4. Derivatives - Schedule of Derivatives Not Designated as Hedging Instruments (Details) - Commodity Contracts [Member] - Non Designated Derivative Instruments [Member] - USD ($) $ in Thousands |
Jun. 30, 2017 |
Dec. 31, 2016 |
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| Commodity contracts - Derivative assets | $ 1,150 | $ 978 |
| Commodity contracts - Derivative liabilities | $ 1,721 | $ 4,115 |
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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://www.xbrl.org/2003/role/presentationRef
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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://www.xbrl.org/2003/role/presentationRef
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