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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 152	$ 181	$ 304	$ 313
Interest cost	204	224	408	398
Net amortization	(199)	(154)	(397)	(308)
Net periodic benefit cost	157	251	315	403
U.S. | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	254	294	508	588
Interest cost	661	747	1,321	1,494
Expected return on plan assets	(944)	(1,175)	(1,888)	(2,350)
Net amortization	641	827	1,283	1,654
Net periodic benefit cost	612	693	1,224	1,386
Non-U.S. | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	494	304	976	603
Interest cost	317	355	625	705
Expected return on plan assets	(270)	(220)	(534)	(439)
Net amortization	395	243	777	481
Net periodic benefit cost	$ 936	$ 682	$ 1,844	$ 1,350