v3.26.1
DEBT - CREDIT FACILITIES AND SHORT-TERM DEBT (Details) - USD ($)
 6 Months Ended
Mar. 31, 2026
Sep. 30, 2025
Letter of Credit | NJR    
Line of Credit Facility [Line Items]    
Letters of credit outstanding, amount $ 25,300,000 $ 21,400,000
Letter of Credit | NJNG    
Line of Credit Facility [Line Items]    
Letters of credit outstanding, amount $ 700,000 700,000
Revolving Credit Facility | NJR    
Line of Credit Facility [Line Items]    
Commitment fee percentage 0.10%  
Revolving Credit Facility | NJNG    
Line of Credit Facility [Line Items]    
Commitment fee percentage 0.075%  
Revolving Credit Facility | Committed Credit Facilities Due August 2029 | NJR    
Line of Credit Facility [Line Items]    
Total borrowing capacity $ 575,000,000 575,000,000
Loans outstanding $ 150,000,000 $ 152,600,000
Weighted average interest rate 4.90% 5.38%
Remaining borrowing capacity $ 399,726,000 $ 401,018,000
Revolving Credit Facility | Committed Credit Facilities Due August 2029 | NJNG    
Line of Credit Facility [Line Items]    
Total borrowing capacity 250,000,000 250,000,000
Loans outstanding $ 0 $ 43,000,000
Weighted average interest rate 0.00% 4.30%
Remaining borrowing capacity $ 249,269,000 $ 206,269,000