SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Utility Plant (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Depreciable plant and equipment
Equipment	$ 4,977,217	$ 4,557,964
Office buildings and other structures	$ 37,212	32,921
Office Buildings and other structures, useful life	50 years
Minimum
Depreciable plant and equipment
Equipment, useful life	5 years
Transmission and distribution plant, useful life	40 years
Maximum
Depreciable plant and equipment
Equipment, useful life	50 years
Transmission and distribution plant, useful life	65 years
Utility Plant
Depreciable plant and equipment
Equipment	$ 1,039,109	976,704
Office buildings and other structures	382,032	354,628
Transmission and distribution plant	3,556,076	3,226,632
Total	$ 4,977,217	$ 4,557,964