INVESTMENTS IN EQUITY INVESTEES - FINANCIAL INFORMATION FOR STECKMAN RIDGE AND PENNEAST (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Operating revenues	$ 2,905,979	$ 2,156,613	$ 1,953,668
Net income	274,922	117,890	163,007
Assets
Current assets	756,087	634,274
Liabilities
Current liabilities	1,104,153	1,051,410
Noncurrent liabilities	854,651	877,842
Steckman Ridge
Income Statement [Abstract]
Operating revenues	19,812	21,847	28,814
Gross profit	11,349	13,350	20,537
Income from continuing operations	8,686	11,483	16,926
Net income	8,686	11,483	16,926
Net (loss) income attributable to NJR	4,343	5,741	8,463
Assets
Current assets	28,609	14,786
Noncurrent assets	198,052	202,670
Liabilities
Current liabilities	23,618	9,738
Noncurrent liabilities	140,810	140,810
PennEast
Income Statement [Abstract]
Operating revenues	0	0	0
Gross profit	0	0	0
Income from continuing operations	(3,778)	(406,305)	34,376
Net income	(3,778)	(406,305)	34,376
Net (loss) income attributable to NJR	(756)	(81,261)	$ 6,875
Assets
Current assets	1,801	822
Noncurrent assets	0	44,998
Liabilities
Current liabilities	82	248
Noncurrent liabilities	$ 500	$ 500