Accounting Policies [Abstract] Accounting Policies [Abstract] Accounts, Notes, Loans and Financing Receivable [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Accounts Payable, Current Accounts payable Accounts Receivable, Net, Current Accounts receivable, net of allowances Accrual for Taxes Other than Income Taxes, Current Accrued general taxes Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Centuri accumulated provision for depreciation and amortization Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax Ending Balance AOCI September 30, 2015, FSIRS - After-Tax Beginning Balance AOCI December 31, 2014, FSIRS - After-Tax Accumulated Other Comprehensive Income Loss Cumulative Changes In Net Gain Loss From Cash Flow Hedges tax effect Accumulated Other Comprehensive Income Loss Cumulative Changes In Net Gain Loss From Cash Flow Hedges Tax Effect Ending Balance AOCI September 30, 2015, FSIRS - Tax (Expense) Benefit Beginning Balance AOCI December 31, 2014, FSIRS - Tax (Expense) Benefit Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax Beginning Balance AOCI December 31, 2014, Defined Benefit Plans After-Tax Ending Balance AOCI September 30, 2015, Defined Benefit Plans After-Tax Accumulated Other Comprehensive Income Loss Defined Benefit Pension And Other Postretirement Plans Tax Effect Accumulated Other Comprehensive Income Loss Defined Benefit Pension And Other Postretirement Plans Tax Effect Ending Balance AOCI September 30, 2015, Defined Benefit Plans Tax (Expense) Benefit Beginning Balance AOCI December 31, 2014, Defined Benefit Plans Tax (Expense) Benefit Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax Ending Balance AOCI September 30, 2015, Foreign Currency items - After-Tax Beginning Balance AOCI December 31, 2014, Foreign Currency items - After-Tax Accumulated Other Comprehensive Income Loss Foreign Currency Translation Adjustment Net Of Tax Attributable To Noncontrolling Interest Accumulated Other Comprehensive Income Loss Foreign Currency Translation Adjustment Net Of Tax Attributable To Noncontrolling Interest Less: Translation adjustment attributable to redeemable noncontrolling interest, AOCI Accumulated Other Comprehensive Income Loss Foreign Currency Translation Adjustment Net Of Tax Attributable To Parent Accumulated Other Comprehensive Income Loss Foreign Currency Translation Adjustment Net Of Tax Attributable To Parent Translation adjustments, AOCI Accumulated Other Comprehensive Income Loss Foreign Currency Translation Adjustments Before Tax Accumulated Other Comprehensive Income Loss Foreign Currency Translation Adjustments Before Tax Ending Balance AOCI September 30, 2015, Foreign Currency Items Before-Tax Beginning Balance AOCI December 31, 2014, Foreign Currency Items Before-Tax Accumulated Other Comprehensive Income Loss Foreign Currency Translation Adjustment Tax Accumulated Other Comprehensive Income Loss Foreign Currency Translation Adjustment Tax Beginning Balance AOCI December 31, 2014, Foreign Currency items - Tax (Expense) Benefit Ending Balance AOCI September 30, 2015, Foreign Currency items - Tax (Expense) Benefit Accumulated Other Comprehensive Income Loss Forward Starting Interest Rate Swap Before Tax Accumulated Other Comprehensive Income Loss Forward Starting Interest Rate Swap Before Tax Ending Balance AOCI September 30, 2015, FSIRS - Before-Tax Beginning Balance AOCI December 31, 2014, FSIRS - Before-Tax Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss), Net of Tax Ending Balance AOCI September 30, 2015, AOCI Beginning Balance AOCI December 31, 2014, AOCI Accumulated other comprehensive income (loss), net Accumulated Other Comprehensive Income Loss Net Of Tax Attributable To Parent Accumulated Other Comprehensive Income Loss Net Of Tax Attributable To Parent Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, AOCI Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] AOCI Attributable to Parent [Member] Accumulated Other Comprehensive Income (Loss) [Member] Additional Paid in Capital, Common Stock Additional paid-in capital Additional Paid-in Capital [Member] Additional Paid-in Capital [Member] Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net income to net cash provided by operating activities: Alternative Base Rate [Member] Alternative Base Rate [Member] Alternative base rate [Member] Amendment Flag Amendment Flag Assets Total assets Assets [Abstract] ASSETS Assets, Current Total current assets Assets, Current [Abstract] Current assets: Assets, Noncurrent Total noncurrent assets Assets, Noncurrent [Abstract] Noncurrent assets: ARIZONA Arizona [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Bank Of New York Mellon Capital Markets LLC [Member] Bank Of New York Mellon Capital Markets Llc [Member] BNY Mellon Capital Markets, LLC [Member] Basis Of Presentation [Policy Text Block] Basis Of Presentation Policy [Text Block] Basis of Presentation Before Amendment [Member] Before Amendment [Member] Before Amendment [Member] Brigadier Pipelines Inc [Member] Brigadier Pipelines Inc [Member] Brigadier Pipelines Inc. [Member] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Business Acquisition [Axis] Business Acquisition [Axis] Business acquisition purchase price allocation goodwill expected tax deductible amount net of tax. Business Acquisition Purchase Price Allocation Goodwill Expected Tax Deductible Amount Net Of Tax Goodwill assigned for deductible tax purpose Business Combination Disclosure [Text Block] Acquisition of Construction Services Businesses Business Combinations [Abstract] Business Combinations [Abstract] CALIFORNIA California [Member] Capitalization, Long-term Debt and Equity Total capitalization Capitalization, Long-term Debt and Equity [Abstract] Capitalization: Reported Value Measurement [Member] Carrying Amount [Member] Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents at end of period Cash and cash equivalents at beginning of period Cash and cash equivalents Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Axis] Cash and Cash Equivalents, Fair Value Disclosure Money market fund investments Cash and Cash Equivalents, Period Increase (Decrease) Change in cash and cash equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Cash and Cash Equivalents Cash Flow Hedging [Member] Cash flow hedging [Member] Cash Surrender Value of Life Insurance Net cash surrender value of COLI policies Centuri Construction Group [Member] Centuri Construction Group [Member] Centuri Construction Group Inc [Member] Centuri Other Debt Obligations [Member] Centuri Other Debt Obligations [Member] Centuri other debt obligations [Member] Centuri Secured Revolving Credit And Term Loan Facility [Member] Centuri Secured Revolving Credit And Term Loan Facility [Member] Centuri secured revolving credit and term loan facility [Member] The net change during the reporting period in the amount of prepayments by customers for goods or services to be provided at a later date. Change In Customer Advances Changes in customer advances Commercial Paper [Member] Commercial Paper Program [Member] Common Stock Disclosure [Text Block] Common Stock Disclosure [Text Block] Common Stock Common Stock, Dividends, Per Share, Declared Dividends declared Common, per share Dividends declared per share Common Stock [Member] Common Stock [Member] Common Stock, Par or Stated Value Per Share Common stock, par Common Stock, Shares Authorized Common stock, authorized Common Stock, Shares, Issued Common stock, issued Common Stock, Shares, Outstanding Balance, shares Balance, shares Common stock, outstanding Common Stock, Value, Issued Common stock, $1 par (authorized-60,000,000 shares; issued and outstanding-47,375,398 and 46,523,184 shares) Common stock weighted average issue price per share. Common Stock Weighted Average Issue Price Per Share Common stock weighted average price Compensation and Retirement Disclosure [Abstract] Compensation and Retirement Disclosure [Abstract] Comprehensive Income (Loss), Net of Tax, Attributable to Parent Comprehensive income (loss) attributable to Southwest Gas Corporation Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Comprehensive income (loss) attributable to noncontrolling interests Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Comprehensive income (loss) Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract] Other comprehensive income (loss), net of tax Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Consolidation less than wholly owned subsidiary parent ownership interest changes issuance of equity by subsidiary to noncontrolling interest and temporary equity redemption value adjustment. Consolidation Less Than Wholly Owned Subsidiary Parent Ownership Interest Changes Issuance Of Equity By Subsidiary To Noncontrolling Interest And Temporary Equity Redemption Value Adjustment Adjustment to redemption value Redemption value adjustments Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Changes, Issuance of Equity by Subsidiary to Noncontrolling Interests Adjustment to redemption value Redemption value adjustments Construction and Development Costs Construction expenses Construction Revenue Construction revenues Construction Services [Member] Construction Services [Member] Construction Services [Member] Costs and Expenses Total operating expenses Costs and Expenses [Abstract] Operating expenses: Counterparty Name [Axis] Counterparty Name [Axis] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Current Fiscal Year End Date Current Fiscal Year End Date Customer Deposits, Current Customer deposits Debentures Eight Percentage Series Due Two Thousand And Twenty Six [Member] Debentures Eight Percentage Series Due Two Thousand And Twenty Six [Member] 8% Series, due 2026 [Member] Debentures Medium Term Notes Seven Point Five Nine Percentage Series Due Two Thousand