Retirement Plans (Details 6) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Amounts Recognized in Other Comprehensive Income [Abstract]
Total recognized in other comprehensive income (loss)	$ 11,780	$ (3,520)	$ 4,634
U.S. Pension Plans
Net Periodic Benefit Cost [Abstract]
Service cost	450	377
Interest cost	6,829	6,931	6,128
Expected return on plan assets	(10,298)	(9,635)	(9,145)
Settlement loss	155
Net amortization: Net actuarial loss	2,770	2,702	3,278
Net periodic pension (benefit) cost	(94)	375	261
Amounts Recognized in Other Comprehensive Income [Abstract]
Net gain (loss) arising during the year	8,879	(3,352)	(6,365)
Amortization: Net loss recognized in net periodic pension cost	2,925	2,702	3,278
Total recognized in other comprehensive income (loss)	11,804	(650)	(3,087)
U.S. Retiree Healthcare Plan
Net Periodic Benefit Cost [Abstract]
Service cost	546	473	577
Interest cost	618	557	470
Expected return on plan assets	(587)	(519)	(497)
Net periodic pension (benefit) cost	577	511	550
Amounts Recognized in Other Comprehensive Income [Abstract]
Net gain (loss) arising during the year	13	(594)	1,126
Total recognized in other comprehensive income (loss)	13	(594)	1,126
Non-U.S. Pension Plans
Net Periodic Benefit Cost [Abstract]
Service cost	5,082	4,954	5,087
Interest cost	1,518	1,699	1,503
Expected return on plan assets	(1,688)	(1,596)	(1,542)
Settlement loss	232		95
Net amortization: Prior service (credit) cost	(168)	(192)	39
Net amortization: Net actuarial loss	959	753	1,031
Net periodic pension (benefit) cost	5,935	5,618	6,213
Amounts Recognized in Other Comprehensive Income [Abstract]
Prior service credit (cost)	(636)		645
Net gain (loss) arising during the year	1,609	(3,361)	3,025
Amortization: Prior service (credit) cost recognized in net periodic pension cost	(168)	(192)	39
Amortization: Net loss recognized in net periodic pension cost	1,191	753	1,126
Other plans' impact on other comprehensive income (loss)		(360)
Foreign currency impact on defined benefit plan amounts recognized in other comprehensive income (loss)	(2,033)	884	1,760
Total recognized in other comprehensive income (loss)	$ (37)	$ (2,276)	$ 6,595

Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan.

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Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan.

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Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan.

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Amount of cost recognized for passage of time related to defined benefit plan.

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Amount of net periodic benefit cost (credit) for defined benefit plan.

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Amount of gain (loss) recognized in net periodic benefit (cost) credit from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk related to obligation and assets used to effect settlement.

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Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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Amount, before tax, of cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Amount, before tax, of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) of defined benefit plan.

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Amount, before tax, after reclassification adjustment, of (increase) decrease in accumulated other comprehensive income for defined benefit plan.

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Amount, before tax, of gain (loss) for (increase) decrease in value of benefit obligation for change in actuarial assumptions and increase (decrease) in value of plan assets from experience different from that assumed of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

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Amount, before tax, of reclassification adjustment from accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan.

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The amount of increase or decrease in other comprehensive income attributed to foreign currency changes. The effects of foreign currency exchange rate changes that are to be disclosed are those applicable to plans of a foreign operation whose functional currency is not the reporting currency.

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Changes recognized in other comprehensive income for defined benefit plans, not otherwise separately disclosed in the financial statements.

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