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Risk Management and Derivatives: Derivatives Not Designated as Hedge Instruments (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Dec. 31, 2020
Derivative [Line Items] |  |  |  |  |
Regulatory Liabilities | $ 526,417 |  | $ 526,417 |  | $ 532,720
Regulatory assets | (830,055) |  | (830,055) |  | (278,258)
Gas price derivatives |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Regulatory Liabilities | 13,234 |  | 13,234 |  | 0
Gas price derivatives |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Regulatory assets | 0 |  | 0 |  | $ (2,226)
Not Designated as Hedging Instrument |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative, Gain (Loss) on Derivative, Net | 6,498 | $ 391 | 3,558 | $ 2,764 |
Not Designated as Hedging Instrument | Fuel, purchased power and cost of natural gas sold | Electricity |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative, Gain (Loss) on Derivative, Net | 2,494 | (1,386) | (2,628) | (228) |
Not Designated as Hedging Instrument | Fuel, purchased power and cost of natural gas sold | Natural Gas, Distribution |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative, Gain (Loss) on Derivative, Net | $ 4,004 | $ 1,777 | $ 6,186 | $ 2,992 |

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