Segment Reporting [Abstract] Segment Information Segment Reporting Disclosure [Text Block] Regulated Operations [Abstract] Schedule of Regulatory Liabilities [Table] Schedule of Regulatory Liabilities [Table] Regulatory Liability [Axis] Regulatory Liability [Axis] Regulatory Liability [Domain] Regulatory Liability [Domain] State mandated public purpose programs (including low income and conservation programs) State Mandated Public Purpose Programs [Member] State and mandated public purpose programs (including low income and conservation programs). Environmental compliance programs Environmental Compliance Programs [Member] Environmental compliance programs. Regulatory accounts for differences related to pension funding Regulatory Accounts For Differences Related To Pension Funding [Member] Regulatory accounts for differences related to pension funding. Other Other Miscellaneous Regulatory Liabilities [Member] Other Miscellaneous Regulatory Liabilities [Member] Other regulatory liabilities Regulatory Liabilities Other [Member] Regulatory Liabilities Other [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Other current liabilities Other Current Liabilities [Member] Other deferred credits and other long-term liabilities Other Deferred Credits And Other Long-term Liabilities [Member] Other Deferred Credits And Other Long-term Liabilities [Member] Regulatory Liabilities [Line Items] Regulatory Liabilities [Line Items] Regulatory liabilities Regulatory Liabilities Public Utility, Property, Plant and Equipment [Table] Public Utility, Property, Plant and Equipment [Table] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Southwest Gas Corporation Southwest Gas Corporation [Member] Southwest gas corporation. Centuri Centuri Group, Inc. [Member] Centuri Group, Inc. [Member] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Update 2016-02 Accounting Standards Update 2016-02 [Member] Public Utility [Axis] Public Utility [Axis] Utility Plant [Domain] Utility Plant [Domain] Gas plant Natural Gas Processing Plant [Member] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Gas, Transmission and Distribution Plant Gas, Transmission and Distribution Equipment [Member] Public Utility, Property, Plant and Equipment [Line Items] Public Utility, Property, Plant and Equipment [Line Items] Annual utility depreciation and amortization expense percentage Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service Amortization of intangibles Amortization of Intangible Assets Operating lease ROU assets Operating Lease, Right-of-Use Asset Operating lease liabilities Operating Lease, Liability Lease renewal term (up to) Lessee, Operating Lease, Renewal Term Lease remaining lease term (up to) Lessee, Operating Lease, Remaining Lease Term Lessee, Operating Lease, Remaining Lease Term Lease termination period Lessee, Operating Lease, Termination Period Lessee, Operating Lease, Termination Period Short-term lease total future lease payments Short-term Lease Commitment, Amount Finance lease Finance Lease, Liability, Current Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] United States UNITED STATES Canada CANADA Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Total Revenues Regulated and Unregulated Operating Revenue Debt Disclosure [Abstract] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] 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] 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] Debt Instrument [Line Items] Debt Instrument [Line Items] Effective interest rates Debt Instrument, Interest Rate, Effective Percentage Revenue from Contract with Customer [Abstract] 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 Derivative Instruments and Hedging Activities Disclosure [Abstract] Notional Amounts under Swaps Contracts Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] Paid to and Received from Counterparties for Settlements of Matured Swaps Paid And Received From Counterparties For Settlements Of Matured Swaps [Table Text Block] Paid and Received From Counterparties for Settlements of Matured Swaps [Table Text Block] Fair Values of Swaps in Consolidated Balance Sheets Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Equity [Abstract] Other Comprehensive Income and Accumulated Other Comprehensive Income ("AOCI") Stockholders' Equity Note Disclosure [Text Block] Retirement Benefits [Abstract] 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] Change in benefit obligations: Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Benefit obligation for service rendered to date at beginning of year (PBO/PBO/APBO) Defined Benefit Plan, Benefit Obligation Service cost Defined Benefit Plan, Service Cost Interest cost Defined Benefit Plan, Interest Cost Plan amendments Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment Actuarial loss (gain) Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) Benefits paid Defined Benefit Plan, Benefit Obligation, Benefits Paid Benefit obligation at end of year (PBO/PBO/APBO) Change in plan assets: Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] Market value of plan assets at beginning of year Defined Benefit Plan, Plan Assets, Amount Actual return on plan assets Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss) Employer contributions Defined Benefit Plan, Plan Assets, Contributions by Employer Benefits paid Defined Benefit Plan, Plan Assets, Benefits Paid Market value of plan assets at end of year Funded status at year end Defined Benefit Plan, Funded (Unfunded) Status of Plan Weighted-average assumptions (benefit obligation): Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract] Discount rate Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate Weighted-average rate of compensation increase Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase Business Combinations [Abstract] Condensed Income Statement [Table] Condensed Income Statement [Table] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Linetec Linetec Services, LLC [Member] Linetec Services, LLC [Member] Condensed Income Statements, Captions [Line Items] Condensed Income Statements, Captions [Line Items] Utility infrastructure services revenues Revenue from Contract with Customer, Including Assessed Tax Net income attributable to Southwest Gas Holdings, Inc. Net Income (Loss) Attributable to Parent Retirement Plan Pension Plan [Member] Retirement plan net actuarial loss Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year PBOP prior service cost Defined Benefit Plan, Expected Amortization of Prior Service Cost (Credit), Next Fiscal Year Schedule of Common Stock Activity Schedule Of Common Stock Activity [Table Text Block] Schedule Of Common Stock Activity [Table Text Block] Storage Storage [Member] Storage [Member] Transmission Gas Transmission [Member] Distribution Gas Distribution [Member] General General [Member] General [Member] Other Other Plant in Service [Member] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Software and software-related intangibles Computer Software, Intangible Asset [Member] 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 Accounts receivable for Centuri services Due from Related Parties, Current Receivables [Abstract] Receivables And Related Allowances [Table] Receivables And Related Allowances [Table] Receivables And Related Allowances [Table] Arizona ARIZONA Nevada NEVADA California CALIFORNIA Receivables And Related Allowances [Line Items] Receivables And Related Allowances [Line Items] Receivables And Related Allowances [Line Items] Percent of customers by state: Percent Of Customers By State Percent Of Customers By State Receivables and Related Allowances Loans, Notes, Trade and Other Receivables Disclosure [Text Block] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Secured Revolving Credit Facility and Term Loan Secured Revolving Credit Facility Term Loan [Member] Secured Revolving Credit Facility Term Loan [Member] Ownership [Axis] Ownership [Axis] Ownership [Domain] Ownership [Domain] Customer relationships Customer Relationships [Member] Trade Names Trade Names [Member] Customer Contracts Customer Contracts [Member] Business Acquisition [Line Items] Business Acquisition [Line Items] Percentage of voting interests acquired Business Acquisition, Percentage of Voting Interests Acquired Net consideration of acquisition less assumed debt Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net Ownership percentage by noncontrolling owners Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners Payments to acquisition Payments to Acquire Businesses, Gross Remaining unpaid consideration Business Combination, Consideration Transferred Credit facility maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Consideration Transferred Goodwill Goodwill Acquired intangible assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill Acquired intangible assets, weighted average useful life Acquired Finite-lived Intangible Assets, Weighted Average Useful Life Acquisition costs Acquisition Costs, Period Cost 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 Gas Infrastructure Services [Member] Gas Infrastructure Services [Member] Electric power infrastructure services Electric Power Infrastructure Services [Member] Electric Power Infrastructure Services [Member] Other Other Infrastructure Services [Member] Other Infrastructure Services [Member] 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 Commitments and Contingencies Disclosure [Abstract] Loss Contingencies [Table] Loss Contingencies [Table] Loss Contingencies [Line Items] Loss Contingencies [Line Items] Self-insured retention amount associated with general liability claims Self Insured Retention Amount Associated With General Liability Claims Amount of risk retained by the entity per incident before the insurance arrangement begins to provide coverage. Additional self-insured retention amount of general liability Additional Self Insured Retention Amount Of General Liability Additional self-insured retention amount of general liability Derivatives Derivative Instruments and Hedging Activities Disclosure [Text Block] Leases [Abstract] Lessee, Lease, Description [Table] Lessee, Lease, Description [Table] Lessee, Lease, Description [Line Items] Lessee, Lease, Description [Line Items] Operating cash flows from operating leases Operating Lease, Payments Operating cash flows from finance leases Finance Lease, Interest Payment on Liability Financing cash flows from finance leases Finance Lease, Principal Payments, Leases Entered Or Modified During Period Finance Lease, Principal Payments, Leases Entered Or Modified During Period Operating leases Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Finance leases Right-of-Use Asset Obtained in Exchange for Finance Lease Liability 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] Maximum value of common stock issuance Maximum Aggregate Market Value Of Potential Stock Issuance The amount of maximum aggregate market value of potential stock issuance under the program. Gross proceeds Proceeds From Issuance Of Common Stock, Gross Proceeds From Issuance Of Common Stock, Gross Less: agent commissions Payments of Stock Issuance Costs Net proceeds Proceeds from Issuance of Common Stock Number of shares sold (in shares) Stock Issued During Period, Shares, New Issues Weighted average price per share (USD per share) Common Stock Weighted Average Issue Price Per Share Common stock weighted average issue price per share. Common stock available for sale under the program Maximum Amount Of Common Stock Available For Sale Maximum amount of common stock available for sale. Number of common stock sold through public offering (in shares) Sale of Stock, Number of Shares Issued in Transaction Common stock issued (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period Common stock issuances Stock Issued During Period, Value, New Issues Shares registered and available for issuance Common Stock, Capital Shares Reserved for Future Issuance 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). Schedule of Estimated Amounts Amortized from Accumulated Other Comprehensive Income or Regulatory Assets into Net Periodic Benefit Cost Schedule Of Estimated Amounts Amortized From Accumulated Other Comprehensive Income Or Regulatory Assets Into Net Periodic Benefit Cost [Table Text Block] Schedule Of Estimated Amounts Amortized From Accumulated Other Comprehensive Income Or Regulatory Assets Into Net Periodic Benefit Cost Table Text Block. 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] Share-based Payment Arrangement [Abstract] Schedule of Share-Based Plan Compensation Expense, Including Cash Award Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block] Schedule of Nonvested Performance and Restricted Stock Unit Plans Schedule of Nonvested Share Activity [Table Text Block] Discount rate Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate Weighted-average rate of compensation increase Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase Asset return assumption Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets 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] IDRBs Industrial Development Revenue Bonds [Member] Industrial Development Revenue Bonds [Member] 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] 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. 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 Less: current maturities Long-term Debt, Current Maturities Long-term debt, less current maturities Long-term Debt, Excluding Current Maturities Unsecured debt, fair value Long-term Debt, Fair Value 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 term loan/secured revolving credit facility Secured Debt Centuri other debt obligations Other Long-term Debt Debt instrument interest rate Debt Instrument, Interest Rate, Stated Percentage 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 Accounts Receivable, after Allowance for Credit Loss Operating lease cost Operating Lease, Cost Amortization of ROU assets Finance Lease, Right-of-Use Asset, Amortization Interest on lease liabilities Finance Lease, Interest Expense Total finance lease cost Finance Lease, Cost Finance Lease, Cost Short-term lease cost Short-term Lease, Cost Total lease cost - Southwest Gas Holdings, Inc. Lease, Cost Expected return on plan assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Amortization of prior service cost 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) Weighted-average assumptions (net benefit cost) Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract] Expected return on plan assets Organization, Consolidation and Presentation of Financial Statements [Abstract] Schedule of Finite-Lived Intangible Assets [Table] Schedule of Finite-Lived Intangible Assets [Table] Finite-Lived Intangible Assets [Line Items] Finite-Lived Intangible Assets [Line Items] 2020 Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months 2021 Finite-Lived Intangible Assets, Amortization Expense, Year Two 2022 Finite-Lived Intangible Assets, Amortization Expense, Year Three 2023 Finite-Lived Intangible Assets, Amortization Expense, Year Four 2024 Finite-Lived Intangible Assets, Amortization Expense, Year Five Thereafter Finite-Lived Intangible Assets, Amortization Expense, after Year Five Net Carrying Amount Finite-Lived Intangible Assets, Net Schedule of Regulatory Assets Schedule of Regulatory Assets [Table Text Block] Schedule of Regulatory Liabilities Schedule of Regulatory Liabilities [Table Text Block] Quarterly Financial Information Disclosure [Abstract] Schedule Of Quarterly Financial Information [Table] Schedule Of Quarterly Financial Information [Table] Schedule Of Quarterly Financial Information [Table] Southwest Gas Corporation Schedule Of Quarterly Financial Information [Line Items] Schedule Of Quarterly Financial Information [Line Items] Schedule Of Quarterly Financial Information [Line Items] Operating revenues Operating income (loss) Operating Income (Loss) Net income (loss) Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Basic earnings per common share (in USD per share) Earnings Per Share, Basic Diluted earnings per common share (in USD per share) Earnings Per Share, Diluted 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] 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] 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 Including Portion Attributable to Noncontrolling