Regulatory Matters - Schedule of Regulatory Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Detail of regulatory liabilities
Total regulatory liabilities	$ 2,094,737	$ 2,062,233
Less: current regulatory liabilities	182,458	206,955
Total non-current regulatory liabilities	1,912,279	1,855,278
Asset retirement obligations and removal costs
Detail of regulatory liabilities
Total regulatory liabilities	357,327	358,403
Other postretirement benefits
Detail of regulatory liabilities
Total regulatory liabilities	228,956	238,113
Four Corners coal reclamation
Detail of regulatory liabilities
Total regulatory liabilities	97,617	77,532
Renewable energy standard
Detail of regulatory liabilities
Total regulatory liabilities	76,796	68,523
Income taxes — deferred investment tax credit
Detail of regulatory liabilities
Total regulatory liabilities	65,449	66,327
Income taxes — change in rates
Detail of regulatory liabilities
Total regulatory liabilities	58,246	59,133
Demand side management
Detail of regulatory liabilities
Total regulatory liabilities	30,983	23,927
Deferred fuel and purchased power — mark-to-market (Note 9)
Detail of regulatory liabilities
Total regulatory liabilities	27,058	0
Sundance maintenance
Detail of regulatory liabilities
Total regulatory liabilities	24,634	23,086
Spent nuclear fuel
Detail of regulatory liabilities
Total regulatory liabilities	23,733	26,818
TCA Balancing Account
Detail of regulatory liabilities
Total regulatory liabilities	14,771	14,834
Tax expense adjustor mechanism
Detail of regulatory liabilities
Total regulatory liabilities	4,041	4,343
Property tax deferral
Detail of regulatory liabilities
Total regulatory liabilities	3,690	4,785
Other
Detail of regulatory liabilities
Total regulatory liabilities	128	113
ACC | Excess deferred income taxes - Tax Cuts and Jobs Act
Detail of regulatory liabilities
Total regulatory liabilities	876,142	888,896
FERC | Excess deferred income taxes - Tax Cuts and Jobs Act
Detail of regulatory liabilities
Total regulatory liabilities	$ 205,166	$ 207,400