Accounting Policies - Taxation (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
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