SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - GAS IN STORAGE (Details) $ in Thousands	Jun. 30, 2015 USD ($) Bcf	Sep. 30, 2014 USD ($) Bcf
Inventory [Line Items]
Gas in Storage	$ 117,115	$ 277,516
Gas in Storage (Bcf) | Bcf	48.7	77.8
NJRES [Member]
Inventory [Line Items]
Gas in Storage	$ 81,829	$ 191,250
Gas in Storage (Bcf) | Bcf	36.6	56.5
NJNG [Member]
Inventory [Line Items]
Gas in Storage	$ 35,286	$ 86,266
Gas in Storage (Bcf) | Bcf	12.1	21.3