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Derivatives. (Details) - Schedule of derivatives not designated as hedging instruments - Not Designated as Hedging Instrument [Member] - USD ($) $ in Thousands | Mar. 31, 2021 | Dec. 31, 2020
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Commodity contracts [Member] |  |
Derivatives. (Details) - Schedule of derivatives not designated as hedging instruments [Line Items] |  |
Assets, fair value | $ 22,355 | $ 17,149
Liabilities, fair value | $ 4,741 |
Cash collateral balance [Member] |  |
Derivatives. (Details) - Schedule of derivatives not designated as hedging instruments [Line Items] |  |
Assets, fair value |  | $ 520

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