Revenues (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Disaggregation of Revenue [Line Items]
General payment period (in days)									30 days
Revenues from contracts with customers									$ 3,180,298	$ 3,248,505
Revenues from other sources									39,552	38,998
Total revenues	$ 799,180	$ 833,239	$ 795,417	$ 792,014	$ 853,424	$ 800,899	$ 798,800	$ 834,380	3,219,850	3,287,503	$ 3,420,917
Operating Segments
Disaggregation of Revenue [Line Items]
Total revenues											3,420,917
Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									11,923	17,540
Revenues from other sources									1,227	442
Total revenues	3,006	3,622	3,086	3,436	3,442	5,912	4,609	4,019	13,150	17,982	12,330
Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									3,180,298	3,248,505
Transferred over Time | Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									11,923	17,540
Electric utility
Disaggregation of Revenue [Line Items]
Revenue taxes, other than income tax expense									285,000	291,000	303,000
Revenue taxes accrued	178,000				182,000				178,000	182,000
Total revenues											3,408,583
Electric utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									3,168,375	3,230,965
Revenues from other sources									38,325	38,556
Total revenues	$ 796,174	$ 829,617	$ 792,331	$ 788,578	$ 849,982	$ 794,987	$ 794,191	$ 830,361	3,206,700	3,269,521	$ 3,408,587
Electric utility | Transferred over Time | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									3,168,375	3,230,965
Electric energy sales - residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									1,012,620	1,026,321
Electric energy sales - residential | Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									0	0
Electric energy sales - residential | Electric utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									1,012,620	1,026,321
Electric energy sales - commercial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									1,013,189	1,044,045
Electric energy sales - commercial | Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									0	0
Electric energy sales - commercial | Electric utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									1,013,189	1,044,045
Electric energy sales - large light and power
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									1,123,884	1,141,128
Electric energy sales - large light and power | Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									0	0
Electric energy sales - large light and power | Electric utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									1,123,884	1,141,128
Electric energy sales - other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									18,682	19,471
Electric energy sales - other | Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									0	0
Electric energy sales - other | Electric utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									18,682	19,471
Other sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									11,923	17,540
Other sales | Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									11,923	17,540
Other sales | Electric utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									0	0
Regulatory revenue
Disaggregation of Revenue [Line Items]
Revenues from other sources									(2,566)	3,708
Regulatory revenue | Other
Disaggregation of Revenue [Line Items]
Revenues from other sources									0	0
Regulatory revenue | Electric utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from other sources									(2,566)	3,708
Other
Disaggregation of Revenue [Line Items]
Revenues from other sources									42,118	35,290
Other | Other
Disaggregation of Revenue [Line Items]
Revenues from other sources									1,227	442
Other | Electric utility | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from other sources									$ 40,891	$ 34,848