Retirement Benefits - Components of Net Periodic Benefit Cost for Defined Benefit Plans and Other Postretirement Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 140	$ 168
Interest cost	212	203
Net amortization	(159)	(184)
Net periodic benefit cost	193	187
U.S. | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	208	254
Interest cost	764	653
Expected return on plan assets	(801)	(983)
Net amortization	487	685
Net periodic benefit cost	658	609
Non-U.S. | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	464	545
Interest cost	365	361
Expected return on plan assets	(264)	(290)
Net amortization	284	330
Net periodic benefit cost	$ 849	$ 946