Organization, Consolidation and Presentation of Financial Statements [Abstract] Significant Accounting Policies [Table] Significant Accounting Policies [Table] Significant Accounting Policies [Table] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Centuri Centuri Group, Inc. [Member] Centuri Group, Inc. [Member] Southwest Gas Corporation Southwest Gas Corporation [Member] Southwest gas corporation. Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] Pooled Funds and Mutual Funds Money Market Funds [Member] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Linetec Linetec Services, LLC [Member] Linetec Services, LLC [Member] Inventory [Axis] Inventory [Axis] Inventory [Domain] Inventory [Domain] Gas Pipe Materials and Supplies Gas Pipe Inventory And Operating Supplies [Member] Gas pipe inventory and operating supplies. Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Prepaid and other current assets Prepaid Expenses and Other Current Assets [Member] Ownership [Axis] Ownership [Axis] Ownership [Domain] Ownership [Domain] Significant Accounting Policies [Line Items] Significant Accounting Policies [Line Items] Significant Accounting Policies [Line Items] Money market fund investments Cash and Cash Equivalents, Fair Value Disclosure Number of states in which entity operates Number of States in which Entity Operates Threshold period after inactivation for write-off of accounts receivable Threshold Period Past Due for Write-off of Trade Accounts Receivable Gas pipe materials and operating supplies Materials, Supplies, and Other Prepaid and other current assets Regulatory Assets, Current Goodwill impairment Goodwill, Impairment Loss Dividends declared but not yet paid Dividends Payable, Current Ownership percentage by noncontrolling owners Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners Schedule of Goodwill [Table] Schedule of Goodwill [Table] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] Natural Gas Operations Natural Gas Operations [Member] Natural Gas Operations [Member] Utility Infrastructure Services Utility Infrastructure Services Segment [Member] Utility Infrastructure Services Segment [Member] Goodwill [Line Items] Goodwill [Line Items] Goodwill [Roll Forward] Goodwill [Roll Forward] Goodwill, beginning balance Goodwill Foreign currency translation adjustment Goodwill, Foreign Currency Translation Gain (Loss) Goodwill, ending balance Revenue from Contract with Customer [Abstract] Contracts receivable, net Accounts Receivable, after 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. 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. Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Product and Service [Axis] Product and Service [Axis] Product and Service [Domain] Product and Service [Domain] Gas infrastructure services Replacement Gas Construction [Member] Replacement gas construction. Electric power infrastructure services New Gas Construction [Member] New Gas Construction [Member] Other Other Construction [Member] Other construction. Contract with Customer, Basis of Pricing [Axis] Contract with Customer, Basis of Pricing [Axis] Contract with Customer, Basis of Pricing [Domain] Contract with Customer, Basis of Pricing [Domain] Master services agreement Master Services Agreement [Member] Master Services Agreement [Member] Bid contract Bid Contract [Member] Bid contract. Unit price contracts Unit Priced Contracts [Member] Unit priced contracts. Fixed price contracts Fixed-price Contract [Member] Time and materials contracts Time-and-materials Contract [Member] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Revenue from contracts with customers Revenue from Contract with Customer, Excluding Assessed Tax Noncontrolling Interest [Abstract] Movement In Redeemable Noncontrolling Interest [Roll Forward] Movement In Redeemable Noncontrolling Interest [Roll Forward] Movement In Redeemable Noncontrolling Interest [Roll Forward] Balance, December 31, 2019 Redeemable Noncontrolling Interest, Equity, Carrying Amount Net income attributable to redeemable noncontrolling interest Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Balance, March 31, 2020 Billed on completed contracts and contracts in progress Billed on completed contracts and contracts in progress Billed on completed contracts and contracts in progress. Other receivables Other Receivables Contracts receivable, gross Accounts Receivable, before Allowance for Credit Loss Allowance for doubtful accounts Accounts Receivable, Allowance for Credit Loss Contracts receivable, net Debt Disclosure [Abstract] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Carrying Amount Reported Value Measurement [Member] Market Value Estimate of Fair Value Measurement [Member] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Debentures Debentures [Member] Debentures [Member] Industrial development revenue bonds Industrial Development Revenue Bonds [Member] Industrial Development Revenue Bonds [Member] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] 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] 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] 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] 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] 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. 