Taxation - Summary of tax years open to examination by jurisdiction (Details)	12 Months Ended
	Dec. 31, 2017
United States | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2013
Year under Examination	2013
Operating Loss Carryforwards, Expiration Date	Jan. 01, 2033
United States | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2017
Year under Examination	2015
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2037
Ireland | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2013
Ireland | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2017
United Kingdom | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2013
Year under Examination	2013
United Kingdom | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2017
Year under Examination	2015
Germany | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2014
Germany | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2017
Switzerland | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2013
Operating Loss Carryforwards, Expiration Date	Jan. 01, 2018
Switzerland | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2017
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2025
France | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2013
Year under Examination	2013
France | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2017
Year under Examination	2014
Spain | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2011
Year under Examination	2011
Spain | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2017
Year under Examination	2012
Italy | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2013
Italy | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2017