XML 143 R120.htm IDEA: XBRL DOCUMENT
v3.19.1

RELATED-PARTY TRANSACTIONS - Debentures (Details) - Direct or indirect shareholders R$ in Thousands | Dec. 31, 2018 BRL (R$) instrument | Dec. 31, 2017 BRL (R$) instrument
--- | --- | ---
RELATED PARTY TRANSACTIONS |  |
Debentures held | R$ | R$ 0 | R$ 348
Number of debentures held | instrument | 0 | 63

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- Definition Number of debt instruments held. + References No definition available. + Details
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Namespace Prefix: | ggb_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

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- Definition The amount of instruments representing indebtedness held by the entity. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 55 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_55&doctype=Standard -URIDate 2018-03-16 + Details
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Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition 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. + Details
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Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | ifrs-full_CategoriesOfRelatedPartiesAxis=ggb_DirectOrIndirectShareholdersMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |