STOCK-BASED COMPENSATION PLAN (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2018
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of options granted (in shares)	0	0
Number of options outstanding (in shares)		0		0
Vesting period of shares			3 years
Service period of shares	3 years
Fair value per share (in dollars per share)	$ 28.60			$ 29.46
Expected volatility, measurement period	3 years
Total Cost	$ 1,306	$ 1,326
Capitalized	(101)	(88)
Net Expense	$ 1,205	1,238
Unrecognized compensation cost of awards granted under the plan				$ 9,300
Weighted average period over which unrecognized compensation cost is to be recognized	2 years 1 month 12 days
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-beginning balance (in dollars per share)	$ 28.60
Weighted average fair value nonvested shares-granted during the period (in dollars per share)	31.17
Weighted average fair value nonvested shares- forfeited during the period (in dollars per share)	28.21
Weighted average fair value nonvested shares-vested during the period (in dollars per share)	30.56
Weighted average fair value nonvested shares-ending balance (in dollars per share)	$ 29.46
South Jersey Gas Company
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Costs capitalized	60.00%
Officers and Key Employees
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of shares granted (in shares)	185,214
Shares outstanding (in shares)	342,793			448,116
Total Cost	$ 1,100	$ 1,070
Number of shares awarded	63,030	65,628
Fair value of shares issued	$ 1,900	$ 2,200
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Nonvested shares outstanding, beginning balance (in shares)	342,793
Granted (in shares)	185,214
Cancelled/Forfeited (in shares)	(34,990)
Vested (in shares)	(44,901)
Nonvested shares outstanding, ending balance (in shares)	448,116
Officers and Key Employees | 2016 - TSR
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	58,205			58,205
Fair value per share (in dollars per share)	$ 22.53			$ 22.53
Expected volatility	18.10%
Risk-free interest rate	1.31%
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Nonvested shares outstanding, ending balance (in shares)	58,205
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance (in dollars per share)	$ 22.53
Officers and Key Employees | 2016 - CEGR, Time
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	73,344			73,344
Fair value per share (in dollars per share)	$ 23.52			$ 23.52
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Nonvested shares outstanding, ending balance (in shares)	73,344
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance (in dollars per share)	$ 23.52
Officers and Key Employees | 2017 - TSR
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	49,981			49,981
Fair value per share (in dollars per share)	$ 32.17			$ 32.17
Expected volatility	20.80%
Risk-free interest rate	1.47%
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Nonvested shares outstanding, ending balance (in shares)	49,981
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance (in dollars per share)	$ 32.17
Officers and Key Employees | 2017 - CEGR, Time
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	81,372			81,372
Fair value per share (in dollars per share)	$ 33.69			$ 33.69
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Nonvested shares outstanding, ending balance (in shares)	81,372
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance (in dollars per share)	$ 33.69
Officers and Key Employees | 2018 - TSR
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	64,290			64,290
Fair value per share (in dollars per share)	$ 31.05			$ 31.05
Expected volatility	21.90%
Risk-free interest rate	2.00%
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Nonvested shares outstanding, ending balance (in shares)	64,290
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance (in dollars per share)	$ 31.05
Officers and Key Employees | 2018 - CEGR, Time
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	120,924			120,924
Fair value per share (in dollars per share)	$ 31.23			$ 31.23
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Nonvested shares outstanding, ending balance (in shares)	120,924
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance (in dollars per share)	$ 31.23
Director
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of shares granted (in shares)	26,416	30,394
Vesting period of shares	12 months
Director shares vested				100.00%
Shares outstanding (in shares)	30,394			26,416
Total Cost	$ 206	$ 256
Fair value of shares issued	$ 800	$ 1,000
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Nonvested shares outstanding, beginning balance (in shares)	30,394
Granted (in shares)	26,416	30,394
Cancelled/Forfeited (in shares)	0
Vested (in shares)	(30,394)
Nonvested shares outstanding, ending balance (in shares)	26,416
Director | 2018
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	26,416			26,416
Fair value per share (in dollars per share)	$ 31.16			$ 31.16
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Nonvested shares outstanding, ending balance (in shares)	26,416
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance (in dollars per share)	$ 31.16
Stock Appreciation Rights
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of shares granted (in shares)	0
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Granted (in shares)	0
Restricted Stock | Year one
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Vesting period of shares	1 year
Restricted Stock | Year two
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Vesting period of shares	2 years
Service period of shares			2 years
Restricted Stock | Year three
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Vesting period of shares	3 years
Service period of shares			3 years
Restricted Stock | Officers and Key Employees
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of shares granted (in shares)	185,214	158,688
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Granted (in shares)	185,214	158,688
Restricted Stock | Officers and Key Employees | Minimum
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Percentage of actual amount of shares that ultimately vest of original share units granted	0.00%
Restricted Stock | Officers and Key Employees | Maximum
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Percentage of actual amount of shares that ultimately vest of original share units granted	200.00%
Restricted Stock | South Jersey Gas Company's officers and other key employees
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of shares granted (in shares)	26,652	21,061
Net Expense	$ 200	$ 100
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Granted (in shares)	26,652	21,061
Time-based Restricted Stock | Minimum
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Return on equity award threshold			7.00%
Time-based Restricted Stock | Officers and Key Employees
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of shares granted (in shares)	56,634	48,790
Vesting period of shares	3 years		3 years
Payout limit			100.00%
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Granted (in shares)	56,634	48,790
Time-based Restricted Stock | Officers and Key Employees | Year one
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Percentage of shares vested			3333.00%
Time-based Restricted Stock | Officers and Key Employees | Year two
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Percentage of shares vested			3333.00%
Time-based Restricted Stock | Officers and Key Employees | Year three
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Percentage of shares vested			3333.00%
Total Shareholder Return
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Vesting period of shares	3 years