Deferred income taxes Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets SUPPLEMENTAL INFORMATION: Supplemental Cash Flow Information [Abstract] Customer [Domain] Customer [Domain] Foreign transaction gain (loss) Foreign Currency Transaction Gain (Loss), Realized Reclassification from AOCI, before Tax Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax Earnings Per Share Earnings Per Share, Policy [Policy Text Block] Net income attributable to Southwest Gas Holdings, Inc. Segment net income (loss) Net Income (Loss) Attributable to Parent Unit price contracts Unit Priced Contracts [Member] Unit priced contracts. Interest cost Defined Benefit Plan, Interest Cost Acquisition-related costs Business Combination, Acquisition Related Costs Receivable Type [Axis] Receivable Type [Axis] Statistical Measurement [Domain] Statistical Measurement [Domain] Accrued utility revenue Accrued utility revenue Increase (Decrease) in Contract with Customer, Asset Billed on completed contracts and contracts in progress Billed On Completed Contracts And Contracts In Progress [Member] Billed on completed contracts and contracts in progress. 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Intersegment revenues Segment Reconciling Items [Member] Term Loan Facility Due December 30, 2022 Term Loan Facility Due December 30, 2022 [Member] Term Loan Facility Due December 30, 2022 Transportation Transportation [Member] Transportation. 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Summary of Revenue Disaggregated by Service Type and Contract Type Disaggregation of Revenue [Table Text Block] Schedule of 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). Measurement Period Adjustments, Other liabilities Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment Noncurrent Liabilities, Other Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment Noncurrent Liabilities, Other Fair Value Measurement [Domain] Fair Value Measurement [Domain] 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 Accrued purchased gas cost Accrued Purchased Gas Costs Accrued Purchased Gas Costs Revenue earned on contracts in progress in excess of billings Revenue Earned On Contracts In Progress In Excess Of Billings Revenue Earned On Contracts In Progress In Excess Of Billings Total assets acquired Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Assets Acquired Including Goodwill Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Assets Acquired Including Goodwill Change in short-term debt Proceeds from (Repayments of) Short-term Debt Notes, 2.2%, due 2030 Debentures Notes Two Point Two Percentage, Due Two Thousand And Thirty [Member] Debentures Notes Two Point Two Percentage, Due Two Thousand And Thirty Foreign currency exchange translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax, Portion Attributable to Parent Long-term debt, gross Long-term Debt, Gross Goodwill [Roll Forward] Goodwill [Roll Forward] Gross proceeds Proceeds From Issuance Of Common Stock, Gross Proceeds From Issuance Of Common Stock, Gross Plan Name [Axis] Plan Name [Axis] Long-term debt Long-term debt outstanding Long-term Debt Residential Residential [Member] Residential. 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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 CAPITALIZATION AND LIABILITIES Liabilities and Equity [Abstract] Accounts payable Increase (Decrease) in Accounts Payable Percentage of redeemable noncontrolling interest redeemed Redeemable Noncontrolling Interest, Percentage Redeemed Redeemable Noncontrolling Interest, Percentage Redeemed Short-term Debt, Type [Domain] Short-term Debt, Type [Domain] Reclassification from AOCI, tax Reclassification from AOCI, Current Period, Tax Entity Interactive Data Current Entity Interactive Data Current Other current assets and liabilities Other current assets and liabilities Increase (Decrease) in Other Current Assets and Liabilities, Net Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] Minimum Minimum [Member] Aggregate carrying value Debt Instrument, Convertible, Carrying Amount of Equity Component Income taxes receivable, net Income Taxes Receivable, Current Gas plant Public Utilities, Property, Plant and Equipment, Gas Plant Public Utilities, Property, Plant and Equipment, Gas Plant Number of Strategic Transactions Committee directors Number Of Strategic Transactions Committee Directors Number Of Strategic Transactions Committee Directors Movement In Redeemable Noncontrolling Interest [Roll Forward] Movement In Redeemable Noncontrolling Interest [Roll Forward] Movement In Redeemable Noncontrolling Interest [Roll Forward] Borrowings outstanding under facility Long-term Line of Credit Effects of currency translation on cash and