SEGMENTS OF BUSINESS - Schedule of EBITDA Margin to Income (loss) before Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
SEGMENTS OF BUSINESS
Other Operating Revenue	$ 1,659	$ 1,263
Depreciation, Depletion and Amortization	(14,977)	(15,443)
Asset Retirement Obligations Accretion	(427)	(399)
Exploration Costs	(21)	(70)
Gain (loss) on disposal or abandonment of assets, net	21	24
Interest Expense	(3,723)	(3,937)
Loss on Extinguishment of Debt		(853)
Equity Method Investment (Loss)	(236)	(249)
Corporate - General and Administrative	(2,977)	(2,448)
Corporate - Other Operating and Maintenance Costs		(92)
NET INCOME (LOSS) BEFORE INCOME TAXES	9,979	(2,306)
Electric sales
SEGMENTS OF BUSINESS
EBITDA Margin	49,560	37,509
Coal sales
SEGMENTS OF BUSINESS
EBITDA Margin	(18,900)	(17,611)
Operating Segment | Electric Operations
SEGMENTS OF BUSINESS
EBITDA Margin	26,143	19,898
Other Operating Revenue	87	157
Depreciation, Depletion and Amortization	(5,161)	(4,697)
Asset Retirement Obligations Accretion	(120)	(111)
Interest Expense	(1,732)	(148)
NET INCOME (LOSS) BEFORE INCOME TAXES	19,217	15,099
Operating Segment | Electric Operations | Electric sales
SEGMENTS OF BUSINESS
EBITDA Margin	26,143	19,898
Operating Segment | Coal Operations
SEGMENTS OF BUSINESS
EBITDA Margin	5,689	(1,205)
Other Operating Revenue	1,324	810
Depreciation, Depletion and Amortization	(9,797)	(10,728)
Asset Retirement Obligations Accretion	(307)	(288)
Exploration Costs	(21)	(70)
Gain (loss) on disposal or abandonment of assets, net	21	24
Interest Expense	(1,991)	(3,209)
NET INCOME (LOSS) BEFORE INCOME TAXES	(5,082)	(14,666)
Operating Segment | Coal Operations | Coal sales
SEGMENTS OF BUSINESS
EBITDA Margin	5,689	(1,205)
Corporate and Other and Eliminations
SEGMENTS OF BUSINESS
Other Operating Revenue	248	296
Depreciation, Depletion and Amortization	(19)	(18)
Interest Expense		(580)
Loss on Extinguishment of Debt		(853)
Equity Method Investment (Loss)	(236)	(249)
Corporate - General and Administrative	(2,977)	(2,448)
Corporate - Other Operating and Maintenance Costs		(92)
NET INCOME (LOSS) BEFORE INCOME TAXES	(4,156)	(2,739)
Corporate and Other and Eliminations | Electric sales
SEGMENTS OF BUSINESS
EBITDA Margin	23,417	17,611
Corporate and Other and Eliminations | Coal sales
SEGMENTS OF BUSINESS
EBITDA Margin	$ (24,589)	$ (16,406)