REPORTABLE SEGMENT DATA - RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Segment Reporting Information [Line Items]
Operating revenues attributable to reportable segments	$ 604,854	$ 488,361
Corporate and other	440,899	358,953
Operation and maintenance	86,681	88,632
Regulatory rider expenses	33,154	22,476
Depreciation and amortization	49,576	45,329
Gain on sale of assets	0	(54,859)
Interest expense, net of capitalized interest	35,676	33,891
Income tax provision	34,225	37,384
Equity in earnings of affiliates	1,823	1,400
Total net income	122,490	131,319
ES
Segment Reporting Information [Line Items]
Operating revenues attributable to reportable segments	4,900	4,900
Corporate and other
Segment Reporting Information [Line Items]
Corporate and other	15,769	15,254
Total net income	1,111	359
Operating Segments
Segment Reporting Information [Line Items]
Operating revenues attributable to reportable segments	588,848	472,728
Natural gas purchases	256,872	198,153
Operation and maintenance	71,979	74,608
Regulatory rider expenses	33,154	22,476
Depreciation and amortization	49,298	45,052
Gain on sale of assets		(54,859)
Interest income	2,904	3,127
Other segment income (expense)	10,646	9,537
Interest expense, net of capitalized interest	36,649	33,682
Income tax provision	34,544	36,660
Equity in earnings of affiliates	1,240	961
Net income attributable to reportable segments	121,379	130,960
Operating Segments | NJNG
Segment Reporting Information [Line Items]
Operating revenues attributable to reportable segments	409,901	333,428
Corporate and other	374,621	296,065
Natural gas purchases	170,724	130,005
Operation and maintenance	48,988	52,094
Regulatory rider expenses	33,154	22,476
Depreciation and amortization	36,960	32,084
Gain on sale of assets		0
Interest income	725	637
Other segment income (expense)	5,323	4,880
Interest expense, net of capitalized interest	19,299	17,454
Income tax provision	23,232	18,261
Equity in earnings of affiliates	0	0
Net income attributable to reportable segments	83,829	66,908
Operating Segments | CEV
Segment Reporting Information [Line Items]
Operating revenues attributable to reportable segments	31,760	26,406
Corporate and other	9,352	8,722
Natural gas purchases	0	0
Operation and maintenance	9,340	10,566
Regulatory rider expenses	0	0
Depreciation and amortization	7,032	6,425
Gain on sale of assets		(54,859)
Interest income	31	0
Other segment income (expense)	5,275	4,371
Interest expense, net of capitalized interest	8,366	6,374
Income tax provision	2,738	14,141
Equity in earnings of affiliates	0	0
Net income attributable to reportable segments	9,590	48,130
Operating Segments | ES
Segment Reporting Information [Line Items]
Operating revenues attributable to reportable segments	119,107	86,308
Corporate and other	12,840	11,947
Natural gas purchases	85,774	67,868
Operation and maintenance	3,185	1,865
Regulatory rider expenses	0	0
Depreciation and amortization	41	47
Gain on sale of assets		0
Interest income	39	34
Other segment income (expense)	170	350
Interest expense, net of capitalized interest	3,418	3,885
Income tax provision	6,301	2,769
Equity in earnings of affiliates	0	0
Net income attributable to reportable segments	20,597	10,258
Operating Segments | S&T
Segment Reporting Information [Line Items]
Operating revenues attributable to reportable segments	28,080	26,586
Corporate and other	28,080	26,586
Natural gas purchases	374	280
Operation and maintenance	10,466	10,083
Regulatory rider expenses	0	0
Depreciation and amortization	5,265	6,496
Gain on sale of assets		0
Interest income	2,109	2,456
Other segment income (expense)	(122)	(64)
Interest expense, net of capitalized interest	5,566	5,969
Income tax provision	2,273	1,489
Equity in earnings of affiliates	1,240	961
Net income attributable to reportable segments	7,363	5,664
Intersegment Eliminations
Segment Reporting Information [Line Items]
Operating revenues attributable to reportable segments	237	379
Intersegment Eliminations | NJNG
Segment Reporting Information [Line Items]
Operating revenues attributable to reportable segments	237	337
Intersegment Eliminations | CEV
Segment Reporting Information [Line Items]
Operating revenues attributable to reportable segments	0	0
Intersegment Eliminations | ES
Segment Reporting Information [Line Items]
Operating revenues attributable to reportable segments	0	0
Intersegment Eliminations | S&T
Segment Reporting Information [Line Items]
Operating revenues attributable to reportable segments	$ 0	$ 42