cash equivalents Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents 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] Comprehensive income attributable to noncontrolling interests Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Address, State or Province Entity Address, State or Province Beginning balance, attributable to parent, before tax Ending balance, attributable to parent, before tax Stockholders' Equity Attributable To Parent, Before Tax Stockholders' Equity Attributable To Parent, Before Tax Other comprehensive income (loss) before reclassifications, before tax Other Comprehensive Income (Loss), before Reclassifications, before Tax Deferred income taxes Deferred Income Tax Assets, Net Cooperation Agreement term, beneficial ownership percentage benchmark Cooperation Agreement Term, Beneficial Ownership Percentage Benchmark Cooperation Agreement Term, Beneficial Ownership Percentage Benchmark Current liabilities: Liabilities, Current [Abstract] Total capitalization Capitalization, Long-term Debt and Equity Receivable [Domain] Receivable [Domain] Common stock issuances Common stock issued, amount Stock Issued During Period, Value, New Issues Acquisition of businesses, net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired Foreign currency items Accumulated Foreign Currency Adjustment Attributable to Parent [Member] Debt Debt Disclosure [Text Block] Line of Credit Line of Credit [Member] Revolving credit facility and commercial paper Revolving Credit Facility And Commercial Paper [Member] Revolving Credit Facility And Commercial Paper [Member] Dividends paid Dividends paid Payments of Ordinary Dividends, Common Stock SERP Supplemental Employee Retirement Plan [Member] Contract assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Contract Assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Contract Assets Measurement Period Adjustments, Accounts receivable Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Accounts Receivable Net Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Accounts Receivable Net Less: agent commissions Payments of Stock Issuance Costs Common stock issuances (in shares) Number of shares sold (in shares) Stock Issued During Period, Shares, New Issues Number of reportable segments Number of Reportable Segments Debt instrument discount rate Debt Instrument Discount Rate Debt Instrument Discount Rate Redeemable noncontrolling interests Redeemable noncontrolling interest, beginning balance Redeemable noncontrolling interest, ending balance Redeemable Noncontrolling Interest, Equity, Carrying Amount Document Transition Report Document Transition Report Common stock Common Stock, Value, Issued Disaggregation of Revenue [Line Items] 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[Table Text Block] Accumulated other comprehensive loss, net Accumulated Other Comprehensive Income (Loss), Net of Tax Entity Emerging Growth Company Entity Emerging Growth Company Notes, 3.18%, due 2051 Debentures Notes Three Point Eighteen Percentage, Due Two Thousand And Fifty One [Member] Debentures Notes Three Point Eighteen Percentage, Due Two Thousand And Fifty One Business Acquisitions Business Combination Disclosure [Text Block] Contracts receivable, gross Contract with Customer, Asset, before Allowance for Credit Loss Components of Net Periodic Benefit Cost Compensation and Employee Benefit Plans [Text Block] Ownership [Axis] Ownership [Axis] Legal Entity [Axis] Legal Entity [Axis] Beginning balance, before tax Ending balance, before tax Stockholders' Equity, Including Portion Attributable To Noncontrolling Interest, Before Tax Stockholders' Equity, Including Portion Attributable To Noncontrolling Interest, Before Tax Cover [Abstract] Cover [Abstract] Receivable from parent Centuri accounts receivable for services provided to Southwest Due from Related Parties, Current 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] Goodwill [Line Items] Goodwill [Line Items] Total operating expenses Costs and Expenses Other comprehensive income (loss) before reclassifications, net of tax Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Amortization of prior service cost Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, after Tax Class of Stock [Axis] Class of Stock [Axis] Deferred purchased gas costs Deferred Gas Purchases, Current Cash and Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Net proceeds from sale of stock Sale of Stock, Consideration Received on Transaction Regulated gas transportation and storage revenues Regulated Gas Transportation And Storage Revenues [Member] Regulated Gas Transportation And Storage Revenues Payments for redemption of redeemable noncontrolling interest Payments for Repurchase