Convertible Senior Notes - Interest Costs Recognized on 2026 Notes (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Debt Instrument [Line Items]
Total interest expense recognized	$ 2,223	$ 0	$ 3,543	$ 0
Convertible Debt \| 2026 Notes
Debt Instrument [Line Items]
Contractual interest expense	290	0	463	0
Amortization of debt discount and issuance costs	1,933	0	3,080	0
Total interest expense recognized	$ 2,223	$ 0	$ 3,543	$ 0

Amount of the cost of borrowed funds accounted for as interest expense.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration