Income Taxes - Tax Jurisdictions and Years Currently under Audit Exam (Details)	3 Months Ended
	Dec. 31, 2018
UNITED STATES | Earliest tax year under exam
Income Tax Examination [Line Items]
Tax years currently under audit exam	2015
UNITED STATES | Latest tax year under exam
Income Tax Examination [Line Items]
Tax years currently under audit exam	2016
BELGIUM | Earliest tax year under exam
Income Tax Examination [Line Items]
Tax years currently under audit exam	2015
BELGIUM | Latest tax year under exam
Income Tax Examination [Line Items]
Tax years currently under audit exam	2017
CHINA | Earliest tax year under exam
Income Tax Examination [Line Items]
Tax years currently under audit exam	2008
CHINA | Latest tax year under exam
Income Tax Examination [Line Items]
Tax years currently under audit exam	2016
France | Tax Year 2010 [Member]
Income Tax Examination [Line Items]
Tax years currently under audit exam	2010
France | Tax Year 2011 [Member]
Income Tax Examination [Line Items]
Tax years currently under audit exam	2011
France | Tax Year 2012 [Member]
Income Tax Examination [Line Items]
Tax years currently under audit exam	2012
France | Tax Year 2015 [Member]
Income Tax Examination [Line Items]
Tax years currently under audit exam	2015
France | Tax Year 2016 [Member]
Income Tax Examination [Line Items]
Tax years currently under audit exam	2016
Germany | Earliest tax year under exam
Income Tax Examination [Line Items]
Tax years currently under audit exam	2007
Germany | Latest tax year under exam
Income Tax Examination [Line Items]
Tax years currently under audit exam	2016
United Kingdom | Earliest tax year under exam
Income Tax Examination [Line Items]
Tax years currently under audit exam	2012
United Kingdom | Latest tax year under exam
Income Tax Examination [Line Items]
Tax years currently under audit exam	2015