gross Unrealized Losses	0	(315)
Fair Value	325,897	315,222
Cash Equivalents	0	34,129
Marketable securities	325,897	281,093
Restricted Cash	0	0
Money Market Funds [Member] \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value	26,355	43,038
Cash Equivalents	11,068	27,215
Marketable securities	0	0
Asset-backed Securities \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	87,267	37,664
Gross Unrealized Gains	699	105
Gross Unrealized Losses	0	(12)
Fair Value	87,966	37,757
Cash Equivalents	0	0
Marketable securities	87,966	37,757
Restricted Cash	$ 0	$ 0

Debt Securities, Available-for-sale, Cash Equivalents And Restricted Cash

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Debt Securities, Available-for-sale, Cash Equivalents And Restricted Cash, Accumulated Gross Unrealized Gain, Before Tax

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Debt Securities, Available-for-sale, Cash Equivalents And Restricted Cash, Accumulated Gross Unrealized Loss, Before Tax

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Debt Securities, Available-for-sale, Cash Equivalents And Restricted Cash, Amortized Cost

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as current.

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Amount of short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of cash and cash equivalents restricted as to withdrawal or usage, classified as noncurrent. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Amount of cash restricted as to withdrawal or usage, classified as noncurrent. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits.

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