Net Income Per Unrestricted Share - Reconciliation of Numerator and Denominator Used in Calculation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Schedule of Basic and Diluted Earnings Per Share [Line Items]
Net Income (Loss)	$ (94.8)	$ 123.2
Dilutive Effect on Income of Equity-based Compensation Equivalent Shares	0.0	0.0
Diluted Net Income (Loss) Attributed to Unrestricted Shares	$ (94.8)	$ 123.1
Weighted-Average Unrestricted Shares Outstanding (in shares)	63,743,700	65,424,600
Equity-based Compensation Equivalent Shares (in shares)	0	1,128,200
Weighted-Average Unrestricted Shares and Equivalent Shares Outstanding Assuming Dilution (in shares)	63,743,700	66,552,800
Basic (in dollars per share)	$ (1.49)	$ 1.88
Diluted (in dollars per share)	$ (1.49)	$ 1.85
Common Stock
Schedule of Basic and Diluted Earnings Per Share [Line Items]
Net Income (Loss)	$ (94.8)	$ 123.1
Participating Awards
Schedule of Basic and Diluted Earnings Per Share [Line Items]
Net Income (Loss)	$ 0.0	$ 0.1