RISK MANAGEMENT - Fair Value of Derivatives (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Derivative Assets [Abstract]
Derivative asset, fair value	$ 18,918	$ 26,613
Derivative asset, liability		(2,662)
Derivative asset	14,137	15,452
Long–term derivative asset	4,781	8,499
Total derivative asset	18,918	23,951
Derivative Liabilities [Abstract]
Derivative liability, fair value		3,827
Derivative liability, asset		(2,662)
Derivative liability		1,165
Total derivative liability		1,165
Current Derivatives Asset
Derivative Assets [Abstract]
Derivative asset, fair value	14,137	18,048
Derivative asset, liability		(2,596)
Derivative asset	14,137	15,452
Noncurrent Derivative Asset
Derivative Assets [Abstract]
Derivative asset, fair value	4,781	8,565
Derivative asset, liability		(66)
Long–term derivative asset	$ 4,781	8,499
Current Derivatives Liability
Derivative Liabilities [Abstract]
Derivative liability, fair value		3,761
Derivative liability, asset		(2,596)
Derivative liability		1,165
Noncurrent Derivative Liability
Derivative Liabilities [Abstract]
Derivative liability, fair value		66
Derivative liability, asset		$ (66)

Fair value of liability associated with 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.

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