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LONG-TERM DEBT: Long-term debt narrative Level 4 (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Sep. 30, 2020
Aug. 01, 2020
Jul. 29, 2020
Jun. 17, 2020
Mar. 31, 2019
May 19, 2016
Debt Instrument [Line Items]                  
Make-Whole Premium $ 3,305 $ 0 $ 4,607            
Repayments of Debt 175,000 166,100 130,000            
First Mortgage Bonds 4.20 K Series due 2048                  
Debt Instrument [Line Items]                  
First mortgage bonds $ 450,000 $ 220,000              
Debt Instrument, Interest Rate, Stated Percentage 4.20% 4.20%           4.20%  
First mortgage bonds 4.20% Series due 2046                  
Debt Instrument [Line Items]                  
First mortgage bonds $ 120,000 $ 120,000              
Debt Instrument, Interest Rate, Stated Percentage 4.05% 4.05%              
Pollution Control Bonds 5.15 due 2024 [Member]                  
Debt Instrument [Line Items]                  
Debt Instrument, Interest Rate, Stated Percentage [1] 1.45% 1.45%              
Pollution Control Bond 5.25 due 2026 [Member]                  
Debt Instrument [Line Items]                  
Debt Instrument, Interest Rate, Stated Percentage [1] 1.70% 1.70%              
First Mortgage Bonds 1.90 Series L Due July 15 2030                  
Debt Instrument [Line Items]                  
First mortgage bonds $ 80,000 $ 0              
Debt Instrument, Interest Rate, Stated Percentage 1.90%                
First mortgage bonds 3.40 Series due 2020                  
Debt Instrument [Line Items]                  
First mortgage bonds $ 0 $ 100,000              
Debt Instrument, Interest Rate, Stated Percentage 3.40% 3.40%              
First Mortgage Bonds 2.95 Series Due 2022                  
Debt Instrument [Line Items]                  
First mortgage bonds $ 0 $ 75,000              
Debt Instrument, Interest Rate, Stated Percentage 2.95% 2.95%              
Idaho Power Company                  
Debt Instrument [Line Items]                  
Make-Whole Premium $ 3,305 $ 0 4,607            
Debt Instrument, Interest Rate, Effective Percentage 4.40% 4.50%              
Repayments of Debt $ 175,000 $ 166,100 $ 130,000            
Principal amount of debt securities and first mortgage bonds authorized $ 500,000                
Extension Period of State Regulatory Authorization to Issue Debt 2 years                
Debt instrument interest rate limit 7.00%                
Indenture, Unused Borrowing Capacity, Amount $ 1,800,000                
Percent of Operating Revenues Required to be Spent or Appropriated 15.00%                
Time Period Expenditures or Appropriations can be Made Up 5 years                
Bonds issuable maximum amount ending $ 2,500,000               $ 2,000,000
Earnings test does not apply to refunding bonds that mature in less than this period of time 2 years                
Indenture, Unused Borrowing Capacity available $ 534,000                
Idaho Power Company | Pollution Control Bonds 5.15 due 2024 [Member]                  
Debt Instrument [Line Items]                  
Debt Instrument, Interest Rate, Stated Percentage       5.15%          
Repayments of Debt $ 49,800                
Idaho Power Company | Humboldt County Pollution Control Revenue Bonds [Domain]                  
Debt Instrument [Line Items]                  
Debt Instrument, Interest Rate, Stated Percentage 1.45%                
Idaho Power Company | Pollution Control Bond 5.25 due 2026 [Member]                  
Debt Instrument [Line Items]                  
Debt Instrument, Interest Rate, Stated Percentage       5.25%          
Repayments of Debt $ 116,300                
Idaho Power Company | Sweetwater County Pollution Control Revenue Bond due 2026 1.7 [Member]                  
Debt Instrument [Line Items]                  
Debt Instrument, Interest Rate, Stated Percentage 1.70%                
Idaho Power Company | First Mortgage Bonds 1.90 Series L Due July 15 2030                  
Debt Instrument [Line Items]                  
Debt Instrument, Face Amount             $ 80,000    
Idaho Power Company | First mortgage bonds 3.40 Series due 2020                  
Debt Instrument [Line Items]                  
Debt Instrument, Repurchased Face Amount         $ 100,000        
Idaho Power Company | First Mortgage Bonds 2.95 Series Due 2022                  
Debt Instrument [Line Items]                  
Debt Instrument, Repurchased Face Amount           $ 75,000      
[1] Humboldt County and Sweetwater County Pollution Control Revenue Bonds are secured by the first mortgage bonds, bringing the total first mortgage bonds outstanding at December 31, 2020, to $1.966 billion. These two bonds were purchased and remarketed in August 2019. See "Long-Term Debt Issuances, Maturities, and Redemptions" below.