Summary of Significant Accounting Policies (Details 5) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock-Based Compensation
Total stock-based compensation	$ 7.8	$ 7.9	$ 6.9
Estimated forfeiture rate (as a percent)	5.70%	5.20%	5.40%
Stock options
Stock-Based Compensation
Total stock-based compensation	6.5	6.6	5.8
Award vesting period, minimum (in years)	P3Y
Award vesting period, maximum (in years)	P5Y
Risk-free interest rate, minimum (as a percent)	0.91%	1.24%	1.73%
Risk-free interest rate, maximum (as a percent)	1.78%	3.12%	3.46%
Expected life (in years)	6.5	6.5	6.5
Volatility (as a percent)	55.90%	57.20%	62.00%
Weighted average fair values of options granted (in dollars per share)	$ 7.11	$ 7.89	$ 8.56
Restricted stock
Stock-Based Compensation
Total stock-based compensation	$ 1.3	$ 1.3	$ 1.1
Award vesting period, minimum (in years)	P3Y
Award vesting period, maximum (in years)	P5Y