COMMITMENTS AND CONTINGENT LIABILITIES - LEGAL PROCEEDINGS (Details) $ in Thousands		1 Months Ended	12 Months Ended
	Sep. 17, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) site
Loss Contingencies [Line Items]
Number of manufactured gas plant sites (in sites) | site			5
Recovery period			7 years
Regulatory assets		$ 375,919	$ 368,592
Minimum
Loss Contingencies [Line Items]
Litigation settlement, gross			117,700
Maximum
Loss Contingencies [Line Items]
Litigation settlement, gross			204,100
Environmental remediation costs, Expended, net of recoveries
Loss Contingencies [Line Items]
Regulatory assets		28,547	33,017
Environmental remediation costs, Liability for future expenditures
Loss Contingencies [Line Items]
Regulatory assets		149,000	130,800
RAC
Loss Contingencies [Line Items]
Approved rate, amount			9,400
Public utilities, requested rate			$ 7,000
Approved rate increase (decrease), amount	$ 1,400	$ (2,400)