STOCK-BASED COMPENSATION PLANS (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	25,028		25,028
Fair Value Per Share (in dollars per share)	$ 47.186		$ 47.186
Vesting period of shares			3 years	3 years
Cost of Restricted Stock Awards	$ 0.1	$ 0.1
Unrecognized compensation cost of awards granted under the plan	0.6		0.6
Weighted average period over which unrecognized compensation cost is to be recognized (in years)			2 years
Restricted stock award activity, excluding accrued dividend equivalents [Rolll Forward}
Nonvested Shares Outstanding, beginning balance (in shares)			17,568
Granted (in shares)			7,913
Canceled / Forfeited (in shares)			(453)
Nonvested Shares Outstanding, ending balance (in shares)	25,028		25,028
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, beginning balance (in dollars per share)			$ 44.139
Weighted Average Grant Date Fair Value, Granted (in dollars per share)			$ 54.080
Weighted Average Grant Date Fair Value, Canceled / Forfeited (in dollars per share)			$ 49.430
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in dollars per share)	$ 47.186		$ 47.186
Number of shares awarded during the period			7,098	15,186
Market value of shares awarded			0.4	0.8
Cash payments to SJI relating to stock awards			$ 0.3	$ 0.3
Grant Date January 2010 - TSR [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	9,920		9,920
Fair Value Per Share (in dollars per share)	$ 39.020		$ 39.020
Expected Volatility			29.00%
Risk-Free Interest Rate			1.65%
Restricted stock award activity, excluding accrued dividend equivalents [Rolll Forward}
Nonvested Shares Outstanding, ending balance (in shares)	9,920		9,920
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in dollars per share)	$ 39.020		$ 39.020
Grant Date January 2011 - TSR [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	7,372		7,372
Fair Value Per Share (in dollars per share)	$ 50.940		$ 50.940
Expected Volatility			27.50%
Risk-Free Interest Rate			1.01%
Restricted stock award activity, excluding accrued dividend equivalents [Rolll Forward}
Nonvested Shares Outstanding, ending balance (in shares)	7,372		7,372
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in dollars per share)	$ 50.940		$ 50.940
Grant Date January 2012 - TSR [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	3,868		3,868
Fair Value Per Share (in dollars per share)	$ 51.230		$ 51.230
Expected Volatility			22.50%
Risk-Free Interest Rate			0.43%
Restricted stock award activity, excluding accrued dividend equivalents [Rolll Forward}
Nonvested Shares Outstanding, ending balance (in shares)	3,868		3,868
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in dollars per share)	$ 51.230		$ 51.230
Grant Date January 2012 - EPS [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	3,868		3,868
Fair Value Per Share (in dollars per share)	$ 56.930		$ 56.930
Restricted stock award activity, excluding accrued dividend equivalents [Rolll Forward}
Nonvested Shares Outstanding, ending balance (in shares)	3,868		3,868
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in dollars per share)	$ 56.930		$ 56.930
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%