Regulatory Assets and Liabilities (Details) (USD $)	3 Months Ended					9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2013 Pension costