Equity [Abstract] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Counterparty Name [Axis] Counterparty Name [Axis] Counterparty Name [Domain] Counterparty Name [Domain] BNY Mellon Capital Markets, LLC Bank Of New York Mellon Capital Markets LLC [Member] Bank Of New York Mellon Capital Markets LLC [Member] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] 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] Value of common stock Maximum Aggregate Market Value Of Potential Stock Issuance The amount of maximum aggregate market value of potential stock issuance under the program. Common stock sold through agent (in shares) Stock Issued During Period, Shares, New Issues Open market weighted average price per share Common Stock Weighted Average Issue Price Per Share Common stock weighted average issue price per share. Net proceeds to company Proceeds from Issuance of Common Stock Agent commissions Payments of Stock Issuance Costs Common stock available for sale under the program (in shares) Maximum Amount Of Common Stock Available For Sale Maximum amount of common stock available for sale. Common stock issued through Restricted Stock/Unit Plan, and Management Incentive Plan (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period Common stock issued, amount Stock Issued During Period, Value, New Issues Debt Disclosure [Abstract] Long-Term Debt Long-term Debt [Text Block] Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt Schedule of Long-term Debt Instruments [Table Text Block] Restructuring and Related Activities [Abstract] Reorganization Impacts - Discontinued Operations Solely Related to Southwest Gas Corporation Restructuring and Related Activities Disclosure [Text Block] Retirement Benefits [Abstract] Schedule of Net Periodic Benefit Costs Schedule of Net Benefit Costs [Table Text Block] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Defined Benefit Plans Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Amortization of prior service cost Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member] Net actuarial gain/(loss) Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member] Regulatory adjustment Accumulated Defined Benefit Plans Adjustment, Regulartory Adjustment, Attributable to Parent [Member] Accumulated Defined Benefit Plans Adjustment, Regulartory Adjustment, Attributable to Parent [Member] FSIRS AOCI, Derivative Qualifying as Hedge, Excluded Component, Parent [Member] Foreign Currency Items Accumulated Foreign Currency Adjustment Attributable to Parent [Member] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Southwest Gas Corporation Southwest Gas Corporation [Member] Southwest gas corporation. Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] 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 Effective income tax rate Effective Income Tax Rate Reconciliation, Percent Segment Reporting [Abstract] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] Natural Gas Operations Natural Gas Operations [Member] Natural Gas Operations [Member] Infrastructure Services Infrastructure Services Segment [Member] Infrastructure Services Segment [Member] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Operating Segments Operating Segments [Member] Intersegment Eliminations Intersegment Eliminations [Member] Segment Reconciling Items Segment Reconciling Items [Member] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Revenues Revenues Segment net income (loss) Net Income (Loss) Attributable to Parent Organization, Consolidation and Presentation of Financial Statements [Abstract] Condensed Income Statement [Table] Condensed Income Statement [Table] Corporate and administrative Corporate, Non-Segment [Member] Centuri Construction Group Inc. Centuri Construction Group [Member] Centuri Construction Group [Member] Condensed Income Statements, Captions [Line Items] Condensed Income Statements, Captions [Line Items] Other income (deductions) Other Nonoperating Income (Expense) [Abstract] Change in COLI policies Life Insurance, Corporate or Bank Owned, Change in Value Interest income Interest Income, Other Equity AFUDC Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity Foreign transaction gain (loss) Foreign Currency Transaction Gain (Loss), Realized Other components of net periodic benefit cost Defined Benefit Plan, Actuarial Gain (Loss), Immediate Recognition as Component in Net Periodic Benefit (Cost) Credit Miscellaneous income and (expense) Miscellaneous Income Expense Miscellaneous income (expense). Total other income (deductions) Other Nonoperating Income (Expense) Revenue from Contract with Customer [Abstract] Revenue Revenue from Contract with Customer [Text Block] Number of operating segment Number of Operating Segments 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 types of agreements with customers Number Of Types Of Agreements With Customers Number Of Types Of Agreements With Customers Number of customers Number Of Customers Number Of Customers Number of customers party to contracts with rate components subject to negotiation Number Of Customers Party To Contracts With Rate Components Subject To Negotiation Number Of Customers Party To Contracts With Rate Components Subject To Negotiation Revenue recognized that included in amounts billed in excess of revenue earned on contracts Revenue recognized that included in amounts billed in excess of revenue earned on contracts Revenue recognized that included in amounts billed in excess of revenue earned on contracts. Increases due to amounts billed to customers in excess of revenue earned during the period Increases Due to Amounts Billed to Customers in Excess of Revenue Earned During Period Increases due to amounts billed to customers in excess of revenue earned during the period. 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 Schedule Of Stockholders Equity [Table] Schedule Of Stockholders Equity [Table] Schedule Of Stockholders Equity [Table] Common Stock Common Stock [Member] Additional Paid-in Capital Additional Paid-in Capital [Member] Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Retained Earnings Retained Earnings [Member] Non-controlling Interest Noncontrolling Interest [Member] Ownership [Axis] Ownership [Axis] Ownership [Domain] Ownership [Domain] IntelliChoice Energy LLC Intellichoice Energy Llc [Member] Intellichoice Energy Llc [Member] Schedule Of Stockholders Equity [Line Items] Schedule Of Stockholders Equity [Line Items] Schedule Of Stockholders Equity [Line Items] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Beginning balance (in shares) Common Stock, Shares, Outstanding Common stock issuances Common stock issuances (in shares) Net income (loss) Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Foreign currency exchange translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax, Portion Attributable to Parent Other comprehensive income (loss): Other Comprehensive Income (Loss), Tax [Abstract] 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 Amounts reclassified to net income, net of tax (FSIRS) Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax Reclassification of excess deferred taxes Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings Tax Effect Tax Cuts and Jobs Act of 2017, reclassification from AOCI to retained earnings tax effect. Change in ownership of noncontrolling interest Noncontrolling Interest, Increase from Subsidiary Equity Issuance Stock-based compensation Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures Dividends declared Dividends, Common Stock Contributions from Southwest Gas Holdings, Inc. Adjustments To Additional Paid In Capital Contributions From Parent Adjustments to additional paid in capital contributions from parent. Ending balance Ending balance (in shares) Dividends declared per share (in USD per share) Common Stock, Dividends, Per Share, Declared Historical ownership interest percentage Noncontrolling Interest, Ownership Percentage by Parent Residual ownership percentage by third party Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners Increased ownership percentage Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions Additional capital contributed Payments to Acquire Additional Interest in Subsidiaries Income Statement [Abstract] Statement [Table] Statement [Table] Statement [Line Items] Statement [Line Items] Operating revenues: Revenues [Abstract] Gas operating revenues Regulated Operating Revenue, Gas Construction revenues Revenue from Contract with Customer, Including Assessed Tax Total operating revenues Regulated and Unregulated Operating Revenue Operating expenses: Costs and Expenses [Abstract] Net cost of gas sold Utilities Operating Expense, Gas and Petroleum Purchased Operations and maintenance Utilities Operating Expense, Maintenance and Operations Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Taxes other than income taxes Taxes, Miscellaneous Construction expenses Cost of Goods and Services Sold Total operating expenses Costs and Expenses Operating income Operating Income (Loss) Other income and (expenses): Nonoperating Income (Expense) [Abstract] Net interest deductions Interest Expense Other income (deductions) 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 Income (loss) from continuing operations Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Net income (loss) attributable to noncontrolling interest Net Income (Loss) Attributable to Noncontrolling Interest Discontinued operations-construction services, income before income taxes Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax Discontinued operations-construction services, Income tax expense Discontinued Operation, Tax Effect of Discontinued Operation Net income from discontinued operations Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Discontinued operations-construction