Share-based Compensation Components of Share-Based Compensation Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block]	$ 2.1	$ 1.9	$ 4.2	$ 2.6
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	0.5	0.7	1.1	1.0
Restricted Shares And Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block]	0.9	0.6	1.6	0.6
Performance Shares And Performance Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block]	0.6	0.7	1.2	0.7
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block]	0.4	0.2	0.8	0.2
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block]	$ 0.2	$ 0.4	$ 0.6	$ 1.1