Share-based Compensation Unrecognized Compensation Expense for Share-Based Awards (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 28.8
Remaining weighted-average recognition period	2 years 6 months
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	23.8
Remaining weighted-average recognition period	2 years 4 months 24 days
Performance Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 5.0
Remaining weighted-average recognition period	2 years 10 months 24 days