SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)	3 Months Ended	12 Months Ended
	Jun. 30, 2015 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2017 USD ($) county mi shares	Dec. 31, 2016 USD ($) shares
Accounting Policies [Abstract]
Length of natural gas pipeline (in miles) | mi					100
Public Utilities Assessment (PUA) included in utility revenue and energy and other taxes		$ 1,200,000	$ 1,100,000	$ 1,200,000
Composite annual rate for all depreciable utility property		2.20%	2.20%	2.20%
Useful life		50 years
Impairment of nonutility property and equipment and other noncurrent assets		$ 0	$ 0	$ 0
Amount of costs related to interests in proved and unproved properties in Pennsylvania, net of amortization					$ 8,700,000	$ 8,800,000
Treasury stock held (in shares) | shares					216,642	212,617
Schedule of Equity Method Investments [Line Items]
Net cash provided by (used in) financing activities		104,728,000	(3,054,000)	183,628,000
Impairment losses		0		0
Interest capitalized		2,000,000	6,600,000	4,900,000
Intangible assets					$ 12,480,000	$ 15,820,000
Increase (decrease) in intangible assets		(3,300,000)
Increase (decrease) adjustment related to purchase price allocations		(2,200,000)
Amortization expense		1,100,000	0
Goodwill		4,838,000	8,880,000	8,880,000	3,578,000	4,838,000
Utilities Operating Expense, Impairments		87,800,000
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
AROs (beginning balance)		59,427,000	57,943,000
Accretion		1,955,000	1,937,000
Additions		1,008,000	1,098,000
Settlements		(2,893,000)	(1,551,000)
AROs (ending balance)		59,497,000	59,427,000	57,943,000
Goodwill [Roll Forward]
Beginning Balance		4,838,000	8,880,000
Impairment of Goodwill		(1,260,000)	0
Fair Value Adjustments During Measurement Period (See Note 3)		0	(4,042,000)
Ending Balance		3,578,000	4,838,000	8,880,000
Noncurrent Assets
Schedule of Equity Method Investments [Line Items]
Intangible assets					12,500,000	15,800,000
Goodwill		4,800,000	4,800,000		$ 3,600,000	$ 4,800,000
Goodwill [Roll Forward]
Beginning Balance		4,800,000
Ending Balance		$ 3,600,000	4,800,000
Minimum
Schedule of Equity Method Investments [Line Items]
Useful life of intangible assets		2 years
Maximum
Schedule of Equity Method Investments [Line Items]
Useful life of intangible assets		20 years
Energenic
Schedule of Equity Method Investments [Line Items]
Impairment losses	$ 7,700,000			7,700,000
Accounting Standards Update 2016-09, Statutory Tax Withholding Component
Schedule of Equity Method Investments [Line Items]
Net cash provided by (used in) financing activities			(400,000)	(300,000)
Accounting Standards Update 2016-09, Excess Tax Benefit Component
Schedule of Equity Method Investments [Line Items]
Net cash provided by operating activities				400,000
Net cash provided by (used in) financing activities				(400,000)
South Jersey Gas Company
Schedule of Equity Method Investments [Line Items]
Number of counties in which entity operates | county					7
Net cash provided by operating activities		$ 106,669,000	142,162,000	164,552,000
Net cash provided by (used in) financing activities		149,761,000	67,928,000	61,218,000
Interest capitalized		1,600,000	5,300,000	2,800,000
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
AROs (beginning balance)		58,674,000	57,219,000
Accretion		1,925,000	1,908,000
Additions		1,008,000	1,098,000
Settlements		(2,893,000)	(1,551,000)
AROs (ending balance)		58,714,000	$ 58,674,000	57,219,000
South Jersey Gas Company | Accounting Standards Update 2016-09, Excess Tax Benefit Component
Schedule of Equity Method Investments [Line Items]
Net cash provided by operating activities				100,000
Net cash provided by (used in) financing activities				$ (100,000)
Maryland Solar Assets
Schedule of Equity Method Investments [Line Items]
Utilities Operating Expense, Impairments		43,900,000
Solar Assets
Schedule of Equity Method Investments [Line Items]
Utilities Operating Expense, Impairments		27,400,000
Landfill
Schedule of Equity Method Investments [Line Items]
Utilities Operating Expense, Impairments		$ 16,500,000