Retirement Benefit Plans (Obligation and Funded Status) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Amounts recognized in the balance sheets consist of:
Non-current liabilities	$ (14,271)	$ (10,046)
U.S. Pension Plan
Change in benefit obligation
Projected benefit obligation at beginning of year	68,490	72,839
Interest cost	2,632	2,627	$ 2,754
Actuarial loss (gain)	2,145	(2,884)
Benefits paid	(3,978)	(4,393)
Foreign currency exchange rate changes	0	0
Settlements	(18)	0
Intercompany transfers	(303)	301
Projected benefit obligation at end of year	68,968	68,490	72,839
Accumulated benefit obligation at end of year	68,968	68,490
Change in plan assets
Fair value of plan assets at beginning of year	64,893	68,675
Actual return on plan assets	682	110
Employer contributions	755	424
Benefits paid	(3,978)	(4,393)
Foreign currency exchange rate changes	0	0
Settlements	(18)	0
Intercompany transfers	(304)	77
Fair value of plan assets at end of year	62,030	64,893	68,675
Funded status at end of year	(6,938)	(3,597)
Amounts recognized in the balance sheets consist of:
Noncurrent assets	5,140	4,261
Current liabilities	(721)	(1,016)
Non-current liabilities	(11,357)	(6,842)
Amount recognized in the balance sheets	(6,938)	(3,597)
Components of accumulated other comprehensive loss (income) consist of:
Actuarial loss	29,857	28,041
Prior service cost	996	1,054
Deferred taxes	(11,957)	(11,324)
Currency differences	0	0
Accumulated other comprehensive (loss) income	18,896	17,771
Non-U.S. Pension Plan
Change in benefit obligation
Projected benefit obligation at beginning of year	3,519	4,549
Interest cost	144	152	196
Actuarial loss (gain)	430	(146)
Benefits paid	(176)	(146)
Foreign currency exchange rate changes	104	(712)
Settlements	0	(178)
Intercompany transfers	0	0
Projected benefit obligation at end of year	4,021	3,519	4,549
Accumulated benefit obligation at end of year	4,021	3,519
Change in plan assets
Fair value of plan assets at beginning of year	4,383	5,286
Actual return on plan assets	356	256
Employer contributions	17	17
Benefits paid	(176)	(146)
Foreign currency exchange rate changes	132	(852)
Settlements	0	(178)
Intercompany transfers	0	0
Fair value of plan assets at end of year	4,712	4,383	5,286
Funded status at end of year	691	864
Amounts recognized in the balance sheets consist of:
Noncurrent assets	691	864
Current liabilities	0	0
Non-current liabilities	0	0
Amount recognized in the balance sheets	691	864
Components of accumulated other comprehensive loss (income) consist of:
Actuarial loss	1,029	737
Prior service cost	0	0
Deferred taxes	(327)	(250)
Currency differences	(89)	(102)
Accumulated other comprehensive (loss) income	613	385
Other Postretirement Benefit Plans, Defined Benefit
Change in benefit obligation
Projected benefit obligation at beginning of year	3,466	3,534
Service cost	70	70	70
Interest cost	116	113	118
Actuarial loss (gain)	(25)	226
Benefits paid	(416)	(477)
Projected benefit obligation at end of year	3,211	3,466	$ 3,534
Change in plan assets
Benefits paid	(416)	(477)
Funded status at end of year	(3,211)	(3,466)
Amounts recognized in the balance sheets consist of:
Current liabilities	(294)	(262)
Non-current liabilities	(2,917)	(3,204)
Amount recognized in the balance sheets	(3,211)	(3,466)
Components of accumulated other comprehensive loss (income) consist of:
Actuarial loss	983	1,140
Prior service cost	(95)	(202)
Deferred taxes	284	263
Accumulated other comprehensive (loss) income	$ 1,172	$ 1,201