Business Risks and Commitments (Details) (Commercial and residential water customers, GSWC)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Commercial and residential water customers \| GSWC
Commercial and residential water customers
Percentage of total revenues	90.00%	90.00%	90.00%

Percentage of revenue generated from a single external customer that accounts for 10 percent or more of an entity's revenues.

No definition available.

Name:	us-gaap_EntityWideRevenueMajorCustomerPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration