Fair Value Measurements - Fair Value Hierarchy for Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Oct. 31, 2020	Jan. 31, 2020
Assets
Short-term investments	$ 956,167	$ 610,015
Corporate notes and bonds
Assets
Short-term investments	417,181	236,214
Certificates of deposits
Assets
Short-term investments	15,612	3,503
Asset-backed securities
Assets
Short-term investments	131,544	100,814
Commercial paper
Assets
Short-term investments	58,636	19,969
Foreign government bonds
Assets
Short-term investments	32,027	3,407
U.S. agency obligations
Assets
Short-term investments	52,822
U.S. treasury securities
Assets
Short-term investments	248,345	246,108
Fair value, measurements recurring
Assets
Total	1,150,506	638,058
Liabilities
Total	65	42
Fair value, measurements recurring \| Money market funds
Assets
Cash equivalents:	193,054	24,107
Fair value, measurements recurring \| Corporate notes and bonds
Assets
Cash equivalents:	1,200	2,245
Short-term investments	417,181	236,214
Fair value, measurements recurring \| Certificates of deposits
Assets
Short-term investments	15,612	3,503
Fair value, measurements recurring \| Asset-backed securities
Assets
Short-term investments	131,544	100,815
Fair value, measurements recurring \| Commercial paper
Assets
Cash equivalents:		1,616
Short-term investments	58,636	19,969
Fair value, measurements recurring \| Foreign government bonds
Assets
Short-term investments	32,027	3,407
Fair value, measurements recurring \| U.S. agency obligations
Assets
Short-term investments	52,822
Fair value, measurements recurring \| U.S. treasury securities
Assets
Short-term investments	248,345	246,107
Fair value, measurements recurring \| Foreign currency derivative contracts
Assets
Short-term investments	85	75
Fair value, measurements recurring \| Foreign currency derivative contracts
Liabilities
Foreign currency derivative contracts	65	42
Fair value, measurements recurring \| Level 1
Assets
Total	193,054	24,107
Liabilities
Total	0	0
Fair value, measurements recurring \| Level 1 \| Money market funds
Assets
Cash equivalents:	193,054	24,107
Fair value, measurements recurring \| Level 1 \| Corporate notes and bonds
Assets
Cash equivalents:	0	0
Short-term investments	0	0
Fair value, measurements recurring \| Level 1 \| Certificates of deposits
Assets
Short-term investments	0	0
Fair value, measurements recurring \| Level 1 \| Asset-backed securities
Assets
Short-term investments	0	0
Fair value, measurements recurring \| Level 1 \| Commercial paper
Assets
Cash equivalents:		0
Short-term investments	0	0
Fair value, measurements recurring \| Level 1 \| Foreign government bonds
Assets
Short-term investments	0	0
Fair value, measurements recurring \| Level 1 \| U.S. agency obligations
Assets
Short-term investments	0
Fair value, measurements recurring \| Level 1 \| U.S. treasury securities
Assets
Short-term investments	0	0
Fair value, measurements recurring \| Level 1 \| Foreign currency derivative contracts
Assets
Short-term investments	0	0
Fair value, measurements recurring \| Level 1 \| Foreign currency derivative contracts
Liabilities
Foreign currency derivative contracts	0	0
Fair value, measurements recurring \| Level 2
Assets
Total	957,452	613,951
Liabilities
Total	65	42
Fair value, measurements recurring \| Level 2 \| Money market funds
Assets
Cash equivalents:	0	0
Fair value, measurements recurring \| Level 2 \| Corporate notes and bonds
Assets
Cash equivalents:	1,200	2,245
Short-term investments	417,181	236,214
Fair value, measurements recurring \| Level 2 \| Certificates of deposits
Assets
Short-term investments	15,612	3,503
Fair value, measurements recurring \| Level 2 \| Asset-backed securities
Assets
Short-term investments	131,544	100,815
Fair value, measurements recurring \| Level 2 \| Commercial paper
Assets
Cash equivalents:		1,616
Short-term investments	58,636	19,969
Fair value, measurements recurring \| Level 2 \| Foreign government bonds
Assets
Short-term investments	32,027	3,407
Fair value, measurements recurring \| Level 2 \| U.S. agency obligations
Assets
Short-term investments	52,822
Fair value, measurements recurring \| Level 2 \| U.S. treasury securities
Assets
Short-term investments	248,345	246,107
Fair value, measurements recurring \| Level 2 \| Foreign currency derivative contracts
Assets
Short-term investments	85	75
Fair value, measurements recurring \| Level 2 \| Foreign currency derivative contracts
Liabilities
Foreign currency derivative contracts	$ 65	$ 42

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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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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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes 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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Fair value as of the balance sheet date of all foreign currency derivative liabilities not designated as hedging instruments.

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Fair value of financial and nonfinancial obligations.

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