Interest [Member] AOCI Including Portion Attributable to Noncontrolling Interest AOCI Including Portion Attributable to Noncontrolling Interest [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, tax Other Comprehensive Income (Loss) before Reclassifications, 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 Total operating revenues Business Acquisition, Pro Forma Revenue Net income attributable to Southwest Gas Holdings, Inc. Business Acquisition, Pro Forma Net Income (Loss) Basic earnings per share (in USD per Share) Business Acquisition, Pro Forma Earnings Per Share, Basic Diluted earnings per share (in USD per Share) Business Acquisition, Pro Forma Earnings Per Share, Diluted Statement of Financial Position [Abstract] Statement [Table] Statement [Table] Statement [Line Items] Statement [Line Items] ASSETS Assets [Abstract] Utility plant: Public Utilities, Property, Plant and Equipment, Net [Abstract] 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 Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital, Common Stock Accumulated other comprehensive income (loss), net Accumulated Other Comprehensive Income (Loss), Net of Tax Retained earnings Retained Earnings (Accumulated Deficit) Total Southwest Gas Holdings, Inc. equity Noncontrolling interest Stockholders' Equity Attributable to Noncontrolling Interest Total equity Redeemable noncontrolling interest Redeemable Noncontrolling Interest, Equity, Carrying Amount Long-term debt, less current maturities Total capitalization Capitalization, Long-term Debt and Equity Commitments and contingencies (Note 10) Commitments and Contingencies Current liabilities: Liabilities, Current [Abstract] Current maturities of long-term debt Short-term debt Short-term Debt Accounts payable Accounts Payable, Current Customer deposits Customer Deposits, Current Income taxes payable, net Income Taxes Payable Net Income taxes payable net. 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 Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Swaps Swap [Member] Prepaid and other current assets Prepaid Expenses and Other Current Assets [Member] Other deferred credits Other Deferred Credits [Member] Other Deferred Credits [Member] Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Asset Derivatives Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value Liability Derivatives Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value Net Total Other Derivatives Not Designated as Hedging Instruments at Fair Value, Net Income Statement [Abstract] Operating revenues: Revenues [Abstract] Gas operating revenues Regulated Operating Revenue, Gas Utility infrastructure services revenues Total operating revenues 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 Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction 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 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 (loss) attributable to noncontrolling interests Net Income (Loss) Attributable to Noncontrolling Interest Net income attributable to Southwest Gas Holdings, Inc. Earnings per share: Earnings Per Share [Abstract] Basic earnings per share (in USD per share) Diluted earnings per share (in USD per share) 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 Schedule Of Regulatory Assets And Liabilities [Table] Schedule Of Regulatory Assets And Liabilities [Table] Schedule Of Regulatory Assets And Liabilities [Table] Regulatory Asset [Axis] Regulatory Asset [Axis] Regulatory Asset [Domain] Regulatory Asset [Domain] Accrued pension and other postretirement benefit costs Accrued Pension And Other Postretirement Benefit Costs [Member] Accrued Pension And Other Postretirement Benefit Costs [Member] Unrealized net loss on non-trading derivatives (Swaps) Unrealized Loss On Non Trading Derivatives, Assets [Member] Unrealized Loss On Non-Trading Derivatives, Assets Deferred purchased gas costs Deferred Purchased Gas Costs, Assets [Member] Deferred Purchased Gas Costs, Assets Accrued purchased gas costs Accrued Purchased Gas Costs [Member] Accrued Purchased Gas Costs [Member] Unamortized premium on reacquired debt Unamortized Premium On Reacquired Debt [Member] Unamortized Premium On Reacquired Debt [Member] Accrued absence time Accrued Absence Time [Member] Accrued absence time. Margin, interest - and property tax-tracking Margin, Interest - and Property Tax-Tracking [Member] Margin, Interest - and Property Tax-Tracking Other regulatory assets Regulatory Assets Other [Member] Regulatory Assets Other [Member] Deferred purchased gas costs Deferred Purchased Gas Costs, Liabilities [Member] Deferred Purchased Gas Costs, Liabilities [Member] Accumulated removal costs Accumulated Removal Costs [Member] Accumulated Removal Costs [Member] Unrealized net gain on non-trading derivatives (Swaps) Unrealized Loss On Non Trading Derivatives, Liabilities [Member] Unrealized Loss On Non Trading Derivatives, Liabilities [Member] Unamortized gain on reacquired debt Unamortized Gain On Reacquired Debt [Member] Unamortized Gain On Reacquired Debt [Member] Regulatory excess deferred taxes and gross -up Regulatory Offsets To Deferred Tax Balances [Member] Regulatory offsets to deferred tax balances. Gross-up related to contributions in aid of construction Gross-Up Related To Contributions In Aid Of Construction [Member] Gross-Up Related To Contributions In Aid Of Construction [Member] Regulatory Assets And Liabilities [Line Items] Regulatory Assets And Liabilities [Line Items] Regulatory Assets And Liabilities [Line Items] Regulatory assets Regulatory Assets Net regulatory liabilities Net Regulatory Liabilities Net Regulatory Liabilities $100 Million Credit Facility $100 Million Credit Facility [Member] $100 Million Credit Facility [Member] $400 Million Credit Facility $400 Million Credit Facility [Member] $400 Million Credit Facility [Member] Southwest Gas Credit Facility Southwest Gas Credit Facility [Member] Southwest Gas Credit Facility [Member] Commercial Paper Program Commercial Paper Program [Member] Commercial Paper Program [Member] Line of Credit Line of Credit [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] Statistical Measurement [Axis] Statistical Measurement [Axis] Statistical Measurement [Domain] Statistical Measurement [Domain] Minimum Minimum [Member] Maximum Maximum [Member] 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 Commitment fee percentage Line of Credit Facility, Commitment Fee Percentage Long-term debt Borrowings outstanding under facility Minimum current borrowing usage Line Of Credit Facility Minimum Amount Outstanding During Period Line Of Credit Facility Minimum Amount Outstanding During Period Maximum current borrowing usage Line of Credit Facility, Maximum Amount Outstanding During Period Debt instrument discount rate Debt Instrument, Discount Rate Debt Instrument, Discount Rate Debt secured by assets Debt Instrument, Collateral Amount Debt instrument percentage 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 Issuance of additional debt Debt Instrument Covenant Compliance Credit Risk Exposure Amount Debt instrument covenant compliance credit risk exposure amount. Equity cushion relating to minimum net worth requirement Equity Cushion Relating To Minimum Net Worth Requirement Equity cushion relating to minimum net worth requirement. Equity cushion relating to minimum fixed charge ratio coverage requirement Equity Cushion Relating To Minimum Fixed Charge Ratio Coverage Requirement Equity cushion relating to minimum fixed charge ratio coverage requirement. Percentage of maximum dividend payout restriction Percentage Of Maximum Dividend Payout Restriction Percentage of maximum dividend payout restriction. Weighted average interest rate Debt, Weighted Average Interest Rate Short term borrowings outstanding Multiemployer Plan Type [Axis] Multiemployer Plan Type [Axis] Multiemployer Plans Type [Domain] Multiemployer Plans Type [Domain] Multiemployer Plans, Pension Multiemployer Plans, Pension [Member] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Maximum contribution of employer Defined Contribution Plan, Employer Matching Contribution, Percent of Match Employee investment plan cost Employees' Investment