VARIABLE INTEREST ENTITIES - Summary (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Variable Interest Entity [Line Items]
Net electric plant	$ 3,156,894		$ 3,146,709
Noncontrolling interest	126,945		134,269
Long-term debt	2,741,491		2,896,506
Accrued interest	43,469		24,549
Interest	42,494	$ 39,781
Variable Interest Entity, Primary Beneficiary | Reportable Legal Entities
Variable Interest Entity [Line Items]
Net electric plant	699,325		703,859
Noncontrolling interest	126,945		134,269
Long-term debt	173,237		206,027
Accrued interest	1,999		$ 5,968
Depreciation, amortization and depletion	4,534	4,534
Interest	$ 3,033	$ 3,667