Summary of Significant Accounting Policies (Details 5) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Stock-Based Compensation
Total stock-based compensation	$ 6.6	$ 7.8	$ 7.9
Estimated forfeiture rate (as a percent)	7.00%	5.70%	5.20%
Stock options
Stock-Based Compensation
Total stock-based compensation	5.3	6.5	6.6
Risk-free interest rate, minimum (as a percent)	1.07%	0.91%	1.24%
Risk-free interest rate, maximum (as a percent)	2.45%	1.78%	3.12%
Expected life	6 years 6 months	6 years 6 months	6 years 6 months
Volatility (as a percent)	54.90%	55.90%	57.20%
Weighted average fair values of options granted (in dollars per share)	$ 10.37	$ 7.11	$ 7.89
Stock options | Minimum
Stock-Based Compensation
Vesting period	3 years
Stock options | Maximum
Stock-Based Compensation
Vesting period	5 years
Restricted stock
Stock-Based Compensation
Total stock-based compensation	$ 1.3	$ 1.3	$ 1.3