REVENUE RECOGNITION - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Disaggregation of Revenue [Line Items]
Revenue (including related party)	$ 108,490	$ 57,393	$ 199,139	$ 118,203
Operating Segments
Disaggregation of Revenue [Line Items]
Revenue (including related party)	112,153		205,408
Operating Segments \| Materials Segment
Disaggregation of Revenue [Line Items]
Revenue (including related party)	95,629	37,532	167,806	93,151
Operating Segments \| Magnetics Segment
Disaggregation of Revenue [Line Items]
Revenue (including related party)	16,524		37,602
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenue (including related party)	(3,663)	0	(6,269)	0
NdPr Oxide And Metal \| Operating Segments \| Materials Segment
Disaggregation of Revenue [Line Items]
Revenue (including related party)	94,434	25,045	165,570	49,366
Rare Earth Concentrate \| Operating Segments \| Materials Segment
Disaggregation of Revenue [Line Items]
Revenue (including related party)	0	11,877	0	41,992
Other Revenue \| Operating Segments \| Materials Segment
Disaggregation of Revenue [Line Items]
Revenue (including related party)	1,195	610	2,236	1,793
Magnetic precursor products \| Operating Segments \| Magnetics Segment
Disaggregation of Revenue [Line Items]
Revenue (including related party)	$ 16,524	$ 19,861	$ 37,602	$ 25,052