Revenue - Schedule of Disaggregation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 1,469,871	$ 1,308,254	$ 3,315,071	$ 3,004,978
Regulatory cost recovery revenue	5,000	4,000	16,000	38,000
Retail Electric Service | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	743,061	681,918	1,647,996	1,554,473
Retail Electric Service | Non-Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	547,979	480,671	1,370,164	1,216,449
Wholesale Energy Sales
Disaggregation of Revenue [Line Items]
Total operating revenues	139,741	108,539	198,546	144,143
Transmission Services for Others
Disaggregation of Revenue [Line Items]
Total operating revenues	36,321	35,816	91,165	77,388
Other Sources
Disaggregation of Revenue [Line Items]
Total operating revenues	2,769	1,310	7,200	12,525
Electric and Transmission Service
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 1,465,000	$ 1,304,000	$ 3,299,000	$ 2,967,000