DEBT - SCHEDULE OF LONG-TERM DEBT (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Debt Instrument [Line Items]
Stated interest rate	4.01%
Finance lease liabilities	$ 14,742	$ 63,743
Total long-term debt	2,162,164	2,259,466
NJNG
Debt Instrument [Line Items]
Less: Debt issuance costs	(9,093)	(9,195)
Less: Current maturities of long-term debt	(5,393)	(10,416)
Total long-term debt	1,098,494	1,147,393
NJNG \| Finance lease obligation-buildings
Debt Instrument [Line Items]
Finance lease liabilities	0	47,597
NJNG \| Finance lease obligation-meters
Debt Instrument [Line Items]
Finance lease liabilities	$ 20,135	26,562
NJNG \| First mortgage bonds: \| Series OO
Debt Instrument [Line Items]
Stated interest rate	3.00%
Long-term debt	$ 46,500	46,500
NJNG \| First mortgage bonds: \| Series PP
Debt Instrument [Line Items]
Stated interest rate	3.15%
Long-term debt	$ 50,000	50,000
NJNG \| First mortgage bonds: \| Series QQ
Debt Instrument [Line Items]
Stated interest rate	3.58%
Long-term debt	$ 70,000	70,000
NJNG \| First mortgage bonds: \| Series RR
Debt Instrument [Line Items]
Stated interest rate	4.61%
Long-term debt	$ 55,000	55,000
NJNG \| First mortgage bonds: \| Series SS
Debt Instrument [Line Items]
Stated interest rate	2.82%
Long-term debt	$ 50,000	50,000
NJNG \| First mortgage bonds: \| Series TT
Debt Instrument [Line Items]
Stated interest rate	3.66%
Long-term debt	$ 100,000	100,000
NJNG \| First mortgage bonds: \| Series UU
Debt Instrument [Line Items]
Stated interest rate	3.63%
Long-term debt	$ 125,000	125,000
NJNG \| First mortgage bonds: \| Series VV
Debt Instrument [Line Items]
Stated interest rate	4.01%
Long-term debt	$ 125,000	125,000
NJNG \| First mortgage bonds: \| Series WW
Debt Instrument [Line Items]
Stated interest rate	3.50%
Long-term debt	$ 10,300	10,300
NJNG \| First mortgage bonds: \| Series XX
Debt Instrument [Line Items]
Stated interest rate	3.38%
Long-term debt	$ 10,500	10,500
NJNG \| First mortgage bonds: \| Series YY
Debt Instrument [Line Items]
Stated interest rate	2.45%
Long-term debt	$ 15,000	15,000
NJNG \| First mortgage bonds: \| Series ZZ
Debt Instrument [Line Items]
Stated interest rate	3.76%
Long-term debt	$ 100,000	100,000
NJNG \| First mortgage bonds: \| Series AAA
Debt Instrument [Line Items]
Stated interest rate	3.86%
Long-term debt	$ 85,000	85,000
NJNG \| First mortgage bonds: \| Series BBB
Debt Instrument [Line Items]
Stated interest rate	2.75%
Long-term debt	$ 9,545	9,545
NJNG \| First mortgage bonds: \| Series CCC
Debt Instrument [Line Items]
Stated interest rate	3.00%
Long-term debt	$ 41,000	41,000
NJNG \| First mortgage bonds: \| Series DDD
Debt Instrument [Line Items]
Stated interest rate	3.13%
Long-term debt	$ 50,000	50,000
NJNG \| First mortgage bonds: \| Series EEE
Debt Instrument [Line Items]
Stated interest rate	3.13%
Long-term debt	$ 50,000	50,000
NJNG \| First mortgage bonds: \| Series FFF
Debt Instrument [Line Items]
Stated interest rate	3.33%
Long-term debt	$ 25,000	25,000
NJNG \| First mortgage bonds: \| Series GGG
Debt Instrument [Line Items]
Stated interest rate	2.87%
Long-term debt	$ 25,000	25,000
NJNG \| First mortgage bonds: \| Series HHH
Debt Instrument [Line Items]
Stated interest rate	2.97%
Long-term debt	$ 50,000	50,000
NJR
Debt Instrument [Line Items]
Less: Debt issuance costs	(3,269)	(3,424)
Less: Current maturities of long-term debt	(50,000)	0
Total long-term debt	$ 956,731	1,006,576
NJR \| Unsecured senior notes 3.25%
Debt Instrument [Line Items]
Stated interest rate	3.25%
Long-term debt	$ 50,000	50,000
NJR \| Unsecured senior notes 3.48%
Debt Instrument [Line Items]
Stated interest rate	3.48%
Long-term debt	$ 100,000	100,000
NJR \| Unsecured senior notes 3.20%
Debt Instrument [Line Items]
Stated interest rate	3.20%
Long-term debt	$ 50,000	50,000
NJR \| Unsecured senior notes 3.54%
Debt Instrument [Line Items]
Stated interest rate	3.54%
Long-term debt	$ 100,000	100,000
NJR \| Unsecured senior notes 3.96%
Debt Instrument [Line Items]
Stated interest rate	3.96%
Long-term debt	$ 100,000	100,000
NJR \| Unsecured senior notes 3.29%
Debt Instrument [Line Items]
Stated interest rate	3.29%
Long-term debt	$ 150,000	150,000
NJR \| Unsecured senior note 3.60%
Debt Instrument [Line Items]
Stated interest rate	3.60%
Long-term debt	$ 130,000	130,000
NJR \| Unsecured senior note 3.50%
Debt Instrument [Line Items]
Stated interest rate	3.50%
Long-term debt	$ 130,000	130,000
NJR \| Unsecured senior notes 3.25%
Debt Instrument [Line Items]
Long-term debt		80,000
NJR \| Unsecured senior note 3.13%
Debt Instrument [Line Items]
Long-term debt		120,000
NJR \| Senior Notes \| Unsecured senior notes 3.25%
Debt Instrument [Line Items]
Stated interest rate	3.25%
Long-term debt	$ 80,000
NJR \| Senior Notes \| Unsecured senior note 3.13%
Debt Instrument [Line Items]
Stated interest rate	3.13%
Long-term debt	$ 120,000
Clean Energy Ventures
Debt Instrument [Line Items]
Long-term debt	124,387	122,317
Less: Current maturities of long-term debt	(17,448)	(16,820)
Total Clean Energy Ventures long-term debt	$ 106,939	$ 105,497

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

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