Debt instrument unamortized discount and debt issuance costs.

No definition available.

Name:	swx_DebtInstrumentUnamortizedDiscountAndDebtIssuanceCosts
Namespace Prefix:	swx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

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 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
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_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the 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))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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

Reference 3: 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))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value portion of contractual arrangement with a lender under which borrowings can be made up to a specific amount at any point in time.

+ References

No definition available.

+ Details

Name:	us-gaap_LinesOfCreditFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=123466204&loc=SL6031897-161870

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 55
-Paragraph 69C
-URI http://asc.fasb.org/extlink&oid=123466577&loc=SL123495737-112612

Reference 3: 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(a)(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 55
-Paragraph 69B
-URI http://asc.fasb.org/extlink&oid=123466577&loc=SL123495735-112612

Reference 5: 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

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1D
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495340-112611

Reference 7: 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))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_LongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

+ Details

Name:	us-gaap_LongTermDebtCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

Name:	us-gaap_LongTermDebtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

+ Details

Name:	us-gaap_LongTermDebtNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

Including the current and noncurrent portions, aggregate carrying amount of all types of notes payable, as of the balance sheet date, with initial maturities beyond one year or beyond the normal operating cycle, if longer.

+ 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(a)(16))
-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 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 3: 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_NotesPayable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value portion of notes payable.

+ References

+ Details

Name:	us-gaap_NotesPayableFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt classified as other.

+ 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))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: 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(a)(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 3: 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_OtherLongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

+ 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(a)(16))
-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

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))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_SecuredDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

+ References

+ Details

Name:	us-gaap_UnamortizedDebtIssuanceExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

+ 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))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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

Reference 3: 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(a)(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

Name:	us-gaap_UnsecuredDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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

- Details

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

- Details

Name:	us-gaap_LongtermDebtTypeAxis=swx_DebenturesNotesSixPointOnePercentageDueTwoThousandAndFortyOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=swx_DebenturesNotesThreePointEightSevenFivePercentageDueTwoThousandAndTwentyTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=swx_DebenturesNotesFourPointEightSevenFivePercentageDueTwoThousandAndFortyThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=swx_DebenturesNotesThreePointEightPercentageDueTwoThousandAndFortySixMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=swx_DebenturesNotesThreePointSevenPercentageDueTwoThousandAndTwentyEightMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=swx_DebenturesNotesFourPointFifteenPercentageDueTwoThousandAndFortyNineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=swx_DebenturesNotesTwoPointTwoPercentageDueTwoThousandAndThirtyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=swx_DebenturesNotesThreePointEighteenPercentageDueTwoThousandAndFiftyOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=swx_DebenturesEightPercentageSeriesDueTwoThousandAndTwentySixMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=swx_DebenturesMediumTermNotesSevenPointSevenEightPercentageSeriesDueTwoThousandAndTwentyTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=swx_DebenturesMediumTermNotesSevenPointNineTwoPercentageSeriesDueTwoThousandAndTwentySevenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=swx_DebenturesMediumTermNotesSixPointSevenSixPercentageSeriesDueTwoThousandAndTwentySevenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_CarryingReportedAmountFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=swx_CenturiGroupInc.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=swx_CenturiSecuredRevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=swx_CenturiTermLoanFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=swx_CenturiOtherDebtObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=swx_RevolvingCreditFacilityAndCommercialPaperMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_LongtermDebtTypeAxis=swx_VariableRateBondsTaxExemptSeriesADueTwoThousandAndTwentyEightMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=swx_VariableRateBondsTwoThousandAndThreeSeriesADueTwoThousandAndThirtyEightMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=swx_VariableRateBondsTwoThousandAndEightSeriesADueTwoThousandAndThirtyEightMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=swx_VariableRateBondsTwoThousandAndNineSeriesADueTwoThousandAndThirtyNineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_EstimateOfFairValueFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt - Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Aug. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Less: current maturities	$ (297,271)		$ (40,433)
Long-term debt, less current maturities	3,573,783		2,732,200
Long-term Debt, Current and Noncurrent Abstract
Less: current maturities	(297,271)		(40,433)
Long-term debt, less current maturities	3,573,783		2,732,200
Southwest Gas Corporation
Debt Instrument [Line Items]
Less: current maturities	(275,000)		0
Long-term debt, less current maturities	2,309,857		2,438,206
Long-term Debt, Current and Noncurrent Abstract
Less: current maturities	(275,000)		0
Long-term debt, less current maturities	$ 2,309,857		2,438,206
Debentures \| Notes, 6.1%, due 2041 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	6.10%
Debentures \| Notes, 3.875%, due 2022 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	3.875%
Debentures \| Notes, 4.875%, due 2043 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	4.875%
Debentures \| Notes, 3.8%, due 2046 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	3.80%
Debentures \| Notes, 3.7%, due 2028 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	3.70%
Debentures \| Notes, 4.15%, due 2049 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	4.15%
Debentures \| Notes, 2.2%, due 2030 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	2.20%
Debentures \| Notes, 3.18%, due 2051 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	3.18%	3.18%
Debentures \| 8% Series, due 2026 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	8.00%
Debentures \| Medium-term notes, 7.78% series, due 2022 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	7.78%
Debentures \| Medium-term notes, 7.92% series, due 2027 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	7.92%
Debentures \| Medium-term notes, 6.76% series, due 2027 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	6.76%
Carrying Amount
Debt Instrument [Line Items]
Less: current maturities	$ (297,271)		(40,433)
Long-term debt, less current maturities	3,573,783		2,732,200
Long-term Debt, Current and Noncurrent Abstract
Less: current maturities	(297,271)		(40,433)
Long-term debt, less current maturities	3,573,783		2,732,200
Carrying Amount \| Southwest Gas Corporation
Debt Instrument [Line Items]
Less: current maturities	(275,000)		0
Long-term debt, less current maturities	2,309,857		2,438,206
Long-term Debt, Current and Noncurrent Abstract
Less: current maturities	(275,000)		0
Long-term debt, less current maturities	2,309,857		2,438,206
Long-term debt	2,584,857		2,438,206
Carrying Amount \| Centuri
Debt Instrument [Line Items]
Less: current maturities	(22,271)		(40,433)
Long-term debt, less current maturities	1,263,926		293,994
Unamortized debt issuance costs	(25,385)		(820)
Long-term Debt, Current and Noncurrent Abstract
Less: current maturities	(22,271)		(40,433)
Long-term debt, less current maturities	1,263,926		293,994
Long-term debt	1,286,197		334,427
Centuri secured revolving credit facility	1,119,615		225,828
Carrying Amount \| Centuri secured revolving credit facility \| Centuri
Long-term Debt, Current and Noncurrent Abstract
Centuri secured revolving credit facility	112,236		26,626
Carrying Amount \| Centuri term loan facility \| Centuri
Long-term Debt, Current and Noncurrent Abstract
Centuri secured revolving credit facility	1,145,000		226,648
Carrying Amount \| Centuri other debt obligations \| Centuri
Long-term Debt, Current and Noncurrent Abstract
Centuri other debt obligations	54,346		81,973
Carrying Amount \| Debentures \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	2,386,773		2,089,678
Unamortized discount and debt issuance costs	(20,727)		(17,822)
Carrying Amount \| Debentures \| Notes, 6.1%, due 2041 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	125,000		125,000
Carrying Amount \| Debentures \| Notes, 3.875%, due 2022 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	250,000		250,000
Carrying Amount \| Debentures \| Notes, 4.875%, due 2043 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	250,000		250,000
Carrying Amount \| Debentures \| Notes, 3.8%, due 2046 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	300,000		300,000
Carrying Amount \| Debentures \| Notes, 3.7%, due 2028 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	300,000		300,000
Carrying Amount \| Debentures \| Notes, 4.15%, due 2049 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	300,000		300,000
Carrying Amount \| Debentures \| Notes, 2.2%, due 2030 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	450,000		450,000
Carrying Amount \| Debentures \| Notes, 3.18%, due 2051 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	300,000		0
Carrying Amount \| Debentures \| 8% Series, due 2026 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	75,000		75,000
Carrying Amount \| Debentures \| Medium-term notes, 7.78% series, due 2022 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	25,000		25,000
Carrying Amount \| Debentures \| Medium-term notes, 7.92% series, due 2027 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	25,000		25,000
Carrying Amount \| Debentures \| Medium-term notes, 6.76% series, due 2027 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	7,500		7,500
Carrying Amount \| Debentures \| Revolving credit facility and commercial paper \| Southwest Gas Corporation
Debt Instrument [Line Items]
Line of credit facility	0		150,000
Carrying Amount \| Industrial development revenue bonds \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unamortized discount and debt issuance costs	(1,916)		(1,472)
Unsecured debt	198,084		198,528
Carrying Amount \| Industrial development revenue bonds \| Tax-exempt Series A, due 2028 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt	50,000		50,000
Carrying Amount \| Industrial development revenue bonds \| 2003 Series A, due 2038 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt	50,000		50,000
Carrying Amount \| Industrial development revenue bonds \| 2008 Series A, due 2038 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt	50,000		50,000
Carrying Amount \| Industrial development revenue bonds \| 2009 Series A, due 2039 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt	50,000		50,000
Fair Value \| Centuri secured revolving credit facility \| Centuri
Long-term Debt, Current and Noncurrent Abstract
Centuri secured revolving credit facility	112,348		26,645
Fair Value \| Centuri term loan facility \| Centuri
Long-term Debt, Current and Noncurrent Abstract
Centuri secured revolving credit facility	1,146,431		230,824
Fair Value \| Centuri other debt obligations \| Centuri
Long-term Debt, Current and Noncurrent Abstract
Centuri other debt obligations	52,682		84,246
Fair Value \| Debentures \| Notes, 6.1%, due 2041 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	167,755		174,858
Fair Value \| Debentures \| Notes, 3.875%, due 2022 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	252,208		258,825
Fair Value \| Debentures \| Notes, 4.875%, due 2043 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	307,385		317,190
Fair Value \| Debentures \| Notes, 3.8%, due 2046 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	326,058		347,046
Fair Value \| Debentures \| Notes, 3.7%, due 2028 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	331,536		344,553
Fair Value \| Debentures \| Notes, 4.15%, due 2049 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	343,950		370,278
Fair Value \| Debentures \| Notes, 2.2%, due 2030 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	447,287		474,552
Fair Value \| Debentures \| Notes, 3.18%, due 2051 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	291,351		0
Fair Value \| Debentures \| 8% Series, due 2026 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	94,752		99,723
Fair Value \| Debentures \| Medium-term notes, 7.78% series, due 2022 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	25,513		26,663
Fair Value \| Debentures \| Medium-term notes, 7.92% series, due 2027 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	31,936		33,802
Fair Value \| Debentures \| Medium-term notes, 6.76% series, due 2027 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	9,116		9,613
Fair Value \| Debentures \| Revolving credit facility and commercial paper \| Southwest Gas Corporation
Debt Instrument [Line Items]
Line of credit facility, fair value	0		150,000
Fair Value \| Industrial development revenue bonds \| Tax-exempt Series A, due 2028 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt	50,000		50,000
Fair Value \| Industrial development revenue bonds \| 2003 Series A, due 2038 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt	50,000		50,000
Fair Value \| Industrial development revenue bonds \| 2008 Series A, due 2038 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt, fair value	50,000		50,000
Fair Value \| Industrial development revenue bonds \| 2009 Series A, due 2039 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt, fair value	$ 50,000		$ 50,000