Document Type Document Type Other income (deductions) Total other income (deductions) Other Nonoperating Income (Expense) Unit price contracts Unit Priced Contracts [Member] Unit priced contracts. Segments [Axis] Segments [Axis] Prepaid and other current assets Regulatory Assets, Current Percentage of total debt with interest rates reference to LIBOR and due after 2021 Debt Instrument, Percentage Of Total With Interest Rates Reference To LIBOR And Due After 2021 Debt Instrument, Percentage Of Total With Interest Rates Reference To LIBOR And Due After 2021 Rollforward of Accumulated Other Comprehensive Income Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Condensed Income Statement [Table] Condensed Income Statement [Table] Notes, 2.2%, due 2030 Debentures Notes 2.2%, Due 2030 [Member] Debentures Notes 2.2%, Due 2030 Net actuarial loss Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, after Tax Schedule of Common Stock Activity Schedule Of Common Stock Activity [Table Text Block] Schedule Of Common Stock Activity [Table Text Block] Statistical Measurement [Domain] Statistical Measurement [Domain] CAPITALIZATION AND LIABILITIES Liabilities and Equity [Abstract] Line of Credit Line of Credit [Member] Proceeds from debt Proceeds from Issuance of Debt Significant Accounting Policies [Line Items] Significant Accounting Policies [Line Items] Significant Accounting Policies [Line Items] Security Exchange Name Security Exchange Name Components of Net Periodic Benefit Cost Compensation and Employee Benefit Plans [Text Block] Issuance of long-term debt, net Proceeds from Issuance of Long-term Debt Operating income (loss) Operating Income (Loss) Number of contracts with original duration more than one year Revenue Recognition, Number Of Contracts With Original Duration More Than One Year Revenue Recognition, Number Of Contracts With Original Duration More Than One Year Total current liabilities Liabilities, Current Industrial/other Industrial/other [Member] Industrial/other. Debt covenant, ratio of funded debt to total capitalization Debt Instrument, Covenant, Ratio Of Funded Debt To Total Capitalization Debt Instrument, Covenant, Ratio Of Funded Debt To Total Capitalization Prepaid and other current assets Prepaid Expense and Other Assets, Current Variable Rate [Domain] Variable Rate [Domain] Variable Rate [Axis] Variable Rate [Axis] ASSETS Assets [Abstract] Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Schedule of Significant Items Included in Other Income (Deductions) Schedule of Other Nonoperating Income, by Component [Table Text Block] Share-based compensation Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture Entity Address, State or Province Entity Address, State or Province Other comprehensive income (loss), before tax Other Comprehensive Income (Loss), before Tax Accounts payable Accounts Payable, Current Foreign currency translation adjustment Goodwill, Foreign Currency Translation Gain (Loss) Other Comprehensive Income and Accumulated Other Comprehensive Income Comprehensive Income (Loss) Note [Text Block] Change in credit facility and commercial paper Proceeds From Repayments Of Lines Of Credit And Commercial Paper The net cash inflow or cash outflow from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with either short term or long term maturity that is collateralized (backed by pledge, mortgage or other lien in the entity's assets) and issuing (borrowing) and repaying commercial paper Schedule of Construction Services Contracts Receivable Schedule of Construction Services Contracts Receivable [Table Text Block] Schedule of Construction Services Contracts Receivable [Table Text Block] Centuri secured revolving credit facility Secured Debt Retained earnings Retained Earnings (Accumulated Deficit) Accumulated removal costs Other Accrued Liabilities, Noncurrent Changes in customer advances Changes In Customer Advances, Investing Activities Changes In Customer Advances, Investing Activities Line of credit designated for working capital purposes Line Of Credit Facility Working Capital Purposes Line Of Credit Facility, Working Capital Purposes Other deferred credits and other long-term liabilities Deferred Credits and Other Liabilities, Noncurrent AOCI Attributable to Parent, Net of Tax [Roll Forward] AOCI Attributable to Parent, Net of Tax [Roll Forward] Customer [Axis] Customer [Axis] Regulatory adjustment Accumulated Defined Benefit Plans Adjustment, Regulartory Adjustment, Attributable to Parent [Member] Accumulated Defined Benefit Plans Adjustment, Regulartory Adjustment, Attributable to Parent [Member] Centuri property, equipment, and intangibles Property Plant Equipment And Intangible Assets Gross Property plant equipment and intangible assets gross. Income Taxes Income Tax, Policy [Policy Text Block] Notes, 4.45%, due 2020 Debentures Notes Four Point Four Five Percentage Due Two Thousand And Twenty [Member] Debentures Notes Four Point Four Five Percentage Due Two Thousand And Twenty [Member] Common stock, par (in USD per share) Common Stock, Par or Stated Value Per Share Transportation Transportation [Member] Transportation. Total deferred income taxes and other