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, 2021	Mar. 31, 2020
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 178	$ 155
Interest cost	102	156
Net amortization	(169)	(136)
Net periodic (benefit) cost	111	175
U.S. | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	38	34
Interest cost	64	461
Expected return on plan assets	(216)	(899)
Settlement loss recognized	48	302
Net amortization	89	442
Net periodic (benefit) cost	23	340
Non-U.S. | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	508	540
Interest cost	183	263
Expected return on plan assets	(253)	(291)
Settlement loss recognized	0	0
Net amortization	548	426
Net periodic (benefit) cost	$ 986	$ 938