SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, EQUITY IN EARNINGS (Details)	12 Months Ended
Sep. 30, 2013 Steckman Ridge [Member] MMcf	Sep. 30, 2013 OwnEnergy [Member]	Sep. 30, 2012 OwnEnergy [Member]
Public utilities, power plant capacity	17,700
Publit utilities, power plant working capacity	12,000
Cost method investment, ownership percentage		18.70%	19.90%

The percentage of ownership of common stock or equity in the investee accounted for under the cost method of accounting.

No definition available.

Name:	njr_CostMethodInvestmentOwnershipPercentage
Namespace Prefix:	njr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant