Convertible Senior Notes - Capped Calls (Details)	3 Months Ended
Apr. 30, 2020 $ / shares
Capped Calls
Option Indexed to Issuer's Equity [Line Items]
Strike price (in dollars per share)	$ 68.15
Cap price (in dollars per share)	106.90
Convertible Debt \| 2026 Notes
Option Indexed to Issuer's Equity [Line Items]
Strike price (in dollars per share)	211.20
Cap price (in dollars per share)	$ 296.42

Exercise or strike price stated in the contract for options indexed to the issuer's equity shares.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 40
-Section 50
-Paragraph 5
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=6445032&loc=d3e90205-114008

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(1)
-URI http://asc.fasb.org/extlink&oid=109262807&loc=d3e22047-110879

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Period Type:	duration