REGULATION - REGULATORY ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Sep. 30, 2024
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-current	$ 64,689	$ 73,070
Regulatory assets-noncurrent	612,595	609,192
Regulatory liability-current	32,610	32,981
Regulatory liabilities-noncurrent	174,726	175,847
Expended, net of recoveries
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	74,100
NJNG
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-current	64,689	73,070
Regulatory assets-noncurrent	607,526	604,097
Regulatory liability-current	32,029	32,457
Regulatory liabilities-noncurrent	174,726	175,847
NJNG | Overrecovered natural gas costs
Regulatory Assets and Liabilities [Line Items]
Regulatory liability-current	26,692	32,457
NJNG | Tax Act impact
Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities-noncurrent	174,074	175,328
NJNG | Derivatives at fair value, net
Regulatory Assets and Liabilities [Line Items]
Regulatory liability-current	5,337	0
Regulatory liabilities-noncurrent	0	404
NJNG | Other noncurrent regulatory liabilities
Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities-noncurrent	652	115
NJNG | New Jersey Clean Energy Program
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-current	16,523	18,491
NJNG | Conservation Incentive Program
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-current	46,052	51,442
NJNG | Derivatives at fair value, net
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-current	570	1,363
NJNG | Other current regulatory assets
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-current	1,544	1,774
Regulatory assets-noncurrent	55,488	59,924
NJNG | Expended, net of recoveries
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	74,146	77,475
NJNG | Liability for future expenditures
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	161,024	161,650
NJNG | Deferred income taxes
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	42,776	42,595
NJNG | SAVEGREEN
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	114,391	107,796
NJNG | Postemployment and other benefit costs
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	24,695	23,772
NJNG | Cost of removal
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	135,006	130,885
Adelphia
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	5,069	5,095
Regulatory liability-current	$ 581	$ 524