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REGULATION - REGULATORY FILINGS (Details)							1 Months Ended							2 Months Ended	4 Months Ended	12 Months Ended
	Apr. 01, 2018 USD ($)	Nov. 01, 2017 USD ($)	Sep. 22, 2017 USD ($)	Jul. 20, 2017 USD ($)	Oct. 01, 2016 USD ($)	Nov. 01, 2015	Sep. 30, 2017 USD ($) station	Sep. 30, 2016 USD ($)	Oct. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jul. 31, 2014 USD ($) project	Oct. 31, 2012 USD ($)	Jun. 30, 2012 USD ($)	Feb. 29, 2016 USD ($)	Feb. 29, 2016 USD ($)	Sep. 30, 2017 USD ($) station	Sep. 30, 2010 USD ($)
Public Utilities, General Disclosures [Line Items]
Return on equity					9.75%
Public utilities, approved equity capital structure, percentage					52.50%
Composite rate of depreciation					2.40%
Program recovery term					5 years
Tax charge resulting from a change in deductibility of federal subsidies																	$ 2,400,000
Regulatory assets, noncurrent							$ 375,919,000	$ 441,294,000								$ 375,919,000
Number of NGV stations opened to the public | station							3									3
Other Regulatory Asset
Public Utilities, General Disclosures [Line Items]
Regulatory asset, maximum amount to be recorded annually								700,000
Regulatory asset, expense benchmark								1,400,000
Regulatory assets, threshold of recording regulatory liability when net liability exceeds amount								1,000,000
Other Regulatory Asset, PIM
Public Utilities, General Disclosures [Line Items]
Regulatory assets, noncurrent							$ 3,800,000									$ 3,800,000
Regulatory assets, amortization period																7 years
September 2016 Base Rate Case
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), amount					$ 45,000,000
June 2015 BGSS/CIP Filing
Public Utilities, General Disclosures [Line Items]
Customer bill credits															$ 61,600,000
June 2016 BGSS/CIP Filing
Public Utilities, General Disclosures [Line Items]
Customer bill credits								48,000,000								$ 42,000,000
June 2016 BGSS/CIP Filing | Basic Gas Supply Service
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), amount								(22,600,000)
June 2016 BGSS/CIP Filing | Conservation Incentive Program
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), amount								43,900,000
June 2017 BGSS/CIP Filing
Public Utilities, General Disclosures [Line Items]
Increase in annual revenues			$ 3,700,000
June 2017 BGSS/CIP Filing | Conservation Incentive Program
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), amount			$ (16,200,000)
Annual Petition With BPU
Public Utilities, General Disclosures [Line Items]
Requested base rate increase, amount				$ 4,100,000
SAFE Program
Public Utilities, General Disclosures [Line Items]
Capital investments approved by the BPU					200,000,000							$ 130,000,000
Capital investments to be recovered approved by the Board of Public Utilities					$ 157,500,000
Capital investments approved by the BPU, period												4 years
SAVEGREEN
Public Utilities, General Disclosures [Line Items]
Capital investments approved by the BPU																219,300,000
Grants, rebates and loans provided to customers																149,700,000
Increase in regulatory funding obligations																$ 20,000,000
SAVEGREEN | Minimum
Public Utilities, General Disclosures [Line Items]
Return on equity																9.75%
Public utilities, approved equity capital structure, percentage																6.69%
Program recovery term																2 years
Regulatory assets, amortization period																2 years
SAVEGREEN | Maximum
Public Utilities, General Disclosures [Line Items]
Return on equity																10.30%
Public utilities, approved equity capital structure, percentage																7.76%
Program recovery term																10 years
Regulatory assets, amortization period																10 years
NJ RISE Program
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), amount									$ 390,000
Return on equity						9.75%
Public utilities, approved equity capital structure, percentage						6.74%
Program recovery term											5 years
Number of capital investment projects | project											6
Originally filed petition for capital investments to Board of Public Utilities											$ 102,500,000
SAFE II and NJ RISE [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity					9.75%
Public utilities, approved equity capital structure, percentage					6.90%
USF
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), amount							$ (2,600,000)	$ 1,300,000		$ (3,900,000)
RAC
Public Utilities, General Disclosures [Line Items]
Approved rate, amount																$ 9,400,000
Compressed Natural Gas Vehicle Refueling Stations
Public Utilities, General Disclosures [Line Items]
Capital investments approved by the BPU													$ 10,000,000
SRL-Southern Reliability Link | Minimum
Public Utilities, General Disclosures [Line Items]
Estimated cost of the SRL																180,000,000
SRL-Southern Reliability Link | Maximum
Public Utilities, General Disclosures [Line Items]
Estimated cost of the SRL																$ 200,000,000
LNG-Liquefied Natural Gas
Public Utilities, General Disclosures [Line Items]
Capital investments to be recovered approved by the Board of Public Utilities					$ 36,500,000
NJNG | June 2015 BGSS/CIP Filing | Conservation Incentive Program
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), amount														$ 1,100,000
Subsequent Event | SAVEGREEN
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), amount		$ (3,900,000)
Scenario, Forecast | RAC
Public Utilities, General Disclosures [Line Items]
Approved rate, amount	$ 7,000,000

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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-Section 45
-Paragraph 28
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
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-Section 50
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