DERIVATIVES. (Details) - Non Designated Derivative Instruments [Member] - USD ($) $ in Thousands  | 
Jun. 30, 2019  | 
Dec. 31, 2018  | 
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| Cash Collateral Balance [Member] | ||
| Derivative assets | $ 1,008 | $ 8,479 | 
| Commodity Contracts [Member] | ||
| Derivative assets | 5,437 | 1,765 | 
| Derivative liabilities | $ 684 | $ 6,309 | 
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- Definition Fair value as of the balance sheet date of derivative instrument not designated as hedging instrument and classified as an asset. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Fair value as of the balance sheet date of derivative instrument not designated as hedging instrument and classified as a liability. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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