Income (Loss) from Continuing Operations Per Unrestricted Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Schedule of Basic and Diluted Earnings Per Share [Line Items]
Income from Continuing Operations	$ 92.3	$ 47.8	$ 183.4	$ 84.0
Dilutive Effect on Income of Equity-based Compensation Equivalent Shares	0.0	0.0	0.0	0.0
Diluted Income from Continuing Operations Attributed to Unrestricted Shares	$ 91.9	$ 47.4	$ 182.4	$ 83.4
Weighted-Average Unrestricted Shares Outstanding (shares)	64,580,400	51,366,800	55,925,700	51,308,700
Equity-based Compensation Equivalent Shares (shares)	769,100	199,600	569,800	171,600
Weighted-Average Unrestricted Shares and Equivalent Shares Outstanding Assuming Dilution (shares)	65,349,500	51,566,400	56,495,500	51,480,300
Basic Income from Continuing Operations Per Unrestricted Share	$ 1.42	$ 0.92	$ 3.26	$ 1.63
Diluted Income from Continuing Operations Per Unrestricted Share	$ 1.40	$ 0.92	$ 3.23	$ 1.62
Unrestricted Shares [Member]
Schedule of Basic and Diluted Earnings Per Share [Line Items]
Income from Continuing Operations	$ 91.9	$ 47.4	$ 182.4	$ 83.4
Participating Awards [Member]
Schedule of Basic and Diluted Earnings Per Share [Line Items]
Income from Continuing Operations	$ 0.4	$ 0.4	$ 1.0	$ 0.6