Revenue - Sources of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Total Operating Revenues	$ 3,803,835	$ 3,586,982	$ 3,471,209
Electric Service | Residential
Disaggregation of Revenue [Line Items]
Total Operating Revenues	1,913,324	1,929,178	1,761,122
Electric Service | Non-Residential
Disaggregation of Revenue [Line Items]
Total Operating Revenues	1,586,940	1,486,098	1,509,514
Electric Service | Wholesale Energy Sales
Disaggregation of Revenue [Line Items]
Total Operating Revenues	187,640	93,345	121,805
Transmission Services for Others
Disaggregation of Revenue [Line Items]
Total Operating Revenues	99,285	65,859	62,460
Other Sources
Disaggregation of Revenue [Line Items]
Total Operating Revenues	$ 16,646	$ 12,502	$ 16,308