REGULATION - REGULATORY ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Sep. 30, 2023
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	$ 93,887	$ 73,587
Regulatory assets-noncurrent	535,104	584,830
Regulatory liability-current	33,163	32,287
Regulatory liabilities-noncurrent	178,276	180,458
Expended, net of recoveries
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	69,200
NJNG
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	93,887	73,587
Regulatory assets-noncurrent	529,943	579,599
Regulatory liability-current	31,628	30,637
Regulatory liabilities-noncurrent	178,276	180,458
NJNG | Overrecovered natural gas costs
Regulatory Assets And Liabilities [Line Items]
Regulatory liability-current	31,628	30,637
NJNG | Tax Act impact
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities-noncurrent	177,838	180,347
NJNG | Other noncurrent regulatory liabilities
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities-noncurrent	438	111
NJNG | New Jersey Clean Energy Program
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	6,827	15,804
NJNG | Conservation Incentive Program
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	55,200	50,356
NJNG | Derivatives at fair value, net
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	30,444	6,017
NJNG | Other current regulatory assets
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	1,416	1,410
Regulatory assets-noncurrent	44,943	51,019
NJNG | Expended, net of recoveries
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	69,229	66,298
NJNG | Liability for future expenditures
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	157,813	169,390
NJNG | Deferred income taxes
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	42,626	41,667
NJNG | SAVEGREEN
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	88,496	83,589
NJNG | Postemployment and other benefit costs
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	7,936	55,274
NJNG | Cost of removal
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	118,900	112,362
Adelphia
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	5,161	5,231
Regulatory liability-current	$ 1,535	$ 1,650