SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) $ in Thousands, number in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Significant Accounting Policies [Line Items]
Operating Loss Carryforwards, Tax Benefit	$ 11,000
Unbilled Receivables, Current	$ 143,200	$ 109,600
Number of natural gas distribution services customers	2
Allowance for Doubtful Accounts Receivable, Current	$ 4,200	3,500
Materials, Supplies, and Other	34,084	33,325
Goodwill	157,953	157,953
Goodwill, Impairment Loss	0	0	$ 0
Asset Impairment Charges	0	0	$ 0
Deferred Tax Assets, Valuation Allowance	0	0
Liability for Uncertain Tax Positions, Current	$ 0	$ 0
Segment Reporting, Disclosure of Major Customers	0	0	0