Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tax expense (benefit)		$ 14.0	$ 14.4	$ 19.1	$ 38.3
Cash and Cash Equivalents, at Carrying Value		269.3	$ 205.9	269.3	$ 205.9		$ 203.0	$ 274.6
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Amount				$ 3.5
Foreign Earnings Repatriated	$ 10.0	$ 55.3				$ 65.0
Effective tax rate		22.30%	29.30%	11.70%	28.10%
Accounting Standards Update 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tax expense (benefit)		$ (4.8)		$ (30.3)