REVENUE - DISAGGREGATED REVENUE - TYPE (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 358,953	$ 321,191
Revenues out of scope	129,408	146,019
Total operating revenues	488,361	467,210
Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	241,473	213,812
Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	87,039	81,223
Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	27,325	24,435
Interruptible, off-tariff and other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3,116	1,721
Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenues	472,728	452,376
Corporate, Non-Segment
Disaggregation of Revenue [Line Items]
Revenues out of scope	0	0
Total operating revenues	15,633	14,834
Corporate, Non-Segment | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	15,544	14,803
Corporate, Non-Segment | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	89	31
Corporate, Non-Segment | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Corporate, Non-Segment | Interruptible, off-tariff and other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
NJNG | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	296,065	257,538
Revenues out of scope	37,363	35,555
Total operating revenues	333,428	293,093
NJNG | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	223,819	195,623
NJNG | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	41,805	35,759
NJNG | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	27,325	24,435
NJNG | Operating Segments | Interruptible, off-tariff and other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3,116	1,721
CEV | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	8,722	9,364
Revenues out of scope	17,684	25,931
Total operating revenues	26,406	35,295
CEV | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,110	3,386
CEV | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	6,612	5,978
CEV | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
CEV | Operating Segments | Interruptible, off-tariff and other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
ES
Disaggregation of Revenue [Line Items]
Total operating revenues	4,900	9,500
ES | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	11,947	16,268
Revenues out of scope	74,361	84,533
Total operating revenues	86,308	100,801
ES | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
ES | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	11,947	16,268
ES | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
ES | Operating Segments | Interruptible, off-tariff and other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
S&T | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	26,586	23,187
Revenues out of scope	0	0
Total operating revenues	26,586	23,187
S&T | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
S&T | Operating Segments | Commercial and industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	26,586	23,187
S&T | Operating Segments | Firm transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
S&T | Operating Segments | Interruptible, off-tariff and other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 0	$ 0