INCOME TAXES - DEFERRED TAX ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Deferred tax assets
Investment tax credits	$ 191,948	$ 212,506
State net operating losses	39,612	36,950
Deferred revenue	8,205	0
Fair value of derivatives	5,386	6,506
Impairment of equity method investment	14,004	14,124
Postemployment benefits	6,502	2,751
Incentive compensation	8,949	7,297
Amortization of intangibles	6,308	6,474
Overrecovered natural gas costs	8,564	4,977
Allowance for doubtful accounts	4,485	5,761
Other	7,636	5,748
Total deferred tax assets	301,599	303,094
Less: Valuation allowance	(5,747)	(22,241)
Total deferred tax assets net of valuation allowance	295,852	280,853
Deferred tax liabilities
Property-related items	(487,294)	(468,115)
Remediation costs	(18,532)	(18,490)
Investments in equity investees	(28,325)	(19,176)
Conservation incentive program	(14,075)	(6,457)
Other	(4,670)	(4,615)
Total deferred tax liabilities	(552,896)	(516,853)
Total net deferred tax liabilities	(257,044)	(236,000)
Tax credit carryforward	191,200	211,800
NJNG
Deferred tax liabilities
Tax credit carryforward	$ 700	$ 700