Stock-Based Compensation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Stock-Based Compensation Activity
Income tax benefit	$ 0.1	$ 0.0	$ 1.9	$ 1.3
Performance Shares [Member]
Stock-Based Compensation Activity
Compensation expense	0.2	(0.1)	4.7	3.1
Restricted Stock [Member]
Stock-Based Compensation Activity
Compensation expense	0.1	0.0	0.1	0.1
Stock Compensation Plan [Member]
Stock-Based Compensation Activity
Compensation expense	0.3	(0.1)	4.8	3.2
Total Shareholder Return [Member] | Performance Shares [Member]
Stock-Based Compensation Activity
Compensation expense	1.6	1.2	4.9	3.4
Performance Units Related to Earnings Per Share [Member] | Performance Shares [Member]
Stock-Based Compensation Activity
Compensation expense	$ (1.4)	$ (1.3)	$ (0.2)	$ (0.3)