Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net Income	$ 259.2	$ 155.9	$ 143.1
Less: Net income allocated to participating securities	(4.9)	0.0	0.0
Net income available to common shareholders	$ 254.3	$ 155.9	$ 143.1
Denominator for basic earnings per share — weighted average shares	35,700	35,400	35,400
Earnings Per Share, Basic	$ 7.13	$ 4.41	$ 4.04
Less: Net income allocated to participating securities	$ (4.9)	$ 0.0	$ 0.0
Net income available to common shareholders	$ 254.3	$ 155.9	$ 143.1
Equity compensation plans (in shares)	100	500	600
Weighted-average shares outstanding - diluted (in shares)	35,700	35,900	36,000
Diluted earnings per share (in dollars per share)	$ 7.12	$ 4.35	$ 3.98