FAIR VALUE MEASUREMENTS AND DERIVATIVE INSTRUMENTS (Financial Impact of Derivative Energy Contracts) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Derivative Instruments, Gain (Loss) [Line Items]
Percent of long-term trading contract gains shared with customers (percentage)	10.00%
Operating Revenues	$ 452,756	$ 435,853
Energy Derivative Contracts | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Net Gain (Loss)	(14,000)	(42,000)
Operating Revenues	$ 27,000	$ 13,000