Fair Value Measurements - Fair Value Hierarchy for Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Apr. 30, 2020	Jan. 31, 2020
Assets
Short-term investments	$ 660,199	$ 610,015
Certificates of deposits
Assets
Short-term investments	11,583	3,503
Commercial paper
Assets
Short-term investments	37,051	19,969
Corporate notes and bonds
Assets
Short-term investments	272,762	236,214
Asset-backed securities
Assets
Short-term investments	104,720	100,814
Foreign government bonds
Assets
Short-term investments	4,800	3,407
U.S. agency obligations
Assets
Short-term investments	5,002
U.S. treasury securities
Assets
Short-term investments	224,281	246,108
Fair value, measurements recurring
Assets
Total	1,126,978	638,058
Liabilities
Total	74	42
Fair value, measurements recurring \| Money market funds
Assets
Cash equivalents:	307,042	24,107
Fair value, measurements recurring \| Certificates of deposits
Assets
Cash equivalents:	150,000
Short-term investments	11,583	3,503
Fair value, measurements recurring \| Commercial paper
Assets
Cash equivalents:	7,496	1,616
Short-term investments	37,051	19,969
Fair value, measurements recurring \| Corporate notes and bonds
Assets
Cash equivalents:	2,229	2,245
Short-term investments	272,761	236,214
Fair value, measurements recurring \| Asset-backed securities
Assets
Short-term investments	104,720	100,815
Fair value, measurements recurring \| Foreign government bonds
Assets
Short-term investments	4,800	3,407
Fair value, measurements recurring \| U.S. agency obligations
Assets
Short-term investments	5,002
Fair value, measurements recurring \| U.S. treasury securities
Assets
Short-term investments	224,281	246,107
Fair value, measurements recurring \| Foreign currency derivative contracts
Assets
Short-term investments	13	75
Fair value, measurements recurring \| Foreign currency derivative contracts
Liabilities
Foreign currency derivative contracts	74	42
Fair value, measurements recurring \| Level 1
Assets
Total	307,042	24,107
Liabilities
Total	0	0
Fair value, measurements recurring \| Level 1 \| Money market funds
Assets
Cash equivalents:	307,042	24,107
Fair value, measurements recurring \| Level 1 \| Certificates of deposits
Assets
Cash equivalents:	0
Short-term investments	0	0
Fair value, measurements recurring \| Level 1 \| Commercial paper
Assets
Cash equivalents:	0	0
Short-term investments	0	0
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 \| Asset-backed securities
Assets
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	819,936	613,951
Liabilities
Total	74	42
Fair value, measurements recurring \| Level 2 \| Money market funds
Assets
Cash equivalents:	0	0
Fair value, measurements recurring \| Level 2 \| Certificates of deposits
Assets
Cash equivalents:	150,000
Short-term investments	11,583	3,503
Fair value, measurements recurring \| Level 2 \| Commercial paper
Assets
Cash equivalents:	7,496	1,616
Short-term investments	37,051	19,969
Fair value, measurements recurring \| Level 2 \| Corporate notes and bonds
Assets
Cash equivalents:	2,229	2,245
Short-term investments	272,761	236,214
Fair value, measurements recurring \| Level 2 \| Asset-backed securities
Assets
Short-term investments	104,720	100,815
Fair value, measurements recurring \| Level 2 \| Foreign government bonds
Assets
Short-term investments	4,800	3,407
Fair value, measurements recurring \| Level 2 \| U.S. agency obligations
Assets
Short-term investments	5,002
Fair value, measurements recurring \| Level 2 \| U.S. treasury securities
Assets
Short-term investments	224,281	246,107
Fair value, measurements recurring \| Level 2 \| Foreign currency derivative contracts
Assets
Short-term investments	13	75
Fair value, measurements recurring \| Level 2 \| Foreign currency derivative contracts
Liabilities
Foreign currency derivative contracts	$ 74	$ 42

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

+ Details

Name:	us-gaap_AssetsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26626-111562

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

Name:	us-gaap_CashAndCashEquivalentsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value as of the balance sheet date of all foreign currency derivative liabilities not designated as hedging instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959

+ Details

Name:	us-gaap_ForeignCurrencyDerivativeInstrumentsNotDesignatedAsHedgingInstrumentsLiabilityAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value of financial and nonfinancial obligations.

+ References

+ Details

Name:	us-gaap_LiabilitiesFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CertificatesOfDepositMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CommercialPaperMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_ForeignGovernmentDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_MoneyMarketFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_DerivativeFinancialInstrumentsAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ForeignExchangeForwardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: