Income Per Common Share Computations (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net income	$ 16.7	$ 8.7	$ 102.3	$ 81.3
Participating Securities, Distributed and Undistributed Earnings (Loss), Basic	0.0	(0.1)	(0.1)	(1.4)
Income (Loss) from Continuing Operations, Basic	16.7	8.6	102.2	79.9
Net Income (Loss) Available to Common Stockholders, Diluted	$ 16.7	$ 8.7	$ 102.3	$ 81.3
Earnings Per Share, Basic and Diluted [Abstract]
Basic-weighted average shares	15.3	16.4	15.9	16.5
Plus dilutive effect of stock awards	0.2	0.2	0.2	0.2
Plus dilutive effect of participating securities	0.0	0.3	0.1	0.3
Diluted-adjusted weighted average shares	15.5	16.9	16.2	17.0
Earnings Per Share, Diluted [Abstract]
Basic	$ 1.09	$ 0.52	$ 6.43	$ 4.85
Diluted	$ 1.08	$ 0.52	$ 6.32	$ 4.79