Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Detail of regulatory assets
Total regulatory assets	$ 1,850,911	$ 2,016,036
Less: current regulatory assets	491,933	625,757
Total non-current regulatory assets	1,358,978	1,390,279
Pension
Detail of regulatory assets
Total regulatory assets	687,741	696,476
Deferred fuel and purchased power
Detail of regulatory assets
Total regulatory assets	322,667	463,195
Income taxes — allowance for funds used during construction (“AFUDC”) equity
Detail of regulatory assets
Total regulatory assets	190,884	189,058
Ocotillo deferral
Detail of regulatory assets
Total regulatory assets	122,197	128,636
Deferred fuel and purchased power — mark-to-market (Note 7)
Detail of regulatory assets
Total regulatory assets	122,147	120,214
SCR deferral
Detail of regulatory assets
Total regulatory assets	86,092	89,477
Retired power plant costs
Detail of regulatory assets
Total regulatory assets	75,958	83,536
Lease incentives
Detail of regulatory assets
Total regulatory assets	57,542	46,615
Income taxes — investment tax credit basis adjustment
Detail of regulatory assets
Total regulatory assets	35,450	34,230
Deferred compensation
Detail of regulatory assets
Total regulatory assets	33,923	33,972
Deferred property taxes
Detail of regulatory assets
Total regulatory assets	28,203	32,488
Palo Verde VIEs (Note 6)
Detail of regulatory assets
Total regulatory assets	20,692	20,772
Active Union Medical Trust
Detail of regulatory assets
Total regulatory assets	13,061	12,747
FERC Transmission true up
Detail of regulatory assets
Total regulatory assets	10,073	616
Navajo coal reclamation
Detail of regulatory assets
Total regulatory assets	9,394	10,883
Mead-Phoenix transmission line contributions in aid of construction (“CIAC”)
Detail of regulatory assets
Total regulatory assets	8,550	8,716
Loss on reacquired debt
Detail of regulatory assets
Total regulatory assets	7,324	7,965
Power supply adjustor - interest
Detail of regulatory assets
Total regulatory assets	5,848	19,416
Tax expense adjustor mechanism
Detail of regulatory assets
Total regulatory assets	4,862	5,190
Four Corners cost deferral
Detail of regulatory assets
Total regulatory assets	3,884	7,922
Other
Detail of regulatory assets
Total regulatory assets	$ 4,419	$ 3,912