Earnings Per 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
Numerator:
Net Income (Loss) Attributable to Parent	$ 91.0	$ 82.5	$ 171.2	$ 120.7
Less Undistributed Earnings (Loss) Allocated to Nonvested Stock	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Denominator:
Weighted Average Number of Shares Outstanding, Basic	77,360,159	77,931,576	77,544,365	77,814,438
Effect of dilutive securities:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	1,136,139	1,097,821	1,207,586	1,129,991
Weighted average number of shares outstanding, assuming dilution of stock options and awards	78,496,298	79,029,397	78,751,951	78,944,429
Basic earnings per share	$ 1.18	$ 1.06	$ 2.21	$ 1.55
Diluted earnings per share	$ 1.16	$ 1.04	$ 2.17	$ 1.53