LONG-TERM DEBT - Credit Facility (Details) - USD ($) $ in Millions		3 Months Ended
	Jan. 13, 2023	Mar. 31, 2024
Credit Agreement
Long-Term Debt
Maximum borrowing capacity	$ 425.0
Minimum liquidity to extend maturity	$ 200.0
Letters of credit outstanding		$ 41.0
Debt available for borrowing		$ 384.0
Annual commitment fee percentage, undrawn portion		0.50%
ARLP debt arrangements requirements, period over which the ratios are required to be maintained		12 months
Credit Agreement | Maximum
Long-Term Debt
Interest coverage ratio	3.0
Actual cash flow to interest expense ratio for trailing twelve months		59.18
Credit Agreement | Minimum
Long-Term Debt
Interest coverage ratio	1.0
Actual cash flow to interest expense ratio for trailing twelve months		1.0
Credit Agreement | Overnight Bank Funding Rate
Long-Term Debt
Basis spread for variable interest rate (as a percent)	0.50%
Credit Agreement | Daily Simple Secured Overnight Financing Rate
Long-Term Debt
Basis spread for variable interest rate (as a percent)	1.00%
Credit Agreement | Alliance Coal | Maximum
Long-Term Debt
ARLP debt arrangements requirements, debt to cash flow ratio	1.5	1.0
Credit Agreement | Alliance Coal | Minimum
Long-Term Debt
ARLP debt arrangements requirements, debt to cash flow ratio	1.0
Actual debt to cash flow ratio for trailing twelve months		0.21
Credit Agreement | Alliance Coal and Intermediate Partnership | Maximum
Long-Term Debt
ARLP debt arrangements requirements, debt to cash flow ratio	2.5
Actual debt to cash flow ratio for trailing twelve months		1.0
Credit Agreement | Alliance Coal and Intermediate Partnership | Minimum
Long-Term Debt
ARLP debt arrangements requirements, debt to cash flow ratio	1.0
Actual debt to cash flow ratio for trailing twelve months		0.59
Letters of credit subfacility
Long-Term Debt
Maximum borrowing capacity	$ 425.0
Swingline subfacility
Long-Term Debt
Maximum borrowing capacity	15.0
Term loan
Long-Term Debt
Maximum borrowing term loan	$ 75.0
Interest rate (as a percent)	6.25%
Effective interest rate (as a percent)		8.46%