Contractual interest rate for funds borrowed, under the debt agreement.

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DEBT - SCHEDULE OF LONG-TERM DEBT (Details) - USD ($)	Sep. 30, 2019	Aug. 15, 2019	Jul. 17, 2019	Sep. 30, 2018
Debt Instrument [Line Items]
Total long-term debt	$ 1,537,177,000			$ 1,180,619,000
NJNG
Debt Instrument [Line Items]
Less: Debt issuance costs	(9,027,000)			(6,515,000)
Less: Current maturities of long-term debt	(10,420,000)			(9,502,000)
Total long-term debt	908,779,000			691,965,000
NJNG \| First mortgage bonds: \| Series OO
Debt Instrument [Line Items]
Long-term debt	$ 46,500,000			46,500,000
Stated interest rate	3.00%
NJNG \| First mortgage bonds: \| Series PP
Debt Instrument [Line Items]
Long-term debt	$ 50,000,000			50,000,000
Stated interest rate	3.15%
NJNG \| First mortgage bonds: \| Series QQ
Debt Instrument [Line Items]
Long-term debt	$ 70,000,000			70,000,000
Stated interest rate	3.58%
NJNG \| First mortgage bonds: \| Series RR
Debt Instrument [Line Items]
Long-term debt	$ 55,000,000			55,000,000
Stated interest rate	4.61%
NJNG \| First mortgage bonds: \| Series SS
Debt Instrument [Line Items]
Long-term debt	$ 50,000,000			50,000,000
Stated interest rate	2.82%
NJNG \| First mortgage bonds: \| Series TT
Debt Instrument [Line Items]
Long-term debt	$ 100,000,000			100,000,000
Stated interest rate	3.66%
NJNG \| First mortgage bonds: \| Series UU
Debt Instrument [Line Items]
Long-term debt	$ 125,000,000			125,000,000
Stated interest rate	3.63%
NJNG \| First mortgage bonds: \| Series VV
Debt Instrument [Line Items]
Long-term debt	$ 125,000,000			125,000,000
Stated interest rate	4.01%
NJNG \| First mortgage bonds: \| Series WW
Debt Instrument [Line Items]
Long-term debt	$ 10,300,000			0
Stated interest rate	3.50%
NJNG \| First mortgage bonds: \| Series XX
Debt Instrument [Line Items]
Long-term debt	$ 10,500,000			0
Stated interest rate	3.38%
NJNG \| First mortgage bonds: \| Series YY
Debt Instrument [Line Items]
Long-term debt	$ 15,000,000			0
Stated interest rate	2.45%
NJNG \| First mortgage bonds: \| Series ZZ
Debt Instrument [Line Items]
Long-term debt	$ 100,000,000			0
Stated interest rate	3.76%
NJNG \| First mortgage bonds: \| Series AAA
Debt Instrument [Line Items]
Long-term debt	$ 85,000,000			0
Stated interest rate	3.86%
NJNG \| First mortgage bonds: \| Series BBB (formally MM)
Debt Instrument [Line Items]
Long-term debt	$ 9,545,000			9,545,000
Stated interest rate	2.75%
NJNG \| First mortgage bonds: \| Series CCC (formally NN)
Debt Instrument [Line Items]
Long-term debt	$ 41,000,000			41,000,000
Stated interest rate	3.00%
NJNG \| Capital lease obligations \| Capital lease obligation-buildings
Debt Instrument [Line Items]
Long-term debt	$ 5,637,000			8,749,000
NJNG \| Capital lease obligations \| Capital lease obligation-meters
Debt Instrument [Line Items]
Long-term debt	29,744,000			27,188,000
NJR
Debt Instrument [Line Items]
Less: Debt issuance costs	(2,004,000)			(1,136,000)
Less: Current maturities of long-term debt	0			(100,000,000)
Total long-term debt	547,996,000			398,864,000
NJR \| Unsecured senior notes 3.25%
Debt Instrument [Line Items]
Long-term debt	$ 50,000,000			50,000,000
Stated interest rate	3.25%
NJR \| Unsecured senior notes 3.48%
Debt Instrument [Line Items]
Long-term debt	$ 100,000,000			100,000,000
Stated interest rate	3.48%
NJR \| Unsecured senior notes 3.20%
Debt Instrument [Line Items]
Long-term debt	$ 50,000,000			50,000,000
Stated interest rate	3.20%
NJR \| Unsecured senior notes 3.54%
Debt Instrument [Line Items]
Long-term debt	$ 100,000,000			100,000,000
Stated interest rate	3.54%
NJR \| Unsecured senior notes 3.96%
Debt Instrument [Line Items]
Long-term debt	$ 100,000,000			100,000,000
Stated interest rate	3.96%
NJR \| Unsecured senior notes 3.29%
Debt Instrument [Line Items]
Long-term debt	$ 150,000,000	$ 100,000,000	$ 50,000,000	0
Stated interest rate	3.29%		3.29%
NJR \| Term loan \| Credit Agreement Due August 16, 2019
Debt Instrument [Line Items]
Long-term debt	$ 0			100,000,000
Clean Energy Ventures
Debt Instrument [Line Items]
Long-term debt	91,401,000			103,923,000
Less: Current maturities of long-term debt	(10,999,000)			(14,133,000)
Total Clean Energy Ventures long-term debt	$ 80,402,000			$ 89,790,000