INCOME TAXES - Income tax reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Income tax reconciliation, Amount
Expected amount	$ 9,178	$ (49,464)
State income taxes, net of federal benefit		(124)
Tax credits:
Mine rescue credits	10	20
Indiana EDGE credit		(169)
Change in valuation allowance	(6,605)	40,327
Nondeductible items	(1,112)	296
Prior period true-ups and other	362	(290)
Total income tax expense (benefit)	$ 1,833	$ (9,404)
Tax Jurisdiction of Domicile [Extensible Enumeration]	country:US	country:US
Income tax reconciliation, Percent
Effective income tax rate reconciliation, at federal statutory income tax rate, percent	21.00%	21.00%
State and local income taxes, net of federal income tax effect		0.05%
Tax credits:
Mine rescue credits	0.02%	(0.01%)
Indiana EDGE credit		0.07%
Change in valuation allowance	(15.11%)	(17.12%)
Nondeductible items	(2.54%)	(0.13%)
Prior period true-ups and other	0.82%	0.12%
Total income tax expense (benefit)	4.19%	3.99%
Effective Income Tax Rate Reconciliation, State and Local Jurisdiction, Contribution Greater than 50 Percent, Tax Effect [Extensible Enumeration]	INDIANA	INDIANA