v3.26.1
Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Dec. 31, 2025
Detail of regulatory assets    
Total regulatory assets $ 1,601,434 $ 1,749,366
Less: current regulatory assets 150,106 286,009
Total non-current regulatory assets 1,451,328 1,463,357
Pension    
Detail of regulatory assets    
Total regulatory assets 712,234 723,042
Income taxes — AFUDC equity    
Detail of regulatory assets    
Total regulatory assets 209,567 203,890
Palo Verde sale leaseback noncontrolling interests acquisition    
Detail of regulatory assets    
Total regulatory assets 151,506 151,506
Ocotillo deferral    
Detail of regulatory assets    
Total regulatory assets 92,509 99,931
Lease incentive (Note 17)    
Detail of regulatory assets    
Total regulatory assets 92,330 90,005
Deferred fuel and purchased power — mark-to-market (Note 10)    
Detail of regulatory assets    
Total regulatory assets 78,831 29,330
SCR deferral    
Detail of regulatory assets    
Total regulatory assets 74,217 77,186
Retired power plant costs    
Detail of regulatory assets    
Total regulatory assets 47,312 56,809
Income taxes — investment tax credit basis adjustment (Note 5)    
Detail of regulatory assets    
Total regulatory assets 41,691 42,459
Deferred compensation    
Detail of regulatory assets    
Total regulatory assets 32,842 32,204
FERC transmission true up    
Detail of regulatory assets    
Total regulatory assets 22,219 21,471
Deferred property taxes    
Detail of regulatory assets    
Total regulatory assets 11,064 15,349
Palo Verde VIEs (Note 9)    
Detail of regulatory assets    
Total regulatory assets 9,085 8,582
Mead-Phoenix transmission line — contributions in aid of construction    
Detail of regulatory assets    
Total regulatory assets 7,886 8,052
Loss on reacquired debt    
Detail of regulatory assets    
Total regulatory assets 5,180 5,653
Active union medical trust    
Detail of regulatory assets    
Total regulatory assets 4,966 3,696
TEAM    
Detail of regulatory assets    
Total regulatory assets 3,551 3,879
PSA - interest    
Detail of regulatory assets    
Total regulatory assets 769 5,679
Navajo coal reclamation    
Detail of regulatory assets    
Total regulatory assets 361 2,516
Deferred fuel and purchased power    
Detail of regulatory assets    
Total regulatory assets 0 149,068
DSM    
Detail of regulatory assets    
Total regulatory assets 0 15,706
Other    
Detail of regulatory assets    
Total regulatory assets $ 3,314 $ 3,353