REVENUE Disaggregated Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Utility	$ 606,677	$ 443,979
Residential
Disaggregation of Revenue [Line Items]
Utility	291,036	155,878
Commercial & Industrial
Disaggregation of Revenue [Line Items]
Utility	310,487	282,234
OSS & Capacity Release
Disaggregation of Revenue [Line Items]
Utility	1,770	5,204
Other
Disaggregation of Revenue [Line Items]
Utility	3,384	663
Gas
Disaggregation of Revenue [Line Items]
Utility	579,612	396,452
Electric
Disaggregation of Revenue [Line Items]
Utility	15,204	28,378
Solar
Disaggregation of Revenue [Line Items]
Utility	2,576	9,308
CHP
Disaggregation of Revenue [Line Items]
Utility	7,359	7,853
Landfills
Disaggregation of Revenue [Line Items]
Utility	1,395	1,468
Other
Disaggregation of Revenue [Line Items]
Utility	531	520
Wholesale Energy Operations
Disaggregation of Revenue [Line Items]
Utility	199,767	173,846
Wholesale Energy Operations | Commercial & Industrial
Disaggregation of Revenue [Line Items]
Utility	199,767	173,846
Wholesale Energy Operations | Gas
Disaggregation of Revenue [Line Items]
Utility	199,767	173,846
Retail Gas and Other Operations
Disaggregation of Revenue [Line Items]
Utility		33,246
Retail Gas and Other Operations | Commercial & Industrial
Disaggregation of Revenue [Line Items]
Utility		33,246
Retail Gas and Other Operations | Gas
Disaggregation of Revenue [Line Items]
Utility		33,246
Retail Electric Operations
Disaggregation of Revenue [Line Items]
Utility	16,811	30,046
Retail Electric Operations | Residential
Disaggregation of Revenue [Line Items]
Utility	3,808	8,096
Retail Electric Operations | Commercial & Industrial
Disaggregation of Revenue [Line Items]
Utility	13,003	21,950
Retail Electric Operations | Electric
Disaggregation of Revenue [Line Items]
Utility	16,811	30,046
On-Site Energy Production
Disaggregation of Revenue [Line Items]
Utility	11,330	21,157
On-Site Energy Production | Commercial & Industrial
Disaggregation of Revenue [Line Items]
Utility	11,330	21,157
On-Site Energy Production | Solar
Disaggregation of Revenue [Line Items]
Utility	2,576	11,836
On-Site Energy Production | CHP
Disaggregation of Revenue [Line Items]
Utility	7,359	7,853
On-Site Energy Production | Landfills
Disaggregation of Revenue [Line Items]
Utility	1,395	1,468
Appliance Service Operations
Disaggregation of Revenue [Line Items]
Utility	531	520
Appliance Service Operations | Residential
Disaggregation of Revenue [Line Items]
Utility	531	520
Appliance Service Operations | Other
Disaggregation of Revenue [Line Items]
Utility	531	520
Corporate Services and Intersegment
Disaggregation of Revenue [Line Items]
Utility	(3,007)	(8,770)
Corporate Services and Intersegment | Commercial & Industrial
Disaggregation of Revenue [Line Items]
Utility	(3,007)	(8,770)
Corporate Services and Intersegment | Gas
Disaggregation of Revenue [Line Items]
Utility	(1,400)	(4,574)
Corporate Services and Intersegment | Electric
Disaggregation of Revenue [Line Items]
Utility	(1,607)	(1,668)
Corporate Services and Intersegment | Solar
Disaggregation of Revenue [Line Items]
Utility	0	(2,528)
SJG Utility Operations
Disaggregation of Revenue [Line Items]
Utility	233,000	193,900
SJG Utility Operations | Utility Operations
Disaggregation of Revenue [Line Items]
Utility	232,984	193,934
SJG Utility Operations | Utility Operations | Residential
Disaggregation of Revenue [Line Items]
Utility	184,954	147,262
SJG Utility Operations | Utility Operations | Commercial & Industrial
Disaggregation of Revenue [Line Items]
Utility	45,588	40,805
SJG Utility Operations | Utility Operations | OSS & Capacity Release
Disaggregation of Revenue [Line Items]
Utility	1,770	5,204
SJG Utility Operations | Utility Operations | Other
Disaggregation of Revenue [Line Items]
Utility	672	663
SJG Utility Operations | Utility Operations | Gas
Disaggregation of Revenue [Line Items]
Utility	232,984	$ 193,934
ETG Utility Operations | Utility Operations
Disaggregation of Revenue [Line Items]
Utility	144,784
ETG Utility Operations | Utility Operations | Residential
Disaggregation of Revenue [Line Items]
Utility	99,989
ETG Utility Operations | Utility Operations | Commercial & Industrial
Disaggregation of Revenue [Line Items]
Utility	42,148
ETG Utility Operations | Utility Operations | Other
Disaggregation of Revenue [Line Items]
Utility	2,647
ETG Utility Operations | Utility Operations | Gas
Disaggregation of Revenue [Line Items]
Utility	144,784
ELK Utility Operations | Utility Operations
Disaggregation of Revenue [Line Items]
Utility	3,477
ELK Utility Operations | Utility Operations | Residential
Disaggregation of Revenue [Line Items]
Utility	1,754
ELK Utility Operations | Utility Operations | Commercial & Industrial
Disaggregation of Revenue [Line Items]
Utility	1,658
ELK Utility Operations | Utility Operations | Other
Disaggregation of Revenue [Line Items]
Utility	65
ELK Utility Operations | Utility Operations | Gas
Disaggregation of Revenue [Line Items]
Utility	$ 3,477