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RELATED PARTY TRANSACTIONS - Related Party Revenue and Cost of Sales (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Related Party Transaction [Line Items]
Total revenue	$ 62,927	$ 52,516	$ 142,869	$ 212,240
Cost of sales (excluding depreciation, depletion and amortization)	57,266	22,217	134,323	69,137
Related party
Related Party Transaction [Line Items]
Cost of sales (excluding depreciation, depletion and amortization)	38,139	21,829	78,848	66,817
Rare earth concentrate
Related Party Transaction [Line Items]
Total revenue	43,053	52,472	107,555	212,139
Rare earth concentrate | Related party
Related Party Transaction [Line Items]
Total revenue	43,053	51,502	107,555	203,186
Other rare earth products
Related Party Transaction [Line Items]
Total revenue	695	44	1,277	101
NdPr oxide and metal (including related party)
Related Party Transaction [Line Items]
Total revenue	19,179	0	34,037	0
NdPr oxide and metal (including related party) | Related party
Related Party Transaction [Line Items]
Total revenue	$ 5,061	$ 0	$ 7,306	$ 0

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