Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Numerator:
Net income	$ 42.1	$ 27.1
Denominator:
Denominator for basic earnings per share — weighted average shares	46.0	46.9
Effect of dilutive securities:
Equity compensation plans	0.8	0.7
Convertible preferred stock	0	0.1
Denominator for diluted earnings per share — adjusted weighted average and assumed conversion	46.8	47.7
Basic earnings per share (in dollars per share)	$ 0.92	$ 0.58
Diluted earnings per share (in dollars per share)	$ 0.90	$ 0.57