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, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Termination of the U.S. pension plan			$ 9,688	$ 0
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 178	$ 154	356	309
Interest cost	103	157	205	313
Net amortization	170	136	(339)	(272)
Net periodic (benefit) cost	111	175	222	350
U.S. | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	37	35	75	69
Interest cost	102	190	166	651
Expected return on plan assets	(560)	(978)	(776)	(1,877)
Termination of the U.S. pension plan	10,448	75	10,496	377
Net amortization	(136)	234	225	208
Net periodic (benefit) cost	10,163	(912)	10,186	(572)
Non-U.S. | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	507	541	1,015	1,081
Interest cost	183	263	366	526
Expected return on plan assets	(252)	(291)	(505)	(582)
Termination of the U.S. pension plan	0	0	0	0
Net amortization	(549)	(426)	1,097	852
Net periodic (benefit) cost	$ 987	$ 939	$ 1,973	$ 1,877