Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net income	$ 45.1	$ 47.0	$ 154.6	$ 162.1
Denominator:
Denominator for basic earnings per share — weighted average shares	35.4	37.7	35.9	37.8
Effect of dilutive securities:
Equity compensation plans	0.6	0.8	0.7	0.7
Denominator for diluted earnings per share — adjusted weighted average and assumed conversion	36.0	38.5	36.6	38.5
Basic earnings per share (in dollars per share)	$ 1.28	$ 1.25	$ 4.30	$ 4.29
Diluted earnings per share (in dollars per share)	$ 1.25	$ 1.22	$ 4.22	$ 4.21