STOCK-BASED COMPENSATION PLAN (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2017
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		0
Vesting period of shares					3 years
Service period of shares			3 years
Fair value per share (in dollars per share)	$ 28.53		$ 24.96			$ 28.53
Expected volatility, measurement period			3 years
Total Cost	$ 1,343	$ 991	$ 4,041	$ 3,026
Capitalized	(96)	(77)	(288)	(289)
Net Expense	$ 1,247	914	$ 3,753	2,737
Unrecognized compensation cost of awards granted under the plan						$ 6,500
Weighted average period over which unrecognized compensation cost is to be recognized			1 year 9 months 18 days
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-beginning balance (in dollars per share)			$ 24.96
Weighted average fair value nonvested shares-granted during the period (in dollars per share)			33.24
Weighted average fair value nonvested shares- forfeited during the period (in dollars per share)			28.70
Weighted average fair value nonvested shares-vested during the period (in dollars per share)			24.75
Weighted average fair value nonvested shares-ending balance (in dollars per share)	$ 28.53		$ 28.53
South Jersey Gas Company
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Costs capitalized			50.00%
Officers and Key Employees
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of shares granted (in shares)			167,734
Shares outstanding (in shares)	428,717		295,515			428,717
Total Cost	$ 1,087	781	$ 3,274	$ 2,396
Number of shares awarded			65,628	13,247
Fair value of shares issued			$ 2,200	$ 300
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Nonvested shares outstanding, beginning balance (in shares)			295,515
Granted (in shares)			167,734
Cancelled/Forfeited (in shares)			(3,891)
Vested (in shares)			(30,641)
Nonvested shares outstanding, ending balance (in shares)	428,717		428,717
Officers and Key Employees | 2015 - TSR
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	33,449		33,449			33,449
Fair value per share (in dollars per share)	$ 26.31		$ 26.31			$ 26.31
Expected volatility			16.00%
Risk-free interest rate			1.10%
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Nonvested shares outstanding, ending balance (in shares)	33,449		33,449
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance (in dollars per share)	$ 26.31		$ 26.31
Officers and Key Employees | 2015 - EGR, ROE, Time
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	61,357		61,357			61,357
Fair value per share (in dollars per share)	$ 29.47		$ 29.47			$ 29.47
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Nonvested shares outstanding, ending balance (in shares)	61,357		61,357
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance (in dollars per share)	$ 29.47		$ 29.47
Officers and Key Employees | 2016 - TSR
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	65,544		65,544			65,544
Fair value per share (in dollars per share)	$ 22.53		$ 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)	65,544		65,544
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance (in dollars per share)	$ 22.53		$ 22.53
Officers and Key Employees | 2016 - CEGR, Time
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	102,616		102,616			102,616
Fair value per share (in dollars per share)	$ 23.52		$ 23.52			$ 23.52
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Nonvested shares outstanding, ending balance (in shares)	102,616		102,616
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance (in dollars per share)	$ 23.52		$ 23.52
Officers and Key Employees | 2017 - TSR
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	56,644		56,644			56,644
Fair value per share (in dollars per share)	$ 32.17		$ 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)	56,644		56,644
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance (in dollars per share)	$ 32.17		$ 32.17
Officers and Key Employees | 2017 - CEGR, Time
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	109,107		109,107			109,107
Fair value per share (in dollars per share)	$ 33.69		$ 33.69			$ 33.69
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Nonvested shares outstanding, ending balance (in shares)	109,107		109,107
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance (in dollars per share)	$ 33.69		$ 33.69
Director
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of shares granted (in shares)			30,394	35,197
Vesting period of shares			12 months
Director shares vested						100.00%
Shares outstanding (in shares)	30,394		35,197			30,394
Total Cost	$ 256	$ 210	$ 767	$ 630
Fair value of shares issued			$ 1,000	$ 800
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Nonvested shares outstanding, beginning balance (in shares)			35,197
Granted (in shares)			30,394	35,197
Cancelled/Forfeited (in shares)			0
Vested (in shares)			(35,197)
Nonvested shares outstanding, ending balance (in shares)	30,394		30,394
Director | 2017
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares outstanding (in shares)	30,394		30,394			30,394
Fair value per share (in dollars per share)	$ 33.64		$ 33.64			$ 33.64
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Nonvested shares outstanding, ending balance (in shares)	30,394		30,394
Additional disclosures [Abstract]
Weighted average fair value nonvested shares-ending balance (in dollars per share)	$ 33.64		$ 33.64
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 two
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Service period of shares					2 years
Restricted Stock | Year three
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
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)			167,734	193,670
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Granted (in shares)			167,734	193,670
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)			24,001	32,732
Net Expense			$ 300	$ 200
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward]
Granted (in shares)			24,001	32,732
Time-based Restricted Stock
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)			53,058	58,101
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)			53,058	58,101
Total Shareholder Return
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Vesting period of shares			3 years