Net Income (Loss) Per Unrestricted Share - Reconciliation of Numerator and Denominator Used in Calculation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Earnings Per Share [Abstract]
Net Income (Loss)	$ 73.7	$ (146.3)	$ 220.4	$ (323.5)
Weighted-Average Unrestricted Shares Outstanding (in shares)	64,216,500	64,056,900	64,288,400	64,004,400
Equity-based Compensation Equivalent Shares (in shares)	681,500	0	575,400	0
Weighted-Average Unrestricted Shares and Equivalent Shares Outstanding Assuming Dilution (in shares)	64,898,000	64,056,900	64,863,800	64,004,400
Basic Net Income (Loss) Per Unrestricted Share (in shares)	$ 1.15	$ (2.28)	$ 3.43	$ (5.05)
Diluted Net Income (Loss) Per Unrestricted Share (in shares)	$ 1.14	$ (2.28)	$ 3.40	$ (5.05)