BUSINESS COMBINATIONS (Details) - USD ($)			1 Months Ended	3 Months Ended	12 Months Ended
	Jul. 01, 2018	Jun. 26, 2018	Oct. 31, 2018	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Payments to acquire businesses	$ 1,740,000,000
Working capital adjustment	40,300,000
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Property, Plant and Equipment	1,089,342,000
Accounts Receivable	45,875,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Provision For Accounts Receivable	(6,579,000)
Natural Gas in Storage	12,204,000
Materials and Supplies	345,000
Other Prepayments and Current Assets	200,000
Deferred Income Taxes	21,024,000
Regulatory Assets	136,213,000
Goodwill	731,029,000				$ 734,607,000	$ 3,578,000	$ 4,838,000
Total assets acquired	2,029,653,000
Accounts Payable	13,089,000
Other Current Liabilities	9,185,000
Environmental Remediation Costs - Current	7,100,000
Pension and Other Postretirement Benefits	3,213,000
Environmental Remediation Costs - Non Current	66,165,000
Regulatory Liabilities	189,509,000
Other	1,107,000
Total liabilities assumed	289,368,000
Total net assets acquired	1,740,285,000
Goodwill deductible for tax purposes	$ 677,600,000
Common Equity Percentage Required, Excluding Goodwill	46.00%
ETG and ELK revenues included in the Company's unaudited consolidated statements of income				$ 128,900,000
ETG and ELK earnings included in the Company's unaudited consolidated statements of income				5,200,000
Payments to customers					15,300,000
Business Acquisition, Pro Forma Information [Abstract]
Revenues					1,829,823,000	1,555,124,000
Net (loss) income					$ 74,770,000	$ (9,824,000)
Earnings (loss) per share					$ 0.89	$ (0.11)
Acquisition and regulatory approval costs					$ 34,100,000
Acquisition related expenses				$ 49,400,000		$ 34,100,000
ETG Utility Operations
Business Acquisition [Line Items]
Payments to acquire businesses	$ 1,730,000,000
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Credits due to customers under conditions of approval					15,000,000
Elkton Gas
Business Acquisition [Line Items]
Payments to acquire businesses	$ 10,900,000
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Credits due to customers under conditions of approval					300,000
Term loan
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Principal amount issued		$ 530,000,000			$ 530,000,000.0
Debt instrument term		364 days			364 days
ETG Utility Operations
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Property, Plant and Equipment					$ 1,077,000,000
ETG Utility Operations | New Jersey Board of Public Utilities
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Investment Requested To Be Recovered Through Rider Recovery Mechanism, Amount of IIP			$ 518,000,000