SEGMENTS OF BUSINESS - Revenuer Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
SEGMENTS OF BUSINESS
Other Operating Revenue	$ 4,766	$ 1,045	$ 6,425	$ 2,308
Total sales and operating revenues	102,889	93,825	220,676	205,619
Delivered Energy
SEGMENTS OF BUSINESS
Operating Revenues	44,132	43,106	116,268	92,234
Capacity Revenue
SEGMENTS OF BUSINESS
Operating Revenues	15,844	16,873	29,651	28,646
Coal Sales
SEGMENTS OF BUSINESS
Operating Revenues	38,147	32,801	68,332	82,431
Coal Sales \| Third-Party
SEGMENTS OF BUSINESS
Operating Revenues	38,147	32,801	68,332	82,431
Electric Operations
SEGMENTS OF BUSINESS
Operating Revenues	59,976	59,979	145,919	120,880
Electric Operations \| Delivered Energy
SEGMENTS OF BUSINESS
Operating Revenues	44,132	43,106	116,268	92,234
Electric Operations \| Capacity Revenue
SEGMENTS OF BUSINESS
Operating Revenues	15,844	16,873	29,651	28,646
Coal Operations
SEGMENTS OF BUSINESS
Operating Revenues	38,147	32,801	68,332	82,431
Operating Segment \| Electric Operations
SEGMENTS OF BUSINESS
Other Operating Revenue	3,134	174	3,221	331
Total sales and operating revenues	63,110	60,153	149,140	121,211
Operating Segment \| Electric Operations \| Delivered Energy
SEGMENTS OF BUSINESS
Operating Revenues	44,132	43,106	116,268	92,234
Operating Segment \| Electric Operations \| Capacity Revenue
SEGMENTS OF BUSINESS
Operating Revenues	15,844	16,873	29,651	28,646
Operating Segment \| Coal Operations
SEGMENTS OF BUSINESS
Other Operating Revenue	1,399	497	2,723	1,307
Total sales and operating revenues	46,928	46,207	103,026	113,053
Operating Segment \| Coal Operations \| Coal Sales
SEGMENTS OF BUSINESS
Operating Revenues	45,529	45,710	100,303	111,746
Operating Segment \| Coal Operations \| Coal Sales \| Third-Party
SEGMENTS OF BUSINESS
Operating Revenues	38,147	32,801	68,332	82,431
Operating Segment \| Coal Operations \| Coal Sales \| Intercompany
SEGMENTS OF BUSINESS
Operating Revenues	7,382	12,909	31,971	29,315
Corporate and Other Eliminations
SEGMENTS OF BUSINESS
Other Operating Revenue	233	374	481	670
Total sales and operating revenues	(7,149)	(12,535)	(31,490)	(28,645)
Corporate and Other Eliminations \| Coal Sales \| Intercompany
SEGMENTS OF BUSINESS
Operating Revenues	$ (7,382)	$ (12,909)	$ (31,971)	$ (29,315)

The total amount of other operating income, the components of which are not separately disclosed on the income statement, from items that are associated with the entity's normal revenue producing operation.

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