Provisions - Employee obligations - Venezuela - (Details) $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($) age	Dec. 31, 2017 USD ($) age
Venezuela
Actuarial Assumptions Used To Calculate Defined Benefit Obligation [Abstract]
Salary increase	400000.00%	207.25%
Discount rate	520004.00%	219.54%
Expected inflation rate	500000.00%	207.00%
Retirement age \| age	64	63
France
Actuarial Assumptions Used To Calculate Defined Benefit Obligation [Abstract]
Discount rate	2.00%	2.00%
Expected inflation rate	1.60%	1.60%
Retirement age \| age	65	65
France \| Minimum
Actuarial Assumptions Used To Calculate Defined Benefit Obligation [Abstract]
Salary increase	1.60%	1.60%
France \| Maximum
Actuarial Assumptions Used To Calculate Defined Benefit Obligation [Abstract]
Salary increase	6.10%	6.10%
South Africa
Actuarial Assumptions Used To Calculate Defined Benefit Obligation [Abstract]
Salary increase	7.20%	8.10%
Discount rate	9.90%	10.30%
Expected inflation rate	6.20%	7.10%
Retirement age \| age	63	63
FerroAtlantica De Venezuela SA \| Venezuela
Disclosure of defined benefit plans [line items]
Years of service	15 years
Percentage of basic salary guaranteed by IVSS	80
Present value of defined benefit obligation [member] \| South Africa
Changes in net defined benefit liability (asset) [abstract]
Obligations at beginning of year	$ 7,872	$ 8,760
Current service cost	139	310
Borrowing costs	740	932
Actuarial differences	2,000	2,226
Benefits paid	226	740
Exchange differences	(1,096)	836
Obligations at end of year	5,429	7,872
Present value of defined benefit obligation [member] \| FerroAtlantica De Venezuela SA \| Venezuela
Changes in net defined benefit liability (asset) [abstract]
Obligations at beginning of year	1,883	2,955
Current service cost	775	158
Borrowing costs		2,255
Benefits paid	(35)	(93)
Exchange differences	(2,089)	(3,392)
Obligations at end of year	$ 534	$ 1,883

n/a

No definition available.

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Represents the number of years of service at the company accumulated by the employee

+ References

No definition available.

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- Definition

Represents the percentage of basic salary guaranteed by Venezuelan Social Security Institute (IVSS).

+ References

No definition available.

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- Definition

The discount rate used as the significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit obligation, at present value; Actuarial assumptions [member]]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2018-01-01
-Paragraph 144
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- Definition

The expected rate of inflation that is used as a significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit plans [member]; Defined benefit obligation, at present value; Actuarial assumptions [member]]

+ References

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- Definition

The expected rate of salary increases used as a significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit plans [member]; Defined benefit obligation, at present value; Actuarial assumptions [member]]

+ References

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- Definition

The retirement age used as a significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit obligation, at present value; Actuarial assumptions [member]]

+ References

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No definition available.

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- Definition

The increase (decrease) in the net defined benefit liability (asset) resulting from employee service in the current period. [Refer: Net defined benefit liability (asset)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
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-Paragraph 141
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Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

+ References

No definition available.

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The decrease (increase) in a net defined benefit liability (asset) resulting from the remeasurement of that net defined benefit liability (asset). [Refer: Net defined benefit liability (asset)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

The increase (decrease) in the net defined benefit liability (asset) resulting from changes in foreign exchange rates. [Refer: Net defined benefit liability (asset)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
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- Definition

The increase (decrease) in the net defined benefit liability (asset) resulting from the passage of time. [Refer: Interest expense; Net defined benefit liability (asset)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

The amount of deficit or surplus in a defined benefit plan, adjusted for any effect of limiting a net defined benefit asset to the asset ceiling. [Refer: Defined benefit plans [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2018-01-01
-Paragraph 140
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- Definition

The decrease (increase) in the net defined benefit liability (asset) resulting from payments from the plan. [Refer: Net defined benefit liability (asset)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
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