Retirement Benefits - Components of Net Periodic Benefit Cost for Defined Benefit Plans and Other Postretirement Plans (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Settlement loss recognized		$ 0	$ 0	$ 3,554
Pension Benefit Plan | U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost		886	976	1,016
Interest cost		2,634	2,677	3,043
Net amortization		(2,712)	(2,566)	(3,226)
Expected return on plan assets		(3,943)	(3,832)	(4,777)
Settlement loss recognized	$ 3,500	(1)	0	3,339
Net periodic benefit cost		2,288	2,387	5,847
Pension Benefit Plan | Non-U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost		2,105	1,975	1,627
Interest cost		1,389	1,283	1,429
Net amortization		(1,271)	(1,809)	(1,008)
Expected return on plan assets		(1,120)	(1,088)	(993)
Settlement loss recognized		(307)	234	215
Net periodic benefit cost		3,338	4,213	3,286
Other Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost		668	610	601
Interest cost		810	818	811
Net amortization		737	795	705
Net periodic benefit cost		$ 741	$ 633	$ 707