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. Notes, 4.15%, due 2049 Debentures Notes 4.15%, Due 2049 [Member] Debentures Notes 4.15%, Due 2049 [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] 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] 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] 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] Revolving credit facility and commercial paper Revolving Credit Facility And Commercial Paper [Member] Revolving Credit Facility And Commercial Paper [Member] 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] 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] 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] 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] Centuri term loan facility Centuri Term Loan Facility [Member] Centuri term loan facility. Centuri other debt obligations Centuri Other Debt Obligations [Member] Centuri Other Debt Obligations [Member] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Centuri secured revolving credit facility Centuri Secured Revolving Credit Facility [Member] Centuri secured revolving credit facility. Debt Instrument [Line Items] Debt Instrument [Line Items] Notes payable Notes Payable Notes payable, fair value disclosure Notes Payable, Fair Value Disclosure Unamortized discount and debt issuance costs Debt Instrument Unamortized Discount And Debt Issuance Costs Debt instrument unamortized discount and debt issuance costs. Line of credit facility Long-term Line of Credit Line of credit facility, fair value Lines of Credit, Fair Value Disclosure Unsecured debt Unsecured Debt Unsecured debt, fair value Long-term Debt, Fair Value Less: current maturities Long-term Debt, Current Maturities Long-term debt, less current maturities Long-term Debt, Excluding Current Maturities Unamortized debt issuance costs Unamortized Debt Issuance Expense Long-term Debt, Current and Noncurrent Abstract Long-term Debt, Current and Noncurrent [Abstract] Long-term debt Long-term Debt Long-term debt, less current maturities Centuri secured revolving credit facility Secured Debt Centuri other debt obligations Other Long-term Debt Debt instrument interest rate Debt Instrument, Interest Rate, Stated Percentage Statement of Cash Flows [Abstract] Statement [Table] Statement [Table] Statement [Line Items] Statement [Line Items] CASH FLOW FROM OPERATING ACTIVITIES: Net Cash Provided by (Used in) Operating Activities [Abstract] Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest 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] Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Deferred income taxes Increase (Decrease) in Deferred Income Taxes Changes in current assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Accounts receivable, net of allowances Increase (Decrease) in Accounts Receivable Accrued utility revenue Increase (Decrease) in Contract with Customer, Asset Deferred purchased gas costs Increase (Decrease) in Deferred Gas Cost Accounts payable Increase (Decrease) in Accounts Payable Accrued taxes Increase (Decrease) In Accrued Taxes Increase (Decrease) In Accrued Taxes Other current assets and liabilities Increase (Decrease) in Other Current Assets and Liabilities, Net Gains on sale of equipment Gain (Loss) on Disposition of Property Plant Equipment Changes in undistributed stock compensation Share-based Payment Arrangement, Noncash Expense Equity AFUDC Increase (Decrease) in Allowance for Equity Funds Used During Construction Changes in deferred charges and other assets Increase (Decrease) in Other Operating Assets Changes in other liabilities and deferred credits Increase (Decrease) in Other Operating Liabilities Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities CASH FLOW FROM INVESTING ACTIVITIES: Net Cash Provided by (Used in) Investing Activities [Abstract] Construction expenditures and property additions Payments to Acquire Property, Plant, and Equipment Acquisition of businesses, net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired Changes in customer advances Changes In Customer Advances, Investing Activities Changes In Customer Advances, Investing Activities Other Payments for (Proceeds from) Other Investing Activities Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities CASH FLOW FROM