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Stock-Based Compensation - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022	Mar. 18, 2021
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Intrinsic value of options exercised	$ 1.4	$ 10.8	$ 3.6	$ 23.3
Stock-based compensation expense	2.2	2.7	4.6	5.7
Unrecognized pre-tax compensation expense	$ 7.6		7.6
Weighted average period to recognize pre-tax compensation expense	1 year
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 18.4	$ 28.2	35.4	$ 49.7
Unrecognized pre-tax compensation expense	$ 153.6		$ 153.6
Weighted average period to recognize pre-tax compensation expense			2 years 6 months
2004 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserve for issuance (in shares)	173,983		173,983
2013 Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserve for issuance (in shares)	3,518,957		3,518,957
Number of shares forfeited (in shares)			139,053
2021 Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized (in shares)	6,126,788		6,126,788		8,000,000
Inducement Awards \| Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserve for issuance (in shares)	743,726		743,726
Inducement Awards \| Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserve for issuance (in shares)	738,875		738,875