Revenues (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 700,831	$ 541,300
Total revenues from other sources	84,237	101,646
Revenues	785,068	642,946
Services/goods transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	12,996	11,378
Services/goods transferred over time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	687,835	529,922
Electric energy sales - residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	224,574	181,239
Electric energy sales - commercial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	219,597	168,465
Electric energy sales - large light and power
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	241,123	176,815
Electric energy sales - other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,426	2,479
Bank fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	12,996	11,378
Other sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,115	924
Regulatory revenue
Disaggregation of Revenue [Line Items]
Total revenues from other sources	12,886	28,429
Bank interest and dividend income
Disaggregation of Revenue [Line Items]
Total revenues from other sources	59,989	58,620
Other bank noninterest income
Disaggregation of Revenue [Line Items]
Total revenues from other sources	2,130	7,133
Other
Disaggregation of Revenue [Line Items]
Total revenues from other sources	9,232	7,464
Electric utility
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	686,720	528,998
Total revenues from other sources	22,072	35,866
Revenues	708,792	564,864
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	686,720	528,998
Electric utility | Electric energy sales - residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	224,574	181,239
Electric utility | Electric energy sales - commercial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	219,597	168,465
Electric utility | Electric energy sales - large light and power
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	241,123	176,815
Electric utility | Electric energy sales - other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,426	2,479
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	12,886	28,429
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	9,186	7,437
Bank
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	12,996	11,378
Total revenues from other sources	62,119	65,753
Revenues	75,115	77,131
Bank | Services/goods transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	12,996	11,378
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	12,996	11,378
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	59,989	58,620
Bank | Other bank noninterest income
Disaggregation of Revenue [Line Items]
Total revenues from other sources	2,130	7,133
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	1,115	924
Total revenues from other sources	46	27
Revenues	1,161	951
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	1,115	924
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	1,115	924
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	$ 46	$ 27