v3.26.1
Revenue from Contracts with Customers - Supply contracts (Details)
$ in Thousands
Jun. 30, 2026
USD ($)
Performance obligations unsatisfied or partially unsatisfied  
Total $ 3,635,759
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-07-01  
Performance obligations unsatisfied or partially unsatisfied  
Total $ 963,225
Expected timing of satisfaction period 9 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01  
Performance obligations unsatisfied or partially unsatisfied  
Total $ 1,389,875
Expected timing of satisfaction period 1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-01-01  
Performance obligations unsatisfied or partially unsatisfied  
Total $ 839,479
Expected timing of satisfaction period 1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2029-01-01  
Performance obligations unsatisfied or partially unsatisfied  
Total $ 443,180
Expected timing of satisfaction period 1 year
Illinois Basin Coal  
Performance obligations unsatisfied or partially unsatisfied  
Total $ 2,677,063
Illinois Basin Coal | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-07-01  
Performance obligations unsatisfied or partially unsatisfied  
Total $ 713,153
Expected timing of satisfaction period 9 months
Illinois Basin Coal | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01  
Performance obligations unsatisfied or partially unsatisfied  
Total $ 1,008,907
Expected timing of satisfaction period 1 year
Illinois Basin Coal | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-01-01  
Performance obligations unsatisfied or partially unsatisfied  
Total $ 549,623
Expected timing of satisfaction period 1 year
Illinois Basin Coal | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2029-01-01  
Performance obligations unsatisfied or partially unsatisfied  
Total $ 405,380
Expected timing of satisfaction period 1 year
Appalachia Coal  
Performance obligations unsatisfied or partially unsatisfied  
Total $ 958,696
Appalachia Coal | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-07-01  
Performance obligations unsatisfied or partially unsatisfied  
Total $ 250,072
Expected timing of satisfaction period 9 months
Appalachia Coal | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01  
Performance obligations unsatisfied or partially unsatisfied  
Total $ 380,968
Expected timing of satisfaction period 1 year
Appalachia Coal | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-01-01  
Performance obligations unsatisfied or partially unsatisfied  
Total $ 289,856
Expected timing of satisfaction period 1 year
Appalachia Coal | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2029-01-01  
Performance obligations unsatisfied or partially unsatisfied  
Total $ 37,800
Expected timing of satisfaction period 1 year