Net Income Per Unrestricted Share - Reconciliation of Numerator and Denominator Used in Calculation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Earnings Per Share [Abstract]
Net Income	$ 72.6	$ 75.4	$ 172.3	$ 146.7
Weighted-Average Unrestricted Shares Outstanding (in shares)	63,938,900	64,395,000	63,912,900	64,324,700
Equity-based Compensation Equivalent Shares (in shares)	661,200	496,600	713,600	507,400
Weighted-Average Unrestricted Shares and Equivalent Shares Outstanding Assuming Dilution (in shares)	64,600,100	64,891,600	64,626,500	64,832,100
Basic Net Income Per Unrestricted Share (in shares)	$ 1.13	$ 1.17	$ 2.69	$ 2.28
Diluted Net Income Per Unrestricted Share (in shares)	$ 1.12	$ 1.16	$ 2.66	$ 2.26