REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Operating revenues	$ 467,210	$ 723,567
Depreciation and amortization	40,287	36,683
Interest income	2,026	1,959
Interest expense, net of capitalized interest	31,473	29,491
Income tax provision (benefit)	22,936	32,978
Equity in earnings of affiliates	1,660	946
Net financial earnings (loss)	72,444	110,284
Capital expenditures	114,622	145,923
ES
Segment Reporting Information [Line Items]
Operating revenues	9,500	20,000
Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	452,376	709,314
Depreciation and amortization	40,058	36,465
Interest income	3,076	2,083
Interest expense, net of capitalized interest	31,257	29,369
Income tax provision (benefit)	22,330	34,553
Equity in earnings of affiliates	993	909
Net financial earnings (loss)	73,437	109,858
Capital expenditures	113,266	145,783
Operating Segments | NJNG
Segment Reporting Information [Line Items]
Operating revenues	293,093	357,409
Depreciation and amortization	26,917	24,890
Interest income	578	413
Interest expense, net of capitalized interest	14,751	13,709
Income tax provision (benefit)	10,656	14,383
Equity in earnings of affiliates	0	0
Net financial earnings (loss)	51,444	54,664
Capital expenditures	79,715	82,071
Operating Segments | CEV
Segment Reporting Information [Line Items]
Operating revenues	35,295	12,792
Depreciation and amortization	6,922	5,576
Interest income	0	0
Interest expense, net of capitalized interest	7,447	5,895
Income tax provision (benefit)	3,131	(1,837)
Equity in earnings of affiliates	0	0
Net financial earnings (loss)	10,522	(3,582)
Capital expenditures	25,766	43,993
Operating Segments | ES
Segment Reporting Information [Line Items]
Operating revenues	100,801	313,399
Depreciation and amortization	57	57
Interest income	128	269
Interest expense, net of capitalized interest	3,126	3,058
Income tax provision (benefit)	7,511	20,064
Equity in earnings of affiliates	0	0
Net financial earnings (loss)	7,831	52,533
Capital expenditures	0	0
Operating Segments | S&T
Segment Reporting Information [Line Items]
Operating revenues	23,187	25,714
Depreciation and amortization	6,162	5,942
Interest income	2,370	1,401
Interest expense, net of capitalized interest	5,933	6,707
Income tax provision (benefit)	1,032	1,943
Equity in earnings of affiliates	993	909
Net financial earnings (loss)	3,640	6,243
Capital expenditures	7,785	19,719
Intersegment Eliminations
Segment Reporting Information [Line Items]
Operating revenues	(121)	9,844
Intersegment Eliminations | NJNG
Segment Reporting Information [Line Items]
Operating revenues	337	337
Intersegment Eliminations | CEV
Segment Reporting Information [Line Items]
Operating revenues	0	0
Intersegment Eliminations | ES
Segment Reporting Information [Line Items]
Operating revenues	(1,133)	8,383
Intersegment Eliminations | S&T
Segment Reporting Information [Line Items]
Operating revenues	675	1,124
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Operating revenues	14,834	14,253
Depreciation and amortization	229	218
Interest income	356	654
Interest expense, net of capitalized interest	216	122
Income tax provision (benefit)	(52)	217
Equity in earnings of affiliates	0	0
Net financial earnings (loss)	(600)	(29)
Capital expenditures	1,356	140
Corporate Reconciling Items And Eliminations
Segment Reporting Information [Line Items]
Operating revenues	0	13
Eliminations
Segment Reporting Information [Line Items]
Operating revenues		(9,857)
Depreciation and amortization	0	0
Interest income	(1,406)	(778)
Interest expense, net of capitalized interest	0	0
Income tax provision (benefit)	658	(1,792)
Equity in earnings of affiliates	667	37
Net financial earnings (loss)	(393)	455
Capital expenditures	0	$ 0
Eliminations And Reconciling Items
Segment Reporting Information [Line Items]
Operating revenues	$ 121