Debt - Convertible Senior Notes Due 2025 (Details)	May 14, 2018 USD ($) day $ / shares	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)
Debt Instrument [Line Items]
Long-Term Debt, Gross		$ 367,762,000	$ 316,250,000
Debt discount and issuance costs		7,650,000	$ 3,347,000
Senior Notes
Debt Instrument [Line Items]
Long-Term Debt, Gross		367,762,000
2025 Convertible Notes | Senior Notes
Debt Instrument [Line Items]
Stated interest rate	2.375%
Principal	$ 172,500,000
Long-Term Debt, Gross		$ 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
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 | day	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) | day	20
Threshold consecutive trading days | day	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 | day	5
Threshold percentage of stock price trigger	98.00%
Business day threshold | day	5