REVENUE - TIMING OF REVENUE RECOGNITION - BALANCE SHEET (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Disaggregation of Revenue [Line Items]
Customer accounts receivable	$ 97,540	$ 222,297
Unbilled revenues	19,100	13,769
Customers’ credit balances and deposits	(44,910)	(33,246)	$ (32,586)
Customers accounts receivables & Customers' credit balances and deposits	71,730	202,820
Operating Segments | NJNG
Disaggregation of Revenue [Line Items]
Customer accounts receivable	55,234	78,508
Unbilled revenues	10,784	10,814
Customers’ credit balances and deposits	(44,898)	(33,246)
Customers accounts receivables & Customers' credit balances and deposits	21,120	56,076
Operating Segments | CEV
Disaggregation of Revenue [Line Items]
Customer accounts receivable	9,962	5,566
Unbilled revenues	8,316	2,955
Customers’ credit balances and deposits	0	0
Customers accounts receivables & Customers' credit balances and deposits	18,278	8,521
Operating Segments | ES
Disaggregation of Revenue [Line Items]
Customer accounts receivable	23,716	129,199
Unbilled revenues	0	0
Customers’ credit balances and deposits	0	0
Customers accounts receivables & Customers' credit balances and deposits	23,716	129,199
Operating Segments | S&T
Disaggregation of Revenue [Line Items]
Customer accounts receivable	6,577	7,012
Unbilled revenues	0	0
Customers’ credit balances and deposits	(12)	0
Customers accounts receivables & Customers' credit balances and deposits	6,565	7,012
Corporate, Non-Segment
Disaggregation of Revenue [Line Items]
Customer accounts receivable	2,051	2,012
Unbilled revenues	0	0
Customers’ credit balances and deposits	0	0
Customers accounts receivables & Customers' credit balances and deposits	$ 2,051	$ 2,012