PENSION AND OTHER POSTRETIREMENT BENEFITS - CONTRIBUTIONS (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
Employer contributions	$ 0	$ 0	$ 0
Pension Benefits
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2021	21,881,000
2022	22,448,000
2023	23,244,000
2024	23,983,000
2025	24,189,000
2026- 2030	131,534,000
Employer contributions	3,875,000	4,127,000
Other Postretirement Benefits
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2021	5,486,000
2022	5,379,000
2023	5,214,000
2024	4,908,000
2025	4,682,000
2026- 2030	19,647,000
Employer contributions	4,347,000	4,498,000
Supplemental Employee Retirement Plan
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
Employer contributions	3,900,000	4,100,000	2,700,000
Expected contribution to plan	3,700,000
South Jersey Gas Company
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
Employer contributions	0	0	$ 0
South Jersey Gas Company | Pension Benefits
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2021	13,090,000
2022	13,539,000
2023	14,014,000
2024	14,683,000
2025	15,332,000
2026- 2030	86,590,000
Employer contributions	3,840,000	3,927,000
South Jersey Gas Company | Other Postretirement Benefits
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2021	3,619,000
2022	3,531,000
2023	3,467,000
2024	3,277,000
2025	3,095,000
2026- 2030	12,684,000
Employer contributions	$ 2,373,000	$ 3,264,000