Revenues (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 822,384	$ 700,831
Total revenues from other sources	105,853	84,237
Revenues	928,237	785,068
Services/goods transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	12,022	12,996
Services/goods transferred over time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	810,362	687,835
Electric energy sales - residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	255,550	224,574
Electric energy sales - commercial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	254,470	219,597
Electric energy sales - large light and power
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	290,978	241,123
Electric energy sales - other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	5,457	1,426
Bank fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	12,022	12,996
Other sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3,907	1,115
Regulatory revenue
Disaggregation of Revenue [Line Items]
Total revenues from other sources	15,604	12,886
Bank interest and dividend income
Disaggregation of Revenue [Line Items]
Total revenues from other sources	79,479	59,989
Other bank noninterest income
Disaggregation of Revenue [Line Items]
Total revenues from other sources	2,356	2,130
Other
Disaggregation of Revenue [Line Items]
Total revenues from other sources	8,414	9,232
Electric utility
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	806,455	686,720
Total revenues from other sources	23,906	22,072
Revenues	830,361	708,792
Electric utility | Services/goods transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Electric utility | Services/goods transferred over time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	806,455	686,720
Electric utility | Electric energy sales - residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	255,550	224,574
Electric utility | Electric energy sales - commercial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	254,470	219,597
Electric utility | Electric energy sales - large light and power
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	290,978	241,123
Electric utility | Electric energy sales - other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	5,457	1,426
Electric utility | Bank fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Electric utility | Other sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Electric utility | Regulatory revenue
Disaggregation of Revenue [Line Items]
Total revenues from other sources	15,604	12,886
Electric utility | Bank interest and dividend income
Disaggregation of Revenue [Line Items]
Total revenues from other sources	0	0
Electric utility | Other bank noninterest income
Disaggregation of Revenue [Line Items]
Total revenues from other sources	0	0
Electric utility | Other
Disaggregation of Revenue [Line Items]
Total revenues from other sources	8,302	9,186
Bank
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	12,022	12,996
Total revenues from other sources	81,835	62,119
Revenues	93,857	75,115
Bank | Services/goods transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	12,022	12,996
Bank | Services/goods transferred over time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Bank | Electric energy sales - residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Bank | Electric energy sales - commercial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Bank | Electric energy sales - large light and power
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Bank | Electric energy sales - other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Bank | Bank fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	12,022	12,996
Bank | Other sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Bank | Regulatory revenue
Disaggregation of Revenue [Line Items]
Total revenues from other sources	0	0
Bank | Bank interest and dividend income
Disaggregation of Revenue [Line Items]
Total revenues from other sources	79,479	59,989
Bank | Other bank noninterest income
Disaggregation of Revenue [Line Items]
Total revenues from other sources	2,356	2,130
Bank | Other
Disaggregation of Revenue [Line Items]
Total revenues from other sources	0	0
Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3,907	1,115
Total revenues from other sources	112	46
Revenues	4,019	1,161
Other | Services/goods transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Other | Services/goods transferred over time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3,907	1,115
Other | Electric energy sales - residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Other | Electric energy sales - commercial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Other | Electric energy sales - large light and power
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Other | Electric energy sales - other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Other | Bank fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Other | Other sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3,907	1,115
Other | Regulatory revenue
Disaggregation of Revenue [Line Items]
Total revenues from other sources	0	0
Other | Bank interest and dividend income
Disaggregation of Revenue [Line Items]
Total revenues from other sources	0	0
Other | Other bank noninterest income
Disaggregation of Revenue [Line Items]
Total revenues from other sources	0	0
Other | Other
Disaggregation of Revenue [Line Items]
Total revenues from other sources	$ 112	$ 46