Earnings Per Share and Common Stock (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share - Basic [Abstract]
Net Income	$ 31.2	$ 30.7	$ 135.9	$ 113.0
Average Common Shares	51.7	51.4	51.6	51.3
Earnings Per Share	$ 0.60	$ 0.59	$ 2.63	$ 2.20
Earnings Per Share - Diluted [Abstract]
Net Income	$ 31.2	$ 30.7	$ 135.9	$ 113.0
Average Common Shares	51.8	51.6	51.7	51.5
Earnings Per Share	$ 0.60	$ 0.59	$ 2.63	$ 2.19
Dilutive Securities (Shares)	0.1	0.2	0.1	0.2