SUPPLEMENTAL INFORMATION: Supplemental Cash Flow Information [Abstract] Customer [Domain] Customer [Domain] Foreign transaction gain (loss) Foreign Currency Transaction Gain (Loss), Realized Reclassification from AOCI, before Tax Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax Earnings Per Share Earnings Per Share, Policy [Policy Text Block] Net income attributable to Southwest Gas Holdings, Inc. Segment net income (loss) Net Income (Loss) Attributable to Parent Unit price contracts Unit Priced Contracts [Member] Unit priced contracts. Entity Emerging Growth Company Entity Emerging Growth Company Interest cost Defined Benefit Plan, Interest Cost Statistical Measurement [Domain] Statistical Measurement [Domain] Receivable Type [Axis] Receivable Type [Axis] Entity Address, Address Line One Entity Address, Address Line One Entity Address, Address Line Two Entity Address, Address Line Two Accrued utility revenue Increase (Decrease) in Contract with Customer, Asset Billed on completed contracts and contracts in progress Billed On Completed Contracts And Contracts In Progress [Member] Billed on completed contracts and contracts in progress. Schedule of Common Stock Activity Schedule Of Common Stock Activity [Table Text Block] Schedule Of Common Stock Activity [Table Text Block] Revenue from Contract with Customer [Abstract] Revenue from Contract with Customer [Abstract] Schedule of Utility Infrastructure Services Contracts Receivable Contract with Customer, Contract Asset, Contract Liability, and Receivable [Table Text Block] Additional paid-in capital Additional Paid in Capital, Common Stock Entity Filer Category Entity Filer Category Significant Accounting Policies [Line Items] Significant Accounting Policies [Line Items] Significant Accounting Policies [Line Items] Deferred charges and other assets Other Assets, Noncurrent Expected return on plan assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Segments [Axis] Segments [Axis] Retirement Benefits [Abstract] Retirement Benefits [Abstract] Change in cash and cash equivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect 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 Industrial/other Industrial/other [Member] Industrial/other. 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Intersegment revenues Segment Reconciling Items [Member] Transportation Transportation [Member] Transportation. $400 Million Credit Facility $400 Million Credit Facility [Member] $400 Million Credit Facility [Member] Deferred purchased gas costs, recovered or refunded period Deferred Purchased Gas Costs, Recovered Or Refunded Period Deferred Purchased Gas Costs, Recovered Or Refunded Period Entity Address, City or Town Entity Address, City or Town Drum Parent, Inc. Drum Parent, Inc. [Member] Drum Parent, Inc. 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Number of Reportable Segments Redeemable noncontrolling interest Redeemable noncontrolling interest, beginning balance Redeemable noncontrolling interest, ending balance Redeemable Noncontrolling Interest, Equity, Carrying Amount Common stock Common Stock, Value, Issued Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Total other income and (expenses) Nonoperating Income (Expense) Contract with Customer, Basis of Pricing [Axis] Contract with Customer, Basis of Pricing [Axis] $250 Million Term Loan $250 Million Term Loan [Member] $250 Million Term Loan Basis of Presentation Basis of Accounting, Policy [Policy 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 PBOP Other Postretirement Benefits Plan [Member] Equity AFUDC Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity 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Goodwill [Line Items] Goodwill [Line Items] Total operating expenses Costs and Expenses Other comprehensive income (loss) before reclassifications, net of tax Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Amortization of prior service cost Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, after Tax Deferred purchased gas costs Deferred Gas Purchases, Current Entity Registrant Name Entity Registrant Name Cash and Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Other comprehensive income (loss) before reclassifications, tax Other Comprehensive Income (Loss) before Reclassifications, Tax Prepaid and other current assets Prepaid Expense and Other Assets, Current Dividends declared per share (in USD per share) Common Stock, Dividends, Per Share, Declared Utility infrastructure services revenues Revenue from contracts with customers Revenue from Contract with Customer, Excluding Assessed Tax Schedule of Accounts Receivable for Services Accounts Receivable For Services [Table Text Block] Accounts Receivable For Services Table Text Block. Other