COMMITMENTS AND CONTINGENT LIABILITIES - LEGAL PROCEEDINGS (Details) - USD ($) $ in Thousands	6 Months Ended
Mar. 31, 2026	Sep. 30, 2025
Site Contingency [Line Items]
Manufactured gas plant remediation	$ 166,110	$ 166,990
Recovery from third party of environmental remediation cost, period	7 years
Regulatory assets	$ 619,754	$ 672,518
Expended, net of recoveries
Site Contingency [Line Items]
Regulatory assets	61,200
Minimum
Site Contingency [Line Items]
Product liability contingency, loss exposure in excess of accrual, best estimate	144,300
Maximum
Site Contingency [Line Items]
Product liability contingency, loss exposure in excess of accrual, best estimate	$ 200,200

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