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Stock-Based Compensation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Stock-Based Compensation (Details) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Stock-Based Compensation Activity
Income tax benefit	$ 1.3	$ 1.0	$ 2.8	$ 2.5
Performance Shares [Member]
Stock-Based Compensation Activity
Compensation expense	4.6	3.9	10.0	9.7
Restricted Stock [Member]
Stock-Based Compensation Activity
Compensation expense	0.3	0.0	0.8	0.0
Share-based Payment Arrangement [Member]
Stock-Based Compensation Activity
Compensation expense	4.9	3.9	$ 10.8	9.7
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture			443,900
Total Shareholder Return [Member] \| Performance Shares [Member]
Stock-Based Compensation Activity
Compensation expense	2.3	2.0	$ 6.8	6.1
Performance Units Related to Earnings Per Share [Member] \| Performance Shares [Member]
Stock-Based Compensation Activity
Compensation expense	$ 2.3	$ 1.9	$ 3.2	$ 3.6