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Revenue - Performance Obligations (Details)
$ in Thousands
Jun. 30, 2026
USD ($)
Disaggregation of Revenue [Line Items]  
Estimated coal revenues $ 124,373
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-07-01  
Disaggregation of Revenue [Line Items]  
Estimated coal revenues $ 53,203
Estimated coal revenues, satisfaction period 6 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01  
Disaggregation of Revenue [Line Items]  
Estimated coal revenues $ 54,370
Estimated coal revenues, satisfaction period 1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-01-01  
Disaggregation of Revenue [Line Items]  
Estimated coal revenues $ 16,800
Estimated coal revenues, satisfaction period 1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2029-01-01  
Disaggregation of Revenue [Line Items]  
Estimated coal revenues $ 0
Estimated coal revenues, satisfaction period 1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2030-01-01  
Disaggregation of Revenue [Line Items]  
Estimated coal revenues $ 0
Estimated coal revenues, satisfaction period 1 year