v3.25.1
REGULATORY MATTERS (Regulatory Assets) (Details) - USD ($)
$ in Thousands
Mar. 31, 2025
Dec. 31, 2024
Regulatory Assets [Line Items]    
Remaining Recovery Period (years) 1 year  
Total Regulatory Assets $ 276,000 $ 276,000
Less Current Portion 102,212 97,720
Total Noncurrent Regulatory Assets 174,213 177,963
Pension and Other Postretirement Benefits (Note 9)    
Regulatory Assets [Line Items]    
Total Regulatory Assets 102,000 103,000
Early Generation Retirement Costs    
Regulatory Assets [Line Items]    
Total Regulatory Assets $ 44,000 46,000
Lost Fixed Cost Recovery    
Regulatory Assets [Line Items]    
Remaining Recovery Period (years) 1 year  
Total Regulatory Assets $ 33,000 31,000
Property Tax Deferrals    
Regulatory Assets [Line Items]    
Remaining Recovery Period (years) 1 year  
Total Regulatory Assets $ 32,000 32,000
Derivatives (Note 10)    
Regulatory Assets [Line Items]    
Remaining Recovery Period (years) 5 years  
Total Regulatory Assets $ 19,000 19,000
Transmission Revenue Requirement Balancing Account    
Regulatory Assets [Line Items]    
Remaining Recovery Period (years) 1 year  
Total Regulatory Assets $ 14,000 11,000
Final Mine Reclamation    
Regulatory Assets [Line Items]    
Remaining Recovery Period (years) 15 years  
Total Regulatory Assets $ 8,000 9,000
Income Taxes Recoverable through Future Rates    
Regulatory Assets [Line Items]    
Total Regulatory Assets 5,000 5,000
Unamortized Loss on Reacquired Debt    
Regulatory Assets [Line Items]    
Total Regulatory Assets 4,000 4,000
Other Regulatory Assets    
Regulatory Assets [Line Items]    
Total Regulatory Assets $ 15,000 $ 16,000