SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Business Acquisition (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Oct. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Business Acquisition [Line Items]
Payment to acquire assets		$ 58,816	$ 67,278
Unamortized debt issuance costs		15,600		$ 17,400
Interest Charges		13,972	$ 16,745
Elizabethtown Gas and Elkton Gas
Business Acquisition [Line Items]
Payment to acquire assets	$ 1,700,000
Legal fees		9,300
Unamortized debt issuance costs				$ 3,800
Interest Charges		2,600
Ticking fees		1,200
Operating Expense | Elizabethtown Gas and Elkton Gas
Business Acquisition [Line Items]
Legal fees		$ 5,500