STOCK-BASED COMPENSATION PLANS (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Service requirement period	3 years
Shares granted (in shares)	33,218
Shares Outstanding (in shares)	46,475	46,475		54,872
Fair Value Per Share (in USD per share)	$ 26.67	$ 26.67		$ 25.31
Expected volatility, measurement period	3 years
Cost of restricted stock awards	$ 0.6	$ 0.3	$ 0.2
Amount to be capitalized to Utility Plant	50.00%	50.00%	50.00%
Unrecognized compensation cost of awards granted under the plan				$ 0.7
Weighted average period over which unrecognized compensation cost is to be recognized (in years)	1 year 8 months 12 days
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward}
Nonvested Shares Outstanding, beginning balance (in shares)	46,475
Shares granted (in shares)	33,218
Vested (in shares)	(21,995)
Cancelled/Forfeited (in shares)	(2,826)
Nonvested Shares Outstanding, ending balance (in shares)	54,872	46,475
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, beginning balance (in USD per share)	$ 26.67
Weighted Average Grant Date Fair Value, Granted (in USD per share)	23.17
Weighted Average Grant Date Fair Value, Vested (in USD per share)	24.88
Weighted Average Grant Date Fair Value, Cancelled/Forfeited (in USD per share)	25.89
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in USD per share)	$ 25.31	$ 26.67
Cash payments to SJI relating to stock awards	$ 0.2	$ 0.2	$ 0.4
Officers and key employees
Weighted Average Grant Date Fair Value
Expected number of shares to be awarded				5,593
Number of shares awarded during the period	2,610
Market value of shares awarded	$ 0.1
2015 - TSR
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	6,884			6,884
Fair Value Per Share (in USD per share)	$ 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)	6,884
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in USD per share)	$ 26.31
2015 - EPS, ROE, Time
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	15,211			15,211
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)	15,211
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in USD per share)	$ 29.47
2016 - TSR
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	11,472			11,472
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)	11,472
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in USD per share)	$ 22.53
2016 - CEGR, Time
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	21,305			21,305
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)	21,305
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in USD per share)	$ 23.52
Performance shares
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Vesting period of shares	3 years
Performance shares | 2012 and 2013 grant dates
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Vesting period of shares	3 years
Weighted Average Grant Date Fair Value
Number of shares awarded during the period	0	0
Restricted stock
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Vesting period of shares	3 years	3 years
Amount of payout limit for one-third of the time-based shares of restricted stock	100.00%
Minimum return on equity requirement	7.00%	7.00%
Shares granted (in shares)	9,965	7,878
Restricted stock award activity, excluding accrued dividend equivalents [Roll Forward}
Shares granted (in shares)	9,965	7,878
Restricted stock | Tranche Two
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Service requirement period		2 years
Restricted stock | Tranche Three
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Service requirement period		3 years
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%
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%