RATES AND REGULATORY ACTIONS (Details) $ in Thousands				1 Months Ended																	12 Months Ended			288 Months Ended
	Oct. 01, 2016 USD ($)	Feb. 29, 2016 USD ($)	Oct. 01, 2014	Oct. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jul. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Apr. 30, 2016 USD ($)	Feb. 29, 2016 USD ($)	Sep. 30, 2015 USD ($)	Aug. 31, 2015 USD ($)	Jul. 31, 2015 USD ($)	Jun. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Aug. 31, 2014 USD ($)	Jul. 31, 2014 USD ($)	May 31, 2014 USD ($)	Sep. 30, 2013 USD ($)	Feb. 28, 2013 USD ($)	Jan. 31, 2009 USD ($)	Dec. 31, 2016 USD ($) site customer	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	Jan. 31, 2016 USD ($)	Apr. 30, 2015 USD ($)	Jan. 31, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jan. 31, 2014 USD ($)	Jun. 30, 2013 USD ($)
Schedule of Capitalization [Line Items]
Approved base rate increase														$ 20,000
Rate of return on base rate														7.10%
Return on common equity														9.75%
Composite depreciation rate			2.10%											2.40%
Amount of AIRP																			$ 141,200
Term of AIRP																			4 years
Annual investment amount																			$ 35,300
Investment amount of SHARP															$ 103,500			$ 280,000					$ 36,600
Term of SHARP															3 years			7 years
Number of gas manufacturing plants (in sites) | site																					12
Regulatory assets																					$ 410,746			$ 323,434
Number of customers purchasing gas commodities from a competitor | customer																					33,467
Energy Efficiency Tracker
Schedule of Capitalization [Line Items]
Requested increase (decrease) in gas cost recoveries							$ (800)
Approved increase (decrease) in gas cost recoveries				$ (1,600)
Approved revenue increase (decrease)		$ (7,900)							$ (7,900)
Regulatory assets																					$ 219			496
Environmental restoration costs expended net
Schedule of Capitalization [Line Items]
Regulatory assets																					71,997			42,032
Other regulatory assets, deferred pipeline integrity costs
Schedule of Capitalization [Line Items]
Regulatory assets																					4,000			2,700
Storm Hardening and Reliability Program | Building
Schedule of Capitalization [Line Items]
SHARP investment																						$ 33,700
New Jersey Board of Public Utilities
Schedule of Capitalization [Line Items]
Approved increase (decrease) in gas cost recoveries				11,000
Authorized replacement investments (up to)				302,500
Roll of AIRP investments into base rates				$ 80,200
Statewide budget for all the State's gas utilities					$ 56,000
New Jersey Board of Public Utilities | South Jersey Gas Company
Schedule of Capitalization [Line Items]
Statewide budget for all the State's gas utilities					5,600
Resulting increase (decrease) to USF recoveries from statewide budget	$ 1,100
New Jersey Board of Public Utilities | Storm Hardening and Reliability Program
Schedule of Capitalization [Line Items]
Requested increase (decrease) in gas cost recoveries								$ 4,300
Approved increase (decrease) in gas cost recoveries					3,900
Accelerated Infrastructure Replacement Program
Schedule of Capitalization [Line Items]
Approved base rate increase														$ 7,500
Requested increase (decrease) in gas cost recoveries									13,000
Amount of AIRP									$ 500,000
Investments to be rolled to base rate														69,900
Extension period of AIRP, requested and then received		7 years		5 years
Basic Gas Supply Service
Schedule of Capitalization [Line Items]
Bill credit																					$ 10,000				$ 20,000				$ 11,200
Requested increase (decrease) in recoveries																	$ 27,000
Requested percentage of increase in gas cost recoveries																	9.30%
Approved increase (decrease) in gas recoveries														27,000
Requested increase (decrease) in gas cost recoveries													$ (28,400)
Approved increase (decrease) in gas cost recoveries										$ (28,400)
Basic Gas Supply Service | New Jersey Board of Public Utilities
Schedule of Capitalization [Line Items]
Requested increase (decrease) in gas cost recoveries							(47,100)
Approved increase (decrease) in gas cost recoveries					$ (47,100)
Conservation Incentive Program
Schedule of Capitalization [Line Items]
Requested increase (decrease) in gas cost recoveries							46,500						(11,300)				$ (21,800)
Conservation Incentive Program | Non weather
Schedule of Capitalization [Line Items]
Requested increase (decrease) in gas cost recoveries							9,900						(8,800)				4,200
Conservation Incentive Program | Weather
Schedule of Capitalization [Line Items]
Requested increase (decrease) in gas cost recoveries							36,600						(2,500)				(26,000)
Allowance for Funds Used Under Construction
Schedule of Capitalization [Line Items]
Approved base rate increase				$ 5,700										3,200
Storm Hardening and Reliability Program
Schedule of Capitalization [Line Items]
Requested increase (decrease) in recoveries																										$ 4,000
Approved increase (decrease) in gas recoveries										4,000
Energy Efficiency Tracker
Schedule of Capitalization [Line Items]
Requested increase (decrease) in recoveries																	$ 1,400										$ 56,000
Approved increase (decrease) in gas recoveries											$ 2,600			2,200
Requested increase (decrease) in gas cost recoveries													(7,600)
Approved budget											$ 36,300									$ 17,000										$ 24,000
Period of time in which energy efficiency measures will be installed																				2 years
Approved extension of EEPs											2 years
Societal Benefits Clause
Schedule of Capitalization [Line Items]
Requested increase (decrease) in gas cost recoveries						$ 16,000						$ (5,000)				$ (25,700)
Remediation Adjustment Clause
Schedule of Capitalization [Line Items]
Number of gas manufacturing plants (in sites) | site																					12
Amortization period to recover costs																					7 years
Amounts recovered through rates																								112,700
Remediation Adjustment Clause | Environmental restoration costs expended net
Schedule of Capitalization [Line Items]
Regulatory assets																					$ 72,000			$ 42,000
New Jersey Clean Energy Program
Schedule of Capitalization [Line Items]
Statewide budget							345,000						345,000									345,000	345,000					$ 345,000		345,000
Statewide budget, entity's responsibility							14,600						14,600									14,600	14,600					14,500		$ 14,500
Universal Service Fund
Schedule of Capitalization [Line Items]
Approved increase (decrease) in gas recoveries										5,200				7,900
Statewide budget										46,400				71,800
Proposed increase (decrease) to statewide gas revenues							56,000						(46,400)									56,000	(46,400)					19,900
Potential impact of proposed increase (decrease) to statewide gas revenues							$ 1,100						$ (3,400)									$ 1,100	$ (3,400)					$ 2,600
Resulting impact of proposed increase (decrease) to USF recoveries										$ (3,400)				$ 2,600