REVENUE (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers									$ 1,343,000	$ 1,360,000	$ 1,272,000
Alternative Revenues									35,000	28,000	24,000
Other									40,000	45,000	45,000
Total Operating Revenues	$ 318,000	$ 441,000	$ 326,000	$ 333,000	$ 344,000	$ 460,000	$ 354,000	$ 275,000	1,418,338	1,432,618	1,340,935
Retail
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers									972,000	1,022,000	1,017,000
Wholesale
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers									247,000	238,000	152,000
Other Services
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers									$ 124,000	$ 100,000	$ 103,000
Lost Fixed Cost Recovery Mechanism
Disaggregation of Revenue [Line Items]
Cap on increase in lost fixed cost recovery rate (percentage)									2.00%