v3.26.3
REGULATORY MATTERS (Regulatory Liabilities) (Details) - USD ($)
$ in Thousands
Sep. 30, 2026
Dec. 31, 2025
Regulatory Liabilities [Line Items]    
Remaining Recovery Period (years) 1 year  
Total Regulatory Liabilities $ 654,000 $ 563,000
Less Current Portion 166,638 143,851
Total Noncurrent Regulatory Liabilities $ 486,892 419,132
Remaining Recovery Period (years) 1 year  
Income Taxes Payable through Future Rates    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities $ 197,000 199,000
Deferred Investment Tax Credits    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 193,000 94,000
Renewable Energy Standard    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 115,000 102,000
Net Cost of Removal    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 53,000 75,000
Pension and Other Postretirement Benefits (Note 8)    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities $ 31,000 32,000
Over-Recovered Fuel and Purchased Energy Costs    
Regulatory Liabilities [Line Items]    
Remaining Recovery Period (years) 1 year  
Total Regulatory Liabilities $ 31,000 32,000
Demand Side Management    
Regulatory Liabilities [Line Items]    
Remaining Recovery Period (years) 1 year  
Total Regulatory Liabilities $ 19,000 9,000
Derivatives (Note 9)    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities $ 14,000 20,000
Remaining Recovery Period (years) 3 years  
Other Regulatory Liabilities    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities $ 1,000 $ 0