credits Other Liabilities, Noncurrent Deferred income taxes Deferred Income Tax Assets, Net $400 Million Credit Facility $400 Million Credit Facility [Member] $400 Million Credit Facility [Member] Other Payments for (Proceeds from) Other Investing Activities Principal payments on finance lease obligations Finance Lease, Principal Payments Effects of currency translation on cash and cash equivalents Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Segment Reconciling Items Segment Reconciling Items [Member] Utility infrastructure services revenues Revenue from contracts with customers Revenue from Contract with Customer, Excluding Assessed Tax 2008 Series A, due 2038 Variable Rate Bonds Two Thousand And Eight Series A- Due Two Thousand And Thirty Eight [Member] Variable Rate Bonds Two Thousand and Eight Series A Due Two Thousand and Thirty Eight [Member] Foreign transaction gain (loss) Foreign Currency Transaction Gain (Loss), Realized Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Inventory [Axis] Inventory [Axis] Statement [Line Items] Statement [Line Items] Deferred income taxes Increase (Decrease) in Deferred Income Taxes Accrued interest Interest Payable, Current Statement [Table] Statement [Table] Statistical Measurement [Axis] Statistical Measurement [Axis] Interest cost Defined Benefit Plan, Interest Cost Credit Facility [Axis] Credit Facility [Axis] Interest income Interest Income, Other Utility plant: Public Utilities, Property, Plant and Equipment, Net [Abstract] Total capitalization Capitalization, Long-term Debt and Equity Accrued utility revenue Accrued Utility Revenue Accrued utility revenue. Entity Small Business Entity Small Business Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Related Tax Effects Allocated to Each Component of Other Comprehensive Income (Loss) Schedule Of Related Tax Effects Allocated To Components Of Other Comprehensive Income (Loss) [Table Text Block] Related tax effects of defined benefit pension plans and designated hedging activities reclassifications and amounts arising during the period included in other comprehensive income (loss). Summary of Information about Receivables, Revenue Earned on Contracts in Progress in Excess of Billings, Which are Included Within Accounts Receivable, Net of Allowances, and Amounts Billed in Excess of Revenue Earned on Contracts Schedule of information about receivables, revenue earned on contracts in progress in excess of billings, and amounts billed in excess of revenue earned on contracts [Table Text Block] Schedule of information about receivables, revenue earned on contracts in progress in excess of billings, and amounts billed in excess of revenue earned on contracts. Unamortized debt issuance costs Unamortized Debt Issuance Expense Debt Debt Disclosure [Text Block] Contracts receivable, gross Accounts Receivable, before Allowance for Credit Loss Revenue earned on contracts in progress in excess of billings Revenue earned on contracts in progress in excess of billings Revenue earned on contracts in progress in excess of billings. Issuance of common stock, net Net proceeds Proceeds from Issuance of Common Stock Goodwill [Roll Forward] Goodwill [Roll Forward] Derivative, Number of Instruments Held Derivative, Number of Instruments Held Amendment Flag Amendment Flag Schedule of Earnings Per Share, Basic and Diluted Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Time and materials contracts Time-and-materials Contract [Member] Notes, 4.15%, due 2049 Debentures Notes 4.15%, Due 2049 [Member] Debentures Notes 4.15%, Due 2049 Effect of dilutive securities: Dilutive Securities, Effect on Basic Earnings Per Share [Abstract] Corporate and administrative Corporate, Non-Segment [Member] Line of credit facility Borrowings outstanding under facility Long-term Line of Credit Qualified Retirement Plan Other Pension Plan [Member] Fair Value Measurements Fair Value Measurement, Policy [Policy Text Block] Gross proceeds Proceeds From Issuance Of Common Stock, Gross Proceeds From Issuance Of Common Stock, Gross Amounts reclassified into net income FSIRS amounts reclassified to net income, net of tax Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Other comprehensive income (loss), net of tax Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract] Deferred income taxes and other credits: Other Liabilities, Noncurrent [Abstract] Entity Central Index Key Entity Central Index Key Residential Residential [Member] Residential. Accounts Receivable, net of allowances Receivables, Trade and Other Accounts Receivable, Allowance for Doubtful Accounts, Policy [Policy Text Block] Expected return on plan assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Fair Value Measurement [Domain] Fair Value Measurement [Domain] Net cost of gas sold Utilities Operating Expense, Gas and Petroleum Purchased Derivatives Derivatives, Policy [Policy Text Block] Income taxes receivable, net Income Taxes Receivable, Current Common stock issued (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period Reclassification from AOCI, tax Reclassification from AOCI, Current Period, Tax Forward-starting interest rate swaps (“FSIRS”): Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax [Abstract] Segments [Domain] Segments [Domain] Net actuarial gain arising during period, less amortization of unamortized benefit plan cost, net of tax Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax Other Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax Other Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding CASH FLOW FROM FINANCING ACTIVITIES: Net Cash Provided by (Used in) Financing Activities [Abstract] Amount of FSIRS existing AOCI losses expected to reclassified income in next twelve months Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net Gas plant Public Utilities, Property, Plant and Equipment, Gas Plant Public Utilities, Property, Plant and Equipment, Gas Plant Movement In Redeemable Noncontrolling Interest [Roll Forward] Movement In Redeemable Noncontrolling Interest [Roll Forward] Movement In Redeemable Noncontrolling Interest [Roll Forward] Deferred charges and other assets Other Assets, Noncurrent Notes, 3.875%, due 2022 Debentures Notes Three Point Eight Seven Five Percentage Due Two Thousand And Twenty Two [Member] Debentures Notes Three Point Eight Seven Five Percentage Due Two Thousand And Twenty Two [Member] Plan Name [Axis] Plan Name [Axis] Segment Information Segment Reporting Disclosure [Text Block] Common stock issuances Common stock issued, amount Stock Issued During Period, Value, New Issues Money market fund investments Cash and Cash Equivalents, Fair Value Disclosure Total assets Assets Total noncurrent assets Assets, Noncurrent, Other than Noncurrent Investments and Property, Plant and Equipment Title of 12(b) Security Title of 12(b) Security Beginning balance, attributable to parent, before tax Ending balance, attributable to parent, before tax Stockholders' Equity Attributable To Parent, Before Tax Stockholders' Equity Attributable To Parent, Before Tax Contract with Customer, Basis of Pricing [Axis] Contract with Customer, Basis of Pricing [Axis] Amortization of prior service costs Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Income taxes payable, net Accrued Income Taxes, Current Total operating revenues Regulated and Unregulated Operating Revenue Net interest deductions Interest Expense Revolving credit facility and commercial paper Revolving Credit Facility And Commercial Paper [Member] Revolving Credit Facility And Commercial Paper [Member] Gas infrastructure services Replacement Gas Construction [Member] Replacement gas construction. Ownership percentage by noncontrolling owners Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners Deferred purchased gas costs Deferred Gas Cost Product and Service [Axis] Product and Service [Axis] Amortization of prior service cost Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member] Amount Recognized Before Income Tax in Accumulated Other Comprehensive Income Schedule of Amounts Recognized in Other Comprehensive Income (Loss) [Table Text Block] Debt instrument discount rate Debt Instrument Discount Rate Debt Instrument Discount Rate Centuri other debt obligations Other Long-term Debt Retirement Plan Type [Axis] Retirement Plan Type [Axis] Line of credit facility, fair value Lines of Credit, Fair Value Disclosure Equipment Loans Loans [Member] Change in contract liability, revenue recognized Contract with Customer, Liability, Revenue Recognized Summary of Redeemable Noncontrolling Interest Redeemable Noncontrolling Interest [Table Text Block] Beginning balance, attributable to parent, tax Ending balance, attributable to parent, tax Stockholders' Equity Attributable To Parent, Tax Stockholders' Equity Attributable To Parent, Tax Other property Property, Plant and Equipment, Other, Net Foreign currency exchange translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax, Portion Attributable to Parent Sale of common stock available for sale (in shares) Sale Of Stock, Common Stock Available For Sale Sale Of Stock, Common Stock Available For Sale Number of states in which entity operates Number of States in which Entity Operates Accounts payable Increase (Decrease) in Accounts Payable Intercompany Transactions Intercompany Profit to Regulated Affiliates, Policy [Policy Text Block] Debt Instrument [Axis] Debt Instrument [Axis] Additional paid-in capital Additional Paid-in Capital [Member] Operating Segments Operating Segments [Member] Beginning balance, before tax Ending balance, before tax Stockholders' Equity, Including Portion Attributable To Noncontrolling Interest, Before Tax Stockholders' Equity, Including Portion Attributable To Noncontrolling Interest, Before Tax Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Class of Stock [Line Items] Class of Stock [Line Items] Restricted Stock/Unit Plan, and Management Incentive Plan Restricted Stock/Unit Plan, And Management Incentive Plan [Member] Restricted Stock/Unit Plan, And Management Incentive Plan [Member] Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue from Contract with Customer [Abstract] Revenue from Contract with Customer [Abstract] Other receivables Other Receivables Common stock, outstanding (in shares) Beginning balance (in shares) Ending balance (in