Provision for Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Provision for Income Taxes
Income tax provision	$ 16.3	$ 12.4	$ 22.0	$ 15.0
Effective tax rates (as a percent)	49.20%	34.70%	45.10%	34.10%
Unrecognized tax benefits, excluding penalties and interest	33.3		33.3		32.7
Portion of unrecognized tax benefits, which if recognized, would result in a reduction of the effective tax rate	14.0		14.0		14.1
Accrued interest and penalties related to uncertain tax positions	4.0		4.0		3.8
Penalties and interest expense relating to unrecognized tax benefits	$ 0	$ 0.4	$ 0	$ 0.7