Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 798,994	$ 842,929	$ 2,285,302	$ 2,390,092
Total revenues from other sources	(8,384)	(9,690)	(4,230)	30,578
Revenues	790,610	833,239	2,281,072	2,420,670
Services/goods transferred over time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	798,994	842,929	2,285,302	2,390,092
Electric energy sales - residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	261,780	272,541	735,308	758,602
Electric energy sales - commercial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	251,288	268,538	724,796	761,788
Electric energy sales - large light and power
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	278,484	294,421	801,179	846,448
Electric energy sales - other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	4,284	4,532	12,989	14,087
Other sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3,158	2,897	11,030	9,167
Regulatory revenue
Disaggregation of Revenue [Line Items]
Total revenues from other sources	(17,864)	(19,924)	(33,522)	780
Other
Disaggregation of Revenue [Line Items]
Total revenues from other sources	9,480	10,234	29,292	29,798
Electric utility
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	795,836	840,032	2,274,272	2,380,925
Total revenues from other sources	(8,408)	(10,415)	(5,996)	29,601
Revenues	787,428	829,617	2,268,276	2,410,526
Electric utility | Services/goods transferred over time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	795,836	840,032	2,274,272	2,380,925
Electric utility | Electric energy sales - residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	261,780	272,541	735,308	758,602
Electric utility | Electric energy sales - commercial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	251,288	268,538	724,796	761,788
Electric utility | Electric energy sales - large light and power
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	278,484	294,421	801,179	846,448
Electric utility | Electric energy sales - other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	4,284	4,532	12,989	14,087
Electric utility | Other sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Electric utility | Regulatory revenue
Disaggregation of Revenue [Line Items]
Total revenues from other sources	(17,864)	(19,924)	(33,522)	780
Electric utility | Other
Disaggregation of Revenue [Line Items]
Total revenues from other sources	9,456	9,509	27,526	28,821
Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3,158	2,897	11,030	9,167
Total revenues from other sources	24	725	1,766	977
Revenues	3,182	3,622	12,796	10,144
Other | Services/goods transferred over time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3,158	2,897	11,030	9,167
Other | Electric energy sales - residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Electric energy sales - commercial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Electric energy sales - large light and power
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Electric energy sales - other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Other sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3,158	2,897	11,030	9,167
Other | Regulatory revenue
Disaggregation of Revenue [Line Items]
Total revenues from other sources	0	0	0	0
Other | Other
Disaggregation of Revenue [Line Items]
Total revenues from other sources	$ 24	$ 725	$ 1,766	$ 977