DERIVATIVE INSTRUMENTS/HEDGING - Derivative assets and liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Asset
Total gross amounts presented in accompanying balance sheet	$ 6,381
Liability
Total gross amounts presented in accompanying balance sheet	10,838	$ 49,370
Not Designated as Hedging Instrument [Member]
Asset
Total gross amounts presented in accompanying balance sheet	8,819
Less: gross amounts not offset in the accompanying balance sheet	(7,531)
Net amount:	1,288
Liability
Total gross amounts presented in accompanying balance sheet	10,838	51,940
Less: gross amounts not offset in the accompanying balance sheet	(7,531)
Net amount:	3,307	51,940
Not Designated as Hedging Instrument [Member] \| Oil Contracts [Member] \| Current Assets [Member]
Asset
Total gross amounts presented in accompanying balance sheet	4,216
Not Designated as Hedging Instrument [Member] \| Oil Contracts [Member] \| Non-Current Assets [Member]
Asset
Total gross amounts presented in accompanying balance sheet	770
Not Designated as Hedging Instrument [Member] \| Oil Contracts [Member] \| Current Liabilities [Member]
Liability
Total gross amounts presented in accompanying balance sheet	6,206	27,892
Not Designated as Hedging Instrument [Member] \| Oil Contracts [Member] \| Non-Current Liabilities [Member]
Liability
Total gross amounts presented in accompanying balance sheet		1,059
Not Designated as Hedging Instrument [Member] \| Natural Gas Contracts [Member] \| Current Assets [Member]
Asset
Total gross amounts presented in accompanying balance sheet	2,165
Not Designated as Hedging Instrument [Member] \| Natural Gas Contracts [Member] \| Non-Current Assets [Member]
Asset
Total gross amounts presented in accompanying balance sheet	1,668
Not Designated as Hedging Instrument [Member] \| Natural Gas Contracts [Member] \| Current Liabilities [Member]
Liability
Total gross amounts presented in accompanying balance sheet	$ 4,632	21,478
Not Designated as Hedging Instrument [Member] \| Natural Gas Contracts [Member] \| Non-Current Liabilities [Member]
Liability
Total gross amounts presented in accompanying balance sheet		$ 1,511

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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-Publisher FASB
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