v3.26.3
REVENUE - Remaining Performance Obligations (Details) - Operating Segment
$ in Thousands
Sep. 30, 2026
USD ($)
REVENUE  
Revenue expected to be recognized $ 1,785,020
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-10-01  
REVENUE  
Revenue expected to be recognized $ 123,845
Unsatisfied or partially unsatisfied performance obligation, period 3 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01  
REVENUE  
Revenue expected to be recognized $ 395,409
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-01-01  
REVENUE  
Revenue expected to be recognized $ 222,146
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2029-01-01  
REVENUE  
Revenue expected to be recognized $ 131,304
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2030-01-01  
REVENUE  
Revenue expected to be recognized $ 87,539
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2031-01-01  
REVENUE  
Revenue expected to be recognized $ 824,777
Unsatisfied or partially unsatisfied performance obligation, period
Electric Operations | Delivered energy revenue  
REVENUE  
Revenue expected to be recognized $ 332,034
Electric Operations | Delivered energy revenue | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-10-01  
REVENUE  
Revenue expected to be recognized $ 56,279
Unsatisfied or partially unsatisfied performance obligation, period 3 months
Electric Operations | Delivered energy revenue | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01  
REVENUE  
Revenue expected to be recognized $ 160,255
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Electric Operations | Delivered energy revenue | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-01-01  
REVENUE  
Revenue expected to be recognized $ 86,570
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Electric Operations | Delivered energy revenue | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2029-01-01  
REVENUE  
Revenue expected to be recognized $ 28,931
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Electric Operations | Delivered energy revenue | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2030-01-01  
REVENUE  
Revenue expected to be recognized $ 0
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Electric Operations | Delivered energy revenue | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2031-01-01  
REVENUE  
Revenue expected to be recognized $ 0
Unsatisfied or partially unsatisfied performance obligation, period
Electric Operations | Accredited capacity revenue  
REVENUE  
Revenue expected to be recognized $ 1,197,265
Electric Operations | Accredited capacity revenue | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-10-01  
REVENUE  
Revenue expected to be recognized $ 16,315
Unsatisfied or partially unsatisfied performance obligation, period 3 months
Electric Operations | Accredited capacity revenue | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01  
REVENUE  
Revenue expected to be recognized $ 75,310
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Electric Operations | Accredited capacity revenue | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-01-01  
REVENUE  
Revenue expected to be recognized $ 90,951
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Electric Operations | Accredited capacity revenue | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2029-01-01  
REVENUE  
Revenue expected to be recognized $ 102,374
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Electric Operations | Accredited capacity revenue | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2030-01-01  
REVENUE  
Revenue expected to be recognized $ 87,539
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Electric Operations | Accredited capacity revenue | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2031-01-01  
REVENUE  
Revenue expected to be recognized $ 824,777
Unsatisfied or partially unsatisfied performance obligation, period
Coal Operations  
REVENUE  
Revenue expected to be recognized $ 255,721
Coal Operations | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-10-01  
REVENUE  
Revenue expected to be recognized $ 51,252
Unsatisfied or partially unsatisfied performance obligation, period 3 months
Coal Operations | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01  
REVENUE  
Revenue expected to be recognized $ 159,845
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  
Revenue expected to be recognized $ 44,625
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  
Revenue expected to be recognized $ 0
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Coal Operations | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2030-01-01  
REVENUE  
Revenue expected to be recognized $ 0
Unsatisfied or partially unsatisfied performance obligation, period 1 year
Coal Operations | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2031-01-01  
REVENUE  
Revenue expected to be recognized $ 0
Unsatisfied or partially unsatisfied performance obligation, period