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 income (loss)	(35.5)			(35.5)
Other comprehensive income (loss), net of tax	(0.7)				(0.7)
Capital contributions and issuance of common stock	2.5		2.5
Capital contributions and issuance of common stock, Shares		0.2
Equity-based compensation	17.9		17.9
Repurchase of common stock and distributions	(0.9)					(0.9)
Balance at Jun. 30, 2020	1,267.1	$ 1.0	1,462.2	(181.8)	(12.4)	(1.9)
Balance, Shares at Jun. 30, 2020		104.9
Balance at Mar. 31, 2020	1,260.6	$ 1.0	1,457.3	(179.4)	(16.6)	(1.7)
Balance, Shares at Mar. 31, 2020		104.9
Net income (loss)	(2.4)			(2.4)
Other comprehensive income (loss), net of tax	4.2				4.2
Equity-based compensation	4.9		4.9
Repurchase of common stock and distributions	(0.2)					(0.2)
Balance at Jun. 30, 2020	1,267.1	$ 1.0	1,462.2	(181.8)	(12.4)	(1.9)
Balance, Shares at Jun. 30, 2020		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 income (loss)	19.5			19.5
Other comprehensive income (loss), net of tax	5.8				5.8
Capital contributions and issuance of common stock	1.6	$ 0.1	1.5
Capital contributions and issuance of common stock, Shares		0.3
Equity-based compensation	15.4		15.4
Repurchase of common stock and distributions	(1.2)					(1.2)
Balance at Jun. 30, 2021	1,312.6	$ 1.1	1,484.7	(168.4)	(1.1)	(3.7)
Balance, Shares at Jun. 30, 2021		105.2
Balance at Mar. 31, 2021	1,281.8	$ 1.1	1,479.4	(193.6)	(1.5)	(3.6)
Balance, Shares at Mar. 31, 2021		105.2
Net income (loss)	25.2			25.2
Other comprehensive income (loss), net of tax	0.4				0.4
Equity-based compensation	5.3		5.3
Repurchase of common stock and distributions	(0.1)					(0.1)
Balance at Jun. 30, 2021	$ 1,312.6	$ 1.1	$ 1,484.7	$ (168.4)	$ (1.1)	$ (3.7)
Balance, Shares at Jun. 30, 2021		105.2