REVENUE - TIMING OF REVENUE RECOGNITION - BALANCE SHEET (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Sep. 30, 2025	Mar. 31, 2025	Sep. 30, 2024
Disaggregation of Revenue [Line Items]
Billed	$ 291,052	$ 109,366
Unbilled	79,011	24,194
Customers' credit balances and deposits	(22,944)	(31,297)	$ (22,849)	$ (38,595)
Total	347,119	102,263
Operating Segments \| NJNG
Disaggregation of Revenue [Line Items]
Billed	247,580	75,789
Unbilled	70,568	14,817
Customers' credit balances and deposits	(22,915)	(31,257)
Total	295,233	59,349
Operating Segments \| CEV
Disaggregation of Revenue [Line Items]
Billed	5,640	6,818
Unbilled	8,443	9,377
Customers' credit balances and deposits	0	0
Total	14,083	16,195
Operating Segments \| ES
Disaggregation of Revenue [Line Items]
Billed	28,513	17,483
Unbilled	0	0
Customers' credit balances and deposits	0	0
Total	28,513	17,483
Operating Segments \| S&T
Disaggregation of Revenue [Line Items]
Billed	7,793	8,172
Unbilled	0	0
Customers' credit balances and deposits	(29)	(40)
Total	7,764	8,132
HSO
Disaggregation of Revenue [Line Items]
Billed	1,526	1,104
Unbilled	0	0
Customers' credit balances and deposits	0	0
Total	$ 1,526	$ 1,104