DEBT - NJR SHORT-TERM DEBT (Details) - NJR	1 Months Ended	12 Months Ended
	Dec. 31, 2018 USD ($)	Sep. 30, 2019 USD ($) Mutual_option debt_instrument	Apr. 18, 2019 USD ($)	Dec. 05, 2018 USD ($)
Revolving line of credit, 4 months
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 100,000,000
Debt instrument, term	4 months
Line of credit facility, fair value of amount outstanding			$ 0
Letters of Credit on Behalf of NJRES
Short-term Debt [Line Items]
Number of debt instruments (in debt instruments) | debt_instrument		2
Letters of credit outstanding, amount		$ 4,800,000
Bank revolving credit facilities
Short-term Debt [Line Items]
Number of mutual options | Mutual_option		2
Number of mutual options, extension period		1 year
Line of credit facility, maximum borrowing capacity, incremental increase		$ 50,000,000
Line of credit facility, maximum borrowing capacity, maximum increase		250,000,000
Committed Credit Facilities Due December 2023 | Bank revolving credit facilities
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		$ 425,000,000		$ 425,000,000