v3.24.0.1
REGULATORY MATTERS (Regulatory Assets) (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Regulatory Assets [Line Items]    
Regulatory Assets, Remaining Recovery Period (years) 1 year  
Total Regulatory Assets $ 330,000 $ 370,000
Less Current Portion 147,389 185,034
Total Non-Current Regulatory Assets 182,997 184,894
Pension and Other Postretirement Benefits    
Regulatory Assets [Line Items]    
Total Regulatory Assets $ 107,000 90,000
Under Recovered Fuel and Purchased Energy Costs    
Regulatory Assets [Line Items]    
Regulatory Assets, Remaining Recovery Period (years) 1 year  
Total Regulatory Assets $ 55,000 124,000
Early Generation Retirement Costs    
Regulatory Assets [Line Items]    
Total Regulatory Assets $ 48,000 58,000
Lost Fixed Cost Recovery    
Regulatory Assets [Line Items]    
Regulatory Assets, Remaining Recovery Period (years) 1 year  
Total Regulatory Assets $ 35,000 25,000
Property Tax Deferrals    
Regulatory Assets [Line Items]    
Regulatory Assets, Remaining Recovery Period (years) 1 year  
Total Regulatory Assets $ 30,000 29,000
Derivatives    
Regulatory Assets [Line Items]    
Regulatory Assets, Remaining Recovery Period (years) 6 years  
Total Regulatory Assets $ 26,000 3,000
Final Mine Reclamation and Retiree Healthcare Costs    
Regulatory Assets [Line Items]    
Regulatory Assets, Remaining Recovery Period (years) 5 years  
Total Regulatory Assets $ 6,000 11,000
Income Taxes Recoverable through Future Rates    
Regulatory Assets [Line Items]    
Total Regulatory Assets 6,000 6,000
Unamortized Loss on Reacquired Debt    
Regulatory Assets [Line Items]    
Total Regulatory Assets 5,000 5,000
Other Regulatory Assets    
Regulatory Assets [Line Items]    
Total Regulatory Assets $ 12,000 $ 19,000