Retirement Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Plan contributions	$ 186		$ 265
U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	0	$ 97	0	$ 177
Interest cost	390	415	780	830
Expected return on plan assets	(586)	(603)	(1,171)	(1,200)
Amortization of net actuarial loss	11	8	21	17
Amortization of prior service cost	0	10	0	21
Settlement charge	205	0	205	0
Foreign currency	0	0	0	0
Net periodic cost (benefit)	20	(73)	(165)	(155)
Non-U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	24	36	48	72
Interest cost	129	103	219	208
Expected return on plan assets	(101)	(97)	(197)	(194)
Amortization of net actuarial loss	0	0	0	0
Amortization of prior service cost	49	32	96	64
Settlement charge	0	0	0	0
Foreign currency	234	(16)	229	24
Net periodic cost (benefit)	335	58	395	174
Postretirement Medical Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans
Plan contributions	86		295
Service cost	20	24	40	48
Interest cost	90	100	181	199
Expected return on plan assets	0	0	0	0
Amortization of net actuarial loss	0	0	0	0
Amortization of prior service cost	0	0	0	0
Settlement charge	0	0	0	0
Foreign currency	0	0	0	0
Net periodic cost (benefit)	$ 110	$ 124	$ 221	$ 247