Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Detail of regulatory assets
Total regulatory assets	$ 1,810,458	$ 2,016,036
Less: current regulatory assets	420,969	625,757
Total non-current regulatory assets	1,389,489	1,390,279
Pension
Detail of regulatory assets
Total regulatory assets	750,976	696,476
Deferred fuel and purchased power
Detail of regulatory assets
Total regulatory assets	287,597	463,195
Income taxes — AFUDC equity
Detail of regulatory assets
Total regulatory assets	192,936	189,058
Ocotillo deferral
Detail of regulatory assets
Total regulatory assets	114,775	128,636
SCR deferral
Detail of regulatory assets
Total regulatory assets	83,123	89,477
Lease incentives
Detail of regulatory assets
Total regulatory assets	70,541	46,615
Retired power plant costs
Detail of regulatory assets
Total regulatory assets	68,380	83,536
Deferred fuel and purchased power — mark-to-market (Note 15)
Detail of regulatory assets
Total regulatory assets	42,275	120,214
FERC Transmission true up
Detail of regulatory assets
Total regulatory assets	35,159	616
Income taxes — investment tax credit basis adjustment
Detail of regulatory assets
Total regulatory assets	34,834	34,230
Deferred compensation
Detail of regulatory assets
Total regulatory assets	33,108	33,972
Deferred property taxes
Detail of regulatory assets
Total regulatory assets	23,918	32,488
Palo Verde VIEs (Note 17)
Detail of regulatory assets
Total regulatory assets	20,611	20,772
Power supply adjustor - interest
Detail of regulatory assets
Total regulatory assets	11,525	19,416
Active Union Medical Trust
Detail of regulatory assets
Total regulatory assets	9,673	12,747
Mead-Phoenix transmission line contributions in aid of construction (“CIAC”)
Detail of regulatory assets
Total regulatory assets	8,384	8,716
Navajo coal reclamation
Detail of regulatory assets
Total regulatory assets	7,905	10,883
Loss on reacquired debt
Detail of regulatory assets
Total regulatory assets	6,682	7,965
Tax expense adjustor mechanism
Detail of regulatory assets
Total regulatory assets	4,534	5,190
Four Corners cost deferral
Detail of regulatory assets
Total regulatory assets	0	7,922
Other
Detail of regulatory assets
Total regulatory assets	$ 3,522	$ 3,912