Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Deficit Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Loss	Treasury Stock
Balance at Sep. 30, 2018	$ 1,227.3		$ 1.0	$ 1,426.3	$ (189.6)		$ (10.4)
Balance, Shares at Sep. 30, 2018			104.5
Net income (loss)	44.4				44.4
Other comprehensive income, net of tax	(1.3)						(1.3)
Capital contributions and issuance of common stock			$ 0.2
Equity-based compensation	15.7			15.7
Repurchase of common stock and distributions	$ (1.2)			(0.2)				$ (1.0)
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201409Member					us-gaap:AccountingStandardsUpdate201409Member
Balance at Sep. 30, 2019	$ 1,283.8	$ (1.1)	$ 1.0	1,441.8	(146.3)	$ (1.1)	(11.7)	(1.0)
Balance, Shares at Sep. 30, 2019			104.7
Net income (loss)	(41.6)				(41.6)
Other comprehensive income, net of tax	4.8						4.8
Capital contributions and issuance of common stock	2.4			2.4
Capital contributions and issuance of common stock, Shares			0.2
Equity-based compensation	23.6			23.6
Repurchase of common stock and distributions	(1.5)							(1.5)
Balance at Sep. 30, 2020	1,271.5		$ 1.0	1,467.8	(187.9)		(6.9)	(2.5)
Balance, Shares at Sep. 30, 2020			104.9
Net income (loss)	46.3				46.3
Other comprehensive income, net of tax	5.4						5.4
Capital contributions and issuance of common stock	1.7		$ 0.1	1.6
Capital contributions and issuance of common stock, Shares			0.3
Equity-based compensation	19.7			19.7
Repurchase of common stock and distributions	1.9							1.9
Balance at Sep. 30, 2021	$ 1,342.7		$ 1.1	$ 1,489.1	$ (141.6)		$ (1.5)	$ (4.4)
Balance, Shares at Sep. 30, 2021			105.2