services - Noncontrolling interests Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Noncontrolling Interest Discontinued operations - construction services - income Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent Net income (loss) Basic earnings per share (in USD per share) Earnings Per Share, Basic Diluted earnings per share (in USD per share) Earnings Per Share, Diluted Average number of common shares (in shares) Weighted Average Number of Shares Outstanding, Basic Average shares (assuming dilution) (in shares) Weighted Average Number of Shares Outstanding, Diluted Schedule of Goodwill Schedule of Goodwill [Table Text Block] Accounts Receivable for Services Accounts Receivable For Services [Table Text Block] Accounts Receivable For Services Table Text Block. Schedule of Other Property and Investments Investment [Table Text Block] Other Income (Deductions) Schedule of Other Nonoperating Income, by Component [Table Text Block] Derivative Instruments and Hedging Activities Disclosure [Abstract] 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] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] 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] Prepaids and other current assets Prepaid Expenses and Other Current Assets [Member] Deferred charges and other assets Deferred Charges And Other Assets [Member] Deferred Charges And Other Assets [Member] Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Net Total Derivative Fair Value Of Regulatory Assets Liabilities Offset Amount The net amount as of the balance sheet date of the fair value of derivative assets and (liabilities) that in accordance with regulatory treatment is recoverable in utility rates. Common Stock Common Stock Disclosure [Text Block] Common Stock Disclosure [Text Block] Summary of Discontinued Operations - Construction Services in Condensed Consolidated Balance Sheet and Condensed Consolidated Statements of Income Disposal Groups, Including Discontinued Operations [Table Text Block] Document And Entity Information [Abstract] Document and entity information. Entities [Table] Entities [Table] Entity Information [Line Items] Entity Information [Line Items] Document Type Document Type Amendment Flag Amendment Flag Entity Emerging Growth Company Entity Emerging Growth Company Entity Small Business Entity Small Business Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Trading Symbol Trading Symbol Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Qualified Retirement Plan Other Pension Plan [Member] SERP Supplemental Employee Retirement Plan [Member] PBOP Other Postretirement Benefits Plan [Member] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Service cost Defined Benefit Plan, Service Cost Interest cost Defined Benefit Plan, Interest Cost Expected return on plan assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Amortization of prior service costs Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Amortization of net actuarial loss Defined Benefit Plan, Amortization of Gain (Loss) Net periodic benefit cost Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Statement of Financial Position [Abstract] Common stock, par (in USD per share) Common Stock, Par or Stated Value Per Share Common stock, authorized (in shares) Common Stock, Shares Authorized Common stock, issued (in shares) Common Stock, Shares, Issued Common stock, outstanding (in shares) ASSETS Assets [Abstract] Utility plant: Public Utilities, Property, Plant and Equipment, Net [Abstract] Gas plant Public Utilities, Property, Plant and Equipment, Plant in Service Less: accumulated depreciation Public Utilities, Property, Plant and Equipment, Accumulated Depreciation Construction work in progress Public Utilities, Property, Plant and Equipment, Construction Work in Progress Net utility plant Public Utilities, Property, Plant and Equipment, Net Other property and investments Other Property And Investments Aggregate carrying amount, as of the balance sheet date, of other property and investments not separately presented elsewhere in the balance sheet. Current assets: Assets, Current [Abstract] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Accounts receivable, net of allowances Accounts Receivable, Net, Current Accrued utility revenue Accrued Utility Revenue Accrued utility revenue. Income taxes receivable Income Taxes Receivable, Current Deferred purchased gas costs Deferred Gas Cost Prepaids and other current assets Prepaid Expense and Other Assets, Current Total current assets Assets, Current Noncurrent assets: Assets, Noncurrent [Abstract] Goodwill Goodwill Deferred income taxes Deferred Income Tax Assets, Net Deferred charges and other assets Other Assets, Noncurrent Total noncurrent assets Assets, Noncurrent, Other than Noncurrent Investments and Property, Plant and Equipment Total assets Assets CAPITALIZATION AND LIABILITIES Liabilities and Equity [Abstract] Capitalization: Capitalization, Long-term Debt and Equity [Abstract] Common stock, $1 par (authorized - 60,000,000 shares; issued and outstanding - 49,422,938 and 48,090,470 shares) 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 Stockholders' Equity Attributable to Parent Noncontrolling interest Stockholders' Equity Attributable to Noncontrolling Interest Total equity Long-term debt, less current maturities Long-term Debt, Excluding Current Maturities Total capitalization Capitalization, Long-term Debt and Equity Current liabilities: Liabilities, Current [Abstract] Current maturities of long-term debt Long-term Debt, Current Maturities Short-term debt Short-term Debt Accounts payable Accounts Payable, Current Customer deposits Customer Deposits, Current Income taxes payable Taxes Payable, Current Accrued general taxes Accrual for Taxes Other than Income Taxes, Current Accrued interest Interest Payable, Current Deferred purchased gas costs Deferred Gas Purchases, Current Payable to parent Due to Affiliate, Current Other current liabilities Other Liabilities, Current Total current liabilities Liabilities, Current Deferred income taxes and other credits: Other Liabilities, Noncurrent [Abstract] Deferred income taxes and investment tax credits 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 Schedule of Goodwill [Table] Schedule of Goodwill [Table] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Neuco Neuco [Member] Neuco. Goodwill [Line Items] Goodwill [Line Items] Goodwill [Roll Forward] Goodwill [Roll Forward] Goodwill, Beginning balance Additional goodwill from Neuco acquisition Goodwill, Acquired During Period Foreign currency translation adjustment Goodwill, Foreign Currency Translation Gain (Loss) Goodwill, Ending balance Centuri accounts receivable for services provided to Southwest Due from Related Parties, Current 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] Early Adoption of Accounting Standards Update New Accounting Standards Early Adoption Policy [Text Block] New Accounting Standards Early Adoption 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] Income Taxes Income Tax, Policy [Policy Text Block] Other current liabilities Other Current Liabilities [Policy Text Block] Other Current Liabilities [Policy Text Block] Cash and Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Goodwill Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block] Intercompany Transactions Intercompany Transactions [Policy Text Block] Intercompany Transactions [Policy Text Block] Other Property and Investments Other Property And Investments [Policy Text Block] Other Property And Investments [Policy Text Block] Other Income (Deductions) Other Income Expense [Policy Text Block] Other Income Expense [Policy Text Block] Recently Issued Accounting Standards Updates New Accounting Pronouncements, Policy [Policy Text Block] Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income Stockholders' Equity Note Disclosure [Text Block] 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 depreciation/amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Contract notional amounts Derivative, Nonmonetary Notional Amount Short-Term Debt Short-term Debt [Text Block] Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Construction revenues Disposal Group, Including Discontinued Operation, Construction Revenues Disposal Group, Including Discontinued Operation, Construction Revenues Operating expenses: Disposal Group Including Discontinued Operation Operating Expense [Abstract] Disposal Group Including Discontinued Operation Operating Expense [Abstract] Construction expenses Disposal Group, Including Discontinued Operation, Construction Expenses Disposal Group, Including Discontinued Operation, Construction Expenses Depreciation and amortization Depreciation and Amortization, Discontinued Operations Operating income Disposal Group, Including Discontinued Operation, Operating Income (Loss) Other income (deductions) Disposal Group Including Discontinued Operation Other Income (Expense) Disposal Group Including Discontinued Operation Other Income Expense Net interest deductions Disposal Group Including Discontinued Operation Interest Income Expense Net Disposal Group Including Discontinued Operation Interest Income Expense Net Income before income taxes Income tax expense Net income attributable to noncontrolling interests Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Level 2 - Significant Other Observable Inputs Fair Value, Inputs, Level 2 [Member] Other current liabilities Other Current Liabilities [Member] Derivative assets Derivative Asset Derivative liabilities Derivative Liability Net Assets (Liabilities) Derivative Assets (Liabilities), at Fair Value, Net 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, Gross Allowance for doubtful accounts Allowance for Doubtful Accounts Receivable Contracts receivable, net Accounts Receivable, Net Segment Information Segment Reporting Disclosure [Text Block] Detailed Activities of Equity and Redeemable Noncontrolling Interest Schedule of Stockholders Equity [Table Text Block] Related Tax Effects Allocated to Each Component of Other Comprehensive Income (Loss) Schedule Of Related Tax Effects Allocated To Components Of Other Comprehensive Income (Loss) [Table Text Block] Related tax effects of defined benefit pension plans and designated hedging activities reclassifications and amounts arising during the period included in other comprehensive income (loss). Rollforward of Accumulated Other Comprehensive Income Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Amount Recognized Before Income Tax in Accumulated Other Comprehensive Income Schedule of Amounts Recognized in Other Comprehensive Income (Loss) [Table Text Block] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Transaction price allocated to unsatisfied performance obligations of contracts Revenue, Remaining Performance Obligation, Amount Revenue, remaining performance obligation, expected timing of satisfaction, period Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Schedule of Segment Reporting Information Schedule of Segment Reporting Information, by Segment [Table Text Block] Statement of Comprehensive Income [Abstract] Net income Net income (loss) from continuing operations 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 gain (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 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: 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 Discontinued operations-construction services, net income Discontinued operations-construction services, foreign currency translation adjustments Other Comprehensive Income Foreign Currency Transaction And Translation Adjustment From Discontinued Operation Net Of Tax Portion Attributable To Parent Other comprehensive income foreign currency transaction and translation adjustment from discontinued operation net of tax portion attributable to parent. Discontinued operations-construction services, comprehensive income Comprehensive Income From Discontinued Operation Net Of Tax Including Portion Attributable To Noncontrolling Interest Comprehensive income from discontinued operation net of tax including portion attributable to noncontrolling interest. Discontinued operations-construction services, comprehensive income (loss) attributable to noncontrolling interests Other Comprehensive Income (Loss) From Discontinued Operation, Net Of Tax, Portion Attributable To Noncontrolling Interest Other Comprehensive Income (Loss) From Discontinued Operation, Net Of Tax, Portion Attributable To Noncontrolling Interest Comprehensive income attributable to discontinued operations - construction services Other Comprehensive Income Loss From Discontinued Operation Net Of Tax Other comprehensive income loss from discontinued operation net of tax. Comprehensive income (loss) Comprehensive Income (Loss), Net of Tax, Attributable to Parent Derivative [Table] Derivative [Table] Forward-starting interest rate swaps Forward-Starting Interest Rate Swaps [Member] Forward-Starting Interest Rate Swaps [Member] Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] Arizona ARIZONA California CALIFORNIA Hedging Relationship [Axis] Hedging Relationship [Axis] Hedging Relationship [Domain] Hedging Relationship [Domain] Cash Flow Hedging Cash Flow Hedging [Member] Derivative [Line Items] Derivative [Line Items] Natural gas portfolios, maximum % rate Natural Gas Portfolios Percentage Rate Range Maximum The maximum percentage of the natural gas portfolio that is fixed Gains (losses) recognized in income or other comprehensive income for derivative designated cash flow hedges Number of derivative instruments held Derivative, Number of Instruments Held Derivative instrument loss at settlement amortization period Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimate of Time to Transfer Schedule of Short-term Debt [Table] Schedule of Short-term Debt [Table] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Southwest Gas Credit Facility Southwest Gas Credit Facility [Member] Southwest Gas Credit Facility [Member] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Credit Facility Credit Facility [Member] Credit Facility [Member] Short-term Debt [Line Items] Short-term Debt [Line Items] Credit facility maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Line of credit designated for working capital purposes Line Of Credit Facility Working Capital Purposes Line Of Credit Facility, Working Capital Purposes Short term borrowings outstanding Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] 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. Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Revenue from contracts with customers Revenue from Contract with Customer, Excluding Assessed Tax 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 Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement [Member] Portion at Fair Value Measurement [Member] Carrying Amount Reported Value Measurement [Member] Fair Value Estimate of Fair Value Measurement [Member] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Debentures Debentures [Member] Debentures [Member] Industrial development revenue bonds Industrial Development Revenue Bonds [Member] Industrial Development Revenue Bonds [Member] 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. 8% Series, due 2026 Debentures Eight Percentage Series Due Two Thousand And Twenty Six [Member] Debentures Eight Percentage Series Due Two Thousand And Twenty Six [Member] Medium-term notes, 7.78% series, due 2022 Debentures Medium Term Notes Seven Point Seven Eight Percentage Series Due Two Thousand And Twenty Two [Member] Debentures Medium Term Notes Seven Point Seven Eight Percentage Series Due Two Thousand and Twenty Two [Member] Medium-term notes, 7.92% series, due 2027 Debentures Medium Term Notes Seven Point Nine Two Percentage Series Due Two Thousand And Twenty Seven [Member] Debentures Medium Term Notes Seven Point Nine Two Percentage Series Due Two Thousand and Twenty Seven [Member] Medium-term notes, 6.76% series, due 2027 Debentures Medium Term Notes Six Point Seven Six Percentage Series Due Two Thousand And Twenty Seven [Member] Debentures Medium Term Notes Six Point Seven Six Percentage Series Due Two Thousand and Twenty Seven [Member] Revolving credit facility and commercial paper Revolving Credit Facility And Commercial Paper [Member] Revolving Credit Facility And Commercial Paper [Member] Tax-exempt Series A, due 2028 Variable Rate Bonds Tax Exempt Series A- Due Two Thousand And Twenty Eight [Member] Variable Rate Bonds Tax Exempt Series Due Two Thousand and Twenty Eight [Member] 2003 Series A, due 2038 Variable Rate Bonds Two Thousand And Three Series A- Due Two Thousand And Thirty Eight [Member] Variable Rate Bonds Two Thousand and Three Series A Due Two Thousand and Thirty Eight [Member] 2008 Series A, due 2038 Variable Rate Bonds Two Thousand And Eight Series A- Due Two Thousand And Thirty Eight [Member] Variable Rate Bonds Two Thousand and Eight Series A Due Two Thousand and Thirty Eight [Member] 2009 Series A, due 2039 Variable Rate Bonds Two Thousand And Nine Series A- Due Two Thousand And Thirty Nine [Member] Variable Rate Bonds Two Thousand and Nine Series A Due Two Thousand and Thirty Nine [Member] Centuri term loan facility Centuri Term Loan Facility [Member] Centuri term loan facility. Centuri other debt obligations Centuri Other Debt Obligations [Member] Centuri Other Debt Obligations [Member] Centuri secured revolving credit facility Centuri Secured Revolving Credit Facility [Member] Centuri secured revolving credit facility. Debt Instrument [Line Items] Debt Instrument [Line Items] Notes payable, fair value disclosure Notes Payable, Fair Value Disclosure Line of credit facility, fair value Lines of Credit, Fair Value Disclosure Unsecured debt, fair value Long-term Debt, Fair Value Unamortized discount and debt issuance costs Debt Instrument Unamortized Discount And Debt Issuance Costs Debt instrument unamortized discount and debt issuance costs. Notes payable Notes Payable Unsecured debt Unsecured Debt Line of credit facility Long-term Line of Credit Less: current maturities Long-term debt, less current maturities Unamortized debt issuance costs Unamortized Debt Issuance Expense Long-term Debt, Current and Noncurrent Abstract Long-term Debt, Current and Noncurrent [Abstract] Long-term debt Long-term Debt Centuri secured revolving credit facility Secured Debt Centuri other debt obligations Other Long-term Debt Debt instrument interest rate Debt Instrument, Interest Rate, Stated Percentage Product and Service [Axis] Product and Service [Axis] Product and Service [Domain] Product and Service [Domain] Replacement gas construction Replacement Gas Construction [Member] Replacement gas construction. New gas construction New Gas Construction [Member] New Gas Construction [Member] Other construction Other Construction [Member] Other construction. Contract with Customer, Basis of Pricing [Axis] Contract with Customer, Basis of Pricing [Axis] Contract with Customer, Basis of Pricing [Domain] Contract with Customer, Basis of Pricing [Domain] Master services agreement Master Services Agreement [Member] Master Services Agreement [Member] Bid contract Bid Contract [Member] Bid contract. Unit priced contracts Unit Priced Contracts [Member] Unit priced contracts. Fixed priced contracts Fixed-price Contract [Member] Commercial Paper Program Commercial Paper Program [Member] Commercial Paper Program [Member] Line of Credit Line of Credit [Member] Equipment Loans Equipment Loans [Member] Equipment loans. Secured Revolving Credit and Term Loan Facility Secured Revolving Credit Facility Term Loan [Member] Secured Revolving Credit Facility Term Loan [Member] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] LIBOR London Interbank Offered Rate (LIBOR) [Member] Alternative Base Rate Alternative Base Rate [Member] Alternative Base Rate [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 Applicable margin Debt Instrument, Basis Spread on Variable Rate Long-term debt Borrowings outstanding under facility Debt instrument discount rate Debt Instrument Discount Rate Debt Instrument Discount Rate Debt secured by assets Debt Instrument, Collateral Amount 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 Asset derivatives not designated as hedging instruments Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value Liability derivatives not designated as hedging instruments Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value Net total not designated as hedging instruments Other Derivatives Not Designated as Hedging Instruments at Fair Value, Net Derivatives and Fair Value Measurements Derivatives and Fair Value [Text Block] Notional Amounts under Swaps Contracts Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] Amount of Gain or Losses Recognized in Income on Derivatives Derivative Instruments, Gain (Loss) [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] 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] Regulatory Assets/Liabilities Offsetting Derivatives at Fair Value in Condensed Consolidated Balance Sheets Regulatory Assets Or Liabilities Offsetting Amounts In Financial Position [Table Text Block] Regulatory Assets or Liabilities Offsetting Amounts In Financial Position [Table Text Block] Summary of Financial Assets and Liabilities at Fair Value Fair Value Measurements, Recurring and Nonrecurring [Table Text Block] Amortization of net actuarial loss AOCI Attributable to Parent 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, 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 Reclassification of excess deferred taxes Accumulated Other Comprehensive Income, Reclassification Of Excess Deferred Taxes Accumulated Other Comprehensive Income, Reclassification Of Excess Deferred Taxes Other Stockholders' Equity, Including Portion Attributable To Noncontrolling Interest, Other Stockholders' Equity, Including Portion Attributable To Noncontrolling Interest, Other 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 Contracts receivable, net Revenue earned on contracts in progress in excess of billings Revenue earned on contracts in progress in excess of billings Revenue earned on contracts in progress in excess of billings. Amounts billed in excess of revenue earned on contracts Amounts billed in excess of revenue earned on contracts Amounts billed in excess of revenue earned on contracts. Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Update 2014-09 Accounting Standards Update 2014-09 [Member] 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] Derivative Instruments, Gain (Loss) [Table] Derivative Instruments, Gain (Loss) [Table] Regulatory Agency [Axis] Regulatory Agency [Axis] Regulatory Agency [Domain] Regulatory Agency [Domain] Regulatory Deferral Accounting Treatment Regulatory Deferral Accounting Treatment [Member] Regulatory Deferral Accounting Treatment [Member] Net cost of gas sold Net Cost Of Gas Sold [Member] Net Cost Of Gas Sold [Member] Derivative Instruments, Gain (Loss) [Line Items] Derivative Instruments, Gain (Loss) [Line Items] Amount of gain or (loss) recognized in income on derivative Derivative, Gain (Loss) on Derivative, Net Net actuarial (loss) gain Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax Prior service cost Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, Prior Service Cost (Credit), before Tax Less: amount recognized in regulatory assets Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Amount Recognized Regulatory Assets, Before Tax Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Amount Recognized Regulatory Assets, Before Tax Recognized in AOCI Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax Nature of Operations and Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Statement of Cash Flows [Abstract] CASH FLOW FROM OPERATING ACTIVITIES: Net Cash Provided by (Used in) Operating Activities [Abstract] Income from discontinued operations Income from continuing operations 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 Gain (Loss) on Disposition of Property Plant Equipment Changes in undistributed stock compensation Share-based Compensation AFUDC Increase (Decrease) in Allowance for Equity Funds Used During Construction Changes in other assets and deferred charges 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, continuing operations Net Cash Provided by (Used in) Operating Activities, Continuing Operations 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 Miscellaneous inflows