REPORTING SEGMENT AND OTHER OPERATIONS DATA - RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Segment Reporting Information [Line Items]
Utility	$ 1,011,284	$ 1,127,417	$ 731,459
Nonutility	951,710	1,778,562	1,425,154
Operating revenues	1,962,994	2,905,979	2,156,613
Depreciation and amortization	152,941	129,249	111,387
Interest income	8,919	2,716	2,167
Interest expense, net of capitalized interest	123,014	85,830	78,559
Income tax provision (benefit)	49,275	76,195	33,286
Equity in earnings of affiliates	3,930	8,177	(83,212)
Net financial earnings	261,827	240,321	207,712
Capital expenditures	540,919	598,428	624,610
Return of capital from equity investees	0	(5,479)
Investments in equity investees			690
ES
Segment Reporting Information [Line Items]
Operating revenues	48,500	53,000
Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	1,905,561	2,850,161	2,105,169
Depreciation and amortization	152,052	128,425	110,683
Interest income	9,789	3,021	2,580
Interest expense, net of capitalized interest	122,367	85,184	74,505
Income tax provision (benefit)	53,169	75,157	32,430
Equity in earnings of affiliates	3,126	9,865	(81,072)
Net financial earnings	257,224	241,102	208,327
Capital expenditures	538,613	597,038	621,980
Return of capital from equity investees		(5,479)
Investments in equity investees			690
Operating Segments | NJNG
Segment Reporting Information [Line Items]
Utility	1,011,284	1,127,417	731,796
Operating revenues	1,011,284	1,127,417	731,796
Depreciation and amortization	102,326	94,579	80,045
Interest income	1,713	895	85
Interest expense, net of capitalized interest	56,595	46,394	36,405
Income tax provision (benefit)	33,065	40,141	19,054
Equity in earnings of affiliates	0	0	0
Net financial earnings	131,414	140,124	107,375
Capital expenditures	390,394	298,374	426,628
Return of capital from equity investees		0
Investments in equity investees			0
Operating Segments | CEV
Segment Reporting Information [Line Items]
Nonutility	124,131	128,280	95,275
Operating revenues	124,131	128,280	95,275
Depreciation and amortization	25,320	21,396	20,567
Interest income	0	0	241
Interest expense, net of capitalized interest	28,569	21,968	22,548
Income tax provision (benefit)	(7,683)	11,361	5,048
Equity in earnings of affiliates	0	0	0
Net financial earnings	44,458	39,403	16,789
Capital expenditures	107,303	146,676	87,852
Return of capital from equity investees		0
Investments in equity investees			0
Operating Segments | ES
Segment Reporting Information [Line Items]
Nonutility	681,446	1,529,178	1,228,846
Operating revenues	681,446	1,529,178	1,228,846
Depreciation and amortization	221	148	111
Interest income	1,119	16	11
Interest expense, net of capitalized interest	11,400	4,725	2,204
Income tax provision (benefit)	24,343	21,776	18,371
Equity in earnings of affiliates	0	0	0
Net financial earnings	68,517	39,121	71,117
Capital expenditures	0	0	0
Return of capital from equity investees		0
Investments in equity investees			0
Operating Segments | ES | CANADA
Segment Reporting Information [Line Items]
Nonutility	8,400	2,400	100
Operating Segments | S&T
Segment Reporting Information [Line Items]
Nonutility	88,700	65,286	49,252
Operating revenues	88,700	65,286	49,252
Depreciation and amortization	24,185	12,302	9,960
Interest income	6,957	2,110	2,243
Interest expense, net of capitalized interest	25,803	12,097	13,348
Income tax provision (benefit)	3,444	1,879	(10,043)
Equity in earnings of affiliates	3,126	9,865	(81,072)
Net financial earnings	12,835	22,454	13,046
Capital expenditures	40,916	151,988	107,500
Return of capital from equity investees		(5,479)
Investments in equity investees			690
Intersegment Eliminations
Segment Reporting Information [Line Items]
Nonutility	(205)	(364)	(785)
Operating revenues	(15,678)	(3,893)	(1,342)
Intersegment Eliminations | NJNG
Segment Reporting Information [Line Items]
Utility	(1,349)	(1,350)	0
Intersegment Eliminations | CEV
Segment Reporting Information [Line Items]
Nonutility	0	0	0
Intersegment Eliminations | ES
Segment Reporting Information [Line Items]
Nonutility	(10,170)	(94)	426
Intersegment Eliminations | S&T
Segment Reporting Information [Line Items]
Nonutility	(4,159)	(2,449)	(1,768)
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Nonutility	57,433	55,818	51,444
Operating revenues	57,433	55,818	51,444
Depreciation and amortization	889	824	980
Interest income	2,977	944	522
Interest expense, net of capitalized interest	647	646	4,054
Income tax provision (benefit)	(1,477)	1,059	(196)
Equity in earnings of affiliates	0	0	0
Net financial earnings	4,758	(781)	(826)
Capital expenditures	2,306	1,390	2,630
Return of capital from equity investees		0
Investments in equity investees			0
Consolidation, Eliminations
Segment Reporting Information [Line Items]
Nonutility	(15,883)	(4,257)	(2,127)
Depreciation and amortization	0	0	(276)
Interest income	(3,847)	(1,249)	(935)
Interest expense, net of capitalized interest	0	0	0
Income tax provision (benefit)	(2,417)	(21)	1,052
Equity in earnings of affiliates	804	(1,688)	(2,140)
Net financial earnings	(155)	0	211
Capital expenditures	$ 0	0	0
Return of capital from equity investees		$ 0
Investments in equity investees			$ 0