FAIR VALUE MEASUREMENTS - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Fair value measurements
Fair value	$ (4,112)	$ 78,129
Fair Value, Measurements, Recurring \| Level 1
Fair value measurements
Fair value	(13,003)	50,938
Fair Value, Measurements, Recurring \| Level 1 \| Physical fixed price derivative contracts
Fair value measurements
Financial assets	0	0
Financial liabilities	0	0
Fair Value, Measurements, Recurring \| Level 1 \| Physical index derivative contracts
Fair value measurements
Financial assets	0	0
Financial liabilities	0	0
Fair Value, Measurements, Recurring \| Level 1 \| Futures contracts for refined petroleum products
Fair value measurements
Financial assets	0	51,641
Financial liabilities	(13,003)	(703)
Fair Value, Measurements, Recurring \| Level 2
Fair value measurements
Fair value	8,891	27,191
Fair Value, Measurements, Recurring \| Level 2 \| Physical fixed price derivative contracts
Fair value measurements
Financial assets	13,129	27,676
Financial liabilities	(4,232)	(456)
Level 2 fixed-price contracts assets, CVA		(200)
Fair Value, Measurements, Recurring \| Level 2 \| Physical index derivative contracts
Fair value measurements
Financial assets	63	25
Financial liabilities	(69)	(54)
Fair Value, Measurements, Recurring \| Level 2 \| Futures contracts for refined petroleum products
Fair value measurements
Financial assets	0	0
Financial liabilities	$ 0	$ 0

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
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-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

Reference 3: http://www.xbrl.org/2003/role/presentationRef
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- Definition

Amount of credit risk valuation adjustment to derivative liabilities to properly reflect the credit quality of the entity.

+ References

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- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
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- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-Section 55
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-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226008-175313

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-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13495-108611

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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