LONG-TERM DEBT (Details) (USD $)	1 Months Ended
	Feb. 28, 2012	Dec. 31, 2012		Dec. 31, 2011
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding		$ 450,000,000	[1]	$ 365,000,000	[1]
Less Current Maturities		(25,000,000)	[1]	(2,187,000)	[1]
Long-Term Debt		425,000,000	[1]	362,813,000	[1]
Long-term Debt, Fiscal Year Maturity [Abstract]
2013		25,000,000
2014		21,000,000
2015		10,909,000
2016		27,909,000
2017		15,909,000
Bonds at variable rates [Member]
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding		25,000,000	[1],[2]	25,000,000	[1],[2]
Long-term Debt, Fiscal Year Maturity [Abstract]
Interest rate at end of period		0.17%
Series Due 2013, 4.46% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding		10,500,000	[1],[3]	10,500,000	[1],[3]
Series Due 2013, 5.027% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding		14,500,000	[1],[3]	14,500,000	[1],[3]
Series Due 2014, 4.52% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding		11,000,000	[1],[3]	11,000,000	[1],[3]
Series Due 2014, 5.115% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding		10,000,000	[1],[3]	10,000,000	[1],[3]
Series Due 2015, 5.387% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding		10,000,000	[1],[3]	10,000,000	[1],[3]
Series Due 2016, 5.437% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding		10,000,000	[1],[3]	10,000,000	[1],[3]
Series Due 2016, 4.6% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding		17,000,000	[1],[3]	17,000,000	[1],[3]
Series Due 2017, 4.657% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding		15,000,000	[1],[3]	15,000,000	[1],[3]
Series Due 2018, 7.97% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding		10,000,000	[1],[3]	10,000,000	[1],[3]
Series Due 2018, 7.125% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding		20,000,000	[1],[3]	20,000,000	[1],[3]
Series Due 2019, 5.587% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding		10,000,000	[1],[3]	10,000,000	[1],[3]
Series Due 2024, 3.00% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Stated interest rate		3.00%
Total Long-Term Debt Outstanding		50,000,000	[1],[3],[4]	0	[1],[3],[4]
Series Due 2024, 3.03% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Stated interest rate		3.03%
Total Long-Term Debt Outstanding		35,000,000	[1],[3],[4]	0	[1],[3],[4]
Series Due 2025, 3.63% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding		10,000,000	[1],[3]	10,000,000	[1],[3]
Series Due 2026, 4.84% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding		15,000,000	[1],[3]	15,000,000	[1],[3]
Series Due 2026, 4.93% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding		45,000,000	[1],[3]	45,000,000	[1],[3]
Series Due 2027, 4.03% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding		45,000,000	[1],[3]	45,000,000	[1],[3]
Series Due 2027, 7.7% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Stated interest rate		7.70%
Total Long-Term Debt Outstanding		0	[1],[3],[5]	35,000,000	[1],[3],[5]
Long-term Debt, Fiscal Year Maturity [Abstract]
Redemption premium	2.00%
Series Due 2027, 7.7% [Member] | Medium-term Notes [Member]
Long-term Debt, Fiscal Year Maturity [Abstract]
Approved borrowing capacity				200,000,000
Available borrowing capacity		80,000,000
Series Due 2032, 3.74% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Stated interest rate		3.74%
Total Long-Term Debt Outstanding		35,000,000	[1],[3],[5]	0	[1],[3],[5]
Series Due 2033, 5.55% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding		32,000,000	[1],[3]	32,000,000	[1],[3]
Series Due 2034, 6.213% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding		10,000,000	[1],[3]	10,000,000	[1],[3]
Series Due 2035, 5.45% [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding		$ 10,000,000	[1],[3]	$ 10,000,000	[1],[3]

[1] Long-term debt maturities and sinking funds requirements for the succeeding five years are as follows (in thousands): 2013, $25,000; 2014, $21,000; 2015, $10,909; 2016, $27,909; 2017, $15,909. Our long-term debt agreements contain no financial covenants.

[2] These variable rate demand bonds bear interest at a floating rate that resets weekly. The interest rate as of December 31, 2012 was 0.17%. Liquidity support on these bonds is provided under a separate letter of credit facility that expires in August, 2015. These bonds contain no financial covenants.

[3] Our First Mortgage dated October 1, 1947, as supplemented, securing the First Mortgage Bonds constitutes a direct first mortgage lien on substantially all utility plant.

[4] In September 2012, SJG issued $50.0 million of 3.00% aggregate principal amount of Medium Term Notes (MTN) due September 2024. In November 2012, SJG issued $35.0 million of 3.03% aggregate principal amount of MTN due November 2024.

[5] In February 2012, SJG called its $35.0 million, 7.70% MTN due April 2027, at par plus a 2.00% premium. The early redemption occurred concurrently with the issuance in April 2012 of $35.0 million, 3.74% MTN due April 2032.