STOCK-BASED COMPENSATION PLANS (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2014	Jun. 30, 2013
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Vesting period of shares					3 years	3 years
Shares Outstanding (in shares)	25,462				25,462
Fair Value Per Share (in dollars per share)	$ 50.18				$ 50.18
Cost of Restricted Stock Awards	$ 0.1	$ 0.1	$ 0.1	$ 0.1
Unrecognized compensation cost of awards granted under the plan	0.7				0.7
Weighted average period over which unrecognized compensation cost is to be recognized (in years)					2 years
Shares [Roll Forward]
Nonvested Shares Outstanding, beginning balance (in shares)		15,068			15,068
Granted (in shares)					10,394
Nonvested Shares Outstanding, ending balance (in shares)	25,462				25,462
Weighted Average Grant Date Fair Value [Roll Forward]
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, beginning balance (in dollars per share)		$ 50.73			$ 50.73
Weighted Average Grant Date Fair Value, Granted (in dollars per share)					$ 49.38
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in dollars per share)	$ 50.18				$ 50.18
Number of shares awarded during the period					0	12,901
Market value of shares awarded						0.6
Cash payments to SJI relating to stock awards					$ 0.4	$ 0.4
Grant Date January 2012 - TSR [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	3,533				3,533
Fair Value Per Share (in dollars per share)	$ 51.23				$ 51.23
Expected Volatility					22.50%
Risk-Free Interest Rate					0.43%
Shares [Roll Forward]
Nonvested Shares Outstanding, ending balance (in shares)	3,533				3,533
Weighted Average Grant Date Fair Value [Roll Forward]
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in dollars per share)	$ 51.23				$ 51.23
Grant Date January 2012 - EPS [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	3,533				3,533
Fair Value Per Share (in dollars per share)	$ 56.93				$ 56.93
Shares [Roll Forward]
Nonvested Shares Outstanding, ending balance (in shares)	3,533				3,533
Weighted Average Grant Date Fair Value [Roll Forward]
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in dollars per share)	$ 56.93				$ 56.93
Grant Date January 2013 - TSR [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	4,001				4,001
Fair Value Per Share (in dollars per share)	$ 44.38				$ 44.38
Expected Volatility					21.10%
Risk-Free Interest Rate					0.40%
Shares [Roll Forward]
Nonvested Shares Outstanding, ending balance (in shares)	4,001				4,001
Weighted Average Grant Date Fair Value [Roll Forward]
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in dollars per share)	$ 44.38				$ 44.38
Grant Date January 2013 - EPS [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	4,001				4,001
Fair Value Per Share (in dollars per share)	$ 51.18				$ 51.18
Shares [Roll Forward]
Nonvested Shares Outstanding, ending balance (in shares)	4,001				4,001
Weighted Average Grant Date Fair Value [Roll Forward]
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in dollars per share)	$ 51.18				$ 51.18
Grant Date January 2014, TSR [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	5,197				5,197
Fair Value Per Share (in dollars per share)	$ 44.32				$ 44.32
Expected Volatility					20.00%
Risk-Free Interest Rate					0.80%
Shares [Roll Forward]
Nonvested Shares Outstanding, ending balance (in shares)	5,197				5,197
Weighted Average Grant Date Fair Value [Roll Forward]
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in dollars per share)	$ 44.32				$ 44.32
Grant Date January 2014, EPS [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	5,197				5,197
Fair Value Per Share (in dollars per share)	$ 54.44				$ 54.44
Shares [Roll Forward]
Nonvested Shares Outstanding, ending balance (in shares)	5,197				5,197
Weighted Average Grant Date Fair Value [Roll Forward]
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in dollars per share)	$ 54.44				$ 54.44
Minimum [Member]
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 [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Percentage of actual amount of shares that ultimately vest of original share units granted					150.00%