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Risk Management and Derivatives: Derivatives by Balance Sheet Classification (Details) - Commodity Contract - USD ($) $ in Thousands | Mar. 31, 2021 | Dec. 31, 2020
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Designated as Hedging Instrument |  |
Derivatives, Fair Value [Line Items] |  |
Fair Value Hedges, Net | $ 289 | $ 116
Designated as Hedging Instrument | Derivative assets — current |  |
Derivatives, Fair Value [Line Items] |  |
Fair Value Hedge Assets | 285 | 181
Designated as Hedging Instrument | Other assets, non-current |  |
Derivatives, Fair Value [Line Items] |  |
Fair Value Hedge Assets | 4 | 43
Designated as Hedging Instrument | Derivative liabilities — current |  |
Derivatives, Fair Value [Line Items] |  |
Fair Value Hedge Liabilities | 0 | (108)
Designated as Hedging Instrument | Other deferred credits and other liabilities |  |
Derivatives, Fair Value [Line Items] |  |
Fair Value Hedge Liabilities | 0 | 0
Not Designated as Hedging Instrument |  |
Derivatives, Fair Value [Line Items] |  |
Fair Value Hedges, Net | (905) | (118)
Not Designated as Hedging Instrument | Derivative assets — current |  |
Derivatives, Fair Value [Line Items] |  |
Fair Value Hedge Assets | 1,632 | 1,667
Not Designated as Hedging Instrument | Other assets, non-current |  |
Derivatives, Fair Value [Line Items] |  |
Fair Value Hedge Assets | 32 | 151
Not Designated as Hedging Instrument | Derivative liabilities — current |  |
Derivatives, Fair Value [Line Items] |  |
Fair Value Hedge Liabilities | (2,526) | (1,936)
Not Designated as Hedging Instrument | Other deferred credits and other liabilities |  |
Derivatives, Fair Value [Line Items] |  |
Fair Value Hedge Liabilities | $ (43) | $ 0

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