And Seventeen [Member] Debentures Medium Term Notes Seven Point Five Nine Percentage Series Due Two Thousand And Seventeen [Member] Medium-term notes, 7.59% series, due 2017 [Member] 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, 7.92% series, due 2027 [Member] 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, 7.78% series, due 2022 [Member] 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] Medium-term notes, 6.76% series, due 2027 [Member] Debentures [Member] Debentures [Member] Debentures [Member] 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, 4.875%, due 2043 [Member] 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, 4.45%, due 2020 [Member] 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, 6.1%, due 2041 [Member] 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, 3.875%, due 2022 [Member] Debt Disclosure [Abstract] Debt Disclosure [Abstract] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Basis Spread on Variable Rate Applicable margin Debt Instrument, Collateral Amount Debt secured by assets Debt Instrument, Interest Rate, Stated Percentage Debt instrument interest rate Debt Instrument [Line Items] Debt Instrument [Line Items] Debt Instrument, Maturity Date Debt instrument due date Debt instrument original due date Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Debt Instrument, Unamortized Discount Unamortized discount Deferred Charges And Other Assets [Member] Deferred Charges And Other Assets [Member] Deferred charges and other assets [Member] Deferred Credits and Other Liabilities, Noncurrent Other deferred credits and other long-term liabilities Deferred Gas Cost Deferred purchased gas costs Deferred Gas Purchases, Current Deferred purchased gas costs The net amount of deferred income taxes and income tax credits. Deferred Income Taxes And Unamortized Investment Tax Credits Deferred income taxes and investment tax credits Deferred Tax Assets, Net of Valuation Allowance, Current Deferred income taxes, net Deferred Tax Assets, Net of Valuation Allowance, Noncurrent Deferred income taxes Deferred Tax Liabilities, Gross, Current Deferred income taxes Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax Ending Balance AOCI September 30, 2015, Defined Benefit Plans Before-Tax Beginning Balance AOCI December 31, 2014, Defined Benefit Plans Before-Tax Recognized in AOCI Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax Net actuarial (loss) gain Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax Prior service cost Defined Benefit Plan, Amortization of Gains (Losses) Amortization of net actuarial loss Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Amortization of prior service costs Defined Benefit Plan, Asset Categories [Axis] Defined Benefit Plan, Asset Categories [Axis] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan, Expected Return on Plan Assets Expected return on plan assets Defined Benefit Plan, Interest Cost Interest cost Defined Benefit Plan, Net Periodic Benefit Cost Net periodic benefit cost Defined benefit plan, regulatory adjustment before-tax. Defined Benefit Plan Regulatory Adjustment Before Tax Regulatory adjustment, Before-Tax Amount Regulatory adjustment, Defined Benefit Plans Before-Tax Defined Benefit Plan Regulatory Adjustment, Net-Of-Tax Amount Defined Benefit Plan Regulatory Adjustment Net Of Tax Amount Regulatory adjustment, AOCI Regulatory adjustment, Defined Benefit Plans After-Tax Defined Benefit Plan Regulatory Adjustment, Tax (Expense) Or Benefit Defined Benefit Plan Regulatory Adjustment Tax Expense Or Benefit Regulatory adjustment, Defined Benefit Plans Tax (Expense) Benefit Regulatory adjustment, Tax (Expense) or Benefit Defined Benefit Plans and Other Postretirement Benefit Plans [Axis] Defined Benefit Plans and Other Postretirement Benefit Plans [Axis] Defined Benefit Plan and Other Postretirement Benefit Plan [Domain] Defined Benefit Plan and Other Postretirement Benefit Plan [Domain] Defined Benefit Plan, Service Cost Service cost Defined Benefit Plans [Member] Defined Benefit Plans [Member] Defined Benefit Plans [Member] Depreciation, Depletion and Amortization, Nonproduction Depreciation and amortization Derivative Assets (Liabilities), at Fair Value, Net Net Assets (Liabilities) Derivative, by Nature [Axis] Derivative, by Nature [Axis] 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. Derivative Fair Value Of Regulatory Assets Liabilities Offset Amount Net Total Derivative, Gain (Loss) on Derivative, Net Amount of gain or (loss) recognized in income on derivative Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative Instruments And Hedging Activities Disclosure [Abstract] Hedging Relationship [Axis] Hedging Relationship [Axis] Derivative Instruments, Gain (Loss) [Table] Derivative Instruments, Gain (Loss) [Table] Derivative Instruments, Gain (Loss) [Line Items] Derivative Instruments, Gain (Loss) [Line