Regulatory Matters - Schedule of Regulatory Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Detail of regulatory liabilities
Total regulatory liabilities	$ 1,868,518	$ 1,947,030
Less: current regulatory liabilities	117,241	210,909
Total non-current regulatory liabilities	1,751,277	1,736,121
AROs and removal costs
Detail of regulatory liabilities
Total regulatory liabilities	242,200	286,907
Other postretirement benefits
Detail of regulatory liabilities
Total regulatory liabilities	231,269	233,952
Four Corners coal reclamation
Detail of regulatory liabilities
Total regulatory liabilities	97,458	97,988
Income taxes — deferred investment tax credit
Detail of regulatory liabilities
Total regulatory liabilities	81,660	81,949
Income taxes — change in state rates
Detail of regulatory liabilities
Total regulatory liabilities	56,040	56,260
RES
Detail of regulatory liabilities
Total regulatory liabilities	53,858	54,551
Sundance maintenance
Detail of regulatory liabilities
Total regulatory liabilities	25,195	25,668
Spent nuclear fuel
Detail of regulatory liabilities
Total regulatory liabilities	18,917	20,492
DSM
Detail of regulatory liabilities
Total regulatory liabilities	11,802	26,228
TCA Balancing Account
Detail of regulatory liabilities
Total regulatory liabilities	0	4,860
TEAM
Detail of regulatory liabilities
Total regulatory liabilities	3,587	3,738
Deferred fuel and purchased power — mark-to-market (Note 10)
Detail of regulatory liabilities
Total regulatory liabilities	0	3,641
Other
Detail of regulatory liabilities
Total regulatory liabilities	2,516	3,063
ACC | Excess deferred income taxes - Tax Cuts and Jobs Act
Detail of regulatory liabilities
Total regulatory liabilities	844,409	847,572
FERC | Excess deferred income taxes - Tax Cuts and Jobs Act
Detail of regulatory liabilities
Total regulatory liabilities	$ 199,607	$ 200,161