Stock-Based Compensation (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 5.1	$ 2.4	$ 7.4	$ 4.1
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	2.1	1.7	3.1	2.5
Performance stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	2.2	0.2	2.9	0.8
Director [Member] | Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation grant	129,680
Stock-based compensation expense	$ 0.9