REVENUE (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	$ 448,000	$ 405,000	$ 1,036,000	$ 988,000
Alternative Revenues	5,000	6,000	20,000	19,000
Other	7,000	6,000	33,000	31,000
Total Operating Revenues	459,760	417,210	1,089,096	1,037,736
Retail
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	345,000	334,000	810,000	801,000
Wholesale
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	79,000	44,000	152,000	116,000
Other Services
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	$ 24,000	$ 27,000	$ 74,000	$ 71,000