INCOME TAXES - Net Deferred Tax Liability (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets
Net operating loss carryforwards	$ 192,591	$ 165,636
Operating lease liabilities	94,862	105,039
Deferred revenues and membership withdrawal	4,812	16,028
Safe harbor lease receivables	9,379	8,939
Other	34,171	43,795
Deferred tax assets, gross	335,815	339,437
Less valuation allowance	0	0
Deferred tax assets, net	335,815	339,437
Deferred tax liabilities
Basis differences- property, plant and equipment and other	168,948	166,568
Operating lease right-of-use assets	121,125	125,939
Capital credits from other associations	35,638	34,236
Deferred debt prepayment transaction costs	25,327	27,381
Other	0	4,588
Deferred tax liabilities, total	351,038	358,712
Net deferred tax liability	(15,223)	(19,275)
Deferred tax treatment of regulatory assets
Increase (decrease) in net deferred tax liabilities	(4,100)
Regulatory assets	919,483	650,421
Deferred Income Tax Expense
Deferred tax treatment of regulatory assets
Regulatory assets	$ 15,223	$ 19,279