Earnings Per 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
Numerator:
Net Income (Loss) Attributable to Parent	$ 71.6	$ 53.5	$ 242.8	$ 174.2
Less Undistributed Earnings (Loss) Allocated to Nonvested Stock	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Denominator:
Weighted Average Number of Shares Outstanding, Basic	76,903,395	77,694,974	77,332,209	77,766,828
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	1,524,710	1,109,322	1,313,294	1,123,102
Weighted average number of shares outstanding, assuming dilution of stock options and awards	78,428,105	78,804,296	78,645,503	78,889,930
Basic earnings per share	$ 0.93	$ 0.69	$ 3.14	$ 2.24
Diluted earnings per share	$ 0.91	$ 0.68	$ 3.09	$ 2.21