Retirement Benefits - Components of Net Periodic Benefit Cost for Defined Benefit Plans and Other Postretirement Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 140	$ 167	$ 280	$ 335
Interest cost	212	203	424	406
Net amortization	(158)	(184)	(317)	(368)
Net periodic benefit cost	194	186	387	373
U.S. | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	209	255	417	509
Interest cost	764	653	1,528	1,306
Expected return on plan assets	(801)	(983)	(1,602)	(1,966)
Net amortization	486	685	973	1,370
Net periodic benefit cost	658	610	1,316	1,219
Non-U.S. | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	460	527	924	1,072
Interest cost	361	351	726	712
Expected return on plan assets	(262)	(282)	(526)	(572)
Net amortization	280	322	564	652
Net periodic benefit cost	$ 839	$ 918	$ 1,688	$ 1,864