RATES AND REGULATORY ACTIONS (Details) $ in Thousands				1 Months Ended																			12 Months Ended					300 Months Ended
	Nov. 01, 2017 USD ($)	Oct. 01, 2016 USD ($)	Feb. 29, 2016 USD ($)	Nov. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jul. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Apr. 30, 2017 USD ($)	Oct. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jul. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Apr. 30, 2016 USD ($)	Feb. 29, 2016 USD ($)	Aug. 31, 2015 USD ($)	Jul. 31, 2015 USD ($)	Jun. 30, 2015 USD ($)	Apr. 30, 2015 USD ($)	Jan. 31, 2015 USD ($)	Aug. 31, 2014 USD ($)	Feb. 28, 2013 USD ($)	Jul. 31, 2009 USD ($)	Dec. 31, 2017 USD ($) site customer	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2016 USD ($)	Jan. 31, 2016 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2013 USD ($)
Schedule of Capitalization [Line Items]
Amount of AIRP																					$ 141,200
Term of AIRP																					4 years
Annual investment amount of AIRP																					$ 35,300
Investment amount of SHARP				$ 110,250																$ 103,500
Investment Requested to be Recovered through SHARP, Term				3 years																3 years
Regulatory assets																							$ 469,224		$ 410,746			$ 410,746
Number of customers purchasing energy commodity from another entity | customer																							29,141
Energy Efficiency Tracker
Schedule of Capitalization [Line Items]
Requested increase (decrease) in rates												$ (800)
Approved request for revenue increase (decrease)			$ (7,900)											$ (7,900)
Regulatory assets																							$ 2,094		219			219
Environmental Remediation Costs: Expended - Net
Schedule of Capitalization [Line Items]
Regulatory assets																							100,327		71,997			71,997
Deferred pipeline integrity costs
Schedule of Capitalization [Line Items]
Regulatory assets																							$ 500		4,000			4,000
New Jersey Board of Public Utilities
Schedule of Capitalization [Line Items]
Approved requested rate increase (decrease)									$ 11,000
Roll of AIRP investments into base rates																									80,200
Approved budget										$ 56,000
South Jersey Gas Company
Schedule of Capitalization [Line Items]
Investment amount of SHARP																											$ 36,600
Number of sites for environmental cleanup (in sites) | site																							12
South Jersey Gas Company | Energy Efficiency Tracker
Schedule of Capitalization [Line Items]
Approved requested rate increase (decrease)									(1,600)
South Jersey Gas Company | Storm Hardening and Reliability Program | Building
Schedule of Capitalization [Line Items]
Investments during the period																								$ 35,700		$ 33,700
South Jersey Gas Company | New Jersey Board of Public Utilities
Schedule of Capitalization [Line Items]
Approved requested rate increase (decrease)	$ 39,500
Approved rate of return on rate base, percentage	6.80%
Approved return on common equity, percentage	9.60%
Authorized replacement investments (up to)									$ 302,500
Approved budget										5,600
Increase (decrease) in Universal Service Fund recoveries		$ 1,100
South Jersey Gas Company | New Jersey Board of Public Utilities | SHARP Investments
Schedule of Capitalization [Line Items]
Approved requested rate increase (decrease)					$ 3,600
Public Utilities, Property, Plant and Equipment, Net					33,300
South Jersey Gas Company | New Jersey Board of Public Utilities | Annual BGSS Filing
Schedule of Capitalization [Line Items]
Approved requested rate increase (decrease)					(4,700)
Public Utilities, Bill Credit								$ 8,000
Requested increase (decrease) in rates							$ (4,700)
South Jersey Gas Company | New Jersey Board of Public Utilities | EET Rate Adjustment Petition
Schedule of Capitalization [Line Items]
Approved requested rate increase (decrease)				$ 2,600
Requested increase (decrease) in rates							3,000
South Jersey Gas Company | New Jersey Board of Public Utilities | Storm Hardening and Reliability Program
Schedule of Capitalization [Line Items]
Approved requested rate increase (decrease)										3,900
Requested increase (decrease) in rates								3,980					$ 4,300
South Jersey Gas Company | New Jersey Board of Public Utilities | AIRP II Investments
Schedule of Capitalization [Line Items]
Approved requested rate increase (decrease)					5,000
Public Utilities, Property, Plant and Equipment, Net					46,100			42,000
South Jersey Gas Company | New Jersey Board of Public Utilities | Annual SBC Filing
Schedule of Capitalization [Line Items]
Requested increase (decrease) in rates						$ 8,500
Accelerated Infrastructure Replacement Program
Schedule of Capitalization [Line Items]
Requested increase (decrease) in rates								$ 4,500						13,000
Amount of AIRP														$ 500,000
Extension period of AIRP, requested and then received			7 years						5 years
Basic Gas Supply Service
Schedule of Capitalization [Line Items]
Requested increase (decrease) in rates																	$ (28,400)
Amount of increase (decrease) in regulatory costs approved																														$ (28,400)
Basic Gas Supply Service | New Jersey Board of Public Utilities
Schedule of Capitalization [Line Items]
Approved requested rate increase (decrease)										$ (47,100)
Basic Gas Supply Service | South Jersey Gas Company
Schedule of Capitalization [Line Items]
Bill credits																									10,000			10,000	$ 20,000
Basic Gas Supply Service | South Jersey Gas Company | New Jersey Board of Public Utilities
Schedule of Capitalization [Line Items]
Requested increase (decrease) in rates												(47,100)
Conservation Incentive Program
Schedule of Capitalization [Line Items]
Requested increase (decrease) in rates							200					46,500					(11,300)
Conservation Incentive Program | Non-weather
Schedule of Capitalization [Line Items]
Requested increase (decrease) in rates							1,100					9,900					(8,800)
Conservation Incentive Program | Weather
Schedule of Capitalization [Line Items]
Requested increase (decrease) in rates							900					36,600					(2,500)
Allowance for Funds Used Under Construction
Schedule of Capitalization [Line Items]
Approved base rate increase									$ 5,700
Storm Hardening and Reliability Program
Schedule of Capitalization [Line Items]
Amount of increase (decrease) in regulatory costs approved																														4,000
Storm Hardening and Reliability Program | South Jersey Gas Company
Schedule of Capitalization [Line Items]
Requested increase (decrease) in rates																		$ 4,000
Energy Efficiency Tracker
Schedule of Capitalization [Line Items]
Requested increase (decrease) in rates																	(7,600)		$ 56,000
Amount of increase (decrease) in regulatory costs approved															$ 2,600
Amount of regulatory costs available for recovery															$ 36,300							$ 17,000
Contract term																						2 years
Extension period															2 years
Energy Efficiency Tracker | South Jersey Gas Company
Schedule of Capitalization [Line Items]
Amount of regulatory costs available for recovery																															$ 24,000
Societal Benefits Clause
Schedule of Capitalization [Line Items]
Requested increase (decrease) in rates											$ 16,000					$ (5,000)
Remediation Adjustment Clause
Schedule of Capitalization [Line Items]
Number of sites for environmental cleanup (in sites) | site																							12
Amortization period																							7 years
Regulated costs recovered																												120,400
Remediation Adjustment Clause | Environmental Remediation Costs: Expended - Net
Schedule of Capitalization [Line Items]
Regulatory assets																							$ 100,300		$ 72,000			$ 72,000
New Jersey Clean Energy Program
Schedule of Capitalization [Line Items]
Amount of statewide funding approved							344,700					345,000					345,000							344,700		345,000	345,000
Regulatory costs entity is expensing							12,700					14,600					14,600							12,700		14,600	14,600
Universal Service Fund
Schedule of Capitalization [Line Items]
Amount of statewide funding approved					38,300																									46,400
Amount of statewide costs proposed							16,300					56,000					(46,400)							16,300		56,000	(46,400)
Universal Service Fund | South Jersey Gas Company
Schedule of Capitalization [Line Items]
Amount of increase (decrease) in regulatory costs approved					3,200																									5,200
Amount of proposed impact of annual costs					$ (2,200)		$ (2,000)					$ 1,100					$ (3,400)							$ (2,000)		$ 1,100	$ (3,400)			$ (3,400)