Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	$ 1,859,465	$ 1,822,100
Less: current regulatory assets	600,802	538,879
Total non-current regulatory assets	1,258,663	1,283,221
Pension
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	628,727	637,656
Deferred fuel and purchased power
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	469,962	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	179,818	179,631
Ocotillo Deferral
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	135,766	138,143
SCR Deferral
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	95,588	97,624
Retired power plant costs
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	94,903	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	61,858	0
Deferred property taxes
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	38,915	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	24,095	23,977
Palo Verde VIEs (Note 6)
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	20,893	20,933
Active Union Medical Trust
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	15,010	18,226
Four Corners cost deferral
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	13,979	15,999
Navajo coal reclamation
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	13,117	13,862
Loss on reacquired debt
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	9,238	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	8,965	9,048
Tax expense adjustor mechanism (b) (e)
Detail of regulatory assets
Regulatory asset including deferred fuel and purchased power regulatory asset current	5,681	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	$ 8,458	$ 8,171