FINANCIAL INSTRUMENTS - Schedule of Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 30,582	$ 19,829
Provision for expected credit losses	2,409	4,863
Regulated Assets	4,134
Recoveries of accounts previously written off	230	243
Uncollectible accounts written off	(1,500)	(1,402)
Balance at end of period	35,855	23,533
SJG
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	17,359	14,032
Provision for expected credit losses	1,760	1,864
Regulated Assets	2,194
Recoveries of accounts previously written off	127	132
Uncollectible accounts written off	(967)	(1,126)
Balance at end of period	$ 20,473	$ 14,902