Debt - Convertible Senior Notes Due 2029 (Details)				1 Months Ended	12 Months Ended
	Dec. 12, 2022 day $ / shares	May 14, 2018 USD ($) day $ / shares	Jul. 05, 2017 USD ($) day $ / shares	Dec. 31, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)
Debt Instrument [Line Items]
Net loss on extinguishment of debt | $				$ 3,500,000	$ 3,545,000	$ 0	$ 0
Debt discount and issuance costs | $					$ 7,650,000	3,347,000
Unamortized debt discount | $							0
2029 Convertible Notes | Common Class A
Debt Instrument [Line Items]
Conversion rate per $1,000 principal amount (in shares)				0.0890313
2029 Convertible Notes | Senior Notes
Debt Instrument [Line Items]
Principal | $				$ 230,000,000
Stated interest rate				3.75%
Interest rate, effective percentage					4.28%
Conversion price, per share (in dollars per share) | $ / shares	$ 11.23
Unamortized debt discount | $					$ 6,700,000
2029 Convertible Notes | Senior Notes | Debt Conversion, Condition One
Debt Instrument [Line Items]
Threshold trading days (whether or not consecutive)	20
Threshold consecutive trading days	30
Threshold percentage of stock price trigger	130.00%
2029 Convertible Notes | Senior Notes | Debt Conversion, Condition One | Debt Instrument, Redemption, Period One
Debt Instrument [Line Items]
Threshold trading days (whether or not consecutive)	20
Threshold consecutive trading days	30
Threshold percentage of stock price trigger	130.00%
Repurchase price, percent of principal amount	100.00%
2029 Convertible Notes | Senior Notes | Debt Conversion, Condition Two
Debt Instrument [Line Items]
Threshold consecutive trading days	5
Threshold percentage of stock price trigger	98.00%
Business day threshold	5
2024 Convertible Notes | Senior Notes
Debt Instrument [Line Items]
Principal | $			$ 143,750,000
Stated interest rate			2.875%
Interest rate, effective percentage					3.35%
Conversion rate per $1,000 principal amount (in shares)			0.1
Conversion price, per share (in dollars per share) | $ / shares			$ 10.00
Net loss on extinguishment of debt | $					$ 8,935,000	0	0
Debt discount and issuance costs | $					$ 100,000
2024 Convertible Notes | Senior Notes | Debt Conversion, Condition One
Debt Instrument [Line Items]
Threshold trading days (whether or not consecutive)			20
Threshold consecutive trading days			30
Threshold percentage of stock price trigger			130.00%
2024 Convertible Notes | Senior Notes | Debt Conversion, Condition One | Debt Instrument, Redemption, Period One
Debt Instrument [Line Items]
Threshold trading days (whether or not consecutive)			20
Threshold consecutive trading days			30
Threshold percentage of stock price trigger			130.00%
Repurchase price, percent of principal amount			100.00%
2024 Convertible Notes | Senior Notes | Debt Conversion, Condition Two
Debt Instrument [Line Items]
Threshold consecutive trading days			5
Threshold percentage of stock price trigger			98.00%
Business day threshold			5
2024 Convertible Notes | Notes Repurchases
Debt Instrument [Line Items]
Repurchased principal amount | $				$ 109,400,000
Repurchased amount | $				117,500,000
2025 Convertible Notes | Senior Notes
Debt Instrument [Line Items]
Principal | $		$ 172,500,000
Stated interest rate		2.375%
Interest rate, effective percentage					2.88%
Conversion rate per $1,000 principal amount (in shares)		0.0628931
Conversion price, per share (in dollars per share) | $ / shares		$ 15.90
Net loss on extinguishment of debt | $					$ (5,389,000)	$ 0	$ 0
Debt discount and issuance costs | $					$ 800,000
2025 Convertible Notes | Senior Notes | Debt Instrument, Redemption, Period One
Debt Instrument [Line Items]
Threshold consecutive trading days		30
Threshold percentage of stock price trigger		130.00%
Repurchase price, percent of principal amount		100.00%
2025 Convertible Notes | Senior Notes | Debt Conversion, Condition One
Debt Instrument [Line Items]
Threshold trading days (whether or not consecutive)		20
Threshold consecutive trading days		30
Threshold percentage of stock price trigger		130.00%
2025 Convertible Notes | Senior Notes | Debt Conversion, Condition Two
Debt Instrument [Line Items]
Threshold consecutive trading days		5
Threshold percentage of stock price trigger		98.00%
Business day threshold		5
2025 Convertible Notes | Notes Repurchases
Debt Instrument [Line Items]
Repurchased principal amount | $				69,100,000
Repurchased amount | $				$ 62,900,000