REVENUE - TIMING OF REVENUE RECOGNITION - BALANCE SHEET (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Sep. 30, 2025	Dec. 31, 2024	Sep. 30, 2024
Disaggregation of Revenue [Line Items]
Billed	$ 260,129	$ 109,366
Unbilled	151,953	24,194
Customers' credit balances and deposits	(40,245)	(31,297)	$ (42,587)	$ (38,595)
Total	371,837	102,263
Operating Segments | NJNG
Disaggregation of Revenue [Line Items]
Billed	170,462	75,789
Unbilled	143,752	14,817
Customers' credit balances and deposits	(40,200)	(31,257)
Total	274,014	59,349
Operating Segments | CEV
Disaggregation of Revenue [Line Items]
Billed	5,108	6,818
Unbilled	8,201	9,377
Customers' credit balances and deposits	0	0
Total	13,309	16,195
Operating Segments | ES
Disaggregation of Revenue [Line Items]
Billed	74,400	17,483
Unbilled	0	0
Customers' credit balances and deposits	0	0
Total	74,400	17,483
Operating Segments | S&T
Disaggregation of Revenue [Line Items]
Billed	8,896	8,172
Unbilled	0	0
Customers' credit balances and deposits	(45)	(40)
Total	8,851	8,132
Corporate, Non-Segment
Disaggregation of Revenue [Line Items]
Billed	1,263	1,104
Unbilled	0	0
Customers' credit balances and deposits	0	0
Total	$ 1,263	$ 1,104