REGULATORY MATTERS (Regulatory Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Regulatory Liabilities [Line Items]
Remaining Recovery Period (years)	1 year
Total Regulatory Liabilities	$ 418,000	$ 489,000
Less Current Portion	98,465	110,782
Total Non-Current Regulatory Liabilities	320,251	377,546
Income Taxes Payable through Future Rates
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	236,000	244,000
Renewable Energy Standard
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 73,000	73,000
Derivatives
Regulatory Liabilities [Line Items]
Remaining Recovery Period (years)	7 years
Total Regulatory Liabilities	$ 39,000	86,000
Net Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 31,000	43,000
Demand Side Management
Regulatory Liabilities [Line Items]
Remaining Recovery Period (years)	1 year
Total Regulatory Liabilities	$ 15,000	16,000
Transmission Balancing Accounts
Regulatory Liabilities [Line Items]
Remaining Recovery Period (years)	1 year
Total Regulatory Liabilities	$ 9,000	9,000
Pension and Other Postretirement Benefits
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	8,000	8,000
Deferred Investment Tax Credits
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	7,000	7,000
Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 0	$ 3,000