of Redeemable Noncontrolling Interest Other comprehensive income (loss) before reclassifications, tax Other Comprehensive Income (Loss) before Reclassifications, Tax Prepaid and other current assets Prepaid and other current assets Prepaid Expense and Other Assets, Current Dividends declared per share (in USD per share) Common Stock, Dividends, Per Share, Declared Entity [Domain] Entity [Domain] Revenue from contracts with customers Revenue from contracts with customers Revenue from Contract with Customer, Excluding Assessed Tax NGL revenues NGL Revenues [Member] NGL Revenues Other current liabilities Other Current Liabilities Policy [Policy Text Block] Other Current Liabilities Policy Amortization of net actuarial loss Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax Consolidation Items [Domain] Consolidation Items [Domain] Carrying Amount Reported Value Measurement [Member] Equity [Abstract] Equity [Abstract] Document Quarterly Report Document Quarterly Report Notes, 4.15%, due 2049 Debentures Notes Four Point Fifteen Percentage, Due Two Thousand And Forty Nine [Member] Debentures Notes Four Point Fifteen Percentage, Due Two Thousand And Forty Nine Southwest Gas Holdings, Inc. Common Stock, $1 Par Value Common Stock [Member] Variable Rate [Axis] Variable Rate [Axis] Other income (deductions) Other Nonoperating Income (Expense) [Abstract] 8% Series, due 2026 Debentures Eight Percentage Series Due Two Thousand And Twenty Six [Member] Debentures Eight Percentage Series Due Two Thousand And Twenty Six [Member] Segment Information Segment Reporting Disclosure [Text Block] Redemption of equity interest from noncontrolling party Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests Operating income Operating Income (Loss) Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Background, Organization, and Summary of Significant Accounting Policies Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Document Fiscal Year Focus Document Fiscal Year Focus Total assets acquired Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Assets, And Goodwill Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Assets, And Goodwill Changes in undistributed stock compensation Share-based Payment Arrangement, Noncash Expense Variable Rate [Domain] Variable Rate [Domain] AOCI Attributable to Parent, Net of Tax [Roll Forward] AOCI Attributable to Parent, Net of Tax [Roll Forward] Additional paid-in capital Additional Paid-in Capital [Member] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Change in short-term debt Change In Short-Term Debt Change In Short-Term Debt Regulated operations plant: Public Utilities, Property, Plant and Equipment, Net [Abstract] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Deferred income taxes Deferred income taxes Increase (Decrease) in Deferred Income Taxes Revenue, Remaining Performance 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[Abstract] MountainWest unsecured senior notes, 3.53%, due in 2028 Senior Notes, 3.53% Due In 2028 [Member] Senior Notes, 3.53% Due In 2028 Consolidation Items [Axis] Consolidation Items [Axis] Total equity Beginning balance, attributable to parent Ending balance, attributable to parent Stockholders' Equity Attributable to Parent Common stock, issued (in shares) Common Stock, Shares, Issued City Area Code City Area Code Recognized in AOCI Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax Prepaid expenses Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Prepaid Expense and Other Assets Fair Values of Assets Acquired and Liabilities Assumed Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract] Linetec Linetec Services, LLC [Member] Linetec Services, LLC [Member] Entity Address, City or Town Entity Address, City or Town Number of new board of directors 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Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net 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] Previous Owner Of Linetec Previous Owner Of Linetec [Member] Previous Owner Of Linetec Retained earnings Retained Earnings (Accumulated Deficit) 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] Revenues from external customers Operating Segments [Member] Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Accrued general taxes Accrual for Taxes Other than Income Taxes, Current Allowance for doubtful accounts 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Income Statement [Abstract] Income Statement [Abstract] Fair Value Estimate of Fair Value Measurement [Member] Entity Registrant Name Entity Registrant Name Accounts receivable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables Centuri Centuri Centuri Group, Inc. [Member] Centuri Group, Inc. [Member] Other receivables Other Receivables [Member] Other Receivables Beginning balance Ending balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Income tax expense Income Tax Expense (Benefit) Accounts receivable, net of allowances Accounts Receivable, after Allowance for Credit Loss, Current Amendment Flag Amendment Flag Unsecured Debt Unsecured Debt [Member] Issuance of long-term debt, net Proceeds from Issuance of Long-term Debt Debt secured by assets Debt Instrument, Collateral Amount Equity Components [Axis] Equity Components [Axis] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Entity Tax Identification Number Entity Tax Identification Number Other property and investments, net 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. Document Fiscal Period Focus Document Fiscal Period Focus Centuri distribution to redeemable noncontrolling interest Distribution To Redeemable Noncontrolling Interest Distribution To Redeemable Noncontrolling Interest Total current assets Assets, Current Sale of Stock [Domain] Sale of Stock [Domain] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Weighted average shares: Weighted Average Number of Shares Outstanding Reconciliation [Abstract] Amounts reclassified into net income FSIRS amounts reclassified to net income, net of tax Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax Schedule of Segment Reporting Information Schedule of Segment Reporting Information, by Segment [Table Text Block] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Threshold amount above self-insured retention Loss Contingency, Threshold Amount Above Self-Insured Retention Loss Contingency, Threshold Amount Above Self-Insured Retention Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Fair Value Measurements Fair Value Measurement, Policy [Policy Text Block] Current maturities of long-term debt Less: current maturities Long-term Debt, Current Maturities Product and Service [Axis] Product and Service [Axis] Utility Infrastructure Services Utility Infrastructure Services Segment [Member] Utility Infrastructure Services Segment [Member] Negative working capital condition Negative Working Capital Condition Negative Working Capital Condition Deferred Purchased Gas Costs Deferred Purchased Costs [Policy Text Block] Deferred Purchased Costs Equity Component [Domain] Equity Component [Domain] Common Stock Common Stock Disclosure [Text Block] Common Stock Disclosure [Text Block] Foreign currency translation adjustments Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax MountainWest unsecured senior notes, 3.91%, due in 2038 Senior Notes, 3.91% Due In 2038 [Member] Senior Notes, 3.91% Due In 2038 Common stock issued (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period Accrued interest Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Accrued Interest Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Accrued Interest Statement [Line Items] Statement [Line Items] Accrued taxes Increase (Decrease) in Accrued Taxes Payable Schedule of Significant Items Included in Other Income (Deductions) Schedule of Other Nonoperating Income, by Component [Table Text Block] Total operating revenues Regulated and Unregulated Operating Revenue Transaction price allocated to unsatisfied performance obligations of contracts Revenue, Remaining Performance Obligation, Amount Share-based compensation Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture Short-term Debt, Type [Axis] Short-term Debt, Type [Axis] Tax-exempt Series A, due 2028 Variable Rate Bonds Tax Exempt Series A- Due Two Thousand And Twenty Eight [Member] Variable Rate Bonds Tax Exempt Series Due Two Thousand and Twenty Eight [Member] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Large commercial Large Commercial [Member] Large commercial. Debt Disclosure [Abstract] Debt Disclosure [Abstract] Time and materials contracts Time-and-materials Contract [Member] Accounts Receivable, net of allowances Receivables, Trade and Other Accounts Receivable, Allowance for Doubtful Accounts, Policy [Policy Text Block] Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Less: amount recognized in regulatory assets Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Amount Recognized Regulatory Assets, Before Tax Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Amount Recognized Regulatory Assets, Before Tax Segment Reporting [Abstract] Segment Reporting [Abstract] Customer [Axis] Customer [Axis] Sale of stock, underwriters' discount Sale of Stock, Underwriters' Discount Sale of Stock, Underwriters' Discount Schedule of Earnings Per Share, Basic and Diluted Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Title of 12(b) Security Title of 12(b) Security Other comprehensive income (loss), tax Other Comprehensive Income (Loss), Tax Issuance of common stock, net Net proceeds Proceeds from Issuance of Common Stock Total assets Assets Accumulated removal costs Other Accrued Liabilities, Noncurrent Plan Name [Domain] Plan Name [Domain] Common stock, authorized (in shares) Common Stock, Shares Authorized Weighted average price per share (in USD per share) Common Stock Weighted Average Issue Price Per Share Common stock weighted average issue price per share. Interest paid, net of amounts capitalized Interest Paid, Excluding Capitalized Interest, Operating Activities Significant Accounting Policies [Table] Significant Accounting Policies [Table] Significant Accounting Policies [Table] Document Type Document Type Product and Service [Domain] Product and Service [Domain] Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Debt instrument interest rate Debt Instrument, Interest Rate, Stated Percentage Prior service cost Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, Prior Service Cost (Credit), before Tax Contract with Customer, Basis of Pricing [Domain] Contract with Customer, Basis of Pricing [Domain] Net income attributable to noncontrolling interests Net Income (Loss) Attributable to Noncontrolling Interest Small commercial Small Commercial [Member] Small commercial. Transaction price allocated to unsatisfied performance obligations of contracts, period Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Net cash provided by (used in) operating activities Net Cash Provided by (Used in) Operating Activities Short-term debt Short-term debt Short-term Debt Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Subsequent Event [Line Items] Subsequent Event [Line Items] Capitalization: Capitalization, Long-term Debt and Equity [Abstract] Basic (in shares) Weighted average basic shares (in shares) Weighted Average Number of Shares Outstanding, Basic Diluted (in USD per share) Earnings Per Share, Diluted Segments [Domain] Segments [Domain] Sale of stock, price per share (in USD per share) Sale of Stock, Price Per Share Service cost Defined Benefit Plan, Service Cost Net actuarial loss Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax Net income attributable to redeemable noncontrolling interests Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Income taxes paid (received), net Income Taxes Paid, Net Other components of net periodic benefit cost Defined Benefit Plan, Actuarial Gain (Loss), Immediate Recognition as Component in Net Periodic Benefit (Cost) Credit Deferred purchased gas costs Deferred Gas Cost Subsequent Events Subsequent Events [Text Block] Comprehensive income attributable to Southwest Gas Holdings, Inc. Comprehensive Income (Loss), Net of Tax, Attributable to Parent Centuri secured revolving credit facility Centuri secured revolving credit facility Centuri Secured Revolving Credit Facility [Member] Centuri secured revolving credit facility. Amortization of prior service cost Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member] Fixed price contracts Fixed-price Contract [Member] Change in COLI policies Life Insurance, Corporate or Bank Owned, Change in Value Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities Southwest Gas Corporation Southwest Gas Corporation [Member] Southwest gas corporation. Loans Payable Loans Payable [Member] Equity in earnings of unconsolidated investments Income (Loss) from Equity Method Investments Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Property and equipment Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment Centuri secured term loan facility Centuri Term Loan Facility [Member] Centuri term loan facility. Commercial Paper Program Commercial Paper Program [Member] Commercial Paper Program [Member] Amounts billed in excess of revenue earned on contracts Contract with Customer, Receivable, after Allowance for Credit Loss Accounts payable Accounts Payable, Current Other property and investments Property, Plant and Equipment, Other, Net Equity AFUDC Equity AFUDC Increase (Decrease) in Allowance for Equity Funds Used During Construction Other revenues Other Revenues [Member] Other Revenues Southwest Gas Holdings, Inc. Parent [Member] Measurement Period Adjustments, Intangible assets Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Intangibles Dividends declared Dividends declared to Southwest Gas Holdings, Inc. Dividends, Common Stock $100 Million Credit Facility $100 Million Credit Facility [Member] $100 Million Credit Facility [Member] Accumulated other comprehensive loss AOCI Attributable to Parent AOCI Attributable to Parent [Member] Contracts receivable, net Contracts receivable, net Contract with Customer, Asset, after Allowance for Credit Loss Common