NATURE OF OPERATIONS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Additional Information) (Details) customer in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) mi² customer	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of retail customers | customer	429
Area in which subsidiary generates transmits and distributes electricity to retail electric customers (sq miles) | mi²	1,155
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and Cash Equivalents	$ 9,762	$ 138,114	$ 38,000
Total Cash, Cash Equivalents, and Restricted Cash	28,472	152,747	49,501	$ 43,325
Investments and Other Property
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted Cash	16,000	14,000	11,000
Current Assets—Other
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted Cash	$ 2,000	$ 1,000	$ 1,000