RATES AND REGULATORY ACTIONS (Details) $ in Millions		1 Months Ended
	Jul. 01, 2017 USD ($)	Sep. 30, 2018 USD ($) mi	Jul. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)
Schedule of Capitalization [Line Items]
Credits due to customers under conditions of approval		$ 15.3
Length of pipeline (in miles) | mi		118
SJG Utility Operations
Schedule of Capitalization [Line Items]
Approved rate increase (decrease)		$ 25.9
New Jersey Board of Public Utilities | Elizabethtown Gas
Schedule of Capitalization [Line Items]
Approved rate increase (decrease)					$ 10.9
Public utilities, requested rate increase (decrease), amount	$ (13.3)
Public Utilities, Approved Return on Equity, Percentage	9.60%
New Jersey Board of Public Utilities | SJG Utility Operations
Schedule of Capitalization [Line Items]
Requested term (in years)					5 years
Public utilities, requested rate increase (decrease), amount					$ (195.4)
Accelerated infrastructure replacement program, remaining balance		60.4
Maryland Public Service Commission [Member] | Elizabethtown Gas
Schedule of Capitalization [Line Items]
Approved rate increase (decrease)					$ 0.3
AIRP | SJG Utility Operations
Schedule of Capitalization [Line Items]
Public utilities, requested rate increase (decrease), amount		(6.6)
Annual BGSS | SJG Utility Operations
Schedule of Capitalization [Line Items]
Approved rate increase (decrease)		65.5
Annual CIP | SJG Utility Operations
Schedule of Capitalization [Line Items]
Public utilities, requested rate increase (decrease), amount		26.4
Energy Efficiency Tracker | SJG Utility Operations
Schedule of Capitalization [Line Items]
Public utilities, requested rate increase (decrease), amount				$ 1.6
Societal Benefits Clause | SJG Utility Operations
Schedule of Capitalization [Line Items]
Public utilities, requested rate increase (decrease), amount			$ 3.4
Universal Service Fund | SJG Utility Operations
Schedule of Capitalization [Line Items]
Increase (Decrease) in Amount of Regulatory Costs Approved		0.9
Over Collected Tax | Elizabethtown Gas
Schedule of Capitalization [Line Items]
Credits due to customers under conditions of approval		4.8
Over Collected Tax | SJG Utility Operations
Schedule of Capitalization [Line Items]
Credits due to customers under conditions of approval		13.8
Unprotected Excess Deferred Income Tax | SJG Utility Operations
Schedule of Capitalization [Line Items]
Credits due to customers under conditions of approval		$ 27.5
Customer Refund Term		5 years
Elkton Gas
Schedule of Capitalization [Line Items]
Credits due to customers under conditions of approval		$ 0.3
Business Combination, Customer Bill Credit Applied		0.3
Elizabethtown Gas
Schedule of Capitalization [Line Items]
Credits due to customers under conditions of approval		15.0
Business Combination, Customer Bill Credit Applied		$ 15.0