Recent Accounting Pronouncements New Accounting Standards - Effect fo changes due to Adoption of ASU 2016-18 (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Cash Provided by (Used in) Operating Activities	$ 55.9	$ 65.3
Cash and cash equivalents	202.7	79.9	$ 51.7	$ 83.0
Cash and Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect	$ 148.8	(3.1)
Scenario, Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Cash Provided by (Used in) Operating Activities		74.6
Cash and cash equivalents		54.9		48.7
Cash and Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect		6.2
Accounting Standards Update 2016-18 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Cash Provided by (Used in) Operating Activities		(9.3)
Cash and cash equivalents		25.0		$ 34.3
Cash and Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect		$ (9.3)