Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Income Tax Disclosure [Abstract]
Effective tax rate	36.60%	36.80%
Net benefits related to federal tax credits	$ 0.1
Net benefits related to the expiration of the statute of limitations		0.1
Decrease of effective income tax rate related to federal tax credits	2.40%
Decrease of effective income tax rate related to expiration of statute of limitations for uncertain tax positions		2.00%
Total gross amount of unrecognized tax benefits that would impact effective tax rate	1.6	1.7
Potential impact on total gross amount of unrecognized tax benefits due to expiration of statute of limitations	$ 1.1