current liabilities Other Current Liabilities Policy [Policy Text Block] Other Current Liabilities Policy Amortization of net actuarial loss Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax Carrying Amount Reported Value Measurement [Member] Equity [Abstract] Equity [Abstract] Consolidation Items [Domain] Consolidation Items [Domain] Notes, 4.15%, due 2049 Debentures Notes Four Point Fifteen Percentage, Due Two Thousand And Forty Nine [Member] Debentures Notes Four Point Fifteen Percentage, Due Two Thousand And Forty Nine Common Stock Common Stock [Member] Variable Rate [Axis] Variable Rate [Axis] Other income (deductions) Other Nonoperating Income (Expense) [Abstract] 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] Segment Information Segment Reporting Disclosure [Text Block] Operating income Operating Income (Loss) Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Background, Organization, and Summary of Significant Accounting Policies Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Changes in undistributed stock compensation Share-based Payment Arrangement, Noncash Expense Variable Rate [Domain] Variable Rate [Domain] AOCI Attributable to Parent, Net of Tax [Roll Forward] AOCI Attributable to Parent, Net of Tax [Roll Forward] Inventory [Axis] Inventory [Axis] Additional paid-in capital Additional Paid-in Capital [Member] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Line of credit facility, fair value Lines of Credit, Fair Value Disclosure Utility plant: Public Utilities, Property, Plant and Equipment, Net [Abstract] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Deferred income taxes Increase (Decrease) in Deferred Income Taxes Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Nature of Operations Nature Of Operations [Policy Text Block] Nature Of Operations [Policy Text Block] Amortization of net actuarial (gain)/loss Amortization of net actuarial loss Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member] Unamortized discount and debt issuance costs Debt Instrument Unamortized Discount And Debt Issuance Costs Debt instrument unamortized discount and debt issuance costs. 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Income Statement [Abstract] Income Statement [Abstract] Amendment Flag Amendment Flag Fair Value Estimate of Fair Value Measurement [Member] Centuri Centuri Group, Inc. [Member] Centuri Group, Inc. [Member] Notes payable, fair value disclosure Notes Payable, Fair Value Disclosure Other receivables Other Receivables [Member] Other Receivables Beginning balance Ending balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Income tax expense (benefit) Income Tax Expense (Benefit) Accounts receivable, net of allowances Accounts Receivable, after Allowance for Credit Loss, Current Issuance of long-term debt, net Proceeds from Issuance of Long-term Debt Debt secured by assets Debt Instrument, Collateral Amount Equity Components [Axis] Equity Components [Axis] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Gas Pipe Materials and Supplies Gas Pipe Inventory And Operating Supplies [Member] Gas pipe inventory and operating supplies. 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] Total current assets Assets, Current Sale of Stock [Domain] Sale of Stock [Domain] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Weighted average shares: Weighted Average Number of Shares Outstanding Reconciliation [Abstract] 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 Schedule of Segment Reporting Information Schedule of Segment Reporting Information, by Segment [Table Text Block] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Entity File Number Entity File Number Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Fair Value Measurements Fair Value Measurement, Policy [Policy Text Block] Current maturities of long-term debt Less: current maturities Current maturities of long-term debt Long-term Debt, Current Maturities Product and Service [Axis] Product and Service [Axis] Utility Infrastructure Services Utility Infrastructure Services Segment Utility Infrastructure Services Segment [Member] Utility Infrastructure Services Segment [Member] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Entity Small Business Entity Small Business Deferred Purchased Gas Costs Deferred Purchased Costs [Policy Text Block] Deferred Purchased Costs Equity Component [Domain] Equity Component [Domain] Common Stock Common Stock Disclosure [Text Block] Common Stock Disclosure [Text Block] Foreign currency translation adjustments Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Common stock issued (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period Accrued taxes Increase (Decrease) in Accrued Taxes Payable Statement [Line Items] Statement [Line Items] Schedule of Significant Items Included in Other Income (Deductions) Schedule of Other Nonoperating Income, by Component [Table Text Block] Total operating revenues Regulated and Unregulated Operating Revenue Transaction price allocated to unsatisfied performance obligations of contracts Revenue, Remaining Performance Obligation, Amount Share-based compensation Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture 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] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Large commercial Large Commercial [Member] Large commercial. Debt Disclosure [Abstract] Debt Disclosure [Abstract] Time and materials contracts Time-and-materials Contract [Member] Payable to parent Due to Affiliate, Current Entity Address, State or Province Entity Address, State or Province Accounts Receivable, net of allowances Receivables, Trade and Other Accounts Receivable, Allowance for Doubtful Accounts, Policy [Policy Text Block] Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest 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 Corporate and administrative Corporate, Non-Segment [Member] Segment Reporting [Abstract] Segment Reporting [Abstract] Entity [Domain] Entity [Domain] Customer [Axis] Customer [Axis] Schedule of Earnings Per Share, Basic and Diluted Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Entity Shell Company Entity Shell Company Local Phone Number Local Phone Number Centuri other debt obligations Other Long-term Debt Prior service cost Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax Other comprehensive income (loss), tax Other Comprehensive Income (Loss), Tax Issuance of common stock, net Net proceeds Proceeds from Issuance of Common Stock Total assets Assets Accumulated removal costs Other Accrued Liabilities, Noncurrent Plan Name [Domain] Plan Name [Domain] Common stock, authorized (in shares) Common Stock, Shares Authorized Weighted average price per share (in USD per share) Common Stock Weighted Average Issue Price Per Share Common stock weighted average issue price per share. Interest paid, net of amounts capitalized Interest Paid, Excluding Capitalized Interest, Operating Activities Significant Accounting Policies [Table] Significant Accounting Policies [Table] Significant Accounting Policies [Table] Product and Service [Domain] Product and Service [Domain] Depreciation and amortization Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Debt instrument interest rate Debt Instrument, Interest Rate, Stated Percentage Prior service cost Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, Prior Service Cost (Credit), before Tax Contract with Customer, Basis of Pricing [Domain] Contract with Customer, Basis of Pricing [Domain] Net income attributable to noncontrolling interest Net Income (Loss) Attributable to Noncontrolling Interest Small commercial Small Commercial [Member] Small commercial. Transaction price allocated to unsatisfied performance obligations of contracts, period Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Short-term debt Short-term Debt Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Entity Tax Identification Number Entity Tax Identification Number Capitalization: Capitalization, Long-term Debt and Equity [Abstract] Basic (in shares) Weighted average basic shares (in shares) Weighted Average Number of Shares Outstanding, Basic Diluted (in USD per share) Earnings Per Share, Diluted Segments [Domain] Segments [Domain] Service cost Defined Benefit Plan, Service Cost Net actuarial loss Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax Net income attributable to redeemable noncontrolling interest Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Deferred purchased gas costs, estimated incremental costs Deferred Purchased Gas Costs, Estimated Incremental Costs Deferred Purchased Gas Costs, Estimated Incremental Costs Income taxes paid (received), net Income Taxes Paid, Net Other components of net periodic benefit cost Defined Benefit Plan, Actuarial Gain (Loss), Immediate Recognition as Component in Net Periodic Benefit (Cost) Credit Deferred purchased gas costs Deferred Gas Cost Comprehensive income attributable to Southwest Gas Holdings, Inc. Comprehensive Income (Loss), Net of Tax, Attributable to Parent Centuri secured revolving credit facility Centuri Secured Revolving Credit Facility [Member] Centuri secured revolving credit facility. Amounts billed in excess of revenue earned on contracts Contract with Customer, Liability Amortization of prior service cost Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member] Fixed price contracts Fixed-price Contract [Member] Change in COLI policies Life Insurance, Corporate or Bank Owned, Change in Value Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities Southwest Gas Corporation Southwest Gas Corporation [Member] Southwest gas corporation. Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Notes payable Notes Payable Centuri term loan facility Centuri Term Loan Facility [Member] Centuri term loan facility. Commercial Paper Program Commercial Paper Program [Member] Commercial Paper Program [Member] Accounts payable Accounts Payable, Current Other property and investments Property, Plant and Equipment, Other, Net Equity AFUDC Increase (Decrease) in Allowance for Equity Funds Used During Construction Southwest Gas Holdings, Inc. Parent [Member] Dividends declared Dividends, Common Stock Entities [Table] Entities [Table] $100 Million Credit Facility $100 Million Credit Facility [Member] $100 Million Credit Facility [Member] Accumulated other comprehensive loss AOCI Attributable to Parent AOCI Attributable to Parent [Member] Contracts receivable, net Contracts receivable, net Contract with Customer, Asset, after Allowance for Credit Loss Common stock, outstanding (in shares) Beginning balance (in shares) Ending balance (in shares) Common Stock, Shares, Outstanding Utility infrastructure services expenses Cost of Goods and Services Sold Operating revenues: Revenues [Abstract] Alternative revenue program revenues (deferrals) Alternative Revenue Program Revenues (Deferrals) Alternative revenue program revenues (deferrals). Goodwill Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block] Inventory [Domain] Inventory [Domain] Other Other Infrastructure Services [Member] Other Infrastructure Services Intercompany Transactions Intercompany Profit to Regulated Affiliates, Policy [Policy Text Block] Debt instrument, term Debt Instrument, Term 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] AOCI Including Portion Attributable to Noncontrolling Interest AOCI Including Portion Attributable to Noncontrolling Interest [Member] Total deferred income taxes and other credits Other Liabilities, Noncurrent Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt Schedule of Long-term Debt Instruments [Table Text Block] Debt Instrument [Line Items] Debt Instrument [Line Items] Retirement of long-term debt Repayments of Long-term Debt Earnings per share: Earnings Per Share [Abstract] 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. Document Quarterly Report Document Quarterly Report Revenues Revenues 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. Changes in deferred charges and other assets Increase (Decrease) in Other Operating Assets Reclassification from AOCI, net of tax Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Condensed Income Statements, Captions [Line Items] Condensed Income Statements, Captions [Line Items] Operations and maintenance Utilities Operating Expense, Maintenance and Operations Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Bid contract Bid Contract [Member] Bid contract. Operating expenses: Costs and Expenses [Abstract] Long-term debt, less current maturities Long-term debt, less current maturities Long-term Debt, Excluding Current Maturities Schedule of Goodwill [Table] Schedule of Goodwill [Table] Equity Shelf Program Equity Shelf Program [Member] Equity Shelf Program [Member] Deferred purchased gas costs, pipeline imbalance charges Deferred Purchased Gas Costs, Pipeline Imbalance Charges Deferred Purchased Gas Costs, Pipeline Imbalance Charges Ownership percentage by noncontrolling owners Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners Document Fiscal Period Focus Document Fiscal Period Focus Effective income tax rate Effective Income Tax Rate Reconciliation, Percent Net income Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Secured Revolving Credit Facility and Term Loan Secured Revolving Credit And Term Loan Facility [Member] Secured Revolving Credit And Term Loan Facility [Member] Long-term Debt, Current and Noncurrent Abstract Long-term Debt, Current and Noncurrent [Abstract] Gains on sale of equipment Gain (Loss) on Disposition of Property Plant Equipment 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 Common stock, par (in USD per share) Common Stock, Par or Stated Value Per Share Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Current assets: Assets, Current [Abstract] Other Proceeds from (Payments for) Other Financing Activities Southwest Gas Credit Facility Southwest Gas Credit Facility [Member] Southwest Gas Credit Facility [Member] Forward-starting interest rate swaps (“FSIRS”): Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax [Abstract] Entity Central Index Key Entity Central Index Key LIBOR London Interbank Offered Rate (LIBOR) [Member] Security Exchange Name Security Exchange