Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss	Treasury Stock
Balance at Sep. 30, 2019	$ 1,283.8	$ 1.0	$ 1,441.8	$ (146.3)	$ (11.7)	$ (1.0)
Balance, Shares at Sep. 30, 2019		104.7
Net (loss)	(12.6)			(12.6)
Other comprehensive income, net of tax	2.1				2.1
Capital contributions and issuance of common stock	2.3		2.3
Capital contributions and issuance of common stock, Shares		0.2
Equity-based compensation	8.2		8.2
Repurchase of common stock and distributions	(0.7)					(0.7)
Balance at Dec. 31, 2019	1,283.1	$ 1.0	1,452.3	(158.9)	(9.6)	(1.7)
Balance, Shares at Dec. 31, 2019		104.9
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 (loss)	(12.0)			(12.0)
Other comprehensive income, net of tax	3.6				3.6
Capital contributions and issuance of common stock	1.8	$ 0.1	1.7
Capital contributions and issuance of common stock, Shares		0.2
Equity-based compensation	4.9		4.9
Repurchase of common stock and distributions	(1.1)					(1.1)
Balance at Dec. 31, 2020	$ 1,268.7	$ 1.1	$ 1,474.4	$ (199.9)	$ (3.3)	$ (3.6)
Balance, Shares at Dec. 31, 2020		105.1