Debt instrument covenant compliance credit risk exposure amount.

No definition available.

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- Definition

Debt Instrument Discount Rate

+ References

No definition available.

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- Definition

Equity cushion relating to minimum fixed charge ratio coverage requirement.

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No definition available.

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- Definition

Equity cushion relating to minimum net worth requirement.

+ References

No definition available.

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- Definition

Line Of Credit Facility, Amount Classified As Long-Term Debt

+ References

No definition available.

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- Definition

Line Of Credit Facility Minimum Amount Outstanding During Period

+ References

No definition available.

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- Definition

Line Of Credit Facility, Working Capital Purposes

+ References

No definition available.

+ Details

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- Definition

Percentage of maximum dividend payout restriction.

+ References

No definition available.

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

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- Definition

Amount of assets pledged to secure a debt instrument.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

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- 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
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- Definition

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

+ References

+ Details

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- 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.

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- 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.

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- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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- Definition

Maximum amount borrowed under the credit facility at any time during the period.

+ References

No definition available.

+ Details

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

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- 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.

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- 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.

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- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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Long-Term Debt - Narrative (Detail) - USD ($)	3 Months Ended	12 Months Ended
Long-Term Debt - Narrative (Detail) - USD ($)	Mar. 31, 2018	Dec. 31, 2018	Nov. 30, 2018	Oct. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Short term borrowings outstanding		$ 152,000,000			$ 214,500,000
Issuance of additional debt		2,100,000,000
Equity cushion relating to minimum net worth requirement		$ 1,200,000,000
Percentage of maximum dividend payout restriction		60.00%
Southwest Gas Corporation
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity		$ 400,000,000
Line of credit designated for working capital purposes		250,000,000
Short term borrowings outstanding		152,000,000			191,000,000
Centuri
Debt Instrument [Line Items]
Issuance of additional debt		101,000,000
Equity cushion relating to minimum fixed charge ratio coverage requirement		78,000,000
Southwest Gas Credit Facility \| Southwest Gas Corporation
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity		400,000,000
Line of credit designated as long term debt		150,000,000
Line of credit designated for working capital purposes		250,000,000
Long-term debt		$ 150,000,000
Effective interest rates		3.41%
Maximum current borrowing usage	$ 378,000,000
Short term borrowings outstanding		$ 152,000,000			$ 191,000,000
Commitment fee percentage		0.10%
Southwest Gas Credit Facility \| LIBOR \| Southwest Gas Corporation
Debt Instrument [Line Items]
Applicable margin		1.00%
Southwest Gas Credit Facility \| Alternative Base Rate \| Southwest Gas Corporation
Debt Instrument [Line Items]
Applicable margin		0.00%
Commercial Paper Program \| Southwest Gas Corporation
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity		$ 50,000,000
Borrowings outstanding under facility		50,000,000
Secured Revolving Credit Facility and Term Loan \| Centuri
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity			$ 590,000,000	$ 450,000,000
Borrowings outstanding under facility		$ 256,000,000
Effective interest rates		4.10%
Maximum current borrowing usage		$ 103,000,000
Minimum current borrowing usage		0
Debt secured by assets		$ 1,100,000,000
Secured Revolving Credit Facility and Term Loan \| Centuri \| Minimum
Debt Instrument [Line Items]
Commitment fee percentage		0.125%
Secured Revolving Credit Facility and Term Loan \| Centuri \| Maximum
Debt Instrument [Line Items]
Commitment fee percentage		0.35%
Secured Revolving Credit Facility and Term Loan \| Canadian Dealer Offered Rate \| Centuri
Debt Instrument [Line Items]
Applicable margin		0.875%
Secured Revolving Credit Facility and Term Loan \| Canadian Dealer Offered Rate \| Centuri \| Maximum
Debt Instrument [Line Items]
Applicable margin		2.25%
Secured Revolving Credit Facility and Term Loan \| Alternative Base Rate \| Centuri \| Minimum
Debt Instrument [Line Items]
Applicable margin		0.00%
Secured Revolving Credit Facility and Term Loan \| Alternative Base Rate \| Centuri \| Maximum
Debt Instrument [Line Items]
Applicable margin		1.25%
Centuri term loan facility \| Centuri
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity			265,000,000
Line of Credit \| Centuri
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity			$ 325,000,000
Notes, 3.7%, due 2028 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable		$ 300,000,000
Debt instrument interest rate	3.70%
Debt instrument discount rate	0.185%