Debt - Convertible Senior Notes Due 2025 (Details)	May 14, 2018 USD ($) $ / shares	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)
Debt Instrument [Line Items]
Amount outstanding		$ 333,373,000	$ 367,762,000
Senior Notes
Debt Instrument [Line Items]
Amount outstanding		333,373,000
2025 Convertible Notes | Senior Notes
Debt Instrument [Line Items]
Stated interest rate	2.375%
Debt instrument, face amount	$ 172,500,000
Amount outstanding		$ 103,373,000	$ 103,373,000
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
Unrecorded debt discount and issuance costs		$ 300,000