IPO and Private Placement - Use of Proceeds from IPO (Details) - USD ($) $ in Millions				1 Months Ended	3 Months Ended	12 Months Ended
	Jul. 06, 2020	Feb. 08, 2019	Aug. 08, 2018	Feb. 07, 2019	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Gross proceeds	$ 2,381.0			$ 0.0		$ 0.0	$ 3,176.8	$ 0.0
Underwriter fees	89.1
IPO related expenses	42.8	$ 21.6	$ 21.6
Redemption of Series A Preferred Stock	1,067.9			0.0		1,067.9	0.0	0.0
Make-whole payment on redemption of Series A Preferred Stock	205.2
Partial redemption of Notes and accrued interest				$ 0.0		0.0	$ 625.1	$ 0.0
Cash to balance sheet	331.7
New Senior Unsecured Notes - 10.250%
Class of Stock [Line Items]
Partial redemption of Notes and accrued interest	312.0
Call premium on partial redemption of Notes	30.8
New Senior Unsecured Notes - 10.250% | Unsecured Debt
Class of Stock [Line Items]
Call premium on partial redemption of Notes					$ 30.8
Interest rate on debt instrument (as a percent)		10.25%
New Senior Secured Notes - 6.875%
Class of Stock [Line Items]
Partial redemption of Notes and accrued interest	282.2
Call premium on partial redemption of Notes	19.3
New Senior Secured Notes - 6.875% | Secured Debt
Class of Stock [Line Items]
Call premium on partial redemption of Notes						$ 19.3
Interest rate on debt instrument (as a percent)		6.875%
Star Parent, L.P. | Affiliated Entity
Class of Stock [Line Items]
IPO related expenses	30.0
THL Managers | Affiliated Entity
Class of Stock [Line Items]
IPO related expenses	2.5
Bilcar | Board of Directors Chairman
Class of Stock [Line Items]
IPO related expenses	2.5
CC Star Holdings, LP | Director
Class of Stock [Line Items]
IPO related expenses	$ 2.5