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Events after the reporting period (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Feb. 22, 2019	Dec. 31, 2017	Feb. 15, 2017
Amended Revolving Credit Facility
Minimum cash liquidity		$ 150
Cash consideration	$ 12,734
Senior Notes due 2022
Amended Revolving Credit Facility
Notional amount	$ 350,000		$ 350,000	$ 350,000
Senior Notes due 2022 issued by Ferroglobe PLC
Amended Revolving Credit Facility
Notional amount				150,000
Senior Notes due 2022 issued by Globe Specialty Metals, Inc
Amended Revolving Credit Facility
Notional amount				200,000
Senior Notes due 2022 issued by Globe Specialty Metals, Inc | Amended revolving credit facility
Amended Revolving Credit Facility
Notional amount		$ 250,000		$ 200,000

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- References

No definition available.

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- Definition

The threshold amount of minimum cash liquidity level which is greater to be maintained under the debt instrument covenant.

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- Definition

The nominal or face amount of a financial instrument, used to calculate payments made on that instrument.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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-IssueDate 2018-01-01
-Paragraph 112
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- Definition

The cash inflow from the disposal of non-current assets or disposal groups classified as held for sale and discontinued operations. [Refer: Discontinued operations [member]; Disposal groups classified as held for sale [member]; Non-current assets or disposal groups classified as held for sale]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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