FINANCIAL INSTRUMENTS - Cash, Cash Equivalents and Restricted Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Cash and Cash Equivalents [Line Items]
Cash and Cash Equivalents	$ 30,386	$ 34,045
Restricted Investments	1,482	7,786
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	31,868	41,831	$ 32,033	$ 28,381
SJG
Cash and Cash Equivalents [Line Items]
Cash and Cash Equivalents	15,984	1,598
Restricted Investments	1,482	4,826
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$ 17,466	$ 6,424	$ 7,646	$ 6,751