Stock-Based Compensation (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock-based compensation expense
Stock-based compensation expense	$ 15.8	$ 13.9	$ 12.4
Tax benefit from stock options exercised during the period	6.8	8.5	3.9
Non-qualified stock options
Stock-based compensation expense
Stock-based compensation expense	4.5	4.1	3.9
RSUs
Stock-based compensation expense
Stock-based compensation expense	6.5	5.0	4.9
PRSUs
Stock-based compensation expense
Stock-based compensation expense	4.6	4.7	3.5
Employee stock purchase plan
Stock-based compensation expense
Stock-based compensation expense	$ 0.2	$ 0.1	$ 0.1