REGULATION - REGULATORY FILINGS (Details) $ in Thousands							1 Months Ended				4 Months Ended	12 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 17, 2018 USD ($)	May 22, 2018 USD ($)	Mar. 01, 2018 USD ($)	Jul. 20, 2017 USD ($)	Oct. 01, 2016 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2017 USD ($)	Oct. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Feb. 28, 2017 USD ($)	Sep. 30, 2018 USD ($) project
Public Utilities, General Disclosures [Line Items]
Regulatory assets-noncurrent	$ 368,592							$ 375,919				$ 368,592
Public utilities, approved equity capital structure, percentage												6.90%
Return on equity										9.75%
Environmental Remediation Costs
Public Utilities, General Disclosures [Line Items]
Regulatory assets, amortization period												7 years
Postemployment and Other Benefit Costs
Public Utilities, General Disclosures [Line Items]
Regulatory assets, amortization period												7 years
Deferred Storm Damage Costs
Public Utilities, General Disclosures [Line Items]
Regulatory assets, amortization period												7 years
Other Regulatory Asset Noncurrent, PIM
Public Utilities, General Disclosures [Line Items]
Regulatory assets, amortization period												7 years
Regulatory assets-noncurrent	3,200											$ 3,200
SAVEGREEN
Public Utilities, General Disclosures [Line Items]
Capital investments approved by the BPU	354,300	$ 135,000
Grants, rebates and loans provided to customers												162,000
Increase in regulatory funding obligations												$ 16,100
SAVEGREEN | Minimum
Public Utilities, General Disclosures [Line Items]
Regulatory assets, amortization period												2 years
Program recovery term												3 years
Public utilities, approved equity capital structure, percentage												6.69%
Return on equity												9.75%
SAVEGREEN | Maximum
Public Utilities, General Disclosures [Line Items]
Regulatory assets, amortization period												10 years
Program recovery term												10 years
Public utilities, approved equity capital structure, percentage												7.76%
Return on equity												10.30%
Energy Efficiency EE
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), amount	$ (8,800)
March 2018 BGSS/CIP Filing
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), amount				$ 19,700
Requested customer refunds				$ 31,000
Approved customer refunds			$ 31,000
June 2016 BGSS/CIP Filing
Public Utilities, General Disclosures [Line Items]
Customer bill credits											$ 42,000
June 2016 BGSS/CIP Filing | Conservation Incentive Program
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), amount										$ 43,900
June 2016 BGSS/CIP Filing | Basic Gas Supply Service
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), amount										$ (22,600)
June 2017 BGSS/CIP Filing | Conservation Incentive Program
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), amount							$ (16,200)
Increase in annual revenues							$ 3,700
May 2018 BGSS/CIP Filing | Conservation Incentive Program
Public Utilities, General Disclosures [Line Items]
Increase in annual revenues		10,300
Requested base rate increase, amount		(30,900)
USF
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), amount		1,000						(2,600)
RAC
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), amount		1,400						(2,400)
NJCEP
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), amount		1,900						$ 1,800
SAFE Program
Public Utilities, General Disclosures [Line Items]
Capital investments approved by the BPU									$ 200,000			$ 130,000
Capital investments approved by the BPU, period												4 years
Capital investments to be recovered approved by the Board of Public Utilities									$ 157,500
NJ RISE Program
Public Utilities, General Disclosures [Line Items]
Program recovery term												5 years
Public utilities, approved equity capital structure, percentage												6.74%
Return on equity												9.75%
Number of capital investment projects | project												6
Originally filed petition for capital investments to Board of Public Utilities												$ 102,500
SAFE II and NJ RISE
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), amount		$ 6,800			$ 4,100
Public utilities, approved equity capital structure, percentage												6.90%
SRL-Southern Reliability Link | Minimum
Public Utilities, General Disclosures [Line Items]
Estimated cost of the SRL												$ 180,000
SRL-Southern Reliability Link | Maximum
Public Utilities, General Disclosures [Line Items]
Estimated cost of the SRL												$ 215,000
LNG-Liquefied Natural Gas
Public Utilities, General Disclosures [Line Items]
Capital investments to be recovered approved by the Board of Public Utilities						$ 36,500