Proceeds From Miscellaneous Investing Activities Proceeds from miscellaneous investing activities. Dividends received Proceeds from Dividends Received, Investing Activities Proceeds from dividends received, investing activities. Net cash used in investing activities, continuing operations Net Cash Provided by (Used in) Investing Activities, Continuing Operations 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 Capital Lease Obligations Redemption of Centuri shares from noncontrolling parties Payments for Repurchase of Redeemable Noncontrolling Interest Withholding remittance - share-based compensation Payments Related to Tax Withholding for Share-based Compensation Other Proceeds from (Payments for) Other Financing Activities Net cash provided by financing activities, continuing operations Net Cash Provided by (Used in) Financing Activities, Continuing Operations Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities Net cash provided by discontinued operating activities Cash Provided by (Used in) Operating Activities, Discontinued Operations Effects of currency translation on cash and cash equivalents Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Net cash used in discontinued investing activities Cash Provided by (Used in) Investing Activities, Discontinued Operations Net cash used in discontinued financing activities Cash Provided by (Used in) Financing Activities, Discontinued Operations Effects of currency translation on cash and cash equivalents Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Disposal Group, Including Discontinued Operations Change in cash and cash equivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Change in cash and cash equivalents of discontinued operations included in discontinued operations construction services assets Net Cash Provided by (Used in) Discontinued Operations Change in cash and cash equivalents of continuing operations Net Cash Provided by (Used in) Continuing Operations 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, continuing operations Interest Paid Net, Continuing Operations Interest paid net, continuing operations. Income taxes paid (received) Income Taxes Paid, Net Interest paid, net of amounts capitalized Interest Paid, Excluding Capitalized Interest, Operating Activities Components of Net Periodic Benefit Cost Compensation and Employee Benefit Plans [Text Block] 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 Number of segments Number of Reportable Segments Significant Accounting Policies [Table] Significant Accounting Policies [Table] Significant Accounting Policies [Table] Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] Pooled Funds and Mutual Funds Money Market Funds [Member] Previous Owners Previous Owners [Member] Previous owners. 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. Investment [Axis] Investment [Axis] Investment [Domain] Investment [Domain] Link-Line and WS Nicholls Link-Line and WS Nicholls [Member] Link-Line and WS Nicholls. New England Utility Constructors Inc. New England Utility Constructors Inc [Member] New England Utility Constructors Inc. Significant Accounting Policies [Line Items] Significant Accounting Policies [Line Items] Significant Accounting Policies [Line Items] Ownership percentage in subsidiary Percentage of earnings attribution by Centuri to previous owners 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 Previous tax effects from TCJA reclassified to retained earnings from AOCI Previous Tax effects from TCJA reclassified to retained earnings from AOCI Previous Tax effects from TCJA reclassified to retained earnings from AOCI. Gas pipe materials and operating supplies Materials, Supplies, and Other Prepaid and other current assets Regulatory Assets, Current Corporate federal income tax rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Other current liabilities, excess cost-of-service rates amount to be refunded Other Current Liabilities, Excess Cost-Of-Service Rates Amount To Be Refunded Other Current Liabilities, Excess Cost-Of-Service Rates Amount To Be Refunded Dividends declared but not yet paid Dividends Payable, Current Money market fund investments Cash and Cash Equivalents, Fair Value Disclosure Restatement [Axis] Restatement [Axis] Restatement [Domain] Restatement [Domain] Previously Reported Previously Reported [Member] Operating Expense Operating Expense [Member] Other Income Other Income [Member] Percentage of eligible participants accepted pension payout offer Percentage Of Eligible Participants Accepted Pension Payout Offer Percentage Of Eligible Participants Accepted Pension Payout Offer Number of eligible participants for pension payout offer Number of Eligible Participants for Pension Payout Offer Number of eligible participants for pension payout offer. Payment from pension assets Defined Benefit Plan, Plan Assets, Increase (Decrease) for Assets Transferred to (from) Plan