stock, outstanding (in shares) Beginning balance (in shares) Ending balance (in shares) Common Stock, Shares, Outstanding Trade and other payables Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable Utility infrastructure services expenses Cost of Goods and Services Sold Operating revenues: Revenues [Abstract] Alternative revenue program revenues (deferrals) Alternative Revenue Program Revenues (Deferrals) Alternative revenue program revenues (deferrals). Goodwill Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block] Document Period End Date Document Period End Date Entity Central Index Key Entity Central Index Key Other Other Infrastructure Services [Member] Other Infrastructure Services Debt instrument, term Debt Instrument, Term Medium-term notes, 7.92% series, due 2027 Debentures Medium Term Notes Seven Point Nine Two Percentage Series Due Two Thousand And Twenty Seven [Member] Debentures Medium Term Notes Seven Point Nine Two Percentage Series Due Two Thousand and Twenty Seven [Member] Certain Members Of Riggs Distler Management Certain Members Of Riggs Distler Management [Member] Certain Members Of Riggs Distler Management Deferred charges and other assets Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed, Deferred Charges And Other Assets Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed, Deferred Charges And Other Assets Incurred and expensed acquisition costs Business Acquisition, Transaction Costs Long-term debt Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt AOCI Including Portion Attributable to Noncontrolling Interest AOCI Including Portion Attributable to Noncontrolling Interest [Member] Total deferred income taxes and other credits Other Liabilities, Noncurrent Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt Schedule of Long-term Debt Instruments [Table Text Block] Debt Instrument [Line Items] Debt Instrument [Line Items] Retirement of long-term debt Retirement of long-term debt Repayments of Long-term Debt Trading Symbol Trading Symbol Earnings per share: Earnings Per Share [Abstract] MountainWest MountainWest [Member] MountainWest Entity separation, completion period Entity Separation, Completion Period Entity Separation, Completion Period Natural Gas Distribution Natural Gas Distribution Segment [Member] Natural Gas Distribution Segment Regulatory adjustment 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. Total Regulated operations revenues Revenues Notes, 3.7%, due 2028 Debentures Notes Three Point Seven Percentage Due Two Thousand And Twenty Eight [Member] Debentures notes three point seven percentage due two thousand and twenty eight. Changes in deferred charges and other assets Changes in deferred charges and other assets Increase (Decrease) in Other Operating Assets Measurement Period Adjustments, Finance lease obligations Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Finance Lease Obligations Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Finance Lease Obligations Reclassification from AOCI, net of tax Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Condensed Income Statements, Captions [Line Items] Condensed Income Statements, Captions [Line Items] Operations and maintenance Utilities Operating Expense, Maintenance and Operations Loss contingency accrual Loss Contingency Accrual Bid contract Bid Contract [Member] Bid contract. Operating expenses: Costs and Expenses [Abstract] Long-term debt, less current maturities Long-term debt, less current maturities Long-term Debt, Excluding Current Maturities Schedule of Goodwill [Table] Schedule of Goodwill [Table] Equity Shelf Program Equity Shelf Program [Member] Equity Shelf Program [Member] Entity Current Reporting Status Entity Current Reporting Status Ownership percentage by noncontrolling owners Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners Effective income tax rate Effective Income Tax Rate Reconciliation, Percent Notes, 4.05%, due 2032 Debentures Notes Four Point Zero Five Percentage Due Two Thousand And Thirty Two [Member] Debentures Notes Four Point Zero Five Percentage Due Two Thousand And Thirty Two Entities [Table] Entities [Table] Other debt obligations Other Debt Obligations [Member] Net income Net income Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Other property and investments Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Other Property And Investments Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Other Property And Investments Total liabilities assumed and noncontrolling interest Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities Gains on sale of property and equipment Gain on sale of property Gain (Loss) on Disposition of Property Plant Equipment Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Sale of stock, number of shares Sale of Stock, Number of Shares Issued in Transaction Common stock, par (in USD per share) Common Stock, Par or Stated Value Per Share Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Notes, 6.1%, due 2041 Debentures Notes 6.1% Due 2041 [Member] Debentures Notes Six Point One Percentage Due Two Thousand And Forty One [Member] Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Current assets: Assets, Current [Abstract] Other Proceeds from (Payments for) Other Financing Activities Forward-starting interest rate swaps (“FSIRS”): Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax [Abstract] LIBOR London Interbank Offered Rate (LIBOR) [Member] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] 2003 Series A, due 2038 Variable Rate Bonds Two Thousand And Three Series A- Due Two Thousand And Thirty Eight [Member] Variable Rate Bonds Two Thousand and Three Series A Due Two Thousand and Thirty Eight [Member] Beginning balance, tax Ending balance, tax Stockholders' Equity, Including Portion Attributable To Noncontrolling Interest, Tax Stockholders' Equity, Including Portion Attributable To Noncontrolling Interest, Tax Deferred income taxes and investment tax credits, net Deferred Income Taxes And Unamortized Investment Tax Credits Represents deferred tax liabilities, which result from applying the applicable tax rate to net taxable temporary differences pertaining to each jurisdiction to which the entity is obligated to pay income tax. Additionally, this element includes the future effects on income taxes attributable to investment tax credits. Money market fund investments Cash and Cash Equivalents, Fair Value Disclosure Entity Address, Postal Zip Code Entity Address, Postal Zip Code Diluted (in shares) Weighted average diluted shares (in shares) Weighted Average Number of Shares Outstanding, Diluted Total other comprehensive income, net of tax Other Comprehensive Income (Loss), Net of Tax Accrued interest Interest Payable, Current Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Debt, basis spread on variable rate Debt Instrument, Basis Spread on Variable Rate Number of performance share units granted (in shares) Number Of Performance Share Units Granted Number Of Performance Share Units Granted. Pipeline and Storage Pipeline And Storage Segment [Member] Pipeline And Storage Segment Schedule of Net Periodic Benefit Costs Schedule of Net Benefit Costs [Table Text Block] Measurement Basis [Axis] Measurement Basis [Axis] Accumulated removal costs Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Accumulated Removal Costs Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Accumulated Removal Costs Deferred income taxes and other credits: Other Liabilities, Noncurrent [Abstract] Electric power infrastructure services Electric Power Infrastructure Services [Member] Electric Power Infrastructure Services Measurement Period Adjustments, Deferred tax liabilities Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Deferred Tax Liabilities Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Deferred Tax Liabilities Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Other income and (expenses): Nonoperating Income (Expense) [Abstract] Deferred purchased gas costs Deferred purchased gas costs Increase (Decrease) in Deferred Gas Cost Regulated operations revenues Total Regulated operations revenues Regulated Operating Revenue, Gas Operating lease obligations Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Operating Lease Obligations Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Operating Lease Obligations Class of Stock [Line Items] Class of Stock [Line Items] Credit Facility [Axis] Credit Facility [Axis] Entity Address, Address Line One Entity Address, Address Line One Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Entity Address, Address Line Two Entity Address, Address Line Two Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Changes in current assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Non-regulated accumulated provision for depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Accrued general taxes Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Accrued General Taxes Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Accrued General Taxes Other deferred credits and other long-term liabilities Other deferred credits and other long-term liabilities Deferred Credits and Other Liabilities, Noncurrent Centuri Secured Term Loan Facility And Revolving Credit Facility Centuri Secured Term Loan Facility And Revolving Credit Facility [Member] Centuri Secured Term Loan Facility And Revolving Credit Facility CASH FLOW FROM OPERATING ACTIVITIES: Net Cash Provided by (Used in) Operating Activities [Abstract] Income taxes receivable, net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Income Taxes Receivable, Net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Income Taxes Receivable, Net Entity Shell Company Entity Shell Company Line of credit designated as long term debt Line Of Credit Facility Amount Classified As Long Term Debt Line Of Credit Facility, Amount Classified As Long-Term Debt Total current liabilities Liabilities, Current Withholding remittance - share-based compensation Withholding remittance - share-based compensation Payment, Tax Withholding, Share-based Payment Arrangement Class of Stock [Domain] Class of Stock [Domain] Debentures Debentures [Member] Debentures [Member] Credit facility maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Foreign currency translation adjustment Goodwill, Foreign Currency Translation Gain (Loss) Money Market Funds Money Market Funds [Member] Cash and cash equivalents Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents MountainWest unsecured senior notes, 4.875%, due in 2041 Senior Notes, 4.875% Due In 2041 [Member] Senior Notes, 4.875% Due In 2041 Measurement Period Adjustments, Deferred income taxes Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Deferred Income Taxes Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Deferred Income Taxes Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Ownership [Domain] Ownership [Domain] Current Fiscal Year End Date Current Fiscal Year End Date Unamortized discount and debt issuance costs Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net Questar Pipelines Dominion Energy Questar Pipeline, LLC [Member] Dominion Energy Questar Pipeline, LLC Taxes other than income taxes Taxes, Miscellaneous Gas pipe materials and operating supplies Materials, Supplies, and Other Medium-term notes, 7.78% series, due 2022 Debentures Medium Term Notes Seven Point Seven Eight Percentage Series Due Two Thousand And Twenty Two [Member] Debentures Medium Term Notes Seven Point Seven Eight Percentage Series Due Two Thousand and Twenty Two [Member] Net income Net income Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Statement [Table] Statement [Table] Industrial development revenue bonds Industrial Development Revenue Bonds [Member] Industrial Development Revenue Bonds [Member] Notes, 3.8%, due 2046 Debentures Notes Three Point Eight Percentage Due Two Thousand And Forty Six [Member] Debentures notes three point eight percentage due two thousand and forty six. Schedule of Other Property and Investments Investment [Table Text Block] Recent Accounting Standards Updates New Accounting Pronouncements, Policy [Policy Text Block] 2009 Series A, due 2039 Variable Rate Bonds Two Thousand And Nine Series A- Due Two Thousand And Thirty Nine [Member] Variable Rate Bonds Two Thousand and Nine Series A Due Two Thousand and Thirty Nine [Member] Effect of dilutive securities: Dilutive Securities, Effect on Basic Earnings Per Share [Abstract] Schedule of Amount Recognized Before Income Tax in Accumulated Other Comprehensive Income Schedule of Amounts Recognized in Other Comprehensive Income (Loss) [Table Text Block] Statistical Measurement [Axis] Statistical Measurement [Axis] Subsequent Event Subsequent Event [Member] Other revenues Other Revenue Other Revenue Prepaid and other current assets Prepaid And Other Current Assets Policy [Policy Text Block] Prepaid And Other Current Assets Policy Goodwill Goodwill Goodwill, beginning balance Goodwill, ending balance Goodwill Gas plant, net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Gas Plant, Net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Gas Plant, Net FSIRS AOCI, Derivative Qualifying as Hedge, Excluded Component, Parent [Member] Income taxes payable, net Income Taxes Payable Net Income Taxes Payable Net Schedule Of Accounts Receivable Not Eliminated During Consolidation Schedule Of Accounts Receivable Not Eliminated During Consolidation [Table Text Block] Schedule Of Accounts Receivable Not Eliminated During Consolidation Schedule of Goodwill Schedule of Goodwill [Table Text Block] Adjustments to reconcile net income to net cash provided by (used in) operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Axis] Pension plans other comprehensive income (loss) Defined Benefit Plans Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Customer deposits Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Customer Deposits Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Customer Deposits Contributions from Southwest Gas Holdings, Inc. Adjustments To Additional Paid In Capital Contributions From Parent Adjustments to additional paid in capital contributions from parent.