Convertible Senior Notes - Schedule of Net Carrying Amount of the Liability Component of the Notes (Details) - USD ($) $ in Thousands		1 Months Ended	2 Months Ended	12 Months Ended
	Jan. 14, 2020	Jan. 31, 2020	Jul. 31, 2018	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018
Debt Instrument [Line Items]
Principal					$ 300,000
Unamortized debt discount					(77,211)
Unamortized debt issuance costs					(5,931)
Net carrying amount					216,858
Proceeds from borrowings on convertible senior notes, net of issuance costs		$ 1,130,000		$ 1,132,991	291,145	$ 0
Less: Net carrying amount of the liability component associated with the 2024 Notes Partial Repurchase	$ (160,619)
Loss from 2024 Notes Partial Repurchase	14,522			(14,522)	$ 0	$ 0
Convertible Debt
Debt Instrument [Line Items]
Unamortized debt issuance costs			$ (8,800)
Proceeds from borrowings on convertible senior notes, net of issuance costs	479,200		291,100
2024 Notes
Debt Instrument [Line Items]
Principal	300,000	90,002		90,002
Unamortized debt discount	(65,366)	(19,435)		(19,435)
Unamortized debt issuance costs	(5,175)	(1,541)		(1,541)
Net carrying amount	229,459	69,026		69,026
2024 Notes Partial Repurchase
Debt Instrument [Line Items]
Principal	209,998
Unamortized debt discount	(45,756)
Unamortized debt issuance costs	(3,623)
Net carrying amount	160,619
Convertible Senior Notes, Liability Component | Convertible Debt
Debt Instrument [Line Items]
Unamortized debt issuance costs			$ (6,300)
Proceeds from borrowings on convertible senior notes, net of issuance costs	$ 175,141
2026 Notes
Debt Instrument [Line Items]
Principal		1,150,000		1,150,000
Unamortized debt discount		(292,932)		(292,932)
Unamortized debt issuance costs		(15,019)		(15,019)
Net carrying amount		842,049		842,049
2026 Notes | Convertible Debt
Debt Instrument [Line Items]
Unamortized debt issuance costs		$ (20,300)		$ (20,300)