Plan, Cost Employees' Investment Plan, Cost Deferment of annual cash compensation Deferment Of Annual Cash Compensation Deferment of annual cash compensation Matching contribution of employer Matching Contribution Of Employer Matching contribution of employer Period of additional option to receive payment Additional Deferred Compensation Payment Options Period Of Payment Period Additional Deferred Compensation Payment Options, period of payment, period Deferred compensation, percentage of multiple interest rate Floating Interest Rate Index Floating Interest Rate Index Increments of change to the discount rate Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate, Increments Of Change Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate, Increments Of Change Decrease of discount rate Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate, Increase (Decrease) Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate, Increase (Decrease) Decrease of asset return assumption Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets, Increase (Decrease) Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets, Increase (Decrease) Future estimated funding amount Future Estimated Funding Amount Future estimated funding amount Per capita cost of covered health care benefits medical rate trend assumption Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year Defined contribution plans, employer contribution amount Defined Contribution Plan, Employer Discretionary Contribution Amount Deferred compensation plan, maximum percentage of salary deferral Deferred Compensation Arrangement With Individual, Maximum Percentage Of Deferral Deferred Compensation Arrangement With Individual, Maximum Percentage Of Deferral Deferred compensation plan, matching percentage Deferred Compensation Arrangement With Individual, Matching Percentage Deferred Compensation Arrangement With Individual, Matching Percentage Deferred compensation plan, maximum percentage of salary with matching Deferred Compensation Arrangement With Individual, Maximum Percentage Of Salary With Matching Deferred Compensation Arrangement With Individual, Maximum Percentage Of Salary With Matching Deferred compensation plan, vesting percentage of deferral Deferred Compensation Arrangement With Individual, Vesting Percentage Of Deferral Deferred Compensation Arrangement With Individual, Vesting Percentage Of Deferral Multiemployer plan, contributions by employer Multiemployer Plan, Contributions by Employer Special surcharges Multiemployer Plan, Special Surcharges Multiemployer Plan, Special Surcharges Number of critical multiemployer plan Multiemployer Plan, Number Of Critical Plan Multiemployer Plan, Number Of Critical Plan Income Tax Disclosure [Abstract] Income Taxes [Table] Income Taxes [Table] Income Taxes [Table] Income Taxes [Line Items] Income Taxes [Line Items] Income Taxes [Line Items] Deferred tax assets: Deferred Tax Assets, Net [Abstract] Deferred income taxes for future amortization of ITC and excess deferred taxes Deferred Tax Assets, Tax Credit Carryforwards Employee benefits Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits Alternative minimum tax credit Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax Federal net operating losses Deferred Tax Assets Operating Loss And Tax Credit Carryforwards Net Deferred Tax Assets, Operating Loss and Tax Credit Carryforwards, Net Interest rate swap Deferred Tax Assets, Derivative Instruments Lease-related item Deferred Tax Assets Lease Related Item Deferred Tax Assets Lease Related Item Other Deferred Tax Assets, Other Valuation allowance Deferred Tax Assets, Valuation Allowance Deferred tax assets, total Deferred Tax Assets, Net of Valuation Allowance Deferred tax liabilities: Deferred Tax Liabilities, Net [Abstract] Property-related items, including accelerated depreciation Deferred Tax Liabilities, Property, Plant and Equipment Regulatory balancing accounts Deferred Tax Liabilities, Regulatory Assets and Liabilities Unamortized ITC Accumulated Deferred Investment Tax Credit Debt-related costs Deferred Tax Liabilities, Deferred Expense, Debt Issuance Costs Intangibles Deferred Tax Liabilities, Intangible Assets Lease-related item Deferred Tax Liabilities Lease Related Item Deferred Tax Liabilities Lease Related Item Other Deferred Tax Liabilities, Other Deferred tax liabilities, total Deferred Tax Liabilities, Net Net deferred tax liabilities Deferred Income Tax Liabilities, Net Contracts receivable, net Revenue earned on contracts in progress in excess of billings Contract with Customer, Asset, after Allowance for Credit Loss Amounts billed in excess of revenue earned on contracts Contract with Customer, Liability 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] Noncontrolling interest Noncontrolling Interest [Member] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning balance (in shares) Common Stock, Shares, Outstanding Common stock issuances (in shares) Change in ownership of noncontrolling interest Noncontrolling Interest, Increase from Subsidiary Equity Issuance 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), Reclassification Adjustment from AOCI on Derivatives, Net of Tax Reclassification of excess deferred taxes Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings, Tax Effect Net income (loss) Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest Redemption value adjustments Noncontrolling Interest, Change in Redemption Value Distribution to Southwest Gas Holdings, Inc. investment in discontinued operations Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Share-based compensation Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture Contributions from Southwest Gas Holdings, Inc. Adjustments To Additional Paid In Capital Contributions From Parent Adjustments to additional paid in capital contributions from parent. Dividends declared Dividends, Common Stock Ending balance (in shares) Dividends declared per share (in USD per share) Common Stock, Dividends, Per Share, Declared Summary of Income Before Taxes and Noncontrolling Interest for Domestic and Foreign Operations Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block] Summary of Income Tax Expense (Benefit) Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Significant Components of Deferred Income Tax Expense (Benefit) Schedule Of Deferred Income Tax Expense Benefit [Table Text Block] Schedule Of Deferred Income Tax Expense (Benefit) [Table Text Block] Reconciliation of U.S Federal Statutory Rate to Consolidated Effective Tax Rate Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Deferred Tax Assets and Liabilities Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Reconciliation of Unrecognized Tax Benefits Summary of Positions for which Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Table Text Block] Summary of Income Before Taxes for Continuing and Discontinued Operations Schedule Of Income Before Income Tax, Continuing And Discontinued Operations [Table Text Block] Schedule Of Income Before Income Tax, Continuing And Discontinued Operations [Table Text Block] Statement of Cash Flows [Abstract] CASH FLOW FROM OPERATING ACTIVITIES: Net Cash Provided by (Used in) Operating Activities [Abstract] Net income 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] 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 Unbilled Receivables Deferred purchased gas costs Increase (Decrease) in Deferred Gas Cost Accounts payable Increase (Decrease) in Accounts Payable Accrued taxes Increase (Decrease) in Accrued Taxes Payable 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 Increase (Decrease) in Customer Advances Other inflows 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 Contributions from parent Proceeds from Contributions from Parent Dividends paid Payments of Ordinary Dividends, Common Stock Centuri distribution to redeemable noncontrolling interest Payments of Ordinary Dividends, Noncontrolling Interest 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 capital lease obligations Repayments of Debt and Lease Obligation Redemption of Centuri shares from noncontrolling parties Payments for Repurchase of Redeemable Noncontrolling Interest 