Calculation of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Calculation of Basic and Diluted Earnings per Share [Abstract]
Net income	$ 38.1	$ 49.5
Weighted-average number of common shares outstanding - basic	46.5	49.3
Dilutive effect of common share equivalents	0.4	0.5
Weighted-average number of common shares and share equivalents outstanding - diluted	46.9	49.8
Basic earnings per share	$ 0.82	$ 1.00
Diluted earnings per share	$ 0.81	$ 0.99