SEGMENT INFORMATION - EBITDA Expense Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Reconciliation of consolidated Segment Adjusted EBITDA Expense
Segment Adjusted EBITDA Expense	$ 1,282,433	$ 952,649	$ 861,249
Outside coal purchases	151	6,372
Other expense (income)	(4,353)	3,020	1,593
Product
Reconciliation of consolidated Segment Adjusted EBITDA Expense
Operating expenses (excluding depreciation, depletion and amortization)	$ 1,286,635	$ 943,257	$ 859,656