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 Income Taxes Income Tax Disclosure [Text Block] Business Acquisitions Business Combination Disclosure [Text Block] Noncontrolling Interest [Abstract] Redeemable Noncontrolling Interest Noncontrolling Interest Disclosure [Text Block] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Management Incentive Plan Management Incentive Plan [Member] Management incentive plan. Restricted Stock/Unit Plan Restricted Stock/Unit Plan [Member] Restricted Stock/Unit Plan [Member] Award Type [Axis] Award Type [Axis] Award Type [Domain] Award Type [Domain] Performance Shares Performance Shares [Member] Vesting [Axis] Vesting [Axis] Vesting [Domain] Vesting [Domain] Vesting Tranche One Share-based Payment Arrangement, Tranche One [Member] Vesting Tranche Two Share-based Payment Arrangement, Tranche Two [Member] Vesting Tranche Three Share-based Payment Arrangement, Tranche Three [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Number of stock-based compensation plans Share-based Compensation Arrangement By Share-based Payment Award, Number Of Plans Share-based Compensation Arrangement By Share-based Payment Award, Number Of Plans Performance measurement period Share-based Compensation Arrangement by Share-based Payment Award, Performance Measurement Period Share-based Compensation Arrangement by Share-based Payment Award, Performance Measurement Period Compensation expense Award vesting percentage Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage Number of shares, granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Award vesting period Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Weighted average grant date fair value (in USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Compensation cost related to nonvested management incentive plan shares, performance shares, and restricted stock/units not yet recognized Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Compensation cost not yet recognized, period for recognition Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition 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 2020 Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months 2021 Long-term Debt, Maturities, Repayments of Principal in Year Two 2022 Long-term Debt, Maturities, Repayments of Principal in Year Three 2023 Long-term Debt, Maturities, Repayments of Principal in Year Four 2024 Long-term Debt, Maturities, Repayments of Principal in Year Five Net actuarial loss 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 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] Consolidation Consolidation, Policy [Policy Text Block] Fair Value Measurements Fair Value Measurement, Policy [Policy Text Block] Net Utility Plant Property, Plant and Equipment, Policy [Policy Text Block] Intangible Assets Intangible Assets, Finite-Lived, Policy [Policy Text Block] Cash and Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Income Taxes Income Tax, Policy [Policy Text Block] Deferred Purchased Gas Costs Deferred Purchased Costs [Policy Text Block] Deferred Purchased Costs Policy Text Block. Prepaids and Other Current Assets Prepaid And Other Current Assets Policy [Policy Text Block] Prepaid And Other Current Assets Policy [Policy Text Block] Goodwill Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block] Other Current Liabilities Other Current Liabilities [Policy Text Block] Other Current Liabilities [Policy Text Block] Accumulated Removal Costs Accumulated Removal Costs [Policy Text Block] Accumulated Removal Costs Policy Text Block. Revenue Recognition Revenue from Contract with Customer [Policy Text Block] Operations and Maintenance Expense Operations And Maintenance Expense [Policy Text Block] Operations And Maintenance Expense Policy Text Block Depreciation and Amortization Regulatory Depreciation and Amortization, Policy [Policy Text Block] Allowance for Funds Used During Construction ("AFUDC") Allowance for Funds Used During Construction, Policy [Policy Text Block] Foreign Currency Translation Foreign Currency Transactions and Translations Policy [Policy Text Block] Earnings Per Share Earnings Per Share, Policy [Policy Text Block] Recently Accounting Standards Updates New Accounting Pronouncements, Policy [Policy Text Block] Subsequent Events Subsequent Events, Policy [Policy Text Block] Debt Debt Disclosure [Text Block] Schedule of Assumptions Used Defined Benefit Plan, Assumptions [Table Text Block] Schedule of Defined Benefit Plans Disclosures Schedule of Defined Benefit Plans Disclosures [Table Text Block] Schedule of Accumulated Benefit Obligation Schedule of Accumulated and Projected Benefit Obligations [Table Text Block] Schedule of Expected Benefit Payments Schedule of Expected Benefit Payments [Table Text Block] Schedule of New Accounting Pronouncements Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block] Schedule of Net Benefit Cost Schedule of Net Benefit Costs [Table Text Block] Schedule of Amounts Recognized in Other Comprehensive Income Schedule of Fair Value of Plan Assets Schedule of Allocation of Plan Assets [Table Text Block] Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt Schedule of Long-term Debt Instruments [Table Text Block] Summary of Effective Interest Rates on Variable-Rate IDRBs Schedule Of Effective Interest Rates On Long Term Debt [Table Text Block] Schedule Of Effective Interest Rates On Long-Term Debt [Table Text Block] Estimated Maturities of Long-Term Debt Schedule of Maturities of Long-term Debt [Table Text Block] SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis] SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis] SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain] SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain] Allowance for Uncollectibles SEC Schedule, 12-09, Allowance, Credit Loss [Member] SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] Beginning Balance SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount Additions charged to expense SEC Schedule, 12-09, Valuation Allowances and Reserves, Additions, Charge to Cost and Expense Accounts written off, less recoveries SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction Ending Balance Income Tax Disclosure [Table] Income Tax Disclosure [Table] Income Tax Disclosure [Table] Income Tax Authority [Axis] Income Tax Authority [Axis] Income Tax Authority [Domain] Income Tax Authority [Domain] Federal Domestic Tax Authority [Member] Tax Credit Carryforward [Axis] Tax Credit Carryforward [Axis] Tax Credit Carryforward, Name [Domain] Tax Credit Carryforward, Name [Domain] Capital Loss Carryforward Capital Loss Carryforward [Member] Income Tax Disclosure [Line Items] Income Tax Disclosure [Line Items] Income Tax Disclosure [Line Items] Unrecognized tax benefits that, if recognized, would affect the effective tax rate Unrecognized Tax Benefits that Would Impact Effective Tax Rate Significant increases or decreases in unrecognized tax benefit within the next 12 months Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit Tax-related interest income Income Tax Examination, Interest Expense Regulatory liability related to TCJA Tax Cuts And Jobs Act Of 2017, Regulatory Liability Tax Cuts And Jobs Act Of 2017, Regulatory Liability Operating loss carryforward Operating Loss Carryforwards Tax credit carryforward Tax Credit Carryforward, Amount Quarterly Financial Data (Unaudited) Quarterly Financial Information [Text Block] Accounts Receivable for Services Accounts Receivable For Services [Table Text Block] Accounts Receivable For Services Table Text Block. Schedule of Revenues by Geographic Area Revenue from External Customers by Geographic Areas [Table Text Block] Schedule of Segment Reporting Information Schedule of Segment Reporting Information, by Segment [Table Text Block] Customer accounts receivable Trade names and trademarks Trademarks and Trade Names [Member] Customer contracts backlog Noncompete agreements Noncompete Agreements [Member] Gross Carrying Amount Finite-Lived Intangible Assets, Gross Accumulated Amortization Finite-Lived Intangible Assets, Accumulated Amortization Summary of Fair Values of Assets Acquired and Liabilities Assumed Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block] Schedule