Nature of Operations and Basis of Presentation - Schedule of Other Property and Investments (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Investment [Line Items]
Net cash surrender value of COLI policies	$ 101,000,000	$ 99,000,000
Other property	12,000,000	10,000,000
Total	319,689,000swx_OtherPropertyAndInvestments	326,743,000swx_OtherPropertyAndInvestments
Centuri Construction Group Inc [Member]
Investment [Line Items]
Centuri property and equipment	402,000,000	405,000,000
Centuri accumulated provision for depreciation and amortization	$ (195,000,000)	$ (187,000,000)

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Aggregate carrying amount, as of the balance sheet date, of other property and investments not separately presented elsewhere in the balance sheet.

+ References

No definition available.

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- Definition

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (c)

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-Publisher FASB

-Name Accounting Standards Codification

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-Section S99

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-Subparagraph (SX 210.5-02.14)

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-Publisher SEC

-Name Regulation S-X (SX)

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- Definition

Carrying amount as of the balance sheet date of amounts which could be received based on the terms of the insurance contract upon surrendering life policies owned by the entity.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 10

-Section S99

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-Section 45

-Paragraph 4

-Subparagraph (d)

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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The net amount of capitalized assets classified as property, plant and equipment not otherwise defined in the taxonomy.

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No definition available.

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