XML 112 R90.htm IDEA: XBRL DOCUMENT
v3.8.0.1

GOODWILL - Goodwill by segment (Details) - BRL (R$) R$ in Thousands | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
--- | --- | --- | --- | ---
Goodwill by segment |  |  |  |
Goodwill | R$ 7,891,142 | R$ 9,470,016 | R$ 15,124,430 | R$ 12,556,404
Brazil |  |  |  |
Goodwill by segment |  |  |  |
Goodwill | 373,135 | 380,644 | 519,327 |
Special Steel |  |  |  |
Goodwill by segment |  |  |  |
Goodwill | 2,487,364 | 2,508,056 | 3,409,429 |
North America |  |  |  |
Goodwill by segment |  |  |  |
Goodwill | R$ 5,030,643 | R$ 6,581,316 | R$ 11,195,674 |

X
- 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
Name: | ifrs-full_DisclosureOfReconciliationOfChangesInGoodwillLineItems
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The amount of assets representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognised. [Refer: Business combinations [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 3 -IssueDate 2017-01-01 -Paragraph B67 -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=3&date=2017-03-01&anchor=para_B67_d&doctype=Appendix&seq=2 -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 36 -IssueDate 2017-01-01 -Paragraph 134 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2017-03-01&anchor=para_134_a&doctype=Standard -URIDate 2017-03-09 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 36 -IssueDate 2017-01-01 -Paragraph 135 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2017-03-01&anchor=para_135_a&doctype=Standard -URIDate 2017-03-09 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 54 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_54_c&doctype=Standard -URIDate 2017-03-09 + Details
Name: | ifrs-full_Goodwill
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | ifrs-full_SegmentsAxis=ggb_BrazilSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_SegmentsAxis=ggb_SpecialSteelSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_SegmentsAxis=ggb_NorthAmericaSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |