REGULATION - REGULATORY ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Sep. 30, 2023
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-current	$ 89,572	$ 73,587
Regulatory assets-noncurrent	557,280	584,830
Regulatory liability-current	31,573	32,287
Regulatory liabilities-noncurrent	176,720	180,458
Expended, net of recoveries
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	74,300
NJNG
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-current	89,572	73,587
Regulatory assets-noncurrent	552,152	579,599
Regulatory liability-current	31,244	30,637
Regulatory liabilities-noncurrent	176,720	180,458
NJNG | Overrecovered natural gas costs
Regulatory Assets and Liabilities [Line Items]
Regulatory liability-current	31,244	30,637
NJNG | Tax Act impact
Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities-noncurrent	176,583	180,347
NJNG | Other noncurrent regulatory liabilities
Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities-noncurrent	137	111
NJNG | New Jersey Clean Energy Program
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-current	20,265	15,804
NJNG | Conservation Incentive Program
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-current	54,169	50,356
NJNG | Derivatives at fair value, net
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-current	13,347	6,017
NJNG | Other current regulatory assets
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-current	1,791	1,410
Regulatory assets-noncurrent	54,846	51,019
NJNG | Expended, net of recoveries
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	74,316	66,298
NJNG | Liability for future expenditures
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	153,818	169,390
NJNG | Deferred income taxes
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	43,107	41,667
NJNG | SAVEGREEN
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	93,713	83,589
NJNG | Postemployment and other benefit costs
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	9,493	55,274
NJNG | Cost of removal
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	122,859	112,362
Adelphia
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	5,128	5,231
Regulatory liability-current	$ 329	$ 1,650