Items] Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimate of Time to Transfer Derivative instrument loss at settlement amortization period Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value Asset derivatives not designated as hedging instruments Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value Liability derivatives not designated as hedging instruments Derivative Liability Derivative Liabilities Derivative [Line Items] Derivative [Line Items] Derivative, Maturity Date Maturities of natural gas swaps Derivative, Name [Domain] Derivative, Name [Domain] Derivative, Nonmonetary Notional Amount Contract notional amounts Derivatives and Fair Value [Text Block] Derivatives and Fair Value Measurements Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Derivative [Table] Derivative [Table] Dividends, Common Stock Dividends declared Common: $1.215 per share Document And Entity Information [Abstract] Document And Entity Information [Abstract] Document And Entity Information [Abstract] Document Fiscal Period Focus Document Fiscal Period Focus Document Fiscal Year Focus Document Fiscal Year Focus Document Period End Date Document Period End Date Document Type Document Type Earnings Per Share, Basic Basic earnings (loss) per share Earnings Per Share, Diluted Diluted earnings (loss) per share Effect of Exchange Rate on Cash and Cash Equivalents, Continuing Operations Effects of currency translation on cash and cash equivalents Entity Central Index Key Entity Central Index Key Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity [Domain] Entity [Domain] Entity Filer Category Entity Filer Category Entity Registrant Name Entity Registrant Name Equity [Abstract] Equity [Abstract] Equity Component [Domain] Equity Component [Domain] Equity interest, dividend rights entitled percentage of cash dividend paid by subsidiary to parent company. Equity Interest Dividend Rights Entitled Percentage Of Cash Dividend Paid By Subsidiary To Parent Company Equity interest dividend rights, percentage of dividends paid by Centuri Equity interest, exchangeable for percentage of holding company equity interest. Equity Interest Exchangeable For Percentage Of Holding Company Equity Interest Equity interest exchangeable percentage in Centuri Investment, Name [Domain] Investment, Name [Domain] Estimate of Fair Value Measurement [Member] Market Value [Member] External Customers [Member] External Customers [Member] Revenues from external customers [Member] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Fair Value, Inputs, Level 2 [Member] Level 2 - Significant other observable inputs [Member] Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Sellers have the ability to redeem their holdings for cash beginning on this date. First Redemption Date First redemption date to exchange holdings for cash Fixed Rate Bonds Five Point Two Five Percentage Two Thousand and Three Series D Due Two Thousand and Thirty Eight [Member] Fixed Rate Bonds Five Point Two Five Percentage Two Thousand And Three Series D Due Two Thousand And Thirty Eight [Member] 5.25% 2003 Series D, due 2038 [Member] Fixed Rate Bonds Five Point Zero Zero Percentage Two Thousand and Four Series B Due Two Thousand and Thirty Three [Member] Fixed Rate Bonds Five Point Zero Zero Percentage Two Thousand And Four Series B Due Two Thousand And Thirty Three [Member] 5.00% 2004 Series B, due 2033 [Member] Fixed Rate Bonds Four Point Eight Five Percentage Two Thousand And Five Series Due Two Thousand And Thirty Five [Member] Fixed Rate Bonds Four Point Eight Five Percentage Two Thousand And Five Series A- Due Two Thousand And Thirty Five [Member] 4.85% 2005 Series A, due 2035 [Member] Fixed Rate Bonds Four Point Seven Five Percentage Two Thousand and Six Series A Due Two Thousand and Thirty Six [Member] Fixed Rate Bonds Four Point Seven Five Percentage Two Thousand And Six Series A- Due Two Thousand And Thirty Six [Member] 4.75% 2006 Series A, due 2036 [Member] Fixed Rate Bonds [Member] Fixed Rate Bonds [Member] Fixed-rate bonds [Member] Foreign Currency Transaction Gain (Loss), Realized Foreign transaction gain (loss) Gain (Loss) on Disposition of Property Plant Equipment Gains on sale Gas Pipe Inventory And Operating Supplies [Member] Gas Pipe Inventory And Operating Supplies [Member] Gas Pipe Materials and Supplies [Member] Goodwill Goodwill, Ending balance Goodwill, Beginning balance Goodwill Goodwill and Intangible Assets Disclosure [Abstract] Goodwill and Intangible Assets Disclosure [Abstract] Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block] Goodwill Goodwill, Impairment Loss Goodwill impairment charges Goodwill [Line Items] Goodwill [Line Items] Goodwill, Purchase Accounting Adjustments Acquisition date adjustment Acquisition date adjustments to goodwill Goodwill, Translation Adjustments Foreign currency translation adjustment Hedging Relationship [Domain] Hedging Relationship [Domain]