REGULATION - REGULATORY ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Sep. 30, 2024
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-current	$ 34,839	$ 73,070
Regulatory assets-noncurrent	602,622	609,192
Regulatory liability-current	53,208	32,981
Regulatory liabilities-noncurrent	173,246	175,847
Expended, net of recoveries
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	67,900
NJNG
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-current	34,839	73,070
Regulatory assets-noncurrent	597,591	604,097
Regulatory liability-current	52,312	32,457
Regulatory liabilities-noncurrent	173,246	175,847
NJNG | Overrecovered natural gas costs
Regulatory Assets and Liabilities [Line Items]
Regulatory liability-current	16,612	32,457
NJNG | Tax Act impact
Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities-noncurrent	172,819	175,328
NJNG | Derivatives at fair value, net
Regulatory Assets and Liabilities [Line Items]
Regulatory liability-current	35,700	0
Regulatory liabilities-noncurrent	0	404
NJNG | Other noncurrent regulatory liabilities
Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities-noncurrent	427	115
NJNG | New Jersey Clean Energy Program
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-current	7,649	18,491
NJNG | Conservation Incentive Program
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-current	25,907	51,442
NJNG | Derivatives at fair value, net
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-current	0	1,363
NJNG | Other current regulatory assets
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-current	1,283	1,774
Regulatory assets-noncurrent	52,930	59,924
NJNG | Expended, net of recoveries
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	67,850	77,475
NJNG | Liability for future expenditures
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	160,058	161,650
NJNG | Deferred income taxes
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	43,595	42,595
NJNG | SAVEGREEN
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	115,135	107,796
NJNG | Postemployment and other benefit costs
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	25,618	23,772
NJNG | Cost of removal
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	132,405	130,885
Adelphia
Regulatory Assets and Liabilities [Line Items]
Regulatory assets-noncurrent	5,031	5,095
Regulatory liability-current	$ 896	$ 524