DERIVATIVE INSTRUMENTS - INCOME STATEMENT RELATED DISCLOSURES (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income on derivatives	$ 14,888	$ 21,401	$ 107,170
ES | Physical commodity contracts | Operating revenues
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Nonutility	Nonutility	Nonutility
Amount of gain (loss) recognized in income on derivatives	$ 3,110	$ 12,070	$ 33,610
ES | Physical commodity contracts | Natural gas purchases
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Natural gas purchases	Natural gas purchases	Natural gas purchases
Amount of gain (loss) recognized in income on derivatives	$ (1,474)	$ (2,391)	$ (6,846)
ES | Physical commodity contracts | Operation and maintenance
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Natural gas purchases	Natural gas purchases	Natural gas purchases
Amount of gain (loss) recognized in income on derivatives	$ 845	$ 0	$ 0
ES | Financial commodity contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income on derivatives	12,407	11,722	80,406
NJNG
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income on derivatives	(20,208)	5,849	(84,371)
NJNG | Physical commodity contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income on derivatives	(16,913)	(5,215)	(34,241)
NJNG | Financial commodity contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income on derivatives	$ (3,295)	$ 11,064	$ (50,130)