REPORTABLE SEGMENT DATA - RECONCILIATION OF CAPITAL EXPENDITURES AND SEGMENT ASSETS TO CONSOLIDATED (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Sep. 30, 2025
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 7,906,211		$ 7,578,775
Corporate and other
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	44,219		60,178
Operating Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Capital expenditures	179,064	$ 151,581
Assets	7,950,430		7,638,953
Operating Segments | NJNG
Segment Reporting, Asset Reconciling Item [Line Items]
Capital expenditures	106,918	109,904
Assets	5,428,674		5,198,116
Operating Segments | CEV
Segment Reporting, Asset Reconciling Item [Line Items]
Capital expenditures	59,701	33,476
Assets	1,324,384		1,308,969
Operating Segments | ES
Segment Reporting, Asset Reconciling Item [Line Items]
Capital expenditures	0	0
Assets	152,555		98,429
Operating Segments | S&T
Segment Reporting, Asset Reconciling Item [Line Items]
Capital expenditures	12,445	$ 8,201
Assets	$ 1,044,817		$ 1,033,439