Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Detail of regulatory assets
Total non-current regulatory assets	$ 2,016,036	$ 1,822,100
Less: current regulatory assets	625,757	538,879
Total non-current regulatory assets	1,390,279	1,283,221
Pension
Detail of regulatory assets
Total non-current regulatory assets	696,476	637,656
Deferred fuel and purchased power
Detail of regulatory assets
Total non-current regulatory assets	463,195	460,561
Income taxes — AFUDC equity
Detail of regulatory assets
Total non-current regulatory assets	189,058	179,631
Ocotillo deferral
Detail of regulatory assets
Total non-current regulatory assets	128,636	138,143
Deferred fuel and purchased power — mark-to-market (Note 16)
Detail of regulatory assets
Total non-current regulatory assets	120,214	0
SCR deferral
Detail of regulatory assets
Total non-current regulatory assets	89,477	97,624
Retired power plant costs
Detail of regulatory assets
Total non-current regulatory assets	83,536	98,692
Lease incentives (Note 8)
Detail of regulatory assets
Total non-current regulatory assets	46,615	0
Income taxes — investment tax credit basis adjustment
Detail of regulatory assets
Total non-current regulatory assets	34,230	23,977
Deferred compensation
Detail of regulatory assets
Total non-current regulatory assets	33,972	33,660
Deferred property taxes
Detail of regulatory assets
Total non-current regulatory assets	32,488	41,057
Palo Verde VIEs (Note 17)
Detail of regulatory assets
Total non-current regulatory assets	20,772	20,933
Power supply adjustor-interest
Detail of regulatory assets
Total non-current regulatory assets	19,416	1,541
Active union medical trust
Detail of regulatory assets
Total non-current regulatory assets	12,747	18,226
Navajo coal reclamation
Detail of regulatory assets
Total non-current regulatory assets	10,883	13,862
Mead-Phoenix transmission line — contributions in aid of construction
Detail of regulatory assets
Total non-current regulatory assets	8,716	9,048
Loss on reacquired debt
Detail of regulatory assets
Total non-current regulatory assets	7,965	9,468
Four Corners cost deferral
Detail of regulatory assets
Total non-current regulatory assets	7,922	15,999
Tax expense adjustor mechanism
Detail of regulatory assets
Total non-current regulatory assets	5,190	5,845
Lost fixed cost recovery
Detail of regulatory assets
Total non-current regulatory assets	0	9,547
Other
Detail of regulatory assets
Total non-current regulatory assets	$ 4,528	$ 6,630