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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)			3 Months Ended		9 Months Ended
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)	Aug. 31, 2019 USD ($)	Jul. 01, 2018 USD ($)	Sep. 30, 2019 USD ($) project county mi shares	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) project county mi shares	Sep. 30, 2018 USD ($)	Dec. 31, 2019 project	Dec. 31, 2018 USD ($) shares
Public Utilities, General Disclosures [Line Items]
Length of pipeline (in miles) \| mi			118		118
Payments to acquire assets					$ 357,844,000	$ 200,770,000
Number of projects closed \| project					7
Number of solar energy sites \| project			1		1
Impairment charge			$ 1,300,000		$ 1,300,000	99,200,000
Identified impairments			0	$ 0	0	0
Amount of costs related to interests in proved and unproved properties			$ 8,600,000		$ 8,600,000			$ 8,600,000
Shares of treasury stock held (in shares) \| shares			227,426		227,426			233,482
Payments to purchase asset management agreement		$ 11,300,000			$ 0	11,389,000
Minimum annual fee for long-term asset management agreement		4,250,000
Current portion of long-term debt			$ 338,909,000		338,909,000			$ 733,909,000
Current portion of long-term debt due in the next fiscal year								320,000,000.0
Early repayment of senior debt					725,000,000.0
Assets held for sale
Public Utilities, General Disclosures [Line Items]
Proceeds from sale of business			2,100,000		24,300,000
Value of unsold solar assets			$ 27,800,000		$ 27,800,000
SJG
Public Utilities, General Disclosures [Line Items]
Number of counties in which entity operates \| county			7		7
Payments to acquire assets					$ 178,666,000	168,654,000
Impairment charge			$ 0	$ 0	0	$ 0
Current portion of long-term debt			$ 338,909,000		$ 338,909,000			$ 18,909,000
ETG Utility Operations
Public Utilities, General Disclosures [Line Items]
Number of counties in which entity operates \| county			7		7
Minimum annual fee for long-term asset management agreement					$ 4,250,000
Series 2018D Senior Notes, Due 2019
Public Utilities, General Disclosures [Line Items]
Early repayment of senior debt					475,000,000.0
Forecast
Public Utilities, General Disclosures [Line Items]
Number of solar energy sites \| project							2
Elizabethtown Gas and Elkton Gas
Public Utilities, General Disclosures [Line Items]
Payments to acquire assets		$ 1,720,000,000
AEP
Public Utilities, General Disclosures [Line Items]
Consideration paid for AEP	$ 4,000,000.0
Unsecured Term Loan \| Credit Agreement \| SJG
Public Utilities, General Disclosures [Line Items]
Current portion of long-term debt			$ 310,000,000.0		310,000,000.0
Draw on term loan					$ 10,000,000.0