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Commitment, Contingencies And Guarentees: Power Purchase and Transmission Services Agreements (Details)
$ in Thousands
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2020
USD ($)
MW
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Jun. 26, 2019
MW
PacifiCorp Transmission          
Long-term Purchase Commitment [Line Items]          
Cost of Purchased Power | $   $ 1,776      
Colorado Electric | Wind          
Long-term Purchase Commitment [Line Items]          
Number of Megawatts Capacity Purchased | MW   60      
Colorado Electric | Coal          
Long-term Purchase Commitment [Line Items]          
Number of Megawatts Capacity Purchased | MW   25      
Black Hills Energy, South Dakota Electric          
Long-term Purchase Commitment [Line Items]          
Number of Megawatts Capacity Purchased | MW   50      
Black Hills Energy, South Dakota Electric | Wind          
Long-term Purchase Commitment [Line Items]          
Number of Megawatts Capacity Purchased | MW   12      
Black Hills Energy, South Dakota Electric | Coal          
Long-term Purchase Commitment [Line Items]          
Number of Megawatts Capacity Purchased | MW   50      
Black Hills Energy, South Dakota Electric | Solar          
Long-term Purchase Commitment [Line Items]          
Number of Megawatts Capacity Purchased | MW   80      
Wyoming Electric | Wind          
Long-term Purchase Commitment [Line Items]          
Number of Megawatts Capacity Purchased | MW   30      
Fall River Solar | Black Hills Energy, South Dakota Electric | Subsequent Event          
Long-term Purchase Commitment [Line Items]          
Purchase Power Agreement Set to Expire after a Certain Number of Years Following Completion of the Facility 20 years        
Platte River Power Authority - Unit Contingent Energy | Wind          
Long-term Purchase Commitment [Line Items]          
Cost of Purchased Power | $   $ 2,791 $ 0 $ 0  
Platte River Power Authority - Unit Contingent Energy | Coal          
Long-term Purchase Commitment [Line Items]          
Cost of Purchased Power | $   4,524 1,802 0  
PacifiCorp Purchase Power Agreement | Coal          
Long-term Purchase Commitment [Line Items]          
Cost of Purchased Power | $   5,897 7,477 13,681  
PacifiCorp Transmission          
Long-term Purchase Commitment [Line Items]          
Cost of Purchased Power | $     1,741 1,742  
Platte River Power Authority Wind Power Agreement          
Long-term Purchase Commitment [Line Items]          
Number of Megawatts Capacity Purchased | MW         60
Platte River Power Authority Wind Power Agreement | Wind          
Long-term Purchase Commitment [Line Items]          
Cost of Purchased Power | $   715 688 223  
Happy Jack Wind Purchase Power Agreement | Wind          
Long-term Purchase Commitment [Line Items]          
Cost of Purchased Power | $   $ 4,531 3,936 3,884  
Happy Jack Wind Purchase Power Agreement | Wyoming Electric | Subsidiary of Common Parent          
Long-term Purchase Commitment [Line Items]          
Long-term Contract for Purchase of Electric Power, Share of Plant Output Being Purchased   50.00%      
Silver Sage Wind Power Purchase Agreement | Wind          
Long-term Purchase Commitment [Line Items]          
Cost of Purchased Power | $   $ 6,203 $ 5,366 $ 5,376  
Silver Sage Wind Power Purchase Agreement | Wyoming Electric | Subsidiary of Common Parent          
Long-term Purchase Commitment [Line Items]          
Long-term Contract for Purchase of Electric Power, Share of Plant Output Being Purchased   67.00%