Retirement Benefits - Components of Net Periodic Benefit Cost for Defined Benefit Plans and Other Postretirement Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits | U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 134	$ 653	$ 886
Interest cost	1,274	2,796	2,634
Expected return on plan assets	(3,750)	(3,319)	(3,943)
Settlement loss recognized	910	713	(1)
Special termination benefit recognized	0	276	0
Net amortization	1,163	1,614	2,712
Net periodic (benefit) cost	(269)	2,733	2,288
Pension Benefits | Non-U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	2,215	1,844	2,105
Interest cost	1,056	1,440	1,389
Expected return on plan assets	(1,170)	(1,047)	(1,120)
Settlement loss recognized	(385)	0	(307)
Special termination benefit recognized	0	0	0
Net amortization	1,730	1,117	1,271
Net periodic (benefit) cost	3,446	3,354	3,338
Other Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	616	561	668
Interest cost	624	849	810
Net amortization	(542)	(635)	(737)
Net periodic (benefit) cost	$ 698	$ 775	$ 741