REVENUE RECOGNITION - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Disaggregation of Revenue [Line Items]
Revenue (including related party)	$ 147,655	$ 53,553	$ 346,794	$ 171,756
Operating Segments
Disaggregation of Revenue [Line Items]
Revenue (including related party)	152,162		357,570
Operating Segments \| Materials Segment
Disaggregation of Revenue [Line Items]
Revenue (including related party)	133,539	31,641	301,345	124,792
Operating Segments \| Magnetics Segment
Disaggregation of Revenue [Line Items]
Revenue (including related party)	18,623		56,225
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenue (including related party)	(4,507)	0	(10,776)	0
NdPr Oxide And Metal \| Operating Segments \| Materials Segment
Disaggregation of Revenue [Line Items]
Revenue (including related party)	100,961	30,911	266,531	80,277
Rare Earth Concentrate \| Operating Segments \| Materials Segment
Disaggregation of Revenue [Line Items]
Revenue (including related party)	0	0	0	41,992
Other Revenue \| Operating Segments \| Materials Segment
Disaggregation of Revenue [Line Items]
Revenue (including related party)	32,578	730	34,814	2,523
Magnetic precursor products \| Operating Segments \| Magnetics Segment
Disaggregation of Revenue [Line Items]
Revenue (including related party)	$ 18,623	$ 21,912	$ 56,225	$ 46,964