Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Detail of regulatory assets
Current	$ 509,176	$ 518,524
Non-Current	1,180,656	1,192,987
Pension
Detail of regulatory assets
Current	0	0
Non-Current	514,330	509,751
Deferred fuel and purchased power
Detail of regulatory assets
Current	390,013	388,148
Non-Current	0	0
Income taxes — allowance for funds used during construction (“AFUDC”) equity
Detail of regulatory assets
Current	7,625	7,625
Non-Current	167,644	164,768
Ocotillo deferral
Detail of regulatory assets
Current	9,507	9,507
Non-Current	133,390	138,143
Retired power plant costs
Detail of regulatory assets
Current	15,157	15,160
Non-Current	91,113	99,681
SCR deferral
Detail of regulatory assets
Current	8,147	8,147
Non-Current	93,551	97,624
Deferred property taxes
Detail of regulatory assets
Current	8,569	8,569
Non-Current	36,772	41,057
Lost fixed cost recovery
Detail of regulatory assets
Current	43,788	63,889
Non-Current	0	0
Deferred compensation
Detail of regulatory assets
Current	0	0
Non-Current	34,251	33,997
Income taxes — investment tax credit basis adjustment
Detail of regulatory assets
Current	826	1,129
Non-Current	23,606	23,639
Palo Verde VIEs (Note 6)
Detail of regulatory assets
Current	0	0
Non-Current	21,013	21,094
Four Corners cost deferral
Detail of regulatory assets
Current	8,077	8,077
Non-Current	11,960	15,998
Coal reclamation
Detail of regulatory assets
Current	2,978	2,978
Non-Current	12,372	13,862
Active Union Medical Trust
Detail of regulatory assets
Current	0	0
Non-Current	13,704	1,175
Loss on reacquired debt
Detail of regulatory assets
Current	1,648	1,648
Non-Current	8,579	9,372
Mead-Phoenix transmission line contributions in aid of construction (“CIAC”)
Detail of regulatory assets
Current	332	332
Non-Current	8,882	9,048
TCA balancing account
Detail of regulatory assets
Current	8,805	170
Non-Current	0	3,663
Tax expense adjustor mechanism
Detail of regulatory assets
Current	656	656
Non-Current	5,518	5,845
Tax expense of Medicare subsidy
Detail of regulatory assets
Current	1,235	1,235
Non-Current	1,968	2,469
Other
Detail of regulatory assets
Current	1,813	1,254
Non-Current	$ 2,003	$ 1,801