SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Other Deferred Credits and Other Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Deferred Credits [Line Items]
Present value of transmission easement payments	$ 17,862	$ 18,636
Other Deferred Credits and Other Liabilities [Abstract]
Transmission easements	17,862	18,636
OATT deposits	27,872	17,476
Financial liabilities - reclamation	16,895	12,429
Customer deposits	12,091	8,616
Contract liabilities (unearned revenue) - noncurrent	3,125	3,765
Operating lease liabilities - noncurrent	1,396	1,251
Other	4,884	6,201
Total other deferred credits and other liabilities	84,125	68,374
Transmission - Right of Way Easements
Deferred Credits [Line Items]
Total due for easement right of way	25,700
Present value of transmission easement payments	17,900	18,600
Other Deferred Credits and Other Liabilities [Abstract]
Transmission easements	$ 17,900	$ 18,600