DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES - Location and Fair Value Amounts of Derivative Instruments Reported in Balance Sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Asset Derivatives
Derivative contracts	$ 417	$ 879
Liability Derivatives
Derivative contracts, liabilities	17,711	12,054
Not Designated as Hedging Instrument | Commodity contracts
Asset Derivatives
Derivative contracts	417	879
Liability Derivatives
Derivative contracts, liabilities	17,711	12,054
Not Designated as Hedging Instrument | Commodity contracts | Current assets: Fair value of derivative contracts
Asset Derivatives
Derivative contracts	417	879
Not Designated as Hedging Instrument | Commodity contracts | Long-term assets: Fair value of derivative contracts
Asset Derivatives
Derivative contracts	0	0
Not Designated as Hedging Instrument | Commodity contracts | Current liabilities: Fair value of derivative contracts
Liability Derivatives
Derivative contracts, liabilities	13,147	8,969
Not Designated as Hedging Instrument | Commodity contracts | Long-term liabilities: Fair value of derivative contracts
Liability Derivatives
Derivative contracts, liabilities	$ 4,564	$ 3,085