REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT ASSETS TO CONSOLIDATED (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Sep. 30, 2024
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 7,265,584	$ 6,981,645
Operating Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	7,372,705	7,081,575
Operating Segments | NJNG
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	5,071,386	4,789,835
Operating Segments | CEV
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	1,141,957	1,157,573
Operating Segments | ES
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	134,245	108,710
Operating Segments | S&T
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	1,025,117	1,025,457
Corporate, Non-Segment
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	171,867	159,444
Intercompany Assets
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ (278,988)	$ (259,374)