FINANCIAL INSTRUMENTS (Details) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Restricted investments held in escrow	$ 1.3	$ 1.3
Margin accounts with selected counterparties to support risk management activities	6.3	7.1
South Jersey Gas Company [Member] \| Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Long-term receivables, net of unamortized discount	10.9	10.4
Imputed interest on long term receivables	$ 1.2	$ 1.2

Unused proceeds on restricted investments that are required to be held in escrow. Includes interest earned.

Name:	sji_RestrictedInvestmentsHeldInEscrow
Namespace Prefix:	sji
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ Details

Name:	us-gaap_AccountsNotesAndLoansReceivableLineItems
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of cash or securities placed with a broker or counterparty as security for a trading or derivatives securities position which was partially obtained with funds provided by the broker dealer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.8,17)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_MarginDepositAssets
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Disclosure of the unamortized amount of the discount on the note or receivable which is deducted from the face amount of the receivable or loan. The discount or premium is the difference between the present value and the face amount.

+ References

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

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 16

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 1A

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28541-108399

+ Details

Name:	us-gaap_ReceivableWithImputedInterestDiscount
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The receivable or note face amount less the unamortized discount or premium.

+ References

+ Details

Name:	us-gaap_ReceivableWithImputedInterestNetAmount
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant