COMMITMENTS AND CONTINGENT LIABILITIES - LEGAL PROCEEDINGS (Details)		9 Months Ended
	Jun. 29, 2016 USD ($)	Jun. 30, 2017 USD ($) site	Sep. 30, 2016 USD ($)
Site Contingency [Line Items]
Number of MGP sites | site		5
Recovery of expenditures, including carrying costs, rolling period approved by the BPU		7 years
Regulatory assets		$ 388,767,000	$ 441,294,000
Manufactured gas plant remediation		161,016,000	172,000,000
Minimum
Site Contingency [Line Items]
Litigation settlement, gross		143,900,000
Loss contingency, estimate of possible loss		600,000
Maximum
Site Contingency [Line Items]
Litigation settlement, gross		231,600,000
Loss contingency, estimate of possible loss		3,200,000
Expended, net of recoveries
Site Contingency [Line Items]
Regulatory assets		23,076,000	19,595,000
Liability for future expenditures
Site Contingency [Line Items]
Regulatory assets		$ 161,016,000	$ 172,000,000
SBC | December 2015 SBC Filing
Site Contingency [Line Items]
Public utilities, approved rate, amount	$ 9,400,000