Convertible Senior Notes - Narrative (Details)		3 Months Ended	8 Months Ended	12 Months Ended
	Feb. 05, 2021 USD ($) patent $ / shares	Sep. 30, 2021 USD ($) shares	Sep. 30, 2021 USD ($) shares	Sep. 30, 2021 USD ($) shares	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Feb. 02, 2021 $ / shares
Debt Instrument [Line Items]
Payment costs related to hedge transactions				$ 33,192,000	$ 0	$ 0
Embedded conversion derivative		$ 48,208,000	$ 48,208,000	48,208,000
Senior notes hedge balance		48,208,000	48,208,000	48,208,000	$ 0
Increase in additional paid-in-capital for sale or warrants				23,909,000
Convertible Debt | Convertible Senior Unsecured Notes Due 2026
Debt Instrument [Line Items]
Debt issued	$ 155,300,000
Debt interest rate	0.75%
Debt conversion ratio (per $1,000 principal amount)	0.0479731000
Debt conversion price (in dollars per share) | $ / shares	$ 20.85
Conversion price premium percentage							0.375
Proceeds from debt offerings, net of discounts, commissions and expenses	$ 149,700,000
Debt issuance costs	$ 5,500,000
Remaining unamortized debt discount		34,332,000	34,332,000	34,332,000
Convertible Debt | Convertible Senior Unsecured Notes Due 2026 | Common Stock
Debt Instrument [Line Items]
Share price (in dollars per share) | $ / shares							$ 15.16
Convertible Debt | Convertible Senior Unsecured Notes Due 2026 | During any calendar quarter commencing after the calendar quarter ending on June 30, 2021
Debt Instrument [Line Items]
Debt conversion price percentage	1.30
Trading days in period | patent	20
Consecutive trading days in period | patent	30
Convertible Debt | Convertible Senior Unsecured Notes Due 2026 | Measurement period
Debt Instrument [Line Items]
Debt conversion price percentage	0.98
Consecutive trading days in period | patent	5
Convertible Debt | Convertible Senior Unsecured Notes Due 2026 | Observation period
Debt Instrument [Line Items]
Consecutive trading days in period | patent	40
Convertible Debt | Convertible Senior Unsecured Notes Due 2026 | Embedded conversion derivative
Debt Instrument [Line Items]
Payment costs related to hedge transactions	$ 9,300,000
Embedded conversion derivative	33,200,000	48,208,000	48,208,000	48,208,000
Value of remaining embedded derivative allocated to host contract	$ 116,500,000
Derivative interest rate	6.71%
Remaining unamortized debt discount		$ 34,300,000	$ 34,300,000	$ 34,300,000
Remaining debt discount amortization period	4 years 3 months 18 days
Convertible Debt | Additional Notes
Debt Instrument [Line Items]
Option period to purchase additional notes	13 days
Additional aggregate principal amount purchased	$ 20,250,000
Convertible Debt | Notes Hedge
Debt Instrument [Line Items]
Debt conversion price (in dollars per share) | $ / shares	$ 20.85
Conversion price premium percentage							0.750
Number of shares that can initially be converted into common stock | patent	7,400,000
Strike price of warrants (in dollar per share) | $ / shares	$ 26.53
Senior notes hedge balance	$ 33,200,000
Shares purchased under the notes hedge (in shares) | shares			0
Increase in additional paid-in-capital for sale or warrants			$ 23,900,000
Warrants exercised (in shares) | shares			0
Warrants outstanding (in shares) | shares		0	0	0
Convertible Debt | Notes Hedge | Observation period
Debt Instrument [Line Items]
Consecutive trading days in period | patent	80
Incremental dilution of earnings per share of warrants (in shares) | shares		0