NATURE OF OPERATIONS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Additional Information) (Details) customer in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) mi² customer	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Retail customers | customer	422
Area in which subsidiary generates transmits and distributes electricity to retail electric customers | mi²	1,155
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and Cash Equivalents	$ 37,701	$ 35,962	$ 56,000
Total Cash, Cash Equivalents, and Restricted Cash	49,501	43,325	59,867	$ 76,379
Investments and Other Property
Restricted Cash and Cash Equivalents Items [Line Items]
Total Cash, Cash Equivalents, and Restricted Cash	11,000	7,000	4,000
Current Assets, Other
Restricted Cash and Cash Equivalents Items [Line Items]
Total Cash, Cash Equivalents, and Restricted Cash	$ 1,000	$ 0	$ 0
Lost Fixed Cost Recovery Mechanism
Restricted Cash and Cash Equivalents Items [Line Items]
Cap on increase in lost fixed cost recovery rate (in percentage)	2.00%