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Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Related Tax Effects Allocated to Each Component of Other Comprehensive Income (Loss) (Parenthetical) (Detail) (USD $)
3 Months Ended
Mar. 31, 2015
Equity [Abstract]  
Other comprehensive income loss, effective income tax rate 38.00%swx_OtherComprehensiveIncomeLossEffectiveIncomeTaxRate
Tax expense or benefit for currency translation adjustment $ 0swx_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentFromDeferredTax