Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Contract with Customer, Asset, Gross	$ 165,700		$ 165,700		$ 160,800
Revenue from Contract with Customer, Excluding Assessed Tax	391,500	$ 379,500	1,100,400	$ 1,083,200
REVENUES	398,456	385,149	1,121,634	1,099,331
Retail Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	369,945	366,030	1,056,438	1,045,286
Other non-606 revenue	6,478	4,293	19,069	12,157
Wholesale Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	18,426	10,844	35,533	30,007
Miscellaneous revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	3,091	2,631	8,474	7,906
Other non-606 revenue	516	1,351	2,120	3,975
Electricity [Member]
Disaggregation of Revenue [Line Items]
REVENUES	$ 398,456	$ 385,149	$ 1,121,634	$ 1,099,331