Revenue - Schedule of Disaggregation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 783,531	$ 696,475
Regulatory cost recovery revenue	12,000	14,000
Retail Electric Service | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	367,346	340,838
Retail Electric Service | Non-Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	359,516	314,783
Wholesale Energy Sales
Disaggregation of Revenue [Line Items]
Total operating revenues	28,903	17,597
Transmission Services for Others
Disaggregation of Revenue [Line Items]
Total operating revenues	25,492	18,993
Other Sources
Disaggregation of Revenue [Line Items]
Total operating revenues	2,274	4,264
Electric and Transmission Service
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 772,000	$ 682,000