Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Contract with Customer, Asset, before Allowance for Credit Loss	$ 152,800		$ 163,800
Revenue from Contract with Customer, Excluding Assessed Tax	353,600	$ 351,900
REVENUES	362,201	357,382
Contract with Customer, Liability	200		$ 500
Contract with Customer, Liability, Revenue Recognized	300	400
Retail Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	334,837	337,892
Other non-606 revenue	7,595	4,896
Wholesale Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	16,109	11,308
Miscellaneous revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	2,681	2,732
Other non-606 revenue	979	554
Electricity [Member]
Disaggregation of Revenue [Line Items]
REVENUES	362,201	357,382
Utility | Retail Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	4,191	3,888
Utility | Retail Revenue [Member] | Residential Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	160,503	155,408
Utility | Retail Revenue [Member] | Small Commercial and Industrial
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	54,517	54,253
Utility | Retail Revenue [Member] | Large Commercial and Industrial
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	113,440	122,038
Utility | Retail Revenue [Member] | Public Lighting
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 2,186	$ 2,305