REGULATION - REGULATORY ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Sep. 30, 2022
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	$ 95,747	$ 40,086
Regulatory assets-noncurrent	528,114	500,666
Total current regulatory liabilities	27,701	31,090
Regulatory liabilities-noncurrent	181,814	185,634
Expended, net of recoveries
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	63,800
NJNG
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	95,747	40,086
Regulatory assets-noncurrent	522,858	495,300
Total current regulatory liabilities	26,774	25,779
Regulatory liabilities-noncurrent	181,814	185,634
NJNG | Overrecovered natural gas costs
Regulatory Assets And Liabilities [Line Items]
Total current regulatory liabilities	26,717	17,807
NJNG | Derivatives at fair value, net
Regulatory Assets And Liabilities [Line Items]
Total current regulatory liabilities	57	7,972
Regulatory liabilities-noncurrent	91	116
NJNG | Tax Act impact
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities-noncurrent	181,602	185,367
NJNG | Other noncurrent regulatory liabilities
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities-noncurrent	121	151
NJNG | New Jersey Clean Energy Program
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	17,943	15,697
NJNG | Conservation Incentive Program
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	52,115	23,099
NJNG | Derivatives at fair value, net
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	24,228	0
NJNG | Other current regulatory assets
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	1,461	1,290
Regulatory assets-noncurrent	43,987	45,828
NJNG | Expended, net of recoveries
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	63,841	66,149
NJNG | Liability for future expenditures
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	123,070	127,070
NJNG | Deferred income taxes
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	41,885	40,520
NJNG | SAVEGREEN
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	72,507	52,690
NJNG | Postemployment and other benefit costs
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	55,878	56,021
NJNG | Deferred storm damage costs
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	543	2,172
NJNG | Cost of removal
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	121,147	104,850
Adelphia
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	5,256	5,366
Total current regulatory liabilities	$ 927	$ 5,311