Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) shares in Millions, $ in Millions	Total	Revision of Prior Period, Accounting Standards Update, Adjustment	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Deficit Revision of Prior Period, Accounting Standards Update, 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)	19.3				19.3
Other comprehensive income (loss), net of tax	(2.5)						(2.5)
Capital contributions and issuance of common stock, Shares			0.3
Equity-based compensation	$ 11.8			11.8
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201409Member
Balance at Jun. 30, 2019	$ 1,254.8	$ (1.1)	$ 1.0	1,438.1	(171.4)	$ (1.1)	(12.9)
Balance, Shares at Jun. 30, 2019			104.8
Balance at Mar. 31, 2019	1,223.9		$ 1.0	1,437.8	(203.1)		(11.8)
Balance, Shares at Mar. 31, 2019			105.0
Net income (loss)	31.7				31.7
Other comprehensive income (loss), net of tax	(1.1)						(1.1)
Capital contributions and issuance of common stock, Shares			(0.2)
Equity-based compensation	0.3			0.3
Balance at Jun. 30, 2019	1,254.8	$ (1.1)	$ 1.0	1,438.1	(171.4)	$ (1.1)	(12.9)
Balance, Shares at Jun. 30, 2019			104.8
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