Condensed Consolidated Statements of Stockholders' Deficit - USD ($) shares in Millions, $ in Millions	Total	Common stock	Paid-in capital	Retained earnings (deficit)	Accumulated other comprehensive income
Common stock outstanding, at beginning of period (shares) at Sep. 30, 2022		176.1
Balance at beginning of period at Sep. 30, 2022	$ 306.6	$ 1.8	$ 44.1	$ 282.0	$ (21.3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	81.9			81.9
Dividends paid	(21.8)		0.1	(21.9)
Stock-based compensation, net of issuances (in shares)		0.3
Stock-based compensation, net of issuances	(3.4)		(3.4)
Repurchases of common stock (shares)		(2.9)
Repurchases of common stock	(87.5)	$ (0.1)		(87.4)
Other comprehensive income, net of tax	13.5				13.5
Common stock outstanding, at end of period (shares) at Dec. 31, 2022		173.5
Balance at end of period at Dec. 31, 2022	$ 289.3	$ 1.7	40.8	254.6	(7.8)
Common stock outstanding, at beginning of period (shares) at Sep. 30, 2023	134.8	134.8
Balance at beginning of period at Sep. 30, 2023	$ 203.2	$ 1.3	48.0	140.7	13.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	31.9			31.9
Stock-based compensation, net of issuances (in shares)		0.2
Stock-based compensation, net of issuances	(1.7)		(1.7)
Repurchases of common stock (shares)		(5.4)
Repurchases of common stock	(172.8)	$ 0.0		(172.8)
Other comprehensive income, net of tax	$ 4.2				4.2
Common stock outstanding, at end of period (shares) at Dec. 31, 2023	129.6	129.6
Balance at end of period at Dec. 31, 2023	$ 64.8	$ 1.3	$ 46.3	$ (0.2)	$ 17.4