REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT ASSETS TO CONSOLIDATED (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Sep. 30, 2023
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 6,749,048	$ 6,537,496
Operating Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	6,883,371	6,679,140
Operating Segments | NJNG
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	4,590,049	4,414,829
Operating Segments | CEV
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	1,131,841	1,128,577
Operating Segments | ES
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	151,932	123,775
Operating Segments | S&T
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	1,009,549	1,011,959
Corporate, Non-Segment
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	170,421	171,275
Intercompany Assets
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ (304,744)	$ (312,919)