Stock-Based Compensation (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Stock-Based Compensation Activity
Income tax benefit	$ 1.0	$ 0.7	$ 1.8	$ 1.3
Performance Shares [Member]
Stock-Based Compensation Activity
Compensation expense	2.4	1.5	4.5	3.2
Restricted Stock [Member]
Stock-Based Compensation Activity
Compensation expense	0.0	0.1	0.0	0.1
Stock Compensation Plan [Member]
Stock-Based Compensation Activity
Compensation expense	2.4	1.6	4.5	3.3
Total Shareholder Return [Member] | Performance Shares [Member]
Stock-Based Compensation Activity
Compensation expense	1.8	1.1	3.3	2.2
Performance Units Related to Earnings Per Share [Member] | Performance Shares [Member]
Stock-Based Compensation Activity
Compensation expense	$ 0.6	$ 0.4	$ 1.2	$ 1.0