Income (Loss) from Continuing Operations Per Unrestricted Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Schedule of Basic and Diluted Earnings Per Share [Line Items]
Income from Continuing Operations	$ 37.5	$ 36.6	$ 91.1	$ 36.2
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	$ 37.4	$ 36.3	$ 90.5	$ 36.0
Weighted-Average Unrestricted Shares Outstanding (shares)	51,549,900	51,286,200	51,526,600	51,279,600
Equity-based Compensation Equivalent Shares (shares)	526,500	124,900	470,100	157,600
Weighted-Average Unrestricted Shares and Equivalent Shares Outstanding Assuming Dilution (shares)	52,076,400	51,411,100	51,996,700	51,437,200
Basic Income from Continuing Operations Per Unrestricted Share	$ 0.73	$ 0.71	$ 1.76	$ 0.70
Diluted Income from Continuing Operations Per Unrestricted Share	$ 0.73	$ 0.71	$ 1.75	$ 0.70
Unrestricted Shares [Member]
Schedule of Basic and Diluted Earnings Per Share [Line Items]
Income from Continuing Operations	$ 37.4	$ 36.3	$ 90.5	$ 36.0
Participating Awards [Member]
Schedule of Basic and Diluted Earnings Per Share [Line Items]
Income from Continuing Operations	$ 0.1	$ 0.3	$ 0.6	$ 0.2