Retirement Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Plan contributions	$ 36		$ 187
Pension Plans \| Domestic Plan
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	0	$ 0	0	$ 0
Interest cost	10	373	32	1,153
Expected return on plan assets	0	(581)	0	(1,752)
Amortization of net actuarial loss	13	12	37	33
Amortization of prior service cost	0	0	0	0
Foreign currency	0	0	0	0
Net periodic benefit cost (credit)	23	(196)	69	(566)
Settlement charge			50	205
Net benefit cost (credit)	23	(196)	119	(361)
Pension Plans \| Foreign Plan
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	33	124	105	172
Interest cost	82	96	240	315
Expected return on plan assets	(77)	(101)	(268)	(298)
Amortization of net actuarial loss	0	0	0	0
Amortization of prior service cost	54	50	160	146
Foreign currency	(118)	135	(212)	364
Net periodic benefit cost (credit)	(26)	304	25	699
Settlement charge			0	0
Net benefit cost (credit)	(26)	304	25	699
Postretirement Medical Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans
Plan contributions	139		695
Service cost	6	6	34	46
Interest cost	70	91	220	272
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
Foreign currency	0	0	0	0
Net periodic benefit cost (credit)	76	97	254	318
Settlement charge			0	0
Net benefit cost (credit)	$ 76	$ 97	$ 254	$ 318

Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Before Curtailment And Settlement Charge

No definition available.

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- Definition

The amount of foreign currency recognized in net periodic benefit cost relating to benefit changes attributable to the company's operations in foreign counties

+ References

No definition available.

+ Details

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- Definition

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

+ References

+ Details

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- Definition

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

+ References

+ Details

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- Definition

Amount of contribution received by defined benefit plan from employer which increases plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(5)(ii)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2709-114920

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(5)(iv)(01)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

+ Details

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Period Type:	duration

- Definition

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.

+ References

+ Details

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Balance Type:	credit
Period Type:	duration

- Definition

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

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Definition

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

+ References

+ Details

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- Definition

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.

+ References

+ Details

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Balance Type:	credit
Period Type:	duration

- Definition

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

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Details

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- Details

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