Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Detail of regulatory assets
Total regulatory assets	$ 1,749,366	$ 1,810,458
Less: current regulatory assets	286,009	420,969
Total non-current regulatory assets	1,463,357	1,389,489
Pension
Detail of regulatory assets
Total regulatory assets	723,042	750,976
Income taxes — AFUDC equity
Detail of regulatory assets
Total regulatory assets	203,890	192,936
Palo Verde sale leaseback noncontrolling interests acquisition
Detail of regulatory assets
Total regulatory assets		0
Deferred fuel and purchased power
Detail of regulatory assets
Total regulatory assets	149,068	287,597
Ocotillo deferral
Detail of regulatory assets
Total regulatory assets	99,931	114,775
Lease incentive (Note 20)
Detail of regulatory assets
Total regulatory assets	90,005	70,541
SCR deferral
Detail of regulatory assets
Total regulatory assets	77,186	83,123
Retired power plant costs
Detail of regulatory assets
Total regulatory assets	56,809	68,380
Income taxes — investment tax credit basis adjustment (Note 5)
Detail of regulatory assets
Total regulatory assets	42,459	34,834
Deferred compensation
Detail of regulatory assets
Total regulatory assets	32,204	33,108
Deferred fuel and purchased power — mark-to-market (Note 13)
Detail of regulatory assets
Total regulatory assets	29,330	42,275
FERC transmission true up
Detail of regulatory assets
Total regulatory assets	21,471	35,159
DSM
Detail of regulatory assets
Total regulatory assets	15,706	0
Deferred property taxes
Detail of regulatory assets
Total regulatory assets	15,349	23,918
Palo Verde VIEs (Note 12)
Detail of regulatory assets
Total regulatory assets	8,582	20,611
Mead-Phoenix transmission line — contributions in aid of construction
Detail of regulatory assets
Total regulatory assets	8,052	8,384
PSA - interest
Detail of regulatory assets
Total regulatory assets	5,679	11,525
Loss on reacquired debt
Detail of regulatory assets
Total regulatory assets	5,653	6,682
TEAM
Detail of regulatory assets
Total regulatory assets	3,879	4,534
Active union medical trust
Detail of regulatory assets
Total regulatory assets	3,696	9,673
Navajo coal reclamation
Detail of regulatory assets
Total regulatory assets	2,516	7,905
Other
Detail of regulatory assets
Total regulatory assets	$ 3,353	$ 3,522