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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) |

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