WORKERS' COMPENSATION AND PNEUMOCONIOSIS (Details) - Pneumoconiosis benefits - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Black lung benefits:
Service cost	$ 861	$ 669
Interest cost	$ 1,558	$ 1,238
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Nonoperating Income (Expense)	Other Nonoperating Income (Expense)
Net amortization	$ 839	$ 346
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Amortization of Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Nonoperating Income (Expense)	Other Nonoperating Income (Expense)
Net periodic benefit cost	$ 3,258	$ 2,253