REVENUE - TIMING OF REVENUE RECOGNITION - BALANCE SHEET (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Sep. 30, 2023	Mar. 31, 2023	Sep. 30, 2022
Disaggregation of Revenue [Line Items]
Billed	$ 185,069	$ 97,540
Unbilled	74,456	19,100
Customers' credit balances and deposits	(24,878)	(44,910)	$ (25,521)	$ (33,246)
Customers accounts receivables & Customers' credit balances and deposits	234,647	71,730
Operating Segments | NJNG
Disaggregation of Revenue [Line Items]
Billed	142,088	55,234
Unbilled	69,904	10,784
Customers' credit balances and deposits	(24,860)	(44,898)
Customers accounts receivables & Customers' credit balances and deposits	187,132	21,120
Operating Segments | CEV
Disaggregation of Revenue [Line Items]
Billed	7,273	9,962
Unbilled	4,552	8,316
Customers' credit balances and deposits	0	0
Customers accounts receivables & Customers' credit balances and deposits	11,825	18,278
Operating Segments | ES
Disaggregation of Revenue [Line Items]
Billed	25,241	23,716
Unbilled	0	0
Customers' credit balances and deposits	0	0
Customers accounts receivables & Customers' credit balances and deposits	25,241	23,716
Operating Segments | S&T
Disaggregation of Revenue [Line Items]
Billed	7,749	6,577
Unbilled	0	0
Customers' credit balances and deposits	(18)	(12)
Customers accounts receivables & Customers' credit balances and deposits	7,731	6,565
Corporate, Non-Segment
Disaggregation of Revenue [Line Items]
Billed	2,718	2,051
Unbilled	0	0
Customers' credit balances and deposits	0	0
Customers accounts receivables & Customers' credit balances and deposits	$ 2,718	$ 2,051