SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Electric Plant and Depreciation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
ELECTRIC PLANT AND DEPRECIATION:
Interest rates charged during construction (as a percent)	5.20%	2.30%	4.40%
Interest capitalized during construction	$ 4.8	$ 1.5	$ 3.8