Actuarial Assumptions used to Compute Benefit Obligations (Details)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Compensation And Retirement Disclosure [Abstract]
Defined Benefit Plan, Sponsor Location [Extensible List]	us-gaap:ForeignPlanMember	us-gaap:ForeignPlanMember	us-gaap:ForeignPlanMember
Weighted-average discount rate	2.40%	2.60%
Rate of inflation	2.90%	3.00%