of Pro Forma Consolidated Financial Information Business Acquisition, Pro Forma Information [Table Text Block] Schedule of Statements of Income Operations Condensed Income Statement [Table Text Block] Background, Organization and Summary of Significant Accounting Policies Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block] Net actuarial loss (gain) Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax Amortization of prior service cost Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax Amortization of net actuarial loss Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax Prior service cost Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Tax Regulatory adjustment Defined Benefit Plan Regulatory Adjustment Before Tax Net Defined benefit plan, regulatory adjustment before-tax net. Recognized in other comprehensive (income) loss Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Reclassification Adjustment, before Tax Net periodic benefit costs recognized in net income Total of amount recognized in net periodic benefit cost and other comprehensive (income) loss Defined Benefit Plan, Amount Recognized in Net Periodic Benefit Cost (Credit) and Other Comprehensive (Income) Loss, before Tax Income Tax [Table] Income Tax [Table] Income Tax [Table] Income Tax [Line Items] Income Tax [Line Items] Income Tax [Line Items] Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] Unrecognized tax benefits at beginning of year Unrecognized Tax Benefits Gross increases – tax positions in prior period Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions Gross decreases – tax positions in prior period Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions Gross increases – current period tax positions Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions Gross decreases – current period tax positions Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions Settlements Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities Lapse in statute of limitations Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations Unrecognized tax benefits at end of year Share-Based Compensation Share-based Payment Arrangement [Text Block] Revenue Revenue from Contract with Customer [Text Block] 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), Derivatives Qualifying as Hedges, Net of Tax 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 (loss) 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 Investment [Table] Investment [Table] Investment [Line Items] Investment [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 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] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Operating Segments Operating Segments [Member] Corporate and administrative Corporate, Non-Segment [Member] 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 Other components of net periodic benefit cost Defined Benefit Plan, Actuarial Gain (Loss), Immediate Recognition as Component in Net Periodic Benefit (Cost) Credit Foreign transaction gain (loss) Foreign Currency Transaction Gain (Loss), Realized Equity in earnings of unconsolidated investment – Western Income (Loss) from Equity Method Investments Miscellaneous income and (expense) Miscellaneous Income Expense Miscellaneous income (expense). Total other income (deductions) Derivative collateral outstanding Derivative, Collateral Outstanding Derivative, Collateral Outstanding Cash and cash equivalents Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents Accounts receivable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables Revenue earned on contracts in progress in excess of billings Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Current Assets Other Receivables Business combination recognized identifiable assets acquired and liabilities assumed current assets other receivables. Prepaid expenses and other current assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Prepaid Expense and Other Assets Property and equipment Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment Intangible assets Goodwill Total assets acquired Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets Accounts payable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable Accrued liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Accrued Liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Accrued Liabilities Deferred compensation and related accrued taxes Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Compensation And Related Accrued Taxes Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Compensation And Related Accrued Taxes Redeemable noncontrolling interest Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other Total liabilities assumed and noncontrolling interest Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities Net assets acquired Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustments [Abstract] Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustments [Abstract] Accounts receivable, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Accounts Receivable Net Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Accounts Receivable Revenue earned on contracts in progress in excess of billings, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Revenue Earned On Contracts In Progress In Excess Of Billings Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Revenue Earned On Contracts In Progress In Excess Of Billings Prepaid expenses and other current assets, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Prepaid Expenses And Other Current Assets Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Prepaid Expenses And Other Current Assets Property and equipment, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Property, Plant, and Equipment Intangible assets, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Intangibles Goodwill, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Goodwill Net Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Goodwill Net Total assets acquired, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Assets Net Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Assets Net Accrued liabilities, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Accrued Liabilities Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Accrued Liabilities Total liabilities assumed and noncontrolling interest, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Liabilities Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Liabilities Measurement Period Adjustments Consolidated rental payments/lease expense Operating Leases, Rent Expense, Net Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Summary of Redeemable Noncontrolling Interest Redeemable Noncontrolling Interest [Table Text Block] Share-based compensation plan expense, net of related tax benefits Share-based Payment Arrangement, Expense, after Tax Share-based compensation plan related tax benefits Share-based Payment Arrangement, Expense, Tax Benefit Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Fair Value, Inputs, Level 1 and 2 Fair Value, Inputs, Level 1, 2 and 3 [Member] Level 1 – Quoted prices in active markets for identical financial assets Fair Value, Inputs, Level 1 [Member] Level 2 – Significant other observable inputs Fair Value, Inputs, Level 2 [Member] Insurance company general account contracts Fair Value Measured at Net Asset Value Per Share [Member] Defined Benefit Plan, Plan Assets, Category [Axis] Defined Benefit Plan, Plan Assets, Category [Axis] Defined Benefit Plan, Plan Assets, Category [Domain] Defined Benefit Plan, Plan Assets, Category [Domain] Mutual funds Mutual Fund [Member] Global Global [Member] Global [Member] International International [Member] International. U.S. equity securities Defined Benefit Plan, Equity Securities, US [Member] Emerging markets Emerging Markets [Member] Emerging markets. Private commingled fixed income funds Defined Benefit Plan, Private Commingled Fixed Income Funds [Member] Defined Benefit Plan, Private Commingled Fixed Income Funds [Member] Pooled funds and mutual funds Pooled Funds And Mutual Funds [Member] Pooled funds and mutual funds. Government fixed income and mortgage backed securities Asset-backed