REVENUE - Concentration risk (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Electric Operations
REVENUE
Revenues	$ 310,737	$ 261,527
Coal Operations
REVENUE
Revenues	148,655	137,448
Revenue concentration | Customer concentration | Customer A | Electric Operations
REVENUE
Revenues	$ 110,006	$ 123,504
Concentration risk percentage	23.40%	30.60%
Revenue concentration | Customer concentration | Customer A | Coal Operations
REVENUE
Revenues	$ 48,983	$ 54,593
Concentration risk percentage	10.40%	13.50%
Revenue concentration | Customer concentration | Customer B | Electric Operations
REVENUE
Revenues	$ 47,248
Concentration risk percentage	10.10%
Revenue concentration | Customer concentration | Customer B | Coal Operations
REVENUE
Revenues	$ 64,799	$ 43,394
Concentration risk percentage	13.80%	10.70%
Revenue concentration | Customer concentration | Customer C | Electric Operations
REVENUE
Revenues		$ 51,639
Concentration risk percentage		12.80%
Accounts receivable concentration | Customer concentration | Customer A | Electric Operations
REVENUE
Revenues	$ 3,275	$ 3,460
Concentration risk percentage	23.40%	22.40%
Accounts receivable concentration | Customer concentration | Customer A | Coal Operations
REVENUE
Revenues	$ 1,871	$ 1,887
Concentration risk percentage	13.40%	12.20%
Accounts receivable concentration | Customer concentration | Customer B | Electric Operations
REVENUE
Revenues	$ 3,184	$ 5,952
Concentration risk percentage	22.80%	38.60%
Accounts receivable concentration | Customer concentration | Customer C | Electric Operations
REVENUE
Revenues	$ 3,188
Concentration risk percentage	22.80%