Name Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] 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 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. Diluted (in shares) Weighted average diluted shares (in shares) Weighted Average Number of Shares Outstanding, Diluted Total other comprehensive income (loss), net of tax Other Comprehensive Income (Loss), Net of Tax Accrued interest Interest Payable, Current Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Current Fiscal Year End Date Current Fiscal Year End Date Applicable margin Debt Instrument, Basis Spread on Variable Rate Number of performance share units granted (in shares) Number Of Performance Share Units Granted Number Of Performance Share Units Granted. Schedule of Net Periodic Benefit Costs Schedule of Net Benefit Costs [Table Text Block] Measurement Basis [Axis] Measurement Basis [Axis] Deferred income taxes and other credits: Other Liabilities, Noncurrent [Abstract] Electric power infrastructure services Electric Power Infrastructure Services [Member] Electric Power Infrastructure Services Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Other income and (expenses): Nonoperating Income (Expense) [Abstract] Deferred purchased gas costs Increase (Decrease) in Deferred Gas Cost Gas operating revenues Total Gas operating revenues Regulated Operating Revenue, Gas Class of Stock [Line Items] Class of Stock [Line Items] Credit Facility [Axis] Credit Facility [Axis] Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Changes in current assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Centuri accumulated provision for depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Other deferred credits and other long-term liabilities Deferred Credits and Other Liabilities, Noncurrent CASH FLOW FROM OPERATING ACTIVITIES: Net Cash Provided by (Used in) Operating Activities [Abstract] 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 Total current liabilities Liabilities, Current Withholding remittance - share-based compensation Payment, Tax Withholding, Share-based Payment Arrangement Debentures Debentures [Member] Debentures [Member] Credit facility maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Foreign currency translation adjustment Goodwill, Foreign Currency Translation Gain (Loss) Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Ownership [Domain] Ownership [Domain] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Taxes other than income taxes Taxes, Miscellaneous Gas pipe materials and operating supplies Materials, Supplies, and Other Revenue earned on contracts in progress in excess of billings Contract with Customer, Asset, Reclassified to Receivable 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] Net income Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Title of 12(b) Security Title of 12(b) Security Statement [Table] Statement [Table] Industrial development revenue bonds Industrial Development Revenue Bonds [Member] Industrial Development Revenue Bonds [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. Schedule of Other Property and Investments Investment [Table Text Block] Recent Accounting Standards Updates New Accounting Pronouncements, Policy [Policy Text Block] 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] Effect of dilutive securities: Dilutive Securities, Effect on Basic Earnings Per Share [Abstract] Prepaid and other current assets Prepaid Expenses and Other Current Assets [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] Schedule of Amount Recognized Before Income Tax in Accumulated Other Comprehensive Income Schedule of Amounts Recognized in Other Comprehensive Income (Loss) [Table Text Block] Statistical Measurement [Axis] Statistical Measurement [Axis] Cover [Abstract] Cover [Abstract] Other revenues Other Revenue Other Revenue Prepaid and other current assets Prepaid And Other Current Assets Policy [Policy Text Block] Prepaid And Other Current Assets Policy Goodwill Goodwill, beginning balance Goodwill, ending balance Goodwill 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] FSIRS AOCI, Derivative Qualifying as Hedge, Excluded Component, Parent [Member] Income taxes payable, net Accrued Income Taxes, Current Schedule of Goodwill Schedule of Goodwill [Table Text Block] 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] Natural Gas Operations Natural Gas Operations Natural Gas Operations [Member] Natural Gas Operations [Member] Pension plans other comprehensive income (loss) Defined Benefit Plans Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Contributions from Southwest Gas Holdings, Inc. Adjustments To Additional Paid In Capital Contributions From Parent Adjustments to additional paid in capital contributions from parent.