REGULATORY MATTERS (Regulatory Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Regulatory Liabilities [Line Items]
Remaining Recovery Period (years)	1 year
Total Regulatory Liabilities	$ 560,000	$ 506,000
Less Current Portion	148,275	142,844
Total Noncurrent Regulatory Liabilities	412,260	362,859
Income Taxes Payable through Future Rates
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	216,000	209,000
Net Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	91,000	110,000
Renewable Energy Standard
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	91,000	88,000
Deferred Investment Tax Credits
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 54,000	4,000
Over-Recovered Fuel and Purchased Energy Costs
Regulatory Liabilities [Line Items]
Remaining Recovery Period (years)	1 year
Total Regulatory Liabilities	$ 49,000	49,000
Derivatives (Note 10)
Regulatory Liabilities [Line Items]
Remaining Recovery Period (years)	5 years
Total Regulatory Liabilities	$ 35,000	22,000
Pension and Other Postretirement Benefits (Note 9)
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 18,000	19,000
Demand Side Management
Regulatory Liabilities [Line Items]
Remaining Recovery Period (years)	1 year
Total Regulatory Liabilities	$ 6,000	$ 5,000