Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Numerator:
Net income	$ 27.1	$ 30.3
Denominator:
Weighted average shares outstanding - basic	46.9	46.7
Effect of dilutive securities:
Equity compensation plans	0.7	0.7
Convertible preferred stock	0.1	0.1
Weighted average shares outstanding - diluted	47.7	47.5
Basic earnings per share (in dollars per share)	$ 0.58	$ 0.65
Diluted earnings per share (in dollars per share)	$ 0.57	$ 0.64