Unconsolidated Subsidiaries (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated subsidiaries	$ 12,371	$ 14,927
Income Statement [Abstract]
Revenues	214,794	241,719
Gross profit	14,591	67,842
Income before income taxes	(64,158)	87,723
Net (loss) income	(39,587)	74,158
Balance Sheet
Current assets	231,998	260,407
Current liabilities	69,986	44,270
NACoal | Unconsolidated Mines
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated subsidiaries	12,400	14,900
Balance Sheet
Dividends from unconsolidated mines	45,800	49,000
NACoal | Unconsolidated Mines
Schedule of Equity Method Investments [Line Items]
Maximum Risk of Loss	5,000	7,100
NACoal | Variable Interest Entity, Not Primary Beneficiary | Unconsolidated Mines
Income Statement [Abstract]
Revenues	610,734	664,824
Gross profit	63,646	47,748
Income before income taxes	49,994	57,250
Net (loss) income	43,714	48,467
Balance Sheet
Current assets	124,387	214,098
Non-current assets	814,226	805,833
Current liabilities	161,606	116,701
Non-current liabilities	$ 772,003	$ 896,134