Net Income Per Common Share Computations (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Numerator for basic and diluted net income per common share:
Net income	$ 42.1	$ 36.1
Denominator for net income per common share:
Basic (in shares)	38.3	39.0
Plus dilutive effect of stock awards (in shares)	0.5	0.6
Diluted (in shares)	38.8	39.6
Net income (loss) per common share data: Basic
Net income (loss) per common share - basic (in dollars per share)	$ 1.10	$ 0.93
Net income (loss) per common share data: Diluted
Net income (loss) per common share - diluted (in dollars per share)	$ 1.08	$ 0.91