Segment Information - Narrative (Details)	12 Months Ended
	Dec. 31, 2021 segment plant mine	Dec. 31, 2020 segment
Segment Reporting Information [Line Items]
Number of reportable segments | segment	1	2
West Virgina | All Other
Segment Reporting Information [Line Items]
Number of active mines | mine	1
Number of preparation plants | plant	1
Met | Virgina
Segment Reporting Information [Line Items]
Number of active mines | mine	5
Number of preparation plants | plant	2
Met | West Virgina
Segment Reporting Information [Line Items]
Number of active mines | mine	14
Number of preparation plants | plant	5