Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012
Numerator:
Net income	$ 53.8		$ 53.8	$ 116.0		$ 107.6
Denominator:
Weighted average shares outstanding - basic	46.2		46.9	46.5		46.8
Effect of dilutive securities:
Equity compensation plans	0.6		0.6	0.7		0.6
Convertible preferred stock		[1]	0.1		[1]	0.1
Weighted average shares outstanding - diluted	46.8		47.6	47.2		47.5
Basic earnings per share (in dollars per share)	$ 1.16		$ 1.15	$ 2.49		$ 2.30
Diluted earnings per share (in dollars per share)	$ 1.15		$ 1.13	$ 2.45		$ 2.26

[1] Antidilutive