COMMITMENTS AND CONTINGENT LIABILITIES, LEGAL PROCEEDINGS (Details) $ in Thousands		1 Months Ended	12 Months Ended
	Jun. 29, 2016 USD ($)	Jun. 30, 2014 USD ($)	Sep. 30, 2016 USD ($) site	Sep. 30, 2015 USD ($)
Loss Contingencies [Line Items]
Number of manufactured gas plant sites (in sites) | site			5
Recovery period			7 years
Regulatory assets			$ 441,294	$ 410,155
Minimum
Loss Contingencies [Line Items]
Litigation settlement, gross			143,900
Loss contingency, estimate of possible loss			600
Maximum
Loss Contingencies [Line Items]
Litigation settlement, gross			231,600
Loss contingency, estimate of possible loss			3,200
Environmental remediation costs, Expended, net of recoveries
Loss Contingencies [Line Items]
Regulatory assets			19,595	18,886
Environmental remediation costs, Liability for future expenditures
Loss Contingencies [Line Items]
Regulatory assets			$ 172,000	$ 180,400
September 2014 SBC Filing | SBC
Loss Contingencies [Line Items]
Approved rate, amount		$ 8,500
December 2015 SBC Filing | SBC
Loss Contingencies [Line Items]
Approved rate, amount	$ 9,400