INVESTMENTS IN EQUITY INVESTEES - FINANCIAL INFORMATION FOR STECKMAN RIDGE AND PENNEAST (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Income Statement [Abstract]
Operating revenues	$ 1,962,994	$ 2,905,979	$ 2,156,613
Net income (loss)	264,724	274,922	117,890
Assets
Current assets	532,077	756,087
Liabilities
Current liabilities	806,603	1,104,153
Noncurrent liabilities	972,141	854,651
Steckman Ridge
Income Statement [Abstract]
Operating revenues	22,659	19,812	21,847
Gross profit	13,385	11,349	13,350
Income (Loss) from continuing operations,	5,769	8,686	11,483
Net income (loss)	5,769	8,686	11,483
Net income (loss) attributable to NJR	2,884	4,343	5,741
Assets
Current assets	12,724	28,609
Noncurrent assets	193,779	198,052
Liabilities
Current liabilities	148,577	23,618
Noncurrent liabilities	0	140,810
PennEast
Income Statement [Abstract]
Operating revenues	0	0	0
Gross profit	0	0	0
Income (Loss) from continuing operations,	(9,543)	(3,778)	(406,305)
Net income (loss)	(9,543)	(3,778)	(406,305)
Net income (loss) attributable to NJR	(1,909)	(756)	$ (81,261)
Assets
Current assets	1,481	1,801
Noncurrent assets	0	0
Liabilities
Current liabilities	127	82
Noncurrent liabilities	$ 0	$ 500