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Stock-Based Compensation (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
Stock-Based Compensation (Details) - USD ($) $ in Millions	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Stock-Based Compensation Activity
Income tax benefit	$ 0.7	$ 0.8	$ 1.5	$ 1.5
Performance Shares [Member]
Stock-Based Compensation Activity
Compensation expense	2.7	3.1	5.4	5.8
Restricted Stock [Member]
Stock-Based Compensation Activity
Compensation expense	0.2	0.0	0.5	0.0
Share-based Payment Arrangement [Member]
Stock-Based Compensation Activity
Compensation expense	$ 2.9	3.1	$ 5.9	5.8
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture	1,111		443,497
Total Shareholder Return [Member] \| Performance Shares [Member]
Stock-Based Compensation Activity
Compensation expense	$ 2.3	2.1	$ 4.5	4.1
Performance Units Related to Earnings Per Share [Member] \| Performance Shares [Member]
Stock-Based Compensation Activity
Compensation expense	$ 0.4	$ 1.0	$ 0.9	$ 1.7