v3.25.2
REVENUE - Remaining performance obligations (Details) - Operating Segment
$ in Thousands
Jun. 30, 2025
USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 991,270
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-07-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 197,330
Unsatisfied or partially unsatisfied performance obligation, period 6 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 361,590
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 290,530
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-01-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 124,580
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2029-01-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 17,240
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Electric Operations | Delivered energy  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 436,530
Electric Operations | Delivered energy | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-07-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 95,510
Unsatisfied or partially unsatisfied performance obligation, period 6 months
Electric Operations | Delivered energy | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 172,220
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Electric Operations | Delivered energy | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 97,280
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Electric Operations | Delivered energy | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-01-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 57,750
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Electric Operations | Delivered energy | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2029-01-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 13,770
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Electric Operations | Energy Capacity  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 183,200
Electric Operations | Energy Capacity | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-07-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 29,460
Unsatisfied or partially unsatisfied performance obligation, period 6 months
Electric Operations | Energy Capacity | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 61,540
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Electric Operations | Energy Capacity | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 51,400
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Electric Operations | Energy Capacity | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-01-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 37,330
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Electric Operations | Energy Capacity | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2029-01-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 3,470
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Coal Operations  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 371,540
Coal Operations | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-07-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 72,360
Unsatisfied or partially unsatisfied performance obligation, period 6 months
Coal Operations | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 127,830
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Coal Operations | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 141,850
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Coal Operations | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-01-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue expected to be recognized $ 29,500
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Coal Operations | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2029-01-01  
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Unsatisfied or partially unsatisfied performance obligation, period 1 year