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OBLIGATIONS WITH FIDC - INVESTMENT FUND IN CREDIT RIGHTS (Details) - BRL (R$) R$ in Thousands | Dec. 31, 2019 | Dec. 31, 2018
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OBLIGATIONS WITH FIDC - INVESTMENT FUND IN CREDIT RIGHTS |  |
Obligations with FIDC | R$ 1,018,501 | R$ 938,526

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- Definition Noncurrent portion of amount payable regarding repurchase receivables from the Credit Right Investment Fund. + References No definition available. + Details
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Namespace Prefix: | ggb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition NA. + References No definition available. + Details
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Namespace Prefix: | ggb_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration