Revision of Prior Period [Axis] Revision of Prior Period [Axis] Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Statistical Measurement [Domain] Statistical Measurement [Domain] Schedule of Significant Items Included in Other Income (Deductions) Schedule of Other Nonoperating Income, by Component [Table Text Block] Total capitalization Total capitalization Capitalization, Long-Term Debt and Equity Amortization of prior service cost, net of tax of $11 and $11, respectively Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, after Tax Expected return on plan assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Award Timing Predetermined Award Timing Predetermined [Flag] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Entity File Number Entity File Number Additional Paid-in Capital Additional Paid-in Capital Additional Paid-in Capital [Member] Equity in earnings of unconsolidated investments Income (Loss) from Equity Method Investments Tabular List, Table Tabular List [Table Text Block] Basic earnings (loss) per share: Earnings Per Share, Basic [Abstract] Notes, 5.45%, due February 2028 Debentures Notes, 5.45%, Due February 2028 [Member] Debentures Notes, 5.45%, Due February 2028 Recent Accounting Standards Updates New Accounting Pronouncements, Policy [Policy Text Block] Operating Activities [Axis] Operating Activities [Axis] Accounts payable Increase (Decrease) in Accounts Payable Secured Overnight Financing Rate (SOFR) Secured Overnight Financing Rate (SOFR) [Member] Net interest deductions Net interest deductions Interest Income (Expense), Nonoperating Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] Measurement Basis [Axis] Measurement Basis [Axis] Significant Accounting Policies [Line Items] Significant Accounting Policies [Line Items] Significant Accounting Policies [Line Items] Net earnings per share - basic (in USD per share) Earnings Per Share, Basic Adjustment to Compensation: Adjustment to Compensation [Axis] Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Net cash used in financing activities of continuing operations Cash Provided by (Used in) Financing Activity, Continuing Operation Revenue Revenue from Contract with Customer [Text Block] Total other comprehensive income, net of tax Other Comprehensive Income (Loss), Net of Tax Accrued utility revenue Accrued utility revenue Increase (Decrease) In Accrued Utility Revenue Increase (Decrease) In Accrued Utility Revenue Discontinued operations (in USD per share) Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share Industrial/other Industrial/other [Member] Industrial/other. Continuing Operations Continuing Operations [Member] Total operating revenues Revenue, Remaining Performance Obligation, Amount Adjustment to Compensation, Amount Adjustment to Compensation Amount Unamortized discount and debt issuance costs Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net Changes in deferred charges and other assets Changes in deferred charges and other assets Increase (Decrease) in Other Operating Assets Share-based compensation expense Share-Based Payment Arrangement, Noncash Expense Employee Stock Option Share-Based Payment Arrangement, Option [Member] Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Total equity Total equity Equity, Attributable to Parent Insider Trading Policies and Procedures [Line Items] Common stock, authorized (in shares) Common Stock, Shares Authorized Notes, 4.05%, due March 2032 Debentures Notes, 4.05%, Due March 2032 [Member] Debentures Notes, 4.05%, Due March 2032 Common stock issuances (in shares) Stock Issued During Period, Shares, New Issues Current assets: Current assets: Assets, Current [Abstract] Total capitalization and liabilities Total capitalization and liabilities Liabilities and Equity Changes in customer advances Changes In Customer Advances, Investing Activities Changes In Customer Advances, Investing Activities Accrued property taxes Accrued Property Taxes Accrued Property Taxes Cash and cash equivalents, including discontinued operations, at beginning of period Cash and cash equivalents, including discontinued operations, at end of period Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Including Discontinued Operation CAPITALIZATION AND LIABILITIES CAPITALIZATION AND LIABILITIES Liabilities and Equity [Abstract] Other income (deductions) Other Nonoperating Income (Expense) [Abstract] Cover [Abstract] Cover [Abstract] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Maximum Maximum [Member] Net loss attributable to noncontrolling interests Net Income (Loss) Attributable to Noncontrolling Interest Bridge Loan Bridge Loan [Member] Accounting Policies [Abstract] Share-based compensation Adjustments To Additional Paid in Capital, Dividends In Excess of Retained Earnings, Netting Adjustments To Additional Paid in Capital, Dividends In Excess of Retained Earnings, Netting Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Debt Instrument [Line Items] Debt Instrument [Line Items] Income from continuing operations Income from continuing operations, net of income tax Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Transportation Transportation [Member] Transportation. Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Pay vs Performance Disclosure [Line Items] Retirement Benefits [Abstract] Retirement Benefits [Abstract] Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] Depreciation and amortization Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Income from continuing operations before income taxes Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Entity Shell Company Entity Shell Company Total deferred income taxes and other credits Total deferred income taxes and other credits Other Liabilities, Noncurrent Schedule of Long-term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Accrued general taxes Accrual for Taxes Other than Income Taxes, Current Schedule of Other Property and Investments Investment [Table Text Block] Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Current maturities of long-term debt Less: current maturities Long-Term Debt, Current Maturities Company Selected Measure Amount Company Selected Measure Amount Comprehensive loss attributable to noncontrolling interests Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Gas pipe materials and operating supplies Gas Pipe Materials And Operating Supplies Gas Pipe Materials And Operating Supplies Comprehensive income attributable to Southwest Gas Holdings, Inc. Comprehensive Income (Loss), Net of Tax, Attributable to Parent Name Measure Name Document Fiscal Period Focus Document Fiscal Period Focus Foreign currency exchange translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax, Portion Attributable to Parent Previously Issued Condensed Consolidated Financial Statement Error Correction [Text Block] Accrued taxes Increase (Decrease) in Accrued Taxes Payable Award Timing Method Award Timing Method [Text Block] Continuing operations (in USD per share) Income (Loss) from Continuing Operations, Per Basic Share Award Type Award Type [Axis] Adjustments Revision of Prior Period, Adjustment [Member] Total Long-term debt outstanding Long-Term Debt Legal Entity [Axis] Legal Entity [Axis] Total assets Assets Total noncurrent assets Assets, Noncurrent, Other than Noncurrent Investments and Property, Plant and Equipment Accrued utility revenue Accrued Utility Revenue Accrued utility revenue. Trading Symbol Trading Symbol Gas plant Public Utilities, Property, Plant And Equipment, Gas Plant Public Utilities, Property, Plant And Equipment, Gas Plant Income Taxes Income Tax, Policy [Policy Text Block] Entity Address, City or Town Entity Address, City or Town Short-Term Debt, Type [Domain] Short-Term Debt, Type [Domain] CASH FLOW FROM OPERATING ACTIVITIES: CASH FLOW FROM OPERATING ACTIVITIES: Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Background and Organization Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block] Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Medium-term notes, 6.76% series, due September 2027 Debentures Medium Term Notes, 6.76% series, Due September 2027 [Member] Debentures Medium Term Notes, 6.76% series, Due September 2027 Entity Emerging Growth Company Entity Emerging Growth Company Dividends declared per common share (in USD per share) Common Stock, Dividends, Per Share, Declared Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year [Member] Other property and investments Property, Plant and Equipment, Other, Net Decrease of capital expenditures in Accounts payable or Other current liabilities Increase (Decrease) In Capital Expenditures Incurred But Not Yet Paid Increase (Decrease) In Capital Expenditures Incurred But Not Yet Paid Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Related Party Related Party [Member] Common stock, outstanding (in shares) Beginning balance (in shares) Ending balance (in shares) Common Stock, Shares, Outstanding Residential Residential [Member] Residential. PEO PEO [Member] Schedule of Revenue Disaggregated by Service Type and Contract Type Disaggregation of Revenue [Table Text Block] Changes in current assets and liabilities: Changes in current assets and liabilities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract] Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year [Member] Retained Earnings Retained Earnings Retained Earnings [Member] Prepaid and other current assets Prepaid and other current assets Prepaid Expense and Other Assets, Current Net actuarial gain arising during period, less amortization of unamortized benefit plan cost, net of tax Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax Other Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax Other Entity Address, Postal Zip Code Entity Address, Postal Zip Code Restatement Determination Date Restatement Determination Date Cash and cash equivalents, including discontinued operations, at beginning of period Cash and cash equivalents, including discontinued operations, at end of period Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Income Statement [Abstract] Income Statement [Abstract] Income tax expense Income tax expense Income tax benefit Income Tax Expense (Benefit) Debt, basis spread on variable rate Debt Instrument, Basis Spread on Variable Rate Interest period Debt Instrument, Interest Period Debt Instrument, Interest Period Discontinued operations (in USD per share) Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share Sale of Stock [Domain] Sale of Stock [Domain] Notes, 3.18%, due August 2051 Debentures Notes, 3.18%, Due August 2051 [Member] Debentures Notes, 3.18%, Due August 2051 Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Continuing operations (in USD per share) Income (Loss) from Continuing Operations, Per Diluted Share Parent Parent [Member] Net income Net income Net income Net income (loss) Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Equity AFUDC capitalized in regulated operations plant Equity AFUDC Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Schedule of Error Corrections and Prior Period Adjustments Schedule of Error Corrections and Prior Period Adjustments [Table Text Block] City Area Code City Area Code Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] All Trading Arrangements All Trading Arrangements [Member] Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Net cash provided (used) in investing activities of discontinued operations Cash Provided by (Used in) Investing Activity, Discontinued Operation CASH FLOW FROM INVESTING ACTIVITIES: CASH FLOW FROM INVESTING ACTIVITIES: Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Net cash provided by operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation 2003 Series A, due March 2038 Variable Rate Bonds 2003 Series A- Due March 2038 [Member] Variable Rate Bonds 2003 Series A- Due March 2038 Regulatory adjustment, tax Other Comprehensive Income Defined Benefit Plans Regulatory Adjustment, Tax Other Comprehensive Income Defined Benefit Plans Regulatory Adjustment, Tax Amortization of net actuarial loss (gain) Defined Benefit Plan, Amortization of Gain (Loss) Goodwill Goodwill Goodwill Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] PEO Total Compensation Amount PEO Total Compensation Amount Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] Equity Components [Axis] Equity Components [Axis] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Amortization of prior service cost, tax Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, Tax Net cash provided (used) in financing activities of discontinued operations Cash Provided by (Used in) Financing Activity, Discontinued Operation Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Number of reportable segments Number of Reportable Segments Components of Net Periodic Benefit Cost Compensation and Employee Benefit Plans [Text Block] Construction work in progress Public Utilities, Property, Plant and Equipment, Construction Work in Progress Deferred income taxes and other credits: Deferred income taxes and other credits: Other Liabilities, Noncurrent [Abstract] Amortization of net actuarial loss, net of tax of $606 and $226, respectively Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax SUPPLEMENTAL INFORMATION: SUPPLEMENTAL INFORMATION: Supplemental Cash Flow Information [Abstract] Other Performance Measure, Amount Other Performance Measure, Amount Entity Address, State or Province Entity Address, State or Province Dividends declared Dividends, Common Stock Related Party [Domain] Related and Nonrelated Parties [Domain] Total current liabilities Liabilities, Current Effects of currency translation in discontinued operations Effect of Exchange Rate on Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Discontinued Operation Deferred purchased gas costs Deferred Gas Purchases, Current Individual: Individual [Axis] Other current assets and liabilities Other current assets and liabilities Increase (Decrease) in Other Current Assets and Liabilities, Net Public Offering And Private Placement Public Offering And Private Placement [Member] Public Offering And Private Placement Accounting Changes and Error Corrections [Abstract] Dividends paid Dividends paid Payments of Ordinary Dividends, Common Stock Additional paid-in capital Additional Paid in Capital, Common Stock Entities [Table] Entities [Table] Entity [Domain] Entity [Domain] Net cash provided (used) in investing activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Transaction price allocated to unsatisfied performance obligations of contracts, period Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table [Member] Interest paid, net of amounts capitalized Interest paid, net of amounts capitalized Interest Paid, Excluding Capitalized Interest, Operating Activity Document Fiscal Year Focus Document Fiscal Year Focus Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Effective income tax rate Effective Income Tax Rate Reconciliation, Percent Entity Interactive Data Current Entity Interactive Data Current Carrying Amount Reported Value Measurement [Member] Taxes other than income taxes Taxes, Miscellaneous Medium-term notes, 7.92% series, due June 2027 Debentures Medium Term Notes, 7.92% series, Due June 2027 [Member] Debentures Medium Term Notes, 7.92% series, Due June 2027 Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Materials, supplies, and gas inventories Materials, Supplies, And Other, Policy [Policy Text Block] Materials, Supplies, And Other, Policy Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Schedule of Net Periodic Benefit Costs Schedule of Net Benefit Costs [Table Text Block] Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] Net cost of gas sold Utilities Operating Expense, Gas and Petroleum Purchased Deferred charges and other assets Deferred charges and other assets Other Assets, Noncurrent Customer [Domain] Customer [Domain] Accrued interest Interest Payable, Current Entity Central Index Key Entity Central Index Key PEO Name PEO Name Error Correction [Table] Error Correction [Table] Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year [Member] Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Revolving Credit Facility Revolving Credit Facility [Member] Schedule of Defined Benefit Plans Disclosures [Table] Defined Benefit Plan [Table] Arrangement Duration Trading Arrangement Duration Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Nature of Operations Nature Of Operations [Policy Text Block] Nature Of Operations [Policy Text Block] Customer deposits Contract with Customer, Liability, Current Exercise Price Award Exercise Price Alternative revenue program revenues Alternative Revenue Program Revenues Alternative Revenue Program Revenues Entity Filer Category Entity Filer Category Local Phone Number Local Phone Number Capitalization: Capitalization, Long-Term Debt and Equity [Abstract] Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Other Payment for (Proceeds from) Other Investing Activity ASSETS ASSETS Assets [Abstract] Long-term debt, less current maturities Long-term debt, less current maturities Long-Term Debt, Excluding Current Maturities Credit Facility [Axis] Credit Facility [Axis] Nonrelated Party Nonrelated Party [Member] Underlying Security Market Price Change Underlying Security Market Price Change, Percent Debt Instrument [Axis] Debt Instrument [Axis] Debt, basis spread on interest variable rate Debt Instrument, Basis Spread On Interest Variable Rate Debt Instrument, Basis Spread On Interest Variable Rate Credit Facility [Domain] Credit Facility [Domain] Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year [Member] Notes, 6.1%, due February 2041 Debentures Notes, 6.1%, Due February 2041 [Member] Debentures Notes, 6.1%, Due February 2041 Entity Address, Address Line One Entity Address, Address Line One 2009 Series A, due December 2039 Variable Rate Bonds 2009 Series A- Due December 2039 [Member] Variable Rate Bonds 2009 Series A- Due December 2039 AOCI AOCI AOCI Attributable to Parent [Member] Debt instrument, stated interest rate Debt Instrument, Interest Rate, Stated Percentage Amortization of prior service costs Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Fair Value as of Grant Date Award Grant Date Fair Value Entity Registrant Name Entity Registrant Name Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Net periodic benefit cost Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt Schedule of Long-Term Debt Instruments [Table Text Block] Total operating expenses Costs and Expenses Document Quarterly Report Document Quarterly Report Revision of Prior Period [Domain] Revision of Prior Period [Domain] Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Revolving Credit Agreement Due August 2029 Revolving Credit Agreement Due August 2029 [Member] Revolving Credit Agreement Due August 2029 Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Interest cost Defined Benefit Plan, Interest Cost Related Party [Axis] Related and Nonrelated Parties [Axis] Title Trading Arrangement, Individual Title Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Net cash provided by operating activities of continuing operations Cash Provided by (Used in) Operating Activity, Continuing Operation Restatement Determination Date: Restatement Determination Date [Axis] Non-PEO NEO Non-PEO NEO [Member] Net cash used in investing activities of continuing operations Cash Provided by (Used in) Investing Activity, Continuing Operation Miscellaneous income and (expense) Miscellaneous Income (Expense) Miscellaneous Income (Expense) Other, including principal payments on finance leases Other, including principal payments on finance leases Proceeds from (Payment for) Other Financing Activity Interest income Interest Income, Other Restricted stock units (in shares) Incremental Common Shares Attributable to Dilutive Effect of Nonvested Shares with Forfeitable Dividends Sale of Stock [Axis] Sale of Stock [Axis] Regulatory Asset [Axis] Regulatory Asset [Axis] Name Trading Arrangement, Individual Name Materials, supplies, and gas inventories Materials, Supplies, and Other All Award Types Award Type [Domain] As Reported Previously Reported [Member] Equity Awards Adjustments Equity Awards Adjustments [Member] Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Compensation Amount Outstanding Recovery Compensation Amount Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Fair Value Estimate of Fair Value Measurement [Member] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Other property and investments, net Total Other Property And Investments Aggregate carrying amount, as of the balance sheet date, of other property and investments not separately presented elsewhere in the balance sheet. Other comprehensive income related to discontinued operations Other Comprehensive Income (Loss) From Discontinued Operations, Net Of Tax Other Comprehensive Income (Loss) From Discontinued Operations, Net Of Tax Notes, 2.2%, due June 2030 Debentures Notes, 2.2%, Due June 2030 [Member] Debentures Notes, 2.2%, Due June 2030 MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] Name Awards Close in Time to MNPI Disclosures, Individual Name Weighted average shares: Weighted Average Number of Shares Outstanding Reconciliation [Abstract] Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Operating revenues: Revenues [Abstract] Accumulated removal costs Other Accrued Liabilities, Noncurrent Accumulated other comprehensive loss, net Accumulated Other Comprehensive Income (Loss), Net of Tax Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Minimum Minimum [Member] Noncurrent assets: Noncurrent assets: Assets, Noncurrent [Abstract] Earnings Per Share Earnings Per Share, Policy [Policy Text Block] Company Selected Measure Name Company Selected Measure Name Fair Value Measurement [Domain] Fair Value Measurement [Domain] Debt Debt Disclosure [Text Block] Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Accounts payable Accounts Payable, Current Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] Large commercial Large Commercial [Member] Large commercial. Discontinued Operations Discontinued Operations [Member] All Executive Categories All Executive Categories [Member] Common stock, $1 par (authorized - 120,000,000 shares; issued and outstanding - 72,373,216 and 72,224,593 shares) Common stock Common Stock, Value, Issued Operating Activities [Domain] Operating Activities [Domain] Diluted (in shares) Weighted average diluted shares (in shares) Weighted Average Number of Shares Outstanding, Diluted Weighted average interest rate Short-Term Debt, Weighted Average Interest Rate, at Point in Time Notes, 5.8%, due December 2027 Debentures Notes, 5.8%, Due December 2027 [Member] Debentures Notes, 5.8%, Due December 2027 Segment Information Segment Reporting, Policy [Policy Text Block] Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Amortization of net actuarial loss, tax Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, Tax Comprehensive income Comprehensive income (loss) Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Entity Small Business Entity Small Business Noncontrolling Interest Noncontrolling Interest [Member] SERP Supplemental Employee Retirement Plan [Member] Document Transition Report Document Transition Report Underlying Securities Award Underlying Securities Amount Equity Component [Domain] Equity Component [Domain] Notes, 3.8%, due September 2046 Debentures Notes, 3.8%, Due September 2046 [Member] Debentures Notes, 3.8%, Due September 2046 Document Period End Date Document Period End Date PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount Significant Accounting Policies [Table] Significant Accounting Policies [Table] Significant Accounting Policies [Table] Diluted earnings (loss) per share: Earnings Per Share, Diluted [Abstract] Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] Revenue from Contract with Customer [Abstract] Revenue from Contract with Customer [Abstract] Beginning balance Ending balance Equity, Including Portion Attributable to Noncontrolling Interest Small commercial Small Commercial [Member] Small commercial. Document Type Document Type Name Outstanding Recovery, Individual Name Net defined benefit pension plans, net of tax Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax Issuance of common stock, net Proceeds from Issuance of Common Stock 8% Series, due August 2026 Debentures 8% Series Due August 2026 [Member] Debentures 8% Series Due August 2026 Revenue from contracts with customers Revenue from Contract with Customer, Excluding Assessed Tax All Individuals All Individuals [Member] Long-term Debt, Type [Domain] Long-Term Debt, Type [Domain] Less: accumulated depreciation Less: accumulated depreciation Public Utilities, Property, Plant and Equipment, Accumulated Depreciation Capital expenditures and property additions Capital expenditures and property additions Payments to Acquire Property, Plant, and Equipment Name Forgone Recovery, Individual Name Total current assets Assets, Current Statistical Measurement [Axis] Statistical Measurement [Axis] Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested [Member] Net cash provided (used) by operating activities of discontinued operations Cash Provided by (Used in) Operating Activity, Discontinued Operation Commitment fee, unfunded portion Line of Credit Facility, Unused Capacity, Commitment Fee Percentage Regulatory Asset [Domain] Regulatory Asset [Domain] Error Corrections and Prior Period Adjustments Restatement [Line Items] Error Corrections and Prior Period Adjustments Restatement [Line Items] Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Withholding remittance - share-based compensation Withholding remittance - share-based compensation Payment, Tax Withholding, Share-Based Payment Arrangement Notes, 4.875%, due October 2043 Debentures Notes, 4.875%, Due October 2043 [Member] Debentures Notes, 4.875%, Due October 2043 Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] Southwest Gas Corporation Southwest Gas Corporation [Member] Southwest gas corporation. Entity Information [Line Items] Entity Information [Line Items] Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Current liabilities: Current liabilities: Liabilities, Current [Abstract] Deferred charges and other assets Deferred Charges And Other Assets, Policy [Policy Text Block] Deferred Charges And Other Assets, Policy Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] 2008 Series A, due March 2038 Variable Rate Bonds 2008 Series A- Due March 2038 [Member] Variable Rate Bonds 2008 Series A- Due March 2038 Net earnings per share - diluted (in USD per share) Earnings Per Share, Diluted Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Accounts receivable, net of allowances Accounts Receivable, after Allowance for Credit Loss, Current Title of 12(b) Security Title of 12(b) Security Notes, 4.15%, due June 2049 Debentures Notes, 4.15%, Due June 2049 [Member] Debentures Notes, 4.15%, Due June 2049 Sale of stock, number of shares Sale of Stock, Number of Shares Issued in Transaction Tax-exempt Series A, due December 2028 Variable Rate Bonds Tax Exempt Series A- Due December 2028 [Member] Variable Rate Bonds Tax Exempt Series Due 2028 Total other (expenses) Nonoperating Income (Expense) Loss from discontinued operations, net of income tax Less: Income (loss) from discontinued operations, net of income tax Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Income taxes payable Income Taxes Payable Income Taxes Payable Short-Term Debt, Type [Axis] Short-Term Debt, Type [Axis] Regulated operations plant: Regulated operations plant: Public Utilities, Property, Plant and Equipment, Net [Abstract] Decoupling Mechanism Decoupling Mechanism [Member] Decoupling Mechanism Net cash surrender value of COLI policies Cash Surrender Value of Life Insurance Income taxes paid, net Income taxes paid, net Income Taxes Paid, Net Deferred purchased gas costs Deferred Gas Cost Award Timing Disclosures [Line Items] Service cost Defined Benefit Plan, Service Cost Long-term debt, gross Long-Term Debt, Gross Net income Net income Net income (loss) Net Income (Loss) Attributable to Parent Equity AFUDC Increase (Decrease) in Allowance for Equity Funds Used During Construction Expiration Date Trading Arrangement Expiration Date Regulatory adjustment, net of tax of ($477) and ($152), respectively Regulatory adjustment, net of tax of ($477) and ($152), respectively 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 regulated operations plant Public Utilities, Property, Plant and Equipment, Net Changes in other liabilities and deferred credits Increase (Decrease) in Other Operating Liabilities Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Adoption Date Trading Arrangement Adoption Date Base Rate Base Rate [Member] Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Accounts receivable, net of allowances Accounts receivable, net of allowance Increase (Decrease) in Accounts Receivable Entity Current Reporting Status Entity Current Reporting Status Customer [Axis] Customer [Axis] Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Operating income Operating income Operating Income (Loss) Line of Credit Line of Credit [Member] Retained earnings Retained Earnings (Accumulated Deficit) Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] Executive Category: Executive Category [Axis] Other comprehensive income, net of tax Other comprehensive income, net of tax Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract] Change in COLI policies Life Insurance, Corporate or Bank Owned, Change in Value Current Fiscal Year End Date Current Fiscal Year End Date Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table [Member] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Notes, 3.7%, due April 2028 Debentures Notes, 3.7%, Due April 2028 [Member] Debentures Notes, 3.7%, Due April 2028 Statement [Table] Statement [Table] Other income Other income Total other income (deductions) Other Nonoperating Income (Expense) Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to reconcile net income to net cash provided by operating activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] Accrued Pension And Other Postretirement Benefit Costs Accrued Pension And Other Postretirement Benefit Costs [Member] Accrued Pension And Other Postretirement Benefit Costs [Member] CASH FLOW FROM FINANCING ACTIVITIES: CASH FLOW FROM FINANCING ACTIVITIES: Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Equity Awards Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] Variable Rate [Domain] Variable Rate [Domain] 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. Anti-dilutive restricted stock (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount All Adjustments to Compensation All Adjustments to Compensation [Member] Amendment Flag Amendment Flag Other deferred credits and other long-term liabilities Other deferred credits and other long-term liabilities Deferred Credits and Other Liabilities, Noncurrent PBOP Other Postretirement Benefits Plan [Member] Total operating revenues Regulated operations revenues Regulated and Unregulated Operating Revenue Termination Date Trading Arrangement Termination Date Number of performance share units granted (in shares) Number Of Performance Share Units Granted Number Of Performance Share Units Granted. Net cash used in financing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Measure: Measure [Axis] Defined benefit pension plans: Defined benefit pension plans: Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax [Abstract] Basic (in shares) Weighted average basic shares (in shares) Weighted Average Number of Shares Outstanding, Basic Schedule of Earnings Per Share, Basic and Diluted Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Debt Disclosure [Abstract] Debt Disclosure [Abstract] Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Other income and (expenses): Nonoperating Income (Expense) [Abstract] Entity Tax Identification Number Entity Tax Identification Number Operating expenses: Costs and Expenses [Abstract] Other components of net periodic benefit cost Defined Benefit Plan, Actuarial Gain (Loss), Immediate Recognition as Component in Net Periodic Benefit (Cost) Credit Margin Tracker for Southern Nevada Margin Tracker For Southern Nevada [Member] Margin Tracker For Southern Nevada Change in short-term portion of credit facility Proceeds from (Repayments of) Lines of Credit Debentures: Debentures [Member] Debentures [Member] Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Common stock, par (in USD per share) Common Stock, Par or Stated Value Per Share Common stock, issued (in shares) Common Stock, Shares, Issued Income taxes receivable, net Income Taxes Receivable, Current Effect of dilutive securities: Dilutive Securities, Effect on Basic Earnings Per Share [Abstract] Industrial development revenue bonds: Industrial Development Revenue Bonds [Member] Industrial Development Revenue Bonds [Member] Regulatory asset Regulatory Asset Dividends declared Dividends Payable, Current Trading Arrangement: Trading Arrangement [Axis] Cloud-based software Software, Cloud-Based Software, Cloud-Based Total Shareholder Return Amount Total Shareholder Return Amount Insider Trading Arrangements [Line Items] Security Exchange Name Security Exchange Name Regulated operations revenues Total Regulated operations revenues Regulated Operating Revenue, Gas QRP Other Pension Plan [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 Credit facility maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Other current liabilities Other current liabilities Other Liabilities, Current Operations and maintenance Utilities Operating Expense, Maintenance and Operations Common stock issuances Stock Issued During Period, Value, New Issues Deferred purchased gas costs Deferred purchased gas costs Increase (Decrease) in Deferred Gas Cost Statement [Line Items] Statement [Line Items] Variable Rate [Axis] Variable Rate [Axis] Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Cash and cash equivalents Cash and Cash Equivalent Common stock shares Common stock shares Common Stock [Member] Deferred income taxes Deferred income taxes Increase (Decrease) in Deferred Income Taxes Net income (loss) Net income Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Non-NEOs Non-NEOs [Member] Change in cash and cash equivalents, including discontinued operations Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation