Income Taxes - Summary of Income Tax Examinations (Details)	12 Months Ended
	Dec. 31, 2018
U.S. Federal | 2015
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2015
U.S. Federal | 2016
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2016
U.S. Federal | 2017
Income Taxes [Line Items]
Income Tax Examinations Not Yet Initiated Years	2017
U.S. Federal | 2018
Income Taxes [Line Items]
Income Tax Examinations Not Yet Initiated Years	2018
U.S. State | 2015
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2015
U.S. State | 2016
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2016
U.S. State | 2017
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2017
U.S. State | 2018
Income Taxes [Line Items]
Income Tax Examinations Not Yet Initiated Years	2018
Germany | 2015
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2015
Germany | 2016
Income Taxes [Line Items]
Income Tax Examinations Not Yet Initiated Years	2016
Germany | 2017
Income Taxes [Line Items]
Income Tax Examinations Not Yet Initiated Years	2017
Germany | 2018
Income Taxes [Line Items]
Income Tax Examinations Not Yet Initiated Years	2018
Germany | Tax Year 2008
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2008
Germany | Tax Year 2009
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2009
Germany | Tax Year 2010
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2010
Germany | Tax Year 2011
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2011
Germany | Tax Year 2012
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2012
Germany | Tax Year 2013
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2013
Germany | Tax Year 2014
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2014
India | 2015
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2015
India | 2016
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2016
India | 2017
Income Taxes [Line Items]
Income Tax Examinations Not Yet Initiated Years	2017
India | 2018
Income Taxes [Line Items]
Income Tax Examinations Not Yet Initiated Years	2018
India | Tax Year 2008
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2008
India | Tax Year 2009
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2009
India | Tax Year 2010
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2010
India | Tax Year 2011
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2011
India | Tax Year 2012
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2012
India | Tax Year 2013
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2013
India | Tax Year 2014
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2014
India | 1999
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	1999
India | 2000
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2000
India | 2001
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2001
India | 2002
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2002
India | 2003
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2003
India | 2004
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2004
India | 2005
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2005
India | 2006
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2006
India | 2007
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2007
United Kingdom | 2015
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2015
United Kingdom | 2016
Income Taxes [Line Items]
Income Tax Examinations Not Yet Initiated Years	2016
United Kingdom | 2017
Income Taxes [Line Items]
Income Tax Examinations Not Yet Initiated Years	2017
United Kingdom | 2018
Income Taxes [Line Items]
Income Tax Examinations Not Yet Initiated Years	2018
United Kingdom | Tax Year 2013
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2013
United Kingdom | Tax Year 2014
Income Taxes [Line Items]
Income Tax Examinations In Progress, Years	2014