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Amount before tax of gain (loss) recognized on the sale or disposal of a disposal group. Excludes discontinued operations.

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The adjustment to expense previously capitalized costs of drilling exploratory wells when proved reserves are not found or when the entity obtains information that raises substantial doubt about the economic or operational viability of the project.

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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)				1 Months Ended	3 Months Ended
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)	Feb. 18, 2020 USD ($)	Aug. 31, 2019 USD ($)	Jul. 01, 2018 USD ($)	Dec. 31, 2019 USD ($) shares	Mar. 31, 2020 USD ($) county project shares	Mar. 31, 2019 USD ($) project	Dec. 31, 2020 project	Apr. 30, 2020 USD ($)
Public Utilities, General Disclosures [Line Items]
Number of projects closed \| project					1	4
Number of solar energy sites expected to be sold \| project					3
Impairment charge					$ 0	$ 0
Identified impairments					0	0
Amount of costs related to interests in proved and unproved properties				$ 8,600,000	$ 8,600,000
Shares of treasury stock held (in shares) \| shares				231,514	219,136
Payments to purchase asset management agreement			$ 11,300,000
Minimum annual fee for long-term asset management agreement			$ 4,250,000
Current portion of long-term debt				$ 467,909,000	$ 470,409,000
Notes payable				848,700,000	697,300,000
Subsequent event
Public Utilities, General Disclosures [Line Items]
Debt refinanced								$ 600,000,000.0
Assets held for sale
Public Utilities, General Disclosures [Line Items]
Consideration received on sales or projects					$ 7,200,000	16,100,000
Gain (loss) on sale of projects						100,000
SJG
Public Utilities, General Disclosures [Line Items]
Number of counties in which entity operates \| county					7
Impairment charge					$ 0	$ 0
Current portion of long-term debt				417,909,000	420,409,000
Notes payable				171,300,000	$ 142,500,000
SJG \| Subsequent event
Public Utilities, General Disclosures [Line Items]
Debt refinanced								$ 400,000,000.0
ETG Utility Operations
Public Utilities, General Disclosures [Line Items]
Number of counties in which entity operates \| county					7
Minimum annual fee for long-term asset management agreement					$ 4,250,000
Forecast
Public Utilities, General Disclosures [Line Items]
Number of solar energy sites expected to be sold \| project							2
AEP
Public Utilities, General Disclosures [Line Items]
Consideration paid for AEP		$ 4,000,000.0
MTF and ACB \| Assets held for sale
Public Utilities, General Disclosures [Line Items]
Consideration received on sales or projects	$ 97,000,000.0			100,000,000.0
ELK Utility Operations \| Assets held for sale
Public Utilities, General Disclosures [Line Items]
Consideration received on sales or projects				$ 15,000,000.0