Retirement Benefits - Components of Net Periodic Benefit Cost for Defined Benefit Plans and Other Postretirement Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 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	$ 179	$ 154	535	463
Interest cost	102	156	307	469
Net amortization	(169)	(135)	(508)	(407)
Net periodic (benefit) cost	112	175	334	525
U.S. | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	38	34	113	103
Interest cost	43	312	209	963
Expected return on plan assets	(39)	(927)	(815)	(2,804)
Termination of the U.S. pension plan	0	326	10,496	702
Net amortization	74	643	299	852
Net periodic (benefit) cost	116	388	10,302	(184)
Non-U.S. | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	508	539	1,523	1,620
Interest cost	183	263	549	789
Expected return on plan assets	(253)	(291)	(758)	(873)
Termination of the U.S. pension plan	0	0	0	0
Net amortization	548	427	1,645	1,279
Net periodic (benefit) cost	$ 986	$ 938	$ 2,959	$ 2,815