DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES - Gains and Losses on Derivative Instruments (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivatives NOT Designated as Hedging Instruments \| Product sales \| Physical fixed-price derivative contracts
Derivatives NOT designated as hedging instruments:
Gain (loss) recognized in income	$ 2,927	$ (4,192)	$ (4,948)	$ (3,887)
Derivatives NOT Designated as Hedging Instruments \| Product sales \| Physical index derivative contracts
Derivatives NOT designated as hedging instruments:
Gain (loss) recognized in income	63	283	171	123
Derivatives NOT Designated as Hedging Instruments \| Cost of product sales \| Physical fixed-price derivative contracts
Derivatives NOT designated as hedging instruments:
Gain (loss) recognized in income	(4,253)	644	(5,884)	697
Derivatives NOT Designated as Hedging Instruments \| Cost of product sales \| Physical index derivative contracts
Derivatives NOT designated as hedging instruments:
Gain (loss) recognized in income	(127)	479	(343)	53
Derivatives NOT Designated as Hedging Instruments \| Cost of product sales \| Futures contracts for refined products
Derivatives NOT designated as hedging instruments:
Gain (loss) recognized in income	2,403	(2,070)	4,251	2,493
Derivatives Designated as Hedging Instruments \| Cost of product sales \| Hedge Ineffectiveness
Ineffectiveness excluding the time value component on fair value hedging instruments:
Fair value hedge ineffectiveness (excluding time value)	2,464	1,000	(245)	1,196
Time value excluded from hedge assessment	(1,619)	(2,601)	2,031	(2,031)
Net (loss) gain for ineffectiveness in income	845	(1,601)	1,786	(835)
Derivatives Designated as Hedging Instruments \| Cost of product sales \| Futures contracts for refined products
Derivatives designated as fair value hedging instruments:
Futures contracts for refined products	1,886	(12,355)	(25,738)	(8,049)
Derivatives Designated as Hedging Instruments \| Cost of product sales \| Physical inventory - hedged items
Derivatives designated as fair value hedging instruments:
Physical inventory - hedged items	$ (1,041)	$ 10,754	$ 27,524	$ 7,214

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Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement.

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Amount of the increase (decrease) in fair value of the hedged item in a fair value hedge recognized in the income statement.

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Amount of gain (loss) from excluded component of derivative hedge, recognized in earnings. Excludes recognition under systematic and rational method.

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Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

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