Debt - Interest Expense (Details) - Senior Notes - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
2024 Convertible Notes
Debt Instrument [Line Items]
Contractual interest expense	$ 1,033	$ 1,033
Amortization of deferred financing costs	167	112
Amortization of debt discount	0	1,430
Total interest expense	1,200	2,575
2025 Convertible Notes
Debt Instrument [Line Items]
Contractual interest expense	1,024	1,024
Amortization of deferred financing costs	207	140
Amortization of debt discount	0	1,679
Total interest expense	$ 1,231	$ 2,843