shares) Common Stock, Shares, Outstanding Less: accumulated depreciation Public Utilities, Property, Plant and Equipment, Accumulated Depreciation Entity Information [Line Items] Entity Information [Line Items] Schedule of Goodwill [Table] Schedule of Goodwill [Table] Income (loss) before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Net actuarial gain/(loss) Amortization of net actuarial loss Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member] Acquisition of businesses, net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired Common stock, authorized (in shares) Common Stock, Shares Authorized Accounts Receivable for Services Accounts Receivable For Services [Table Text Block] Accounts Receivable For Services Table Text Block. Schedule of Segment Reporting Information Schedule of Segment Reporting Information, by Segment [Table Text Block] Defined benefit pension plans: Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax [Abstract] Gas pipe materials and operating supplies Materials, Supplies, and Other Goodwill Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block] Market Value Estimate of Fair Value Measurement [Member] Income Statement [Abstract] Income Statement [Abstract] Accumulated other comprehensive loss AOCI Attributable to Parent AOCI Attributable to Parent [Member] 8% Series, due 2026 Debentures Eight Percentage Series Due Two Thousand And Twenty Six [Member] Debentures Eight Percentage Series Due Two Thousand And Twenty Six [Member] Change in COLI policies Life Insurance, Corporate or Bank Owned, Change in Value Net defined benefit pension plans Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Current assets: Assets, Current [Abstract] Nature of Operations Nature Of Operations [Policy Text Block] Nature Of Operations [Policy Text Block] Comprehensive income attributable to Southwest Gas Holdings, Inc. Comprehensive Income (Loss), Net of Tax, Attributable to Parent Unamortized discount and debt issuance costs Debt Instrument Unamortized Discount And Debt Issuance Costs Debt instrument unamortized discount and debt issuance costs. Construction expenditures and property additions Payments to Acquire Property, Plant, and Equipment City Area Code City Area Code Legal Entity [Axis] Legal Entity [Axis] Electric power infrastructure services New Gas Construction [Member] New Gas Construction [Member] Consolidation Items [Domain] Consolidation Items [Domain] Dividend Reinvestment and Stock Purchase Plan Dividend Reinvestment And Stock Purchase Plan [Member] Dividend Reinvestment And Stock Purchase Plan [Member] Document Period End Date Document Period End Date Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Centuri accounts receivable for services provided to Southwest Due from Related Parties, Current Master services agreement Master Services Agreement [Member] Master Services Agreement [Member] Net income (loss) Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Summary of Revenue Disaggregated by Service Type and Contract Type Disaggregation of Revenue [Table Text Block] Reclassification from AOCI, net of tax Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Other comprehensive income (loss) before reclassifications, tax Other Comprehensive Income (Loss) before Reclassifications, Tax Other comprehensive income (loss) before reclassifications, before tax Other Comprehensive Income (Loss), before Reclassifications, before Tax Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Changes in undistributed stock compensation Share-based Payment Arrangement, Noncash Expense Change in short-term debt Proceeds from (Repayments of) Short-term Debt Entity [Domain] Entity [Domain] Other Proceeds from (Payments for) Other Financing Activities Withholding remittance - share-based compensation Payment, Tax Withholding, Share-based Payment Arrangement Unsecured debt Unsecured Debt Cover [Abstract] Cover [Abstract] Alternative base rate Base Rate [Member] Linetec Linetec Services, LLC [Member] Linetec Services, LLC [Member] Other comprehensive income (loss) before reclassifications, net of tax Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Prior service cost Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax Schedule of Other Property and Investments Schedule Of Other Property And Investments [Table Text Block] Schedule Of Other Property And Investments [Table Text Block] Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] Long-term debt Long-term debt Long-term Debt Goodwill [Line Items] Goodwill [Line Items] Contributions from parent Proceeds from Contributions from Parent Service cost Defined Benefit Plan, Service Cost Utility infrastructure services expenses Cost of Goods and Services Sold Total operating expenses Costs and Expenses Equity Components [Axis] Equity Components [Axis] Net forward-starting interest rate swaps Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax Medium-term notes, 6.76% series, due 2027 Debentures Medium Term Notes Six Point Seven Six Percentage Series Due Two Thousand And Twenty Seven [Member] Debentures Medium Term Notes Six Point Seven Six Percentage Series Due Two Thousand and Twenty Seven [Member] Construction work in progress Public Utilities, Property, Plant and Equipment, Construction Work in Progress Notes, 4.875%, due 2043 Debentures Notes Four Point Eight Seven Five Percentage Due Two Thousand And Forty Three [Member] Debentures Notes Four Point Eight Seven Five Percentage Due Two Thousand And Forty Three [Member] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Minimum Minimum [Member] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Miscellaneous income and (expense) Miscellaneous Income Expense Miscellaneous income (expense). Net income attributable to noncontrolling interest Net Income (Loss) Attributable to Noncontrolling Interest Amortization of net actuarial loss Defined Benefit Plan, Amortization of Gain (Loss) Entity Interactive Data Current Entity Interactive Data Current Net periodic benefit cost Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Operating revenues: Revenues [Abstract] CASH FLOW FROM OPERATING ACTIVITIES: Net Cash Provided by (Used in) Operating Activities [Abstract] Centuri Centuri Group, Inc. [Member] Centuri Group, Inc. [Member] Commitment fee percentage Line of Credit Facility, Commitment Fee Percentage Interest Rate Swap Interest Rate Swap [Member] Customer [Domain] Customer [Domain] Additional paid-in capital Additional Paid in Capital, Common Stock Entity Registrant Name Entity Registrant Name Gas Pipe Materials and Supplies Gas Pipe Inventory And Operating Supplies [Member] Gas pipe inventory and operating supplies. Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Changes in other liabilities and deferred credits Increase (Decrease) in Other Operating Liabilities Other property and investments Total Other Property And Investments Aggregate carrying amount, as of the balance sheet date, of other property and investments not separately presented elsewhere in the balance sheet. Centuri other debt obligations Centuri Other Debt Obligations [Member] Centuri Other Debt Obligations [Member] Equity AFUDC Increase (Decrease) in Allowance for Equity Funds Used During Construction Number of reportable segments Number of Reportable Segments Retirement Plan Type [Domain] Retirement Plan Type [Domain] Other income (deductions) Other Nonoperating Income (Expense) [Abstract] Condensed Income Statements, Captions [Line Items] Condensed Income Statements, Captions [Line Items] Dividends paid Payments of Ordinary Dividends, Common Stock Consolidation Items [Axis] Consolidation Items [Axis] Utility Infrastructure Services Utility Infrastructure Services Segment [Member] Utility Infrastructure Services Segment [Member] Net utility plant Public Utilities, Property, Plant and Equipment, Net Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Goodwill impairment Goodwill, Impairment Loss Accounts receivable, net of allowances Accounts Receivable, after Allowance for Credit Loss, Current Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Noncontrolling Interest [Abstract] Noncontrolling Interest [Abstract] Other Other Construction [Member] Other construction. Common Stock Common Stock Disclosure [Text Block] Common Stock Disclosure [Text Block] Sale of Stock [Axis] Sale of Stock [Axis] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Goodwill Goodwill, beginning balance Goodwill, ending balance Goodwill Payable to parent Due to Affiliate, Current Document Transition Report Document Transition Report Tax-exempt Series A, due 2028 Variable Rate Bonds Tax Exempt Series A- Due Two Thousand And Twenty Eight [Member] Variable Rate Bonds Tax Exempt Series Due Two Thousand and Twenty Eight [Member] Large commercial Large Commercial [Member] Large commercial. Other income and (expenses): Nonoperating Income (Expense) [Abstract] Dividends declared per share (in USD per share) Common Stock, Dividends, Per Share, Declared Amortization of prior service cost Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, after Tax Debt instrument, face amount Debt Instrument, Face Amount Document Quarterly Report Document Quarterly Report Schedule of Goodwill Schedule of Goodwill [Table Text Block] Equity [Abstract] Equity [Abstract] Less: amount recognized in regulatory assets Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Amount Recognized Regulatory Assets, Before Tax Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Amount Recognized Regulatory Assets, Before Tax Customer deposits Contract with Customer, Liability, Current Entities [Table] Entities [Table] Credit Facility [Domain] Credit Facility [Domain] Diluted (in shares) Weighted average diluted shares (in shares) Weighted Average Number of Shares Outstanding, Diluted Basic (in USD per share) Earnings Per Share, Basic Entity File Number Entity File Number Debt Disclosure [Abstract] Debt Disclosure [Abstract] Accrued general taxes Accrual for Taxes Other than Income Taxes, Current SERP Supplemental Employee Retirement Plan [Member] Weighted average price per share Common Stock Weighted Average Issue Price Per Share Common stock weighted average issue price per share. Significant Accounting Policies [Table] Significant Accounting Policies [Table] Significant Accounting Policies [Table] Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities Retirement of long-term debt Repayments of Long-term Debt Dividends declared Dividends, Common Stock Prior service cost Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, Prior Service Cost (Credit), before Tax Transaction price allocated to unsatisfied performance obligations of contracts Revenue, Remaining Performance Obligation, Amount Debt secured by assets Debt Instrument, Collateral Amount Balance Sheet Location [Axis] Balance Sheet Location [Axis] Common stock, $1 par (authorized - 120,000,000 shares; issued and outstanding - 56,459,346 and 55,007,433 shares) Common Stock, Value, Issued Sale of stock, maximum amount of stock allowed to be offered Sale Of Stock, Maxumum Amount Of Stock Allowed To Be Offered Sale Of Stock, Maxumum Amount Of Stock Allowed To Be Offered Document Fiscal Year Focus Document Fiscal Year Focus Small commercial Small Commercial [Member] Small commercial. Noncurrent assets: Assets, Noncurrent [Abstract] Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Axis] Current maturities of long-term debt Less: current maturities Long-term Debt, Current Maturities Entity Current Reporting Status Entity Current Reporting Status Retirement Benefits [Abstract] Retirement Benefits [Abstract] Earnings Per Share Earnings Per Share, Policy [Policy Text Block] Comprehensive income (loss) Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Accrued utility revenue Increase (Decrease) in Contract with Customer, Asset Long-term Debt, Current and Noncurrent Abstract Long-term Debt, Current and Noncurrent [Abstract] Short-term debt Short term borrowings outstanding Short-term Debt CASH FLOW FROM INVESTING ACTIVITIES: Net Cash Provided by (Used in) Investing Activities [Abstract] Common stock, issued (in shares) Common Stock, Shares, Issued Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Operations and maintenance Utilities Operating Expense, Maintenance and Operations Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Centuri secured revolving credit facility Centuri Secured Revolving Credit Facility [Member] Centuri secured revolving credit facility. Long-term debt, less current maturities Long-term debt, less current maturities Long-term Debt, Excluding Current Maturities Segment Reporting [Abstract] Segment Reporting [Abstract] Contracts receivable, net Contracts receivable, net Accounts Receivable, after Allowance for Credit Loss Contract with Customer, Basis of Pricing [Domain] Contract with Customer, Basis of Pricing [Domain] Other components of net periodic benefit cost Defined Benefit Plan, Actuarial Gain (Loss), Immediate Recognition as Component in Net Periodic Benefit (Cost) Credit Accounts receivable, net of allowances Increase (Decrease) in Accounts Receivable Southwest Gas Corporation Southwest Gas Corporation [Member] Southwest gas corporation. Debt Instrument [Line Items] Debt Instrument [Line Items] Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Total equity Beginning balance, attributable to parent Ending balance, attributable to parent Stockholders' Equity Attributable to Parent Less: agent commissions Payments of Stock Issuance Costs Total capitalization and liabilities Liabilities and Equity Deferred purchased gas costs Deferred Gas Purchases, Current Accumulated other comprehensive loss, net Accumulated Other Comprehensive Income (Loss), Net of Tax Entity Address, City or Town Entity Address, City or Town Notes payable Notes Payable Centuri term loan facility Centuri Term Loan Facility [Member] Centuri term loan facility. Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Commercial Paper Program Commercial Paper Program [Member] Commercial Paper Program [Member] Fixed price contracts Fixed-price Contract [Member] Southwest Gas Holdings, Inc. Parent [Member] $100 Million Credit Facility $100 Million Credit Facility [Member] $100 Million Credit Facility [Member] Gains on sale of equipment Gain (Loss) on Disposition of Property Plant Equipment Capitalization: Capitalization, Long-term Debt and Equity [Abstract] Equity Component [Domain] Equity Component [Domain] Alternative revenue program revenues (deferrals) Alternative Revenue Program Revenues (Deferrals) Alternative revenue program revenues (deferrals). Entity Tax Identification Number Entity Tax Identification Number Net income attributable to Southwest Gas Holdings, Inc. Segment net income (loss) Net Income (Loss) Attributable to Parent Southwest Gas Holdings Southwest Gas Holdings [Member] Southwest Gas Holdings Changes in current assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Other current liabilities Other Liabilities, Current FSIRS AOCI, Derivative Qualifying as Hedge, Excluded Component, Parent [Member] Amounts billed in excess of revenue earned on contracts Amounts billed in excess of revenue earned on contracts Amounts billed in excess of revenue earned on contracts. LIBOR London Interbank Offered Rate (LIBOR) [Member] Total other comprehensive income (loss), net of tax Other Comprehensive Income (Loss), Net of Tax Other current assets and liabilities Increase (Decrease) in Other Current Assets and Liabilities, Net Background, Organization, and Summary of Significant Accounting Policies Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block] Taxes other than income taxes Taxes, Miscellaneous Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Total current assets Assets, Current Current Fiscal Year End Date Current Fiscal Year End Date Medium-term notes, 7.92% series, due 2027 Debentures Medium Term Notes Seven Point Nine Two Percentage Series Due Two Thousand And Twenty Seven [Member] Debentures Medium Term Notes Seven Point Nine Two Percentage Series Due Two Thousand and Twenty Seven [Member] Comprehensive income attributable to noncontrolling interest Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Earnings per share: Earnings Per Share [Abstract] Defined Benefit Plans Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Change in ownership of noncontrolling interest Noncontrolling Interest, Increase from Subsidiary Equity Issuance Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Document Fiscal Period Focus Document Fiscal Period Focus Accrued taxes Increase (Decrease) In Accrued Taxes Increase (Decrease) In Accrued Taxes Amortization of net actuarial loss Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax Deferred purchased gas costs Increase (Decrease) in Deferred Gas Cost Regulatory adjustment Other Comprehensive Income Defined Benefit Plans Regulatory Adjustment Net of Tax The portion of the pension, PBOP, and SERP liability that is recoverable in rates net-of-tax. Notes, 3.7%, due 2028 Debentures Notes Three Point Seven Percentage Due Two Thousand And Twenty Eight [Member] Debentures notes three point seven percentage due two thousand and twenty eight. SUPPLEMENTAL INFORMATION: Supplemental Cash Flow Information [Abstract] Debt redemption price, percentage Debt Instrument, Redemption Price, Percentage Entity Filer Category Entity Filer Category Common Stock Common Stock [Member] Foreign Currency Items Accumulated Foreign Currency Adjustment Attributable to Parent [Member] Bid contract Bid Contract [Member] Bid contract. Product and Service [Domain] Product and Service [Domain] Net income attributable to redeemable noncontrolling interest Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Inventory [Domain] Inventory [Domain] Equity Shelf Program Equity Shelf Program [Member] Equity Shelf Program [Member] Other comprehensive income (loss), tax Other Comprehensive Income (Loss), Tax Common stock issuances (in shares) Number of shares sold (in shares) Stock Issued During Period, Shares, New Issues Recognized in AOCI Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax Debt instrument interest rate Debt Instrument, Interest Rate, Stated Percentage Secured Revolving Credit Facility and Term Loan Secured Revolving Credit And Term Loan Facility [Member] Secured Revolving Credit And Term Loan Facility [Member] Dividends declared but not yet paid Dividends Payable, Current Transaction price allocated to unsatisfied performance obligations of contracts, period Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Pooled Funds and Mutual Funds Money Market Funds [Member] Centuri accumulated provision for depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Net actuarial loss Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax Change in cash and cash equivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Total other income and (expenses) Nonoperating Income (Expense) Restricted stock units (in shares) Incremental Common Shares Attributable to Dilutive Effect of Nonvested Shares with Forfeitable Dividends Basis of Presentation Basis of Accounting, Policy [Policy Text Block] 2003 Series A, due 2038 Variable Rate Bonds Two Thousand And Three Series A- Due Two Thousand And Thirty Eight [Member] Variable Rate Bonds Two Thousand and Three Series A Due Two Thousand and Thirty Eight [Member] Beginning balance, tax Ending balance, tax Stockholders' Equity, Including Portion Attributable To Noncontrolling Interest, Tax Stockholders' Equity, Including Portion Attributable To Noncontrolling Interest, Tax Basic (in shares) Weighted average basic shares (in shares) Weighted Average Number of Shares Outstanding, Basic Deferred income taxes and investment tax credits, net Deferred Income Taxes And Unamortized Investment Tax Credits Represents deferred tax liabilities, which result from applying the applicable tax rate to net taxable temporary differences pertaining to each jurisdiction to which the entity is obligated to pay income tax. Additionally, this element includes the future effects on income taxes attributable to investment tax credits. Applicable margin Debt Instrument, Basis Spread on Variable Rate Operating expenses: Costs and Expenses [Abstract] Ownership [Axis] Ownership [Axis] Foreign currency translation adjustments Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Sale of Stock [Domain] Sale of Stock [Domain] Ownership [Domain] Ownership [Domain] Carrying Amount Reported Value Measurement [Member] Plan Name [Domain] Plan Name [Domain] Revenue Revenue from Contract with Customer [Text Block] Interest paid, net of amounts capitalized Interest Paid, Excluding Capitalized Interest, Operating Activities Number of performance share units granted (in shares) Number Of Performance Share Units Granted Number Of Performance Share Units Granted. Beginning balance Ending balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Revenues Revenues Unsecured debt, fair value Long-term Debt, Fair Value Cash and Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Income tax expense (benefit) Income Tax Expense (Benefit) Income taxes paid (received), net Income Taxes Paid, Net Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Redemption value adjustments Redemption value adjustment Noncontrolling Interest, Change in Redemption Value Diluted (in USD per share) Earnings Per Share, Diluted Local Phone Number Local Phone Number Reclassification from AOCI, before Tax Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Line of credit designated as long term debt Line Of Credit Facility Amount Classified As Long Term Debt Line Of Credit Facility, Amount Classified As Long-Term Debt Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt Schedule of Long-term Debt Instruments [Table Text Block] Entity Address, Address Line One Entity Address, Address Line One Entity Address, Address Line Two Entity Address, Address Line Two Debentures Debentures [Member] Debentures [Member] Changes in deferred charges and other assets Increase (Decrease) in Other Operating Assets Entity Emerging Growth Company Entity Emerging Growth Company Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Gas operating revenues Total Gas operating revenues Regulated Operating Revenue, Gas Threshold period after inactivation for write-off of accounts receivable Threshold Period Past Due for Write-off of Trade Accounts Receivable Credit facility maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Medium-term notes, 7.78% series, due 2022 Debentures Medium Term Notes Seven Point Seven Eight Percentage Series Due Two Thousand And Twenty Two [Member] Debentures Medium Term Notes Seven Point Seven Eight Percentage Series Due Two Thousand and Twenty Two [Member] Prepaid and other current assets Prepaid Expenses and Other Current Assets [Member] Net income Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest Maximum Maximum [Member] Industrial development revenue bonds Industrial Development Revenue Bonds [Member] Industrial Development Revenue Bonds [Member] Noncontrolling interest Noncontrolling Interest [Member] Notes, 3.8%, due 2046 Debentures Notes Three Point Eight Percentage Due Two Thousand And Forty Six [Member] Debentures notes three point eight percentage due two thousand and forty six. Retained earnings Retained Earnings [Member] 2009 Series A, due 2039 Variable Rate Bonds Two Thousand And Nine Series A- Due Two Thousand And Thirty Nine [Member] Variable Rate Bonds Two Thousand and Nine Series A Due Two Thousand and Thirty Nine [Member] Notes, 6.1%, due 2041 Debentures Notes Six Point One Percentage Due Two Thousand And Forty One [Member] Debentures Notes Six Point One Percentage Due Two Thousand And Forty One [Member] Measurement Basis [Axis] Measurement Basis [Axis] Management Incentive Plan shares (in shares) Incremental Common Shares Attributable to Dilutive Effect of Equity Forward Agreements Billed on completed contracts and contracts in progress Billed on completed contracts and contracts in progress Billed on completed contracts and contracts in progress. Effective income tax rate Effective Income Tax Rate Reconciliation, Percent Schedule of Net Periodic Benefit Costs Schedule of Net Benefit Costs [Table Text Block] Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Allowance for doubtful accounts Accounts Receivable, Allowance for Credit Loss Other revenues (1) Other Revenue Other Revenue PBOP Other Postretirement Benefits Plan [Member] Trading Symbol Trading Symbol Prior service cost Accumulated Defined Benefit Plans Adjustment, Prior Service Cost, Attributable to Parent [Member] Accumulated Defined Benefit Plans Adjustment, Prior Service Cost, Attributable to Parent [Member] Weighted average shares: Weighted Average Number of Shares Outstanding Reconciliation [Abstract] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Net cash surrender value of COLI policies Cash Surrender Value of Life Insurance Equity AFUDC Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity Notes payable, fair value disclosure Notes Payable, Fair Value Disclosure Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Natural Gas Operations Natural Gas Operations [Member] Natural Gas Operations [Member] Current liabilities: Liabilities, Current [Abstract] Redeemable noncontrolling interest Redeemable noncontrolling interest, beginning balance Redeemable noncontrolling interest, ending balance Redeemable Noncontrolling Interest, Equity, Carrying Amount Entity Shell Company Entity Shell Company Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Recent Accounting Standards Updates New Accounting Pronouncements, Policy [Policy Text Block] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Contributions from Southwest Gas Holdings, Inc. Adjustments To Additional Paid In Capital Contributions From Parent Adjustments to additional paid in capital contributions from parent.