Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Detail of regulatory assets
Total regulatory assets	$ 1,661,230	$ 1,810,458
Less: current regulatory assets	303,848	420,969
Total non-current regulatory assets	1,357,382	1,389,489
Pension
Detail of regulatory assets
Total regulatory assets	733,970	750,976
Income taxes — allowance for funds used during construction equity
Detail of regulatory assets
Total regulatory assets	196,476	192,936
Deferred fuel and purchased power
Detail of regulatory assets
Total regulatory assets	182,412	287,597
Ocotillo deferral
Detail of regulatory assets
Total regulatory assets	107,353	114,775
Lease incentives
Detail of regulatory assets
Total regulatory assets	92,379	70,541
SCR deferral
Detail of regulatory assets
Total regulatory assets	80,154	83,123
Retired power plant costs
Detail of regulatory assets
Total regulatory assets	62,607	68,380
FERC Transmission true up
Detail of regulatory assets
Total regulatory assets	52,720	35,159
Income taxes — investment tax credit basis adjustment
Detail of regulatory assets
Total regulatory assets	34,338	34,834
Deferred compensation
Detail of regulatory assets
Total regulatory assets	33,977	33,108
Palo Verde VIEs (Note 8)
Detail of regulatory assets
Total regulatory assets	20,531	20,611
Deferred property taxes
Detail of regulatory assets
Total regulatory assets	19,634	23,918
Deferred fuel and purchased power — mark-to-market (Note 9)
Detail of regulatory assets
Total regulatory assets	9,598	42,275
Mead-Phoenix transmission line — contributions in aid of construction ("CIAC")
Detail of regulatory assets
Total regulatory assets	8,218	8,384
Loss on reacquired debt
Detail of regulatory assets
Total regulatory assets	6,168	6,682
Active union medical trust
Detail of regulatory assets
Total regulatory assets	5,032	9,673
Navajo Coal reclamation
Detail of regulatory assets
Total regulatory assets	4,670	7,905
Tax expense adjustor mechanism
Detail of regulatory assets
Total regulatory assets	4,206	4,534
Power supply adjustor - interest
Detail of regulatory assets
Total regulatory assets	3,329	11,525
Other
Detail of regulatory assets
Total regulatory assets	$ 3,458	$ 3,522