Fair Value Measurements - Narrative (Details)	Jan. 31, 2020 USD ($) securities	Jan. 31, 2019 USD ($) securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Number of available-for-sale securities \| securities	178	119
Convertible Debt \| Convertible Senior Notes Due 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt interest rate percentage	0.50%
Aggregate principal amount of debt issued	$ 575,000,000.0
Convertible Debt \| Convertible Senior Notes Due 2023 \| Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Convertible debt, fair value disclosures	$ 743,500,000	$ 575,000,000.0

Number Of Available-for-sale Securities

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- Definition

Fair value portion of borrowing which can be exchanged for a specified number of another security at the option of the issuer or the holder, for example, but not limited to, the entity's common stock.

+ References

No definition available.

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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

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.

+ References

No definition available.

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