FAIR VALUE MEASUREMENTS AND DERIVATIVE INSTRUMENTS (Financial Impact of Derivative Energy Contracts) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Percent of gains shared with ratepayers	10.00%
Operating Revenues	$ 1,592,586	$ 1,424,741	$ 1,418,338
Energy Derivative | Not Designated
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Net Loss	62,000	21,000	(45,000)
Operating Revenues	$ 7,000	$ 5,000	$ 6,000