Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	$ 1,842,223	$ 1,822,100
Less: current regulatory assets	561,879	538,879
Total non-current regulatory assets	1,280,344	1,283,221
Pension
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	640,148	637,656
Deferred fuel and purchased power
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	433,279	460,561
Income taxes — allowance for funds used during construction (“AFUDC”) equity
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	181,859	179,631
Ocotillo deferral
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	133,390	138,143
SCR deferral
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	93,551	97,624
Retired power plant costs
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	91,114	98,692
Deferred fuel and purchased power — mark-to-market (Note 7)
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	67,188	0
Deferred property taxes
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	36,772	41,057
Deferred compensation
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	34,492	33,660
Income taxes — investment tax credit basis adjustment
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	29,654	23,977
Palo Verde VIEs (Note 6)
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	20,852	20,933
Active Union Medical Trust
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	17,675	18,226
Four Corners cost deferral
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	11,960	15,999
Navajo coal reclamation
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	12,372	13,862
Loss on reacquired debt
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	9,007	9,468
Mead-Phoenix transmission line contributions in aid of construction (“CIAC”)
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	8,882	9,048
Power supply adjustor - interest
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	7,171	1,541
Tax expense adjustor mechanism (b) (e)
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	5,518	5,845
Lost fixed cost recovery
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	0	9,547
Other
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	$ 7,339	$ 6,630