Restricted Stock Awards and Restricted Stock Units Description of Performance Incentive Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Schedule of Restricted Stock Award and Restricted Stock Unit Activity [Line Items]
Share-based compensation expense	$ 3.8	$ 4.0	$ 8.5	$ 7.5
Performance-based Restricted Stock Units [Member]
Schedule of Restricted Stock Award and Restricted Stock Unit Activity [Line Items]
Share grants approved in period			1.0	0.7
Time-based Restricted Stock Units [Member]
Schedule of Restricted Stock Award and Restricted Stock Unit Activity [Line Items]
Share grants approved in period			0.3	0.3
Restricted Stock Units [Member]
Schedule of Restricted Stock Award and Restricted Stock Unit Activity [Line Items]
Share-based compensation expense	$ 2.8	$ 3.0	$ 6.5	$ 6.0