RELATED-PARTY TRANSACTIONS - Related Party Purchases (Details) - Affiliated Entity - USD ($)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Related Party Transaction [Line Items]
Coal purchases from related party	$ 1,256,919	$ 213,790
Fuel Service and Beneficial Use Agreement ("FBUA") | Northampton Fuel Supply Company, Inc.
Related Party Transaction [Line Items]
Coal purchases from related party	953,419	138,790
Waste Coal Agreement (the “WCA”) | Coal Valley Sales, LLC
Related Party Transaction [Line Items]
Coal purchases from related party	$ 303,500	$ 75,000