Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2012
Income Tax Examination [Line Items]
U.S. statutory income tax rate			21.00%	35.00%
Income tax expense	$ 18.3	$ 14.6	$ 14.0	$ 11.1
Income before income tax	44.0	38.1	50.1	38.2
Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Amount			(5.6)
Income Tax Reconciliation Deductions Excess Tax Benefits	0.1	0.2	$ 2.6	5.5
State and Local Jurisdiction | Minimum
Income Tax Examination [Line Items]
Statutes of limitation, period			2 years
State and Local Jurisdiction | Maximum
Income Tax Examination [Line Items]
Statutes of limitation, period			5 years
Domestic Tax Authority | Internal Revenue Service (IRS)
Income Tax Examination [Line Items]
Tax Cuts and Jobs Act, Incomplete Accounting, Provisional Income Tax Expense (Benefit)					$ (25.7)
Tax Cuts and Jobs Act, Incomplete Accounting, Transition Toll Tax for Accumulated Foreign Earnings, Provisional Income Tax Expense, net of foreign tax credits					24.0
Deferred Tax Assets, Tax Credit Carryforwards, Foreign					14.0
Tax Cuts and Jobs Act, Incomplete Accounting, Change in Tax Rate, Deferred Tax Liability, Provisional Income Tax Benefit					$ 49.7
Domestic Tax Authority | Internal Revenue Service (IRS) | Earliest Tax Year
Income Tax Examination [Line Items]
Open tax year			2014
Foreign Tax Authority | Minimum
Income Tax Examination [Line Items]
Statutes of limitation, period			2 years
Foreign Tax Authority | Maximum
Income Tax Examination [Line Items]
Statutes of limitation, period			5 years
Foreign Tax Authority | Australian Taxation Office | Earliest Tax Year
Income Tax Examination [Line Items]
Open tax year			2013
Foreign Tax Authority | Secretariat of the Federal Revenue Bureau of Brazil
Income Tax Examination [Line Items]
Income Tax Examination, Interest Expense	0.3	$ 0.6	$ 0.6	$ 1.3
Foreign Tax Authority | Secretariat of the Federal Revenue Bureau of Brazil | Earliest Tax Year
Income Tax Examination [Line Items]
Open tax year			2012
Foreign Tax Authority | Secretariat of the Federal Revenue Bureau of Brazil | Tax Year 2008 to 2010
Income Tax Examination [Line Items]
Unrecognized Tax Benefits	21.6		$ 21.6
Foreign Tax Authority | Secretariat of the Federal Revenue Bureau of Brazil | Tax Year 2007 to 2012
Income Tax Examination [Line Items]
Unrecognized Tax Benefits	$ 29.2		$ 29.2			$ 44.5
Income Tax Contingency, Potential Assessment, Acquisition, Fair Value of Liabilities Accrued						$ 43.3
Foreign Tax Authority | Secretariat of the Federal Revenue Bureau of Brazil | Minimum
Income Tax Examination [Line Items]
Penalty rate	75.00%		75.00%
Foreign Tax Authority | Secretariat of the Federal Revenue Bureau of Brazil | Maximum
Income Tax Examination [Line Items]
Penalty rate	150.00%		150.00%
Foreign Tax Authority | Canada Revenue Agency | Earliest Tax Year
Income Tax Examination [Line Items]
Open tax year			2010
Foreign Tax Authority | Federal Ministry of Finance, Germany | Earliest Tax Year
Income Tax Examination [Line Items]
Open tax year			2011
Foreign Tax Authority | Swedish Tax Agency (Skatteverket) | Earliest Tax Year
Income Tax Examination [Line Items]
Open tax year			2011
Foreign Tax Authority | Her Majesty's Revenue and Customs (HMRC) | Earliest Tax Year
Income Tax Examination [Line Items]
Open tax year			2016