REGULATION - REGULATORY ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Sep. 30, 2021
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	$ 38,653	$ 30,118
Overrecovered natural gas costs	18,999	28,007
Regulatory liabilities-noncurrent	190,714	193,051
NJNG
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	38,280	29,701
Regulatory assets-noncurrent	524,658	519,600
Overrecovered natural gas costs	18,999	28,007
Regulatory liabilities-noncurrent	189,819	191,888
Adelphia
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	373	417
Regulatory assets-noncurrent	3,416	2,499
Regulatory liabilities-noncurrent	895	1,163
Total current regulatory liabilities | NJNG
Regulatory Assets And Liabilities [Line Items]
Overrecovered natural gas costs	11,659	5,510
Derivatives at fair value, net | NJNG
Regulatory Assets And Liabilities [Line Items]
Overrecovered natural gas costs	7,340	22,497
Regulatory liabilities-noncurrent	0	1,166
Tax Act impact | NJNG
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities-noncurrent	189,131	190,386
Other noncurrent regulatory liabilities | NJNG
Regulatory Assets And Liabilities [Line Items]
Regulatory liabilities-noncurrent	688	336
New Jersey Clean Energy Program | NJNG
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	14,416	16,308
Conservation Incentive Program | NJNG
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	22,493	11,839
Other current regulatory assets | NJNG
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-current	1,371	1,554
Regulatory assets-noncurrent	38,685	32,695
Expended, net of recoveries | NJNG
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	64,662	58,483
Liability for future expenditures | NJNG
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	126,881	135,012
Deferred income taxes | NJNG
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	39,613	39,694
SAVEGREEN | NJNG
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	37,342	32,941
Postemployment and other benefit costs | NJNG
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	114,515	117,194
Deferred storm damage costs | NJNG
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	3,800	4,343
Cost of removal | NJNG
Regulatory Assets And Liabilities [Line Items]
Regulatory assets-noncurrent	$ 99,160	$ 99,238