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Income Taxes - Income Tax Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
Expected tax (benefit)/expense													$ 0.0	$ 0.0	$ 0.0
Overseas statutory tax rates differential													(41.5)	(19.3)	6.4
Prior year adjustments													1.3	3.3	(4.5)
Valuation allowance													(37.9)	21.0	11.8
Impact of unrecognized tax benefits													0.1	(1.9)	0.0
Restricted foreign tax credits													1.6	1.9	0.6
Share-based payments													(0.9)	0.0	0.0
Foreign exchange													(2.1)	0.2	(0.4)
Non-deductible expenses													0.4	0.8	1.7
Non-taxable items													(0.9)	(0.9)	(1.3)
Impact of changes in statutory tax rates													64.5	1.0	0.1
Total income tax expense/(benefit)	$ (10.2)	$ (9.2)	$ 1.2	$ 2.8	$ (2.6)	$ 4.9	$ 1.3	$ 2.5	$ 5.3	$ 1.8	$ 2.2	$ 5.1	(15.4)	6.1	$ 14.4
Effective Income Rate Tax Reconciliation, Tax Settlement, Foreign Credit, Amount													0.3	3.2
Income tax examination, interest accrued	$ 0.4				$ 1.3								$ 0.4	$ 1.3

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Effective Income Rate Tax Reconciliation, Tax Settlement, Foreign Credit, Amount

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The amount of estimated interest accrued as of the balance sheet date arising from income tax examinations.

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