FAIR VALUE MEASUREMENTS - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Fair value measurements
Fair value	$ (21,002)	$ 78,129
Fair Value, Measurements, Recurring | Level 1
Fair value measurements
Fair value	(23,786)	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	(23,786)	(703)
Fair Value, Measurements, Recurring | Level 1 | Interest rate derivatives
Fair value measurements
Financial assets	0	0
Fair Value, Measurements, Recurring | Level 2
Fair value measurements
Fair value	2,784	27,191
Fair Value, Measurements, Recurring | Level 2 | Physical fixed price derivative contracts
Fair value measurements
Financial assets	3,893	27,676
Financial liabilities	(2,187)	(456)
Fair Value, Measurements, Recurring | Level 2 | Physical index derivative contracts
Fair value measurements
Financial assets	66	25
Financial liabilities	(40)	(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, Measurements, Recurring | Level 2 | Interest rate derivatives
Fair value measurements
Financial assets	$ 1,052	$ 0