COMMITMENTS AND CONTINGENT LIABILITIES - LEGAL PROCEEDINGS (Details) - USD ($) $ in Thousands		6 Months Ended		12 Months Ended
	Sep. 27, 2019	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2019	Sep. 30, 2018
Loss Contingencies [Line Items]
Regulatory assets		$ 496,637		$ 496,637	$ 368,592
Regulatory liabilities-noncurrent		202,435		$ 202,435	209,139
Recovery period				7 years
Minimum
Loss Contingencies [Line Items]
Litigation settlement, gross				$ 115,900
Maximum
Loss Contingencies [Line Items]
Litigation settlement, gross				186,200
Environmental remediation costs, Liability for future expenditures
Loss Contingencies [Line Items]
Regulatory assets		131,080		131,080	130,800
Regulatory liabilities-noncurrent		131,100		131,100
Environmental remediation costs, Expended, net of recoveries
Loss Contingencies [Line Items]
Regulatory assets		38,351		$ 38,351	$ 33,017
RAC
Loss Contingencies [Line Items]
Approved rate, amount		$ 8,500	$ 7,100
NJNG | RAC
Loss Contingencies [Line Items]
Requested base rate increase, amount	$ 1,400