Regulatory Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
Jun. 30, 2011
Regulatory Assets and Liabilities
Period considered while calculating regulatory liability (in years)	3
Regulatory liability	$ 2.9
Portion of litigation proceeds received by Cal Water to replace infrastructure damaged by the gasoline additive Methyl tert-butyl ether (MTBE)	$ 34.2

The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 71
-Paragraph 11
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_RegulatoryLiabilities
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant