LONG-TERM DEBT - Credit Facility (Details) $ in Millions			12 Months Ended
	Jan. 13, 2023 USD ($)	Mar. 09, 2020 USD ($)	Dec. 31, 2022 USD ($)
Credit Agreement
Long-Term Debt
Maximum borrowing capacity	$ 425.0
Minimum liquidity to extend maturity	$ 200.0
Interest rate (as a percent)	6.25%
Interest coverage ratio	3.0
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
Long-Term Debt
ARLP debt arrangements requirements, debt to cash flow ratio	1.5
Credit Agreement | Alliance Coal and Intermediate Partnership
Long-Term Debt
ARLP debt arrangements requirements, debt to cash flow ratio	2.5
Letters of credit subfacility
Long-Term Debt
Maximum borrowing capacity	$ 425.0	$ 125.0
Swingline subfacility
Long-Term Debt
Maximum borrowing capacity	15.0	15.0
Term Loan
Long-Term Debt
Maximum borrowing term loan	$ 75.0
Replaced credit facility
Long-Term Debt
Maximum borrowing capacity		$ 459.5
Letters of credit outstanding			$ 41.1
Debt available for borrowing			$ 418.4
Annual commitment fee percentage, undrawn portion			0.35%
ARLP debt arrangements requirements, debt to cash flow ratio		2.5
ARLP debt arrangements requirements, cash flow to interest expense ratio		3.0
Actual debt to cash flow ratio for trailing twelve months			0.52
Actual cash flow to interest expense ratio for trailing twelve months			21.76
Restricted net assets of subsidiaries			$ 537.3
Replaced credit facility | Eurodollar Rate
Long-Term Debt
Effective interest rate (as a percent)			6.74%
Replaced credit facility | Credit Agreement, first lien
Long-Term Debt
ARLP debt arrangements requirements, debt to cash flow ratio		1.5
Actual debt to cash flow ratio for trailing twelve months			0.03
Other
Long-Term Debt
Maximum borrowing capacity			$ 5.0
Letters of credit outstanding			$ 5.0