Incremental Shares Included In Diluted EPS Calculation

No definition available.

Name:	sji_IncrementalSharesIncludedInDilutedEPSCalculation
Namespace Prefix:	sji_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Sale Of Stock, Interest In Notes Issued, Percent In 1000% Principal Amount

+ References

No definition available.

+ Details

Name:	sji_SaleOfStockInterestInNotesIssuedPercentIn1000PrincipalAmount
Namespace Prefix:	sji_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Sale Of Stock, Quarterly Cash Distribution, Price Per Share

+ References

No definition available.

+ Details

Name:	sji_SaleOfStockQuarterlyCashDistributionPricePerShare
Namespace Prefix:	sji_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Sale Of Stock, Quarterly Contract Adjustment Payments, Percent

+ References

No definition available.

+ Details

Name:	sji_SaleOfStockQuarterlyContractAdjustmentPaymentsPercent
Namespace Prefix:	sji_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Sale Of Stock, Shares Held For Forward Contract

+ References

No definition available.

+ Details

Name:	sji_SaleOfStockSharesHeldForForwardContract
Namespace Prefix:	sji_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Sale Of Stock, Shares Received For Each Stock Purchase Contract Held

+ References

No definition available.

+ Details

Name:	sji_SaleOfStockSharesReceivedForEachStockPurchaseContractHeld
Namespace Prefix:	sji_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Sale of Stock, Consideration Received on Transaction, Gross

+ References

No definition available.

+ Details

Name:	sji_SaleofStockConsiderationReceivedonTransactionGross
Namespace Prefix:	sji_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Sale of Stock, Shares Available for Issuance

+ References

No definition available.

+ Details

Name:	sji_SaleofStockSharesAvailableforIssuance
Namespace Prefix:	sji_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Face amount or stated value per share of common stock.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_CommonStockParOrStatedValuePerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_CommonStockSharesOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6036836-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateEffectivePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the portion of interest incurred in the period on debt arrangements that was charged against earnings, excluding amortization of debt discount (premium) and financing costs.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph 8
-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

+ Details

Name:	us-gaap_InterestExpenseDebtExcludingAmortization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_PreferredStockParOrStatedValuePerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Cash received on stock transaction after deduction of issuance costs.

+ References

No definition available.

+ Details

Name:	us-gaap_SaleOfStockConsiderationReceivedOnTransaction
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The number of shares issued or sold by the subsidiary or equity method investee per stock transaction.

+ References

No definition available.

+ Details

Name:	us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Per share amount received by subsidiary or equity investee for each share of common stock issued or sold in the stock transaction.

+ References

No definition available.

+ Details

Name:	us-gaap_SaleOfStockPricePerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16(a))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

Name:	us-gaap_SeniorNotes
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_CapitalUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsidiarySaleOfStockAxis=sji_PublicStockOfferingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_CommonStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsidiarySaleOfStockAxis=us-gaap_PrivatePlacementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsidiarySaleOfStockAxis=us-gaap_OverAllotmentOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=sji_SeriesAJuniorSubordinatedNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=sji_SeriesBJuniorSubordinatedNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=us-gaap_ConvertibleDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=sji_SouthJerseyGasCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

COMMON STOCK - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions					1 Months Ended	3 Months Ended		12 Months Ended
	Apr. 15, 2021	Apr. 01, 2021	Mar. 25, 2021	Mar. 22, 2021	Mar. 31, 2021	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2018	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Par value of common stock (in dollars per share)					$ 1.25	$ 1.25
Shares of common stock outstanding (in shares)					102,571,850	102,571,850			100,591,940
Number of shares issued (in shares)				1,899,859
Gross proceeds from public offering				$ 42.3
Net proceeds from public offering, after underwriting discounts and commissions				$ 40.6
Incremental shares included in diluted EPS calculation (in shares)						1,091,313	111,077
Corporate Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Gross proceeds from public offering					$ 300.0
Net proceeds from public offering, after underwriting discounts and commissions					$ 291.0
Public Stock Offering
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Par value of common stock (in dollars per share)				$ 1.25
Number of shares offered (in shares)				10,250,000
Price per share (in dollars per share)				$ 22.25
Number of shares issued (in shares)				362,359
Quarterly contract adjustment payments, percent								3.55%
Public Stock Offering \| Corporate Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued (in shares)				6,000,000				5,750,000
Corporate Unit, stated value per share (in dollars per share)				$ 50	$ 50	$ 50		$ 50
Quarterly contract adjustment payments, percent				7.10%
Gross proceeds from public offering				$ 300.0
Net proceeds from public offering, after underwriting discounts and commissions				$ 291.0
Public Stock Offering \| Corporate Units \| Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price per share (in dollars per share)	$ 50.00
Quarterly cash distribution per share (in dollars per share)		$ 0.90625
Public Stock Offering \| Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares to be received for each stock purchase contract held (in shares)								1.6949
Public Stock Offering \| Common Stock \| Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued (in shares)	9,800,000
Net proceeds from public offering, after underwriting discounts and commissions	$ 287.5
Shares to be received for each stock purchase contract held (in shares)	1.7035	1.7035
Private Placement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares held for forward contract (in shares)				9,887,641
Over-Allotment Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price per share (in dollars per share)			$ 22.25
Number of shares issued (in shares)			1,537,500
Over-Allotment Option \| Corporate Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued (in shares)								750,000
Over-Allotment Option \| Corporate Units \| Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares offered (in shares)		900,000
Number of shares issued (in shares)		700,000
Gross proceeds from public offering		$ 35.0
Net proceeds from public offering, after underwriting discounts and commissions		$ 34.0
2018 Series A Remarketable Junior Notes due 2031
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Interest rate			5.02%					3.70%
Subordinated notes			$ 287.5
Effective interest rate (as a percent)					4.00%	4.00%
2018 Series A Remarketable Junior Notes due 2031 \| Public Stock Offering \| Corporate Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Interest in notes issued, percent								5.00%
2021 Series B Remarketable Junior Subordinated Notes due 2029
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Interest rate				1.65%
Effective interest rate (as a percent)					2.10%	2.10%
2021 Series B Remarketable Junior Subordinated Notes due 2029 \| Public Stock Offering \| Corporate Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Interest in notes issued, percent				5.00%
Convertible
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Interest expense, coupon						$ 2.7	$ 2.6
SJG
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Par value of common stock (in dollars per share)					$ 2.50	$ 2.50
Shares of common stock outstanding (in shares)					2,339,139	2,339,139