STOCK-BASED COMPENSATION PLANS (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	24,432
Fair Value Per Share (in dollars per share)	$ 50.728
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	0.7
Weighted average period over which unrecognized compensation cost is to be recognized (in years)	2 years 2 months 12 days
Shares [Roll Forward]
Nonvested Shares Outstanding, beginning balance (in shares)	15,108
Granted (in shares)	9,324
Nonvested Shares Outstanding, ending balance (in shares)	24,432
Weighted Average Grant Date Fair Value [Roll Forward]
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, beginning balance (in dollars per share)	$ 52.548
Weighted Average Grant Date Fair Value, Granted (in dollars per share)	$ 47.780
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in dollars per share)	$ 50.728
Number of shares awarded during the period	12,901	7,098
Market value of shares awarded	0.6	0.4
Cash payments to SJI relating to stock awards	$ 0.4	$ 0.4
Grant Date January 2011 - TSR [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	7,372
Fair Value Per Share (in dollars per share)	$ 50.940
Expected Volatility	27.50%
Risk-Free Interest Rate	1.01%
Shares [Roll Forward]
Nonvested Shares Outstanding, ending balance (in shares)	7,372
Weighted Average Grant Date Fair Value [Roll Forward]
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in dollars per share)	$ 50.940
Grant Date January 2012 - TSR [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	3,868
Fair Value Per Share (in dollars per share)	$ 51.230
Expected Volatility	22.50%
Risk-Free Interest Rate	0.43%
Shares [Roll Forward]
Nonvested Shares Outstanding, ending balance (in shares)	3,868
Weighted Average Grant Date Fair Value [Roll Forward]
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in dollars per share)	$ 51.230
Grant Date January 2012 - EPS [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	3,868
Fair Value Per Share (in dollars per share)	$ 56.930
Shares [Roll Forward]
Nonvested Shares Outstanding, ending balance (in shares)	3,868
Weighted Average Grant Date Fair Value [Roll Forward]
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in dollars per share)	$ 56.930
Grant Date January 2013 - TSR [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	4,662,000
Fair Value Per Share (in dollars per share)	$ 44,380.000
Expected Volatility	21.10%
Risk-Free Interest Rate	0.40%
Shares [Roll Forward]
Nonvested Shares Outstanding, ending balance (in shares)	4,662,000
Weighted Average Grant Date Fair Value [Roll Forward]
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in dollars per share)	$ 44,380.000
Grant Date January 2013 - EPS [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Shares Outstanding (in shares)	4,662,000
Fair Value Per Share (in dollars per share)	$ 51,180.000
Shares [Roll Forward]
Nonvested Shares Outstanding, ending balance (in shares)	4,662,000
Weighted Average Grant Date Fair Value [Roll Forward]
Weighted Average Grant Date Fair Value, Nonvested Shares Outstanding, ending balance (in dollars per share)	$ 51,180.000
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%

Deferred Compensation Arrangement with Individual, Cash Payments To Parent Company

No definition available.

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- Definition

The range, in percentages, of the original share units granted that may ultimately vest due to restricted shares being subject to certain market-based performance targets.

+ References

No definition available.

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- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-Section F

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- Definition

The total fair value of shares issued during the period under a deferred compensation arrangement.

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-Paragraph 64, 65

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- Definition

The number of shares issued pursuant to the terms of the deferred compensation plan as of the balance sheet date.

+ References

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- Definition

As of the balance sheet date, the aggregate unrecognized cost of equity-based awards made to employees under equity-based compensation awards that have yet to vest.

+ References

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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- Definition

The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

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