FINANCING ACTIVITIES: Net Cash Provided by (Used in) Financing Activities [Abstract] Issuance of common stock, net Proceeds from Issuance of Common Stock Contributions from parent Proceeds from Contributions from Parent Dividends paid Payments of Ordinary Dividends, Common Stock Issuance of long-term debt, net Proceeds from Issuance of Long-term Debt Retirement of long-term debt Repayments of Long-term Debt 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 Change in short-term debt Proceeds from (Repayments of) Short-term Debt Principal payments on finance lease obligations Finance Lease, Principal Payments Withholding remittance - share-based compensation Payment, Tax Withholding, Share-based Payment Arrangement Other Proceeds from (Payments for) Other Financing Activities Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities Effects of currency translation on cash and cash equivalents Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Change in cash and cash equivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Cash and cash equivalents at beginning of period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Cash and cash equivalents at end of period SUPPLEMENTAL INFORMATION: Supplemental Cash Flow Information [Abstract] Interest paid, net of amounts capitalized Interest Paid, Excluding Capitalized Interest, Operating Activities Income taxes paid (received), net Income Taxes Paid, Net Segment Reporting [Abstract] Segment Information Segment Reporting Disclosure [Text Block] Statement of Financial Position [Abstract] Common stock, par (in USD per share) Common Stock, Par or Stated Value Per Share Common stock, authorized (in shares) Common Stock, Shares Authorized Common stock, issued (in shares) Common Stock, Shares, Issued Common stock, outstanding (in shares) Common Stock, Shares, Outstanding Equity [Abstract] 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). Rollforward of Accumulated Other Comprehensive Income Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Amount Recognized Before Income Tax in Accumulated Other Comprehensive Income Schedule of Amounts Recognized in Other Comprehensive Income (Loss) [Table Text Block] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Centuri accounts receivable for services provided to Southwest Due from Related Parties, Current Debt Debt Disclosure [Text Block] Retirement Benefits [Abstract] Components of Net Periodic Benefit Cost Compensation and Employee Benefit Plans [Text Block] Common Stock Common Stock Disclosure [Text Block] Common Stock Disclosure [Text Block] 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 Number of reportable segments Number of Reportable Segments Background, Organization, and Summary of Significant Accounting Policies Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Sale of Stock [Axis] Sale of Stock [Axis] Sale of Stock [Domain] Sale of Stock [Domain] Equity Shelf Program Equity Shelf Program [Member] Equity Shelf Program [Member] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] 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] Dividend Reinvestment and Stock Purchase Plan Dividend Reinvestment And Stock Purchase Plan [Member] Dividend Reinvestment And Stock Purchase Plan [Member] Class of Stock [Line Items] Class of Stock [Line Items] 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 Gross proceeds Proceeds From Issuance Of Common Stock, Gross Proceeds From Issuance Of Common Stock, Gross Agent commissions Payments of Stock Issuance Costs Net proceeds to company Number of shares sold (in shares) Stock Issued During Period, Shares, New Issues Weighted average price per share Common Stock Weighted Average Issue Price Per Share Common stock weighted average issue price per share. Sale of stock, common stock available for sale Sale Of Stock, Common Stock Available For Sale Sale Of Stock, Common Stock Available For Sale Common stock issued (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period Common stock issued, amount Stock Issued During Period, Value, New Issues Schedule of Common Stock Activity Schedule Of Common Stock Activity [Table Text Block] Schedule Of Common Stock Activity [Table Text Block] Nature of Operations Nature Of Operations [Policy Text Block] Nature Of Operations [Policy Text Block] Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Fair Value Measurements Fair Value Measurement, Policy [Policy Text Block] Cash and Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Intercompany Transactions Intercompany Profit to Regulated Affiliates, Policy [Policy Text Block] Accounts Receivable, net of allowances Receivables, Trade and Other Accounts Receivable, Allowance for Doubtful Accounts, Policy [Policy Text Block] Income Taxes Income Tax, Policy [Policy Text Block] Goodwill Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block] Derivatives Derivatives, Policy [Policy Text Block] Earnings Per Share Earnings Per Share, Policy [Policy Text Block] Recent Accounting Standards Updates New Accounting Pronouncements, Policy [Policy Text Block] Net actuarial (loss) gain Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax Prior service cost Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, Prior Service Cost (Credit), before Tax 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 Recognized in AOCI Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax 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] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Defined Benefit Plans Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Amortization of prior service cost Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member] Amortization of net actuarial loss Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member] Regulatory adjustment Accumulated Defined Benefit Plans Adjustment, Regulartory Adjustment, Attributable to Parent [Member] Accumulated Defined Benefit Plans Adjustment, Regulartory Adjustment, Attributable to Parent [Member] FSIRS AOCI, Derivative Qualifying as Hedge, Excluded Component, Parent [Member] Foreign Currency Items Accumulated Foreign Currency Adjustment Attributable to Parent [Member] AOCI Attributable to Parent AOCI Attributable to Parent [Member] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] AOCI Attributable to Parent, Net of Tax [Roll Forward] AOCI Attributable to Parent, Net of Tax [Roll Forward] Beginning balance, before tax Stockholders' Equity, Including Portion Attributable To Noncontrolling Interest, Before Tax Stockholders' Equity, Including Portion Attributable To Noncontrolling Interest, Before Tax Beginning balance, tax Stockholders' Equity, Including Portion Attributable To Noncontrolling Interest, Tax Stockholders' Equity, Including Portion Attributable To Noncontrolling Interest, Tax Beginning balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Beginning balance, attributable to parent, before tax Stockholders' Equity Attributable To Parent, Before Tax Stockholders' Equity Attributable To Parent, Before Tax Beginning balance, attributable to parent, tax Stockholders' Equity Attributable To Parent, Tax Stockholders' Equity Attributable To Parent, Tax Beginning balance, attributable to parent Stockholders' Equity Attributable to Parent Other comprehensive income (loss) before reclassifications, before tax Other Comprehensive Income (Loss), before Reclassifications, before Tax Other comprehensive income (loss) before reclassifications, net of tax Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Reclassification from AOCI, before Tax Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax Reclassification from AOCI, tax Reclassification from AOCI, Current Period, Tax Reclassification from AOCI, net of tax Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Other comprehensive income (loss), before tax Other Comprehensive Income (Loss), before Tax Other comprehensive income (loss), tax Other Comprehensive Income (Loss), Tax Total other comprehensive income (loss), net of tax Other Comprehensive Income (Loss), Net of Tax Ending balance, attributable to parent, before tax Ending balance, attributable to parent, tax Ending balance, attributable to parent Ending balance, before tax Ending balance, tax Ending balance Effective income tax rate Effective Income Tax Rate Reconciliation, Percent Customer [Axis] Customer [Axis] Customer [Domain] Customer [Domain] Residential Residential [Member] Residential. Small commercial Small Commercial [Member] Small commercial. Large commercial Large Commercial [Member] Large commercial. Industrial/other Industrial/other [Member] Industrial/other. Transportation Transportation [Member] Transportation. Revenue from contracts with customers Alternative revenue program revenues (deferrals) Alternative Revenue Program Revenues (Deferrals) Alternative revenue program revenues (deferrals). Other revenues Other Revenue Other Revenue Total Gas operating revenues Regulated Operating Revenue, Gas ASSETS Assets [Abstract] Utility plant: Public Utilities, Property, Plant and Equipment, Net [Abstract] Gas plant Public Utilities, Property, Plant and Equipment, Gas Plant Public Utilities, Property, Plant and Equipment, Gas Plant Less: accumulated depreciation Public Utilities, Property, Plant and Equipment, Accumulated Depreciation Construction work in progress Public Utilities, Property, Plant and Equipment, Construction Work in Progress Net utility plant Public Utilities, Property, Plant and Equipment, Net Other property and investments 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. Current assets: Assets, Current [Abstract] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Accounts receivable, net of allowances Accounts Receivable, after Allowance for Credit Loss, Current Accrued utility revenue Accrued Utility Revenue Accrued utility revenue. Income taxes receivable, net Income Taxes Receivable, Current Deferred purchased gas costs Deferred Gas Cost Prepaid and other current assets Prepaid Expense and Other Assets, Current Total current assets Assets, Current Noncurrent assets: Assets, Noncurrent [Abstract] Goodwill Deferred income taxes Deferred Income Tax Assets, Net Deferred charges and other assets Other Assets, Noncurrent Total noncurrent assets Assets, Noncurrent, Other than Noncurrent Investments and Property, Plant and Equipment Total assets Assets CAPITALIZATION AND LIABILITIES Liabilities and Equity [Abstract] Capitalization: Capitalization, Long-term Debt and Equity [Abstract] Common stock, $1 par (authorized - 120,000,000 shares; issued and outstanding - 55,126,386 and 55,007,433 shares) Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital, Common Stock Accumulated other comprehensive loss, net Accumulated Other Comprehensive Income (Loss), Net of Tax Retained earnings Retained Earnings (Accumulated Deficit) Total equity Redeemable noncontrolling interest Total capitalization Capitalization, Long-term Debt and Equity Current liabilities: Liabilities, Current [Abstract] Current maturities of long-term debt Short-term debt Short-term Debt Accounts payable Accounts Payable, Current Customer deposits Contract with Customer, Liability, Current Income taxes payable, net Accrued Income Taxes, Current Accrued general taxes Accrual for Taxes Other than Income Taxes, Current Accrued interest Interest Payable, Current Deferred purchased gas costs Deferred Gas Purchases, Current Payable to parent Due to Affiliate, Current Other current liabilities Other Liabilities, Current Total current liabilities Liabilities, Current Deferred income taxes and other credits: Other Liabilities, Noncurrent [Abstract] 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. Accumulated removal costs Other Accrued Liabilities, Noncurrent Other deferred credits and other long-term liabilities Deferred Credits and Other Liabilities, Noncurrent Total deferred income taxes and other credits Other Liabilities, Noncurrent Total capitalization and liabilities Liabilities and Equity Statement of Stockholders' Equity [Abstract] Common Stock Common Stock [Member] Additional paid-in capital Additional Paid-in Capital [Member] Accumulated other comprehensive loss Retained Earnings Retained Earnings [Member] Southwest Gas Holdings, Inc. Parent [Member] Non-controlling Interest Noncontrolling Interest [Member] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning balance (in shares) Common stock issuances (in shares) Common stock issuances Net income Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest Foreign currency exchange translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax, Portion Attributable to Parent Net actuarial gain (loss) 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 FSIRS amounts reclassified to net income, net of tax Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax Share-based compensation Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture Dividends declared Dividends, Common Stock Contributions from Southwest Gas Holdings, Inc. Adjustments To Additional Paid In Capital Contributions From Parent Adjustments to additional paid in capital contributions from parent. Ending balance (in shares) Dividends declared per share (in USD per share) Common Stock, Dividends, Per Share, Declared Summary of Revenue Disaggregated by Service Type and Contract Type Disaggregation of Revenue [Table Text Block] 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. Schedule of Construction Services Contracts Receivable Schedule of Construction Services Contracts Receivable [Table Text Block] Schedule of Construction Services Contracts Receivable [Table Text Block] Schedule of Net Periodic Benefit Costs Schedule of Net Benefit Costs [Table Text Block] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Transaction price allocated to unsatisfied performance obligations of contracts Revenue, Remaining Performance Obligation, Amount Revenue, remaining performance obligation, expected timing of satisfaction, period Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt Schedule of Long-term Debt Instruments [Table Text Block] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Statistical Measurement [Axis] Statistical Measurement [Axis] Statistical Measurement [Domain] Statistical Measurement [Domain] Minimum Minimum [Member] Maximum Maximum [Member] $400 Million Credit Facility $400 Million Credit Facility [Member] $400 Million Credit Facility [Member] $100 Million Credit Facility $100 Million Credit Facility [Member] $100 Million Credit Facility [Member] Commercial Paper Program Commercial Paper Program [Member] Commercial Paper Program [Member] Secured Revolving Credit Facility and Term Loan Secured Revolving Credit Facility Term Loan [Member] Secured Revolving Credit Facility Term Loan [Member] Line of Credit Line of Credit [Member] Equipment Loans Loans [Member] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] LIBOR London Interbank Offered Rate (LIBOR) [Member] Alternative base rate Base Rate [Member] Credit facility maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity 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 Line of credit designated for working capital purposes Line Of Credit Facility Working Capital Purposes Line Of Credit Facility, Working Capital Purposes Applicable margin Debt Instrument, Basis Spread on Variable Rate Long-term debt Commitment fee percentage Line of Credit Facility, Commitment Fee Percentage 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 Borrowings outstanding under facility Proceeds from debt Proceeds from Issuance of Debt Debt secured by assets Debt Instrument, Collateral Amount Short term borrowings outstanding 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 Income Statement [Abstract] Operating revenues: Revenues [Abstract] Gas operating revenues Utility infrastructure services revenues Revenue from Contract with Customer, Including Assessed Tax Total operating revenues Regulated and Unregulated Operating Revenue Operating expenses: Costs and Expenses [Abstract] Net cost of gas sold Utilities Operating Expense, Gas and Petroleum Purchased Operations and maintenance Utilities Operating Expense, Maintenance and Operations Taxes other than income taxes Taxes, Miscellaneous Utility infrastructure services expenses Cost of Goods and Services Sold Total operating expenses Costs and Expenses Operating income Operating Income (Loss) Other income and (expenses): Nonoperating Income (Expense) [Abstract] Net interest deductions Interest Expense Other income (deductions) Other Nonoperating Income (Expense) Total other income and (expenses) Nonoperating Income (Expense) Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Income tax expense Income Tax Expense (Benefit) Net income Net income attributable to noncontrolling interests Net Income (Loss) Attributable to Noncontrolling Interest Net income attributable to Southwest Gas Holdings, Inc. Net Income (Loss) Attributable to Parent Earnings per share: Earnings Per Share [Abstract] Basic (in USD per share) Earnings Per Share, Basic Diluted (in USD per share) Earnings Per Share, Diluted Weighted average shares: Weighted Average Number of Shares Outstanding Reconciliation [Abstract] Basic (in shares) Weighted Average Number of Shares Outstanding, Basic Diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Net cash surrender value of COLI policies Cash Surrender Value of Life Insurance Other property Property, Plant and Equipment, Other, Net Total Centuri property, equipment, and intangibles Property Plant Equipment And Intangible Assets Gross Property plant equipment and intangible assets gross. Centuri accumulated provision for depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Condensed Income Statement [Table] Condensed Income Statement [Table] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Operating Segments Operating Segments [Member] Corporate and administrative Corporate, Non-Segment [Member] Condensed Income Statements, Captions [Line Items] Condensed Income Statements, Captions [Line Items] Other income (deductions) Other Nonoperating Income (Expense) [Abstract] Change in COLI policies Life Insurance, Corporate or Bank Owned, Change in Value Interest income Interest Income, Other Equity AFUDC Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity Foreign transaction gain (loss) Foreign Currency Transaction Gain (Loss), Realized Other components of net periodic benefit cost Defined Benefit Plan, Actuarial Gain (Loss), Immediate Recognition as Component in Net Periodic Benefit (Cost) Credit Miscellaneous income and (expense) Miscellaneous Income Expense Miscellaneous income (expense). Total other income (deductions) Statement of Comprehensive Income [Abstract] Other comprehensive income (loss), net of tax Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract] Defined benefit pension plans: Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax [Abstract] Net actuarial loss Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, after Tax Amortization of prior service cost Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, after Tax Amortization of net actuarial loss Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax Prior service cost Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax 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. Net defined benefit pension plans Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax Forward-starting interest rate swaps (“FSIRS”): Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax [Abstract] Amounts reclassified into net income Net forward-starting interest rate swaps Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax, Parent Foreign currency translation adjustments Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Comprehensive income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Comprehensive income attributable to noncontrolling interests Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Comprehensive income attributable to Southwest Gas Holdings, Inc. Comprehensive Income (Loss), Net of Tax, Attributable to Parent Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Qualified Retirement Plan Other Pension Plan [Member] SERP Supplemental Employee Retirement Plan [Member] PBOP Other Postretirement Benefits Plan [Member] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Service cost Defined Benefit Plan, Service Cost Interest cost Defined Benefit Plan, Interest Cost Expected return on plan assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Amortization of prior service costs Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Amortization of net actuarial loss Defined Benefit Plan, Amortization of Gain (Loss) Net periodic benefit cost Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Revenue Revenue from Contract with Customer [Text Block] Schedule of Other Property and Investments Schedule Of Other Property And Investments [Table Text Block] Schedule Of Other Property And Investments [Table Text Block] Schedule of Goodwill Schedule of Goodwill [Table Text Block] Other Income (Deductions) Schedule of Other Nonoperating Income, by Component [Table Text Block] Summary of Redeemable Noncontrolling Interest Redeemable Noncontrolling Interest [Table Text Block] Schedule of Earnings Per Share, Basic and Diluted Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Average basic shares (in shares) Effect of dilutive securities: Dilutive Securities, Effect on Basic Earnings Per Share [Abstract] Management Incentive Plan shares (in shares) Incremental Common Shares Attributable to Dilutive Effect of Equity Forward Agreements Restricted stock units (in shares) Incremental Common Shares Attributable to Dilutive Effect of Nonvested Shares with Forfeitable Dividends Average diluted shares (in shares) Number of performance share units granted (in shares) Number Of Performance Share Units Granted Number Of Performance Share Units Granted. Intersegment Eliminations Intersegment Eliminations [Member] Segment Reconciling Items Segment Reconciling Items [Member] Revenues Revenues Segment net income (loss) Net actuarial gain/(loss) 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] Other comprehensive income (loss) before reclassifications, tax Other Comprehensive Income (Loss) before Reclassifications, Tax Cover [Abstract] Entities [Table] Entities [Table] Entity Information [Line Items] Entity Information [Line Items] Document Type Document Type Document Quarterly Report Document Quarterly Report Document Period End Date Document Period End Date Document Transition Report Document Transition Report Entity File Number Entity File Number Entity Registrant Name Entity Registrant Name Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Entity Tax Identification Number Entity Tax Identification Number Entity Address, Address Line One Entity Address, Address Line One Entity Address, Address Line Two Entity Address, Address Line Two Entity Address, City or Town Entity Address, City or Town Entity Address, State or Province Entity Address, State or Province Entity Address, Postal Zip Code Entity Address, Postal Zip Code City Area Code City Area Code Local Phone Number Local Phone Number Title of 12(b) Security Title of 12(b) Security Trading Symbol Trading Symbol Security Exchange Name Security Exchange Name Entity Current Reporting Status Entity Current Reporting Status Entity Interactive Data Current Entity Interactive Data Current Entity Filer Category Entity Filer Category Entity Small Business Entity Small Business Entity Emerging Growth Company Entity Emerging Growth Company Entity Shell Company Entity Shell Company Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Amendment Flag Amendment Flag Other Comprehensive Income and Accumulated Other Comprehensive Income Comprehensive Income (Loss) Note [Text Block] Change in contract liability, revenue recognized Contract with Customer, Liability, Revenue Recognized 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