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FINANCIAL INSTRUMENTS - Prospective and retrospective tests (Details) - BRL (R$) R$ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Unrealized gains on financial instruments |  |  |
Current assets |  | R$ 2,557 |
Non-current assets |  | 10,394 |
Unrealized losses on financial instruments |  |  |
Current liabilities |  | (6,584) |
Non-current liabilities | R$ (1,267) |  |
Net Income |  |  |
Gains on financial instruments | 9,666 | 33,753 |
Losses on financial instruments | (19,107) | (72,683) |
Gains (losses) on financial instruments recognized in Net Income | (9,441) | (38,930) | R$ 87,085
Other comprehensive income |  |  |
Gains on financial instruments | (11,364) | 212 | R$ 17,283
Gains on financial instruments recognized in other comprehensive income | (11,364) | 212 |
Unrealized gains on financial instruments |  |  |
Unrealized gains on financial instruments |  |  |
Current assets |  | 2,557 |
Non-current assets |  | 10,394 |
Unrealized gains on financial instruments |  | 12,951 |
Unrealized losses on financial instruments |  |  |
Unrealized losses on financial instruments |  |  |
Current liabilities |  | (6,584) |
Non-current liabilities | (1,267) |  |
Unrealized losses on financial instruments | R$ (1,267) | R$ (6,584) |

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