REVENUE - TIMING OF REVENUE RECOGNITION - BALANCE SHEET (Details) - USD ($) $ in Thousands	Jun. 30, 2026	Sep. 30, 2025	Jun. 30, 2025	Sep. 30, 2024
Disaggregation of Revenue [Line Items]
Billed	$ 190,779	$ 109,366
Unbilled	27,689	24,194
Customers' credit balances and deposits	(16,207)	(31,297)	$ (23,884)	$ (38,595)
Total	202,261	102,263
Operating Segments \| NJNG
Disaggregation of Revenue [Line Items]
Billed	136,646	75,789
Unbilled	12,211	14,817
Customers' credit balances and deposits	(16,175)	(31,257)
Total	132,682	59,349
Operating Segments \| CEV
Disaggregation of Revenue [Line Items]
Billed	9,065	6,818
Unbilled	15,478	9,377
Customers' credit balances and deposits	0	0
Total	24,543	16,195
Operating Segments \| ES
Disaggregation of Revenue [Line Items]
Billed	29,611	17,483
Unbilled	0	0
Customers' credit balances and deposits	0	0
Total	29,611	17,483
Operating Segments \| S&T
Disaggregation of Revenue [Line Items]
Billed	10,418	8,172
Unbilled	0	0
Customers' credit balances and deposits	(32)	(40)
Total	10,386	8,132
HSO
Disaggregation of Revenue [Line Items]
Billed	5,039	1,104
Unbilled	0	0
Customers' credit balances and deposits	0	0
Total	$ 5,039	$ 1,104