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'Monetary' elements on report '1080 - Disclosure - Stock-Based Compensation - Additional Information (Detail)' had a mix of different decimal attribute values. 'Monetary' elements on report '1091 - Disclosure - Income Taxes - Additional Information (Detail)' had a mix of different decimal attribute values. 'Monetary' elements on report '1092 - Disclosure - Derivatives and Fair Value Measurements - Additional Information (Detail)' had a mix of different decimal attribute values. Process Flow-Through: 1003 - Statement - Consolidated Balance Sheets Process Flow-Through: Removing column 'Dec. 31, 2011' Process Flow-Through: Removing column 'Dec. 31, 2010' Process Flow-Through: 1004 - Statement - Consolidated Balance Sheets (Parenthetical) Process Flow-Through: 1005 - Statement - Consolidated Statements of Income Process Flow-Through: Removing column '3 Months Ended Dec. 31, 2013' Process Flow-Through: Removing column '3 Months Ended Sep. 30, 2013' Process Flow-Through: Removing column '3 Months Ended Jun. 30, 2013' Process Flow-Through: Removing column '3 Months Ended Mar. 31, 2013' Process Flow-Through: Removing column '3 Months Ended Dec. 31, 2012' Process Flow-Through: Removing column '3 Months Ended Sep. 30, 2012' Process Flow-Through: Removing column '3 Months Ended Jun. 30, 2012' Process Flow-Through: Removing column '3 Months Ended Mar. 31, 2012' Process Flow-Through: Removing column '3 Months Ended Dec. 31, 2011' Process Flow-Through: Removing column '3 Months Ended Sep. 30, 2011' Process Flow-Through: Removing column '3 Months Ended Jun. 30, 2011' Process Flow-Through: Removing column '3 Months Ended Mar. 31, 2011' Process Flow-Through: 1006 - Statement - Consolidated Statements of Comprehensive Income Process Flow-Through: Removing column '3 Months Ended Dec. 31, 2013' Process Flow-Through: Removing column '3 Months Ended Sep. 30, 2013' Process Flow-Through: Removing column '3 Months Ended Jun. 30, 2013' Process Flow-Through: Removing column '3 Months Ended Mar. 31, 2013' Process Flow-Through: Removing column '3 Months Ended Dec. 31, 2012' Process Flow-Through: Removing column '3 Months Ended Sep. 30, 2012' Process Flow-Through: Removing column '3 Months Ended Jun. 30, 2012' Process Flow-Through: Removing column '3 Months Ended Mar. 31, 2012' Process Flow-Through: Removing column '3 Months Ended Dec. 31, 2011' Process Flow-Through: Removing column '3 Months Ended Sep. 30, 2011' Process Flow-Through: Removing column '3 Months Ended Jun. 30, 2011' Process Flow-Through: Removing column '3 Months Ended Mar. 31, 2011' Process Flow-Through: 1007 - Statement - Consolidated Statements of Cash Flows Process Flow-Through: 1009 - Statement - Consolidated Statements of Equity (Parenthetical) Process Flow-Through: Removing column 'Dec. 31, 2010' swx-20131231.xml swx-20131231.xsd swx-20131231_cal.xml swx-20131231_def.xml swx-20131231_lab.xml swx-20131231_pre.xml true true