SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Significant Accounting Policies [Line Items]
Segment Reporting, Disclosure of Major Customer	0	0	0
Impact of reclassification upon adoption of ASU 2017-07			$ 17,300
Operating Lease, Right-of-Use Asset	$ 34,200	$ 32,000
Operating Lease, Liability	$ 34,500	32,000
Number of natural gas distribution services customers	2,200,000
Accounts Receivable, Allowance for Credit Loss, Current	$ 6,600	4,700
Goodwill, Impairment Loss	0	0	0
Asset Impairment Charges	0	0	0
Deferred Tax Assets, Valuation Allowance	0	0	$ 0
Liability for Uncertainty in Income Taxes, Current	$ 0	$ 0