Income From Continuing Operations Per Unrestricted Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Basic and Diluted Earnings Per Share [Line Items]
Income (Loss) from Continuing Operations	$ 35.9	$ 47.8	$ 36.6	$ (0.4)	$ 29.1	$ (18.3)	$ 4.1	$ (2.2)	$ 119.9	$ 12.7	$ 80.2
Dilutive Effect on Income of Equity-based Compensation Equivalent Shares									0.0	0.0	0.0
Diluted Income from Continuing Operations Attributed to Unrestricted Shares									$ 119.1	$ 12.9	$ 79.8
Weighted-Average Unrestricted Shares Outstanding (in shares)									51,345,600	51,156,100	51,606,900
Equity-based Compensation Equivalent Shares (in shares)									232,300	58,600	76,600
Weighted-average Unrestricted Shares and Equivalent Shares Outstanding Assuming Dilution ( in shares)									51,577,900	51,214,700	51,683,500
Basic Income from Continuing Operations Per Unrestricted Share (per share)	$ 0.69	$ 0.92	$ 0.71	$ (0.01)	$ 0.56	$ (0.36)	$ 0.08	$ (0.04)	$ 2.32	$ 0.25	$ 1.55
Diluted Income from Continuing Operations Per Unrestricted Share (per share)	$ 0.69	$ 0.92	$ 0.71	$ (0.01)	$ 0.56	$ (0.36)	$ 0.08	$ (0.04)	$ 2.31	$ 0.25	$ 1.55
Common Stock [Member]
Schedule of Basic and Diluted Earnings Per Share [Line Items]
Income (Loss) from Continuing Operations									$ 119.1	$ 12.9	$ 79.8
Participating Awards [Member]
Schedule of Basic and Diluted Earnings Per Share [Line Items]
Income (Loss) from Continuing Operations									$ 0.8	$ (0.2)	$ 0.4