Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013
Commitments And Contingencies Disclosure [Abstract]
Self-insured retention amount associated with general liability claims	$ 1
Additional self-insured retention amount of general liability	$ 4

Amount of risk retained by the entity per incident before the insurance arrangement begins to provide coverage.

No definition available.

Name:	swx_SelfInsuredRetentionAmountAssociatedWithGeneralLiabilityClaims
Namespace Prefix:	swx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant