FAIR VALUE MEASUREMENTS AND DERIVATIVE INSTRUMENTS (Financial Impact of Derivative Energy Contracts) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Derivative Instruments, Gain (Loss) [Line Items]
Percent of long-term trading contract gains shared with customers (percentage)			10.00%
Operating Revenues	$ 418,236	$ 439,527	$ 854,089	$ 776,253
Energy Derivative Contracts | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized net gain (loss)	(5,000)	18,000	(47,000)	107,000
Operating Revenues	$ 4,000	$ 2,000	$ 17,000	$ 10,000