Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss	Treasury Stock
Balance at Dec. 31, 2016	$ 705.2	$ 0.7	$ 891.3	$ (164.0)	$ (22.8)
Balance, Shares at Dec. 31, 2016		77.0
Net income (loss)	(14.0)			(14.0)
Other comprehensive income (loss), net of tax	2.3				2.3
Capital contributions and issuance of common stock	0.1		0.1
Capital contributions and issuance of common stock, Shares		0.1
Equity-based compensation	3.8		3.8
Repurchase of common stock and distributions	(1.2)		(1.2)
Balance at Sep. 30, 2017	696.2	$ 0.7	894.0	(178.0)	(20.5)
Balance, Shares at Sep. 30, 2017		77.1
Net income (loss)	(15.1)			(15.1)
Other comprehensive income (loss), net of tax	13.6				13.6
Capital contributions and issuance of common stock	506.7	$ 0.3	506.4
Capital contributions and issuance of common stock, Shares		27.5
Equity-based compensation	28.8		28.8
Repurchase of common stock and distributions	(2.9)		(2.9)
Repurchase of common stock and distributions, Shares		(0.1)
Reclassification of effects of tax reform enactment				3.5	(3.5)
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 (loss), net of tax	(1.3)				(1.3)
Capital contributions and issuance of common stock, Shares		0.2
Equity-based compensation	15.7		15.7
Repurchase of common stock and distributions	(1.2)		(0.2)			$ (1.0)
Adoption of ASC 606 | ASC 606	(1.1)			(1.1)
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