Stock-based Compensation (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award
Share-based Compensation Arrangement by Share-based Payment Award, Market Based Award Measurement Period	3 years
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation expense for nonvested stock units	$ 18.3	$ 19.8
Performance-based Restricted Stock Units | Minimum
Share-based Compensation Arrangement by Share-based Payment Award
Share-based compensation arrangement by share-based payment award, restricted stock units, expected payout (in shares)	0
Performance-based Restricted Stock Units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award
Share-based compensation arrangement by share-based payment award, restricted stock units, expected payout (in shares)	774,000