REGULATORY ASSETS & REGULATORY LIABILITIES - LIABILITIES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Regulatory Liabilities [Line Items]
Regulatory Liability, Noncurrent	$ 478,499	$ 287,105
Decrease in Deferred ARO costs	11,300
Total Regulatory Liabilities		287,105
Regulatory assets		469,224
Excess Plant Removal Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities		23,295
Tax Reform
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities		263,810
Deferred Revenue [Domain]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities		0
Conservation Incentive Program
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities		0
Revenue Subject to Refund
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities		0
Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities		0
South Jersey Gas Company
Regulatory Liabilities [Line Items]
Regulatory Liability, Noncurrent	286,539	$ 287,105
Total Regulatory Liabilities	286,539
Regulatory assets	492,365
South Jersey Gas Company | Excess Plant Removal Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	20,805
South Jersey Gas Company | Tax Reform
Regulatory Liabilities [Line Items]
Increase (Decrease) in Regulatory Liabilities	3,900
Total Regulatory Liabilities	259,863
South Jersey Gas Company | Deferred Revenue [Domain]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0
South Jersey Gas Company | Conservation Incentive Program
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	5,871
South Jersey Gas Company | Revenue Subject to Refund
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0
South Jersey Gas Company | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0
South Jersey Gas Company | Unprotected Excess Deferred Income Tax
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 26,100
Regulatory Liability, Refund Period	5 years
SJI
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 478,499
Regulatory assets	662,969
SJI | Excess Plant Removal Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	70,107
SJI | Tax Reform
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	379,851
SJI | Deferred Revenue [Domain]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	3,188
SJI | Conservation Incentive Program
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	5,871
SJI | Revenue Subject to Refund
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	17,039
SJI | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,443
ETG Utility Operations
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	189,336
Regulatory assets	169,921
ETG Utility Operations | Excess Plant Removal Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	47,909
ETG Utility Operations | Tax Reform
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	118,757
ETG Utility Operations | Deferred Revenue [Domain]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	3,188
ETG Utility Operations | Conservation Incentive Program
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0
ETG Utility Operations | Revenue Subject to Refund
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	17,039
ETG Utility Operations | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,443
ELK Utility Operations
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,624
Regulatory assets	683
ELK Utility Operations | Excess Plant Removal Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,393
ELK Utility Operations | Tax Reform
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,231
ELK Utility Operations | Deferred Revenue [Domain]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0
ELK Utility Operations | Conservation Incentive Program
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0
ELK Utility Operations | Revenue Subject to Refund
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0
ELK Utility Operations | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 0