Fair Value Measurements - Fair Value Hierarchy for Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jul. 31, 2019	Jan. 31, 2019
Assets
Short-term investments	$ 604,688	$ 539,190
Commercial paper
Assets
Short-term investments	12,273	9,117
Corporate notes and bonds
Assets
Short-term investments	224,542	185,130
U.S. treasury securities
Assets
Short-term investments	276,915	243,135
Certificates of deposits
Assets
Short-term investments	3,508	6,010
Asset-backed securities
Assets
Short-term investments	82,952	78,395
Foreign government bonds
Assets
Short-term investments	1,498	1,491
U.S. agency obligations
Assets
Short-term investments	3,000	15,912
Fair value, measurements recurring
Assets
Total	630,124	620,897
Liabilities
Total	49	88
Fair value, measurements recurring \| Money market funds
Assets
Cash equivalents:	17,180	39,168
Fair value, measurements recurring \| Commercial paper
Assets
Cash equivalents:	5,609
Short-term investments	12,273	9,117
Fair value, measurements recurring \| Corporate notes and bonds
Assets
Cash equivalents:	2,647	1,034
Short-term investments	224,542	185,130
Fair value, measurements recurring \| U.S. treasury securities
Assets
Cash equivalents:		41,505
Short-term investments	276,915	243,135
Fair value, measurements recurring \| Certificates of deposits
Assets
Short-term investments	3,508	6,010
Fair value, measurements recurring \| Asset-backed securities
Assets
Short-term investments	82,952	78,395
Fair value, measurements recurring \| Foreign government bonds
Assets
Short-term investments	1,498	1,491
Fair value, measurements recurring \| U.S. agency obligations
Assets
Short-term investments	3,000	15,912
Fair value, measurements recurring \| Foreign currency derivative contracts
Liabilities
Foreign currency derivative contracts	49	88
Fair value, measurements recurring \| Level 1
Assets
Total	17,180	39,168
Liabilities
Total	0	0
Fair value, measurements recurring \| Level 1 \| Money market funds
Assets
Cash equivalents:	17,180	39,168
Fair value, measurements recurring \| Level 1 \| Commercial paper
Assets
Cash equivalents:	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 \| U.S. treasury securities
Assets
Cash equivalents:		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 \| Foreign government bonds
Assets
Short-term investments	0	0
Fair value, measurements recurring \| Level 1 \| U.S. agency obligations
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	612,944	581,729
Liabilities
Total	49	88
Fair value, measurements recurring \| Level 2 \| Money market funds
Assets
Cash equivalents:	0	0
Fair value, measurements recurring \| Level 2 \| Commercial paper
Assets
Cash equivalents:	5,609
Short-term investments	12,273	9,117
Fair value, measurements recurring \| Level 2 \| Corporate notes and bonds
Assets
Cash equivalents:	2,647	1,034
Short-term investments	224,542	185,130
Fair value, measurements recurring \| Level 2 \| U.S. treasury securities
Assets
Cash equivalents:		41,505
Short-term investments	276,915	243,135
Fair value, measurements recurring \| Level 2 \| Certificates of deposits
Assets
Short-term investments	3,508	6,010
Fair value, measurements recurring \| Level 2 \| Asset-backed securities
Assets
Short-term investments	82,952	78,395
Fair value, measurements recurring \| Level 2 \| Foreign government bonds
Assets
Short-term investments	1,498	1,491
Fair value, measurements recurring \| Level 2 \| U.S. agency obligations
Assets
Short-term investments	3,000	15,912
Fair value, measurements recurring \| Level 2 \| Foreign currency derivative contracts
Liabilities
Foreign currency derivative contracts	$ 49	$ 88

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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
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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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
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Fair value of financial and nonfinancial obligations.

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