Convertible Senior Notes - Components of Debt (Details) - USD ($) $ in Thousands		Jul. 31, 2022	Sep. 30, 2021	Jul. 31, 2021	Jan. 31, 2018
2023 Convertible Senior Notes
Debt Instrument [Line Items]
Principal amount					$ 1,000
2027 Convertible Senior Notes
Debt Instrument [Line Items]
Principal amount			$ 1,000
Convertible Debt | 2023 Convertible Senior Notes
Debt Instrument [Line Items]
Principal amount		$ 145,704		$ 575,000	$ 575,000
Unamortized debt discount	[1]	0		(48,616)
Unamortized debt issuance costs	[1]	(248)		(2,713)
Net carrying amount		145,456		523,671
Carrying amount of equity component	[2]	0		148,598
Convertible Debt | 2026 Convertible Senior Notes
Debt Instrument [Line Items]
Principal amount		750,000		750,000
Non-cash interest expense converted to principal		27,997		8,906
Unamortized debt discount	[3]	(169,438)		(203,619)
Unamortized debt issuance costs	[3]	(19,359)		(23,264)
Net carrying amount		589,200		$ 532,023
Convertible Debt | 2027 Convertible Senior Notes
Debt Instrument [Line Items]
Principal amount		575,000
Unamortized debt issuance costs	[4]	(7,995)
Net carrying amount		$ 567,005

[1] Included in our consolidated balance sheets within convertible senior notes, net and amortized over the remaining life of the 2023 Notes using the effective interest rate method. As of July 31, 2021, the effective interest rate was 6.62%. As of July 31, 2022, the effective interest rate was 0.41%.

[2] Included in our consolidated balance sheets as of July 31, 2021 within additional paid-in capital, net of $3.0 million in equity issuance costs.

[3] Included in our consolidated balance sheets within convertible senior notes, net and amortized over the remaining life of the 2026 Notes using the effective interest rate method. The effective interest rate is 7.05%

[4] Included in our consolidated balance sheets within convertible senior notes, net and amortized over the remaining life of the 2027 Notes using the effective interest rate method. The effective interest rate is 0.52%.