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Commitment, Contingencies And Guarantees: Power Purchase and Transmission Services Agreements (Details) $ in Thousands | 12 Months Ended
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Dec. 31, 2021 USD ($) MW | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($)
Platte River Power Authority - Unit Contingent Energy | Colorado Electric | Wind |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Number of Megawatts Capacity Purchased | 60 |  |
Cost of Purchased Power | $ | $ 4,246 | $ 2,791 | $ 0
Platte River Power Authority - Unit Contingent Energy | Colorado Electric | Coal |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Number of Megawatts Capacity Purchased | 25 |  |
Cost of Purchased Power | $ | $ 4,447 | 4,524 | 1,802
Platte River Power Authority - Unit Contingent Energy | South Dakota Electric | Wind |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Number of Megawatts Capacity Purchased | 12 |  |
Cost of Purchased Power | $ | $ 596 | 715 | 688
TC Colorado Solar, LLC | Colorado Electric | Solar |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Number of Megawatts Capacity Purchased | 200 |  |
Purchase Power Agreement Set to Expire after a Certain Number of Years Following Completion of the Facility | 15 years |  |
PacifiCorp Purchase Power Agreement | South Dakota Electric | Coal |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Number of Megawatts Capacity Purchased | 50 |  |
Cost of Purchased Power | $ | $ 8,923 | 5,897 | 7,477
PacifiCorp Transmission | South Dakota Electric |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Number of Megawatts Capacity Purchased | 50 |  |
Cost of Purchased Power | $ | $ 1,783 | 1,776 | 1,741
Fall River Solar | South Dakota Electric | Solar |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Number of Megawatts Capacity Purchased | 80 |  |
Purchase Power Agreement Set to Expire after a Certain Number of Years Following Completion of the Facility | 20 years |  |
Happy Jack Wind Purchase Power Agreement | Wyoming Electric | Wind |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Number of Megawatts Capacity Purchased | 30 |  |
Long-term Contract for Purchase of Electric Power, Share of Plant Output Being Purchased | 50.00% |  |
Cost of Purchased Power | $ | $ 3,544 | 4,531 | 3,936
Silver Sage Wind Power Purchase Agreement | Wyoming Electric | Wind |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Number of Megawatts Capacity Purchased | 30 |  |
Long-term Contract for Purchase of Electric Power, Share of Plant Output Being Purchased | 67.00% |  |
Cost of Purchased Power | $ | $ 4,717 | $ 6,203 | $ 5,366

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