Accounting Policies - Taxation (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Income tax expense			$ 5.1
Valuation allowance			5.1
Provisional income tax expense (benefit)			2.4
Transition tax for accumulated foreign earnings, provisional income tax expense			10.4
Change in tax rate			7.1
Other provisional income tax expense (benefit)			$ 0.9
Change in tax rate, adjustment	$ (1.5)	$ (1.5)