REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Segment Reporting Information [Line Items]
Operating revenues	$ 488,361	$ 467,210
Depreciation and amortization	45,329	40,287
Interest income	2,055	2,026
Interest expense, net of capitalized interest	33,891	31,473
Income tax provision (benefit)	37,384	22,936
Equity in earnings of affiliates	1,400	1,660
Net financial earnings (loss)	128,894	72,444
Capital expenditures	151,870	114,622
ES
Segment Reporting Information [Line Items]
Operating revenues	4,900	9,500
Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	472,728	452,376
Depreciation and amortization	45,052	40,058
Interest income	3,127	3,076
Interest expense, net of capitalized interest	33,682	31,257
Income tax provision (benefit)	36,660	22,330
Equity in earnings of affiliates	961	993
Net financial earnings (loss)	128,535	73,437
Capital expenditures	151,581	113,266
Operating Segments | NJNG
Segment Reporting Information [Line Items]
Operating revenues	333,428	293,093
Depreciation and amortization	32,084	26,917
Interest income	637	578
Interest expense, net of capitalized interest	17,454	14,751
Income tax provision (benefit)	18,261	10,656
Equity in earnings of affiliates	0	0
Net financial earnings (loss)	66,908	51,444
Capital expenditures	109,904	79,715
Operating Segments | CEV
Segment Reporting Information [Line Items]
Operating revenues	26,406	35,295
Depreciation and amortization	6,425	6,922
Interest income	0	0
Interest expense, net of capitalized interest	6,374	7,447
Income tax provision (benefit)	14,141	3,131
Equity in earnings of affiliates	0	0
Net financial earnings (loss)	48,130	10,522
Capital expenditures	33,476	25,766
Operating Segments | ES
Segment Reporting Information [Line Items]
Operating revenues	86,308	100,801
Depreciation and amortization	47	57
Interest income	34	128
Interest expense, net of capitalized interest	3,885	3,126
Income tax provision (benefit)	2,769	7,511
Equity in earnings of affiliates	0	0
Net financial earnings (loss)	7,833	7,831
Capital expenditures	0	0
Operating Segments | S&T
Segment Reporting Information [Line Items]
Operating revenues	26,586	23,187
Depreciation and amortization	6,496	6,162
Interest income	2,456	2,370
Interest expense, net of capitalized interest	5,969	5,933
Income tax provision (benefit)	1,489	1,032
Equity in earnings of affiliates	961	993
Net financial earnings (loss)	5,664	3,640
Capital expenditures	8,201	7,785
Intersegment Eliminations
Segment Reporting Information [Line Items]
Operating revenues	379	(121)
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	0	(1,133)
Intersegment Eliminations | S&T
Segment Reporting Information [Line Items]
Operating revenues	42	675
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Operating revenues	15,633	14,834
Depreciation and amortization	277	229
Interest income	273	356
Interest expense, net of capitalized interest	209	216
Income tax provision (benefit)	469	(52)
Equity in earnings of affiliates	0	0
Net financial earnings (loss)	615	(600)
Capital expenditures	289	1,356
Corporate Reconciling Items and Eliminations
Segment Reporting Information [Line Items]
Operating revenues	161	0
Eliminations
Segment Reporting Information [Line Items]
Operating revenues	(540)
Depreciation and amortization	0	0
Interest income	(1,345)	(1,406)
Interest expense, net of capitalized interest	0	0
Income tax provision (benefit)	255	658
Equity in earnings of affiliates	439	667
Net financial earnings (loss)	(256)	(393)
Capital expenditures	$ 0	0
Eliminations and Reconciling Items
Segment Reporting Information [Line Items]
Operating revenues		$ 121