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RELATED PARTY TRANSACTIONS - Intercompany loans (Details) - BRL (R$) R$ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
RELATED PARTY TRANSACTIONS |  |  |
Assets | R$ 51,839 | R$ 57,541 |
Net financial income | 95 | (2,457) | R$ 2,712
Gerdau Corsa S.A.P.I de C.V. |  |  |
RELATED PARTY TRANSACTIONS |  |  |
Assets | 7 | 48 |
Fundacao Gerdau |  |  |
RELATED PARTY TRANSACTIONS |  |  |
Assets | R$ 51,832 | R$ 57,493 |

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