REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT ASSETS TO CONSOLIDATED (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Sep. 30, 2023
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 6,647,377	$ 6,537,496
Operating Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	6,768,843	6,679,140
Operating Segments | NJNG
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	4,527,458	4,414,829
Operating Segments | CEV
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	1,124,392	1,128,577
Operating Segments | ES
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	104,094	123,775
Operating Segments | S&T
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	1,012,899	1,011,959
Corporate, Non-Segment
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	171,594	171,275
Intercompany Assets
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ (293,060)	$ (312,919)