STOCK-BASED COMPENSATION PLAN (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Service period of shares	3 years
Fair Value Per Share (in USD per share)	$ 24.96	$ 24.96		$ 28.60	$ 24.96
Expected volatility, measurement period	3 years
Net Expense	$ 3,966	$ 3,507	$ 1,681
Capitalized	$ (288)	$ (385)	(216)
Unrecognized compensation cost of awards granted under the plan				$ 5,000
Weighted average period over which unrecognized compensation cost is to be recognized (in years)	1 year 8 months 12 days
Weighted Average Fair Value
Nonvested Shares Outstanding, beginning balance (in USD per share)	$ 24.96
Granted (in USD per share)	33.24
Vested (in USD per share)	24.81
Cancelled/Forfeited (in USD per share)	28.77
Nonvested Shares Outstanding, ending balance (in USD per share)	$ 28.60	$ 24.96
South Jersey Gas Company
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Net Expense	$ 400	$ 600	300
Total Cost
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Net Expense	4,254	3,892	1,897
EPS | Total Cost
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Net Expense	$ (1,100)	$ (100)	$ (1,200)
Officers and other key employees
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of awards granted (in shares)	167,734	194,347	158,929
Actual amount of shares that ultimately vest of the original share units granted, minimum	0.00%
Actual amount of shares that ultimately vest of the original share units granted, maximum	200.00%
Shares Outstanding (in shares)	295,515	295,515		342,793	295,515
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward}
Nonvested Shares Outstanding, beginning balance (in shares)	295,515
Granted (in shares)	167,734	194,347	158,929
Vested (in shares)	(114,199)
Cancelled/Forfeited (in shares)	(6,257.4)
Nonvested Shares Outstanding, ending balance (in shares)	342,793	295,515
Expected number of shares to be awarded (in shares)				15,092
Weighted Average Fair Value
Number of shares awarded during the period (in shares)	65,628	13,247	0
Market value of shares awarded (in shares)	$ 2,200	$ 300
Officers and other key employees | South Jersey Gas Company
Weighted Average Fair Value
Number of shares awarded during the period (in shares)	24,001	33,218	26,266
Officers and other key employees | Total Cost
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Net Expense	$ 3,232	$ 3,051	$ 1,128
Officers and other key employees | 2015 - Time
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	11,142			11,142
Fair Value Per Share (in USD per share)	$ 29.47			$ 29.47
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward}
Nonvested Shares Outstanding, ending balance (in shares)	11,142
Weighted Average Fair Value
Nonvested Shares Outstanding, ending balance (in USD per share)	$ 29.47
Officers and other key employees | 2016 - TSR
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	65,206			65,206
Fair Value Per Share (in USD 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)	65,206
Weighted Average Fair Value
Nonvested Shares Outstanding, ending balance (in USD per share)	$ 22.53
Officers and other key employees | 2016 - CEGR, Time
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	101,987			101,987
Fair Value Per Share (in USD per share)	$ 23.52			$ 23.52
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward}
Nonvested Shares Outstanding, ending balance (in shares)	101,987
Weighted Average Fair Value
Nonvested Shares Outstanding, ending balance (in USD per share)	$ 23.52
Officers and other key employees | 2017 - TSR
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	56,191			56,191
Fair Value Per Share (in USD 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)	56,191
Weighted Average Fair Value
Nonvested Shares Outstanding, ending balance (in USD per share)	$ 32.17
Officers and other key employees | 2017 - CEGR, Time
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	108,267			108,267
Fair Value Per Share (in USD per share)	$ 33.69			$ 33.69
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward}
Nonvested Shares Outstanding, ending balance (in shares)	108,267
Weighted Average Fair Value
Nonvested Shares Outstanding, ending balance (in USD per share)	$ 33.69
Directors
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of awards granted (in shares)	30,394
Vesting period of shares	12 months
Shares Outstanding (in shares)	35,197	35,197		30,394	35,197
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward}
Nonvested Shares Outstanding, beginning balance (in shares)	35,197
Granted (in shares)	30,394
Vested (in shares)	(35,197)
Cancelled/Forfeited (in shares)	0
Nonvested Shares Outstanding, ending balance (in shares)	30,394	35,197
Weighted Average Fair Value
Market value of shares awarded (in shares)	$ 1,000	$ 800	800
Directors | Total Cost
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Net Expense	$ 1,022	$ 841	$ 769
Directors | 2016
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	30,394			30,394
Fair Value Per Share (in USD per share)	$ 33.64			$ 33.64
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward}
Nonvested Shares Outstanding, ending balance (in shares)	30,394
Weighted Average Fair Value
Nonvested Shares Outstanding, ending balance (in USD per share)	$ 33.64
Stock appreciation rights
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of awards granted (in shares)	0	0	0
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward}
Granted (in shares)	0	0	0
Performance-based restricted shares
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Return on equity award threshold			7.00%
Performance-based restricted shares | Officers and other key employees
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Vesting period of shares	3 years
Restricted stock
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Return on equity award threshold			7.00%
Restricted stock | Tranche Two
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Service period of shares			2 years
Restricted stock | Tranche Three
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Service period of shares			3 years
Restricted stock | Officers and other key employees
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of awards granted (in shares)	53,058	58,304	47,678
Vesting period of shares			3 years
Payout limit, percentage			100.00%
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward}
Granted (in shares)	53,058	58,304	47,678
Restricted stock | Directors
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of awards granted (in shares)	30,394	35,197	26,338
Percent of shares granted that generally vest				100.00%
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward}
Granted (in shares)	30,394	35,197	26,338
2015 Omnibus Equity Compensation Plan
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of options granted (in shares)	0	0	0
Number of options outstanding (in shares)			0	0	0