REVENUE - TIMING OF REVENUE RECOGNITION - BALANCE SHEET (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Disaggregation of Revenue [Line Items]
Billed	$ 170,472	$ 97,540
Unbilled	91,931	19,100
Customers' credit balances and deposits	(45,461)	(44,910)	$ (40,970)	$ (33,246)
Customers accounts receivables & Customers' credit balances and deposits	216,942	71,730
Operating Segments | NJNG
Disaggregation of Revenue [Line Items]
Billed	112,364	55,234
Unbilled	86,961	10,784
Customers' credit balances and deposits	(45,446)	(44,898)
Customers accounts receivables & Customers' credit balances and deposits	153,879	21,120
Operating Segments | CEV
Disaggregation of Revenue [Line Items]
Billed	8,391	9,962
Unbilled	4,970	8,316
Customers' credit balances and deposits	0	0
Customers accounts receivables & Customers' credit balances and deposits	13,361	18,278
Operating Segments | ES
Disaggregation of Revenue [Line Items]
Billed	40,372	23,716
Unbilled	0	0
Customers' credit balances and deposits	0	0
Customers accounts receivables & Customers' credit balances and deposits	40,372	23,716
Operating Segments | S&T
Disaggregation of Revenue [Line Items]
Billed	7,169	6,577
Unbilled	0	0
Customers' credit balances and deposits	(15)	(12)
Customers accounts receivables & Customers' credit balances and deposits	7,154	6,565
Corporate, Non-Segment
Disaggregation of Revenue [Line Items]
Billed	2,176	2,051
Unbilled	0	0
Customers' credit balances and deposits	0	0
Customers accounts receivables & Customers' credit balances and deposits	$ 2,176	$ 2,051