Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 835,984	$ 604,827	$ 1,536,815	$ 1,146,127
Total revenues from other sources	59,623	75,430	143,860	177,076
Revenues	895,607	680,257	1,680,675	1,323,203
Services/goods transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	11,797	11,569	24,793	22,947
Services/goods transferred over time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	824,187	593,258	1,512,022	1,123,180
Electric energy sales - residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	259,433	196,318	484,007	377,557
Electric energy sales - commercial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	264,701	192,103	484,298	360,568
Electric energy sales - large light and power
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	293,847	201,536	534,970	378,351
Electric energy sales - other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	4,873	2,212	6,299	4,691
Bank fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	11,797	11,569	24,793	22,947
Other sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,333	1,089	2,448	2,013
Regulatory revenue
Disaggregation of Revenue [Line Items]
Total revenues from other sources	(11,428)	2,854	1,458	31,283
Bank interest and dividend income
Disaggregation of Revenue [Line Items]
Total revenues from other sources	62,822	62,066	122,811	120,686
Other bank noninterest income
Disaggregation of Revenue [Line Items]
Total revenues from other sources	705	3,625	2,835	10,758
Other
Disaggregation of Revenue [Line Items]
Total revenues from other sources	7,524	6,885	16,756	14,349
Electric utility
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	822,854	592,169	1,509,574	1,121,167
Total revenues from other sources	(3,981)	9,710	18,091	45,576
Revenues	818,873	601,879	1,527,665	1,166,743
Electric utility | Services/goods transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Electric utility | Services/goods transferred over time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	822,854	592,169	1,509,574	1,121,167
Electric utility | Electric energy sales - residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	259,433	196,318	484,007	377,557
Electric utility | Electric energy sales - commercial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	264,701	192,103	484,298	360,568
Electric utility | Electric energy sales - large light and power
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	293,847	201,536	534,970	378,351
Electric utility | Electric energy sales - other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	4,873	2,212	6,299	4,691
Electric utility | Bank fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
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	(11,428)	2,854	1,458	31,283
Electric utility | Bank interest and dividend income
Disaggregation of Revenue [Line Items]
Total revenues from other sources	0	0	0	0
Electric utility | Other bank noninterest income
Disaggregation of Revenue [Line Items]
Total revenues from other sources	0	0	0	0
Electric utility | Other
Disaggregation of Revenue [Line Items]
Total revenues from other sources	7,447	6,856	16,633	14,293
Bank
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	11,797	11,569	24,793	22,947
Total revenues from other sources	63,527	65,691	125,646	131,444
Revenues	75,324	77,260	150,439	154,391
Bank | Services/goods transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	11,797	11,569	24,793	22,947
Bank | Services/goods transferred over time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Bank | Electric energy sales - residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Bank | Electric energy sales - commercial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Bank | Electric energy sales - large light and power
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Bank | Electric energy sales - other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Bank | Bank fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	11,797	11,569	24,793	22,947
Bank | Other sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Bank | Regulatory revenue
Disaggregation of Revenue [Line Items]
Total revenues from other sources	0	0	0	0
Bank | Bank interest and dividend income
Disaggregation of Revenue [Line Items]
Total revenues from other sources	62,822	62,066	122,811	120,686
Bank | Other bank noninterest income
Disaggregation of Revenue [Line Items]
Total revenues from other sources	705	3,625	2,835	10,758
Bank | Other
Disaggregation of Revenue [Line Items]
Total revenues from other sources	0	0	0	0
Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,333	1,089	2,448	2,013
Total revenues from other sources	77	29	123	56
Revenues	1,410	1,118	2,571	2,069
Other | Services/goods transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Services/goods transferred over time
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,333	1,089	2,448	2,013
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 | Bank fees
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	1,333	1,089	2,448	2,013
Other | Regulatory revenue
Disaggregation of Revenue [Line Items]
Total revenues from other sources	0	0	0	0
Other | Bank interest and dividend income
Disaggregation of Revenue [Line Items]
Total revenues from other sources	0	0	0	0
Other | Other bank noninterest income
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	$ 77	$ 29	$ 123	$ 56