Securities [Member] Defined benefit plan, plan assets, amount 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. Retirement plan Accumulated benefit obligation Defined Benefit Plan, Accumulated Benefit Obligation Significant Components Of Deferred Income Tax Expense [Table] Significant Components Of Deferred Income Tax Expense [Table] Significant Components Of Deferred Income Tax Expense [Table] Property-related items Property Related Items [Member] Property-Related Items [Member] Purchased gas cost adjustments Purchased Gas Cost Adjustments [Member] Purchased Gas Cost Adjustments [Member] Employee benefits Employee Benefits [Member] Employee Benefits [Member] Regulatory adjustments Regulatory Adjustments [Member] Regulatory Adjustments [Member] All other deferred All Other Deferred [Member] All Other Deferred [Member] Significant Components Of Deferred Income Tax Expense [Line Items] Significant Components Of Deferred Income Tax Expense [Line Items] Significant Components Of Deferred Income Tax Expense [Line Items] Deferred federal and state: Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract] Total deferred federal and state Deferred Federal And State Income Tax Expense Benefit Deferred federal and state income tax expense benefit Deferred ITC, net Deferred Investment Tax Credit, Net Deferred Investment Tax Credit, Net Total deferred income tax expense Deferred Income Tax Expense (Benefit) Schedule of Quarterly Financial Data Quarterly Financial Information [Table Text Block] U.S. Income (Loss) from Continuing Operations before Income Taxes, Domestic Foreign Income (Loss) from Continuing Operations before Income Taxes, Foreign Total income before income taxes Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Operating lease liabilities, current Operating Lease, Liability, Current Operating lease liabilities, noncurrent Operating Lease, Liability, Noncurrent Total Operating lease, weighted average remaining lease term (in years) Operating Lease, Weighted Average Remaining Lease Term Finance lease, weighted average remaining lease term (in years) Finance Lease, Weighted Average Remaining Lease Term Finance lease, weighted average discount rate Operating Lease, Weighted Average Discount Rate, Percent Finance lease ROU assets Finance Lease, Right-of-Use Asset Finance lease liabilities, current Finance lease liabilities, noncurrent Finance Lease, Liability, Noncurrent Finance lease liabilities Finance Lease, Liability Finance lease, weighted average discount rate Finance Lease, Weighted Average Discount Rate, Percent Movement In Redeemable Noncontrolling Interest [Roll Forward] Movement In Redeemable Noncontrolling Interest [Roll Forward] Movement In Redeemable Noncontrolling Interest [Roll Forward] Balance, Beginning Redeemable noncontrolling interest acquired Temporary Equity, Stock Issued During Period, Value, New Issues Net income attributable to redeemable noncontrolling interest Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Balance, Ending Schedule of Other Property and Investments Investment [Table Text Block] Summary of Intangible Assets Schedule of Finite-Lived Intangible Assets [Table Text Block] Schedule of Estimated Future Amortization of Intangible Assets Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Schedule of Goodwill Schedule of Goodwill [Table Text Block] Schedule of Capitalized and Debt Portion of AFUDC Schedule of Capitalization [Table Text Block] Schedule of Other Income (Deductions) Schedule of Other Nonoperating Income, by Component [Table Text Block] Schedule of Earnings Per Share, Basic and Diluted Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Noncontrolling Interest [Table] Noncontrolling Interest [Table] Noncontrolling Interest [Line Items] Noncontrolling Interest [Line Items] Percentage of interest retained by noncontrolling party subject to election Noncontrolling Interest, Percentage Of Interest Retained By Noncontrolling Party Subject To Election Noncontrolling Interest, Percentage Of Interest Retained By Noncontrolling Party Subject To Election Paid to counterparties Payments For Derivative Instrument Operating Activities The cash outflow for derivative instruments during the period, which are classified as operating activities, excluding those designated as hedging instruments. Received from counterparties Proceeds from Derivative Instrument, Investing Activities Schedule of Regulatory Assets [Table] Schedule of Regulatory Assets [Table] Prepaids and other current assets Deferred charges and other assets Deferred Charges And Other Assets [Member] Deferred Charges And Other Assets [Member] Infrastructure replacement programs and similar Infrastructure Replacement Programs and Similar [Member] Infrastructure replacement programs and similar. Other Other Miscellaneous Regulatory Asset [Member] Other Miscellaneous Regulatory Asset [Member] Regulatory Assets [Line Items] Regulatory Assets [Line Items] 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] Number of types of services provided to customers Number Of Types Of Services Provided To Customers Number Of Types Of Services Provided To Customers Number of customers Number Of Customers Number Of Customers Number of types of agreements with customers Number Of Types Of Agreements With Customers Number Of Types Of Agreements With Customers Number of customers party to contracts with rate components subject to negotiation (less than) Number Of Customers Party To Contracts With Rate Components Subject To Negotiation Number Of Customers Party To Contracts With Rate Components Subject To Negotiation 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 Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Net Assets, Geographic Area Net Assets, Geographic Area [Member] Concentration Risk Type [Axis] Concentration Risk Type [Axis] Concentration Risk Type [Domain] Concentration Risk Type [Domain] Geographic Concentration Risk Geographic Concentration Risk [Member] Long-lived assets Concentration Risk, Percentage Number of reportable segments Number of Reportable Segments Significant Accounting Policies [Table] Significant Accounting Policies [Table] Significant Accounting Policies [Table] 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. Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] Money Market Funds Money Market Funds [Member] Investment, Name [Axis] Investment, Name [Axis] Investment, Name [Domain] Investment, Name [Domain] W.S. Nicholls Western Construction LTD WS Nicholls Western Construction Ltd [Member] WS Nicholls Western Construction Ltd. Significant Accounting Policies [Line Items] Significant Accounting Policies [Line Items] Significant Accounting Policies [Line Items] VIR ownership percentage Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage Exposure to loss as a result of its investment Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount Amortization expenses Money market fund investments Cash and Cash Equivalents, Fair Value Disclosure Cumulative foreign earnings Undistributed Earnings of Foreign Subsidiaries Gas pipe materials and operating supplies Materials, Supplies, and Other Prepaid and other current assets Regulatory Assets, Current Goodwill impairment charges Goodwill, Impairment Loss Business combination consideration Regulatory Assets and Liabilities Schedule of Regulatory Assets and Liabilities [Text Block] 2020 Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months 2021 Lessee, Operating Lease, Liability, Payments, Due Year Two 2022 Lessee, Operating Lease, Liability, Payments, Due Year Three 2023 Lessee, Operating Lease, Liability, Payments, Due Year Four 2024 Lessee, Operating Lease, Liability, Payments, Due Year Five Thereafter Lessee, Operating Lease, Liability, Payments, Due after Year Five Total lease payments Lessee, Operating Lease, Liability, Payments, Due Less imputed interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount Finance Lease, Liability, Payment, Due [Abstract] Finance Lease, Liability, Payment, Due [Abstract] 2020 Finance Lease, Liability, Payments, Due Next Twelve Months 2021 Finance Lease, Liability, Payments, Due Year Two 2022 Finance Lease, Liability, Payments, Due Year Three 2023 Finance Lease, Liability, Payments, Due Year Four 2024 Finance Lease, Liability, Payments, Due Year Five Thereafter Finance Lease, Liability, Payments, Due after Year Five Total lease payments Finance Lease, Liability, Payment, Due Less imputed interest Finance Lease, Liability, Undiscounted Excess Amount Finance lease liabilities Schedule of Net Utility Plant Public Utility Property, Plant, and Equipment [Table Text Block] Schedule of Depreciation and Amortization Expense Schedule Of Depreciation And Amortization Expense [Table Text Block] Schedule Of Depreciation And Amortization Expense Table Text Block Components of Lease Expense, and Supplemental Cash Flow Information Related to Leases Lease, Cost [Table Text Block] Supplemental Information Related to Leases Included in Balance Sheet Assets And Liabilities, Lessee [Table Text Block] Assets And Liabilities, Lessee [Table Text Block] Schedule of Maturities of Operating Lease Liabilities Lessee, Operating Lease, Liability, Maturity [Table Text Block] Schedule of Maturities of Finance Lease Liabilities Finance Lease, Liability, Maturity [Table Text Block] Schedule of Rental and Lease Payments Schedule of Rent Expense [Table Text Block] Schedule of Future Minimum Lease Payments for Operating Leases Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block] Restatement [Axis] Restatement [Axis] Restatement [Domain] Restatement [Domain] Originally Reported Previously Reported [Member] Reclassification Restatement Adjustment [Member] Gas utility customer accounts receivable balance Gas Utility Customer Accounts Receivable Gas Utility Customer Accounts Receivable 2019 Operating Leases, Future Minimum Payments Due, Next Twelve Months 2020 Operating Leases, Future Minimum Payments, Due in Two Years 2021 Operating Leases, Future Minimum Payments, Due in Three Years 2022 Operating Leases, Future Minimum Payments, Due in Four Years 2023 Operating Leases, Future Minimum Payments, Due in Five Years Thereafter Operating Leases, Future Minimum Payments, Due Thereafter Total minimum lease payments Operating Leases, Future Minimum Payments Due Debt portion Public Utilities, Allowance for Funds Used During Construction, Capitalized, Debt Portion Public Utilities, Allowance for Funds Used During Construction, Capitalized, Debt Portion Equity portion AFUDC capitalized as part of utility plant Public Utilities, Allowance for Funds Used During Construction, Additions AFUDC rate Public Utilities, Allowance for Funds Used During Construction, Rate Contract notional amounts Derivative, Nonmonetary Notional Amount Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Abstract] Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Table] Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Table] Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] Total income before income taxes Income (Loss), Including Portion Attributable to Noncontrolling Interest, before Tax Utility Infrastructure Services Intersegment sales Intersegment Eliminations [Member] Other Segment Reconciling Items [Member] Revenues Revenues Interest income Interest expense Depreciation and amortization Income tax expense Segment net income Segment assets Capital expenditures Number of nonvested/unissued shares Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Nonvested/unissued at beginning of year (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Granted (in shares) Dividends (in shares) Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Dividends Share based compensation arrangement by share based payment award equity instruments other than options dividends Forfeited or expired (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Vested and issued (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Nonvested/unissued at year end (in shares) Weighted- average grant date fair value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Beginning balance (in USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Granted (in USD per share) Forfeited or expired (in USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Vested and issued (in USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Ending balance (in USD per share) Pension and Other Postretirement Benefits Pension and Other Postretirement Benefits Disclosure [Text Block] U.S. federal statutory income tax rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Net state taxes Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent Tax credits Effective Income Tax Rate Reconciliation, Tax Credit, Percent Company-owned life insurance Effective Income Tax Rate Reconciliation Company Owned Life Insurance Effective income tax rate reconciliation, company owned life insurance. Change in U.S. Federal Income Tax Rate Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent Amortization of excess deferred taxes Effective Income Tax Rate Reconciliation, Amortization Of Excess Deferred Taxes, Percent Effective Income Tax Rate Reconciliation, Amortization Of Excess Deferred Taxes, Percent All other differences Effective Income Tax Rate Reconciliation, Other Adjustments, Percent Consolidated effective income tax rate Common Stock Common Stock Disclosure [Text Block] Common Stock Disclosure [Text Block] 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. Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Tax Reform Savings Revenue Adjustments Tax Reform Savings Revenue Adjustments [Member] Tax reform savings revenue adjustments. 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 Current: Current Income Tax Expense (Benefit), Continuing Operations [Abstract] Federal Current Federal Tax Expense (Benefit) State Current State and Local Tax Expense (Benefit) Foreign Current Foreign Tax Expense (Benefit) Total current income tax expense Current Income Tax Expense (Benefit) Deferred: Federal Deferred Federal Income Tax Expense (Benefit) State Deferred State and Local Income Tax Expense (Benefit) Foreign Deferred Foreign Income Tax Expense (Benefit) Total income tax expense Utility Plant and Leases Utility Plant And Leases Disclosure [Text Block] Utility Plant And Leases Disclosure [Text Block] Schedule of Accounts Receivable Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Schedule of Percent of Customers by State Schedule Of Percent Of Customers By State [Table Text Block] Schedule of percent of customers by state table text block. Schedule of Allowance for Uncollectibles SEC Schedule, 12-09, Schedule of Valuation and Qualifying Accounts Disclosure [Text Block] Pension 2020 Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months 2021 Defined Benefit Plan, Expected Future Benefit Payment, Year Two 2022 Defined Benefit Plan, Expected Future Benefit Payment, Year Three 2023 Defined Benefit Plan, Expected Future Benefit Payment, Year Four 2024 Defined Benefit Plan, Expected Future Benefit Payment, Year Five 2025-2029 Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter Net actuarial gain/(loss) Foreign currency items Accumulated Foreign Currency Adjustment Attributable to Parent [Member] Schedule of Goodwill [Table] Schedule of Goodwill [Table] Natural Gas Operations Southwest [Member] Southwest [Member] Neuco Neuco [Member] Neuco. Goodwill [Line Items] Goodwill [Line Items] Goodwill [Roll Forward] Goodwill [Roll Forward] Goodwill, Beginning balance Goodwill from acquisition Goodwill, Acquired During Period Measurement-period adjustments Goodwill, Purchase Accounting Adjustments Foreign currency translation adjustment Goodwill, Foreign Currency Translation Gain (Loss) Goodwill, Ending balance Depreciation and amortization expense 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) Cover page. Entities [Table] Entities [Table] Entity Information [Line Items] Entity Information [Line Items] Document Type Document Type Document Annual Report Document Annual 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 Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Voluntary Filers 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 Public Float Entity Public Float Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Documents Incorporated by Reference Documents Incorporated by Reference [Text Block] 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