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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 152	$ 181	$ 456	$ 494
Interest cost	203	224	611	622
Net amortization	(198)	(154)	(595)	(462)
Net periodic benefit cost	157	251	472	654
U.S. | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	224	181	732	769
Interest cost	687	788	2,008	2,282
Expected return on plan assets	(986)	(1,233)	(2,874)	(3,583)
Net amortization	641	766	1,924	2,420
Net periodic benefit cost	566	502	1,790	1,888
Non-U.S. | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	520	331	1,496	934
Interest cost	332	344	957	1,049
Expected return on plan assets	(277)	(203)	(811)	(642)
Net amortization	418	241	1,195	722
Net periodic benefit cost	$ 993	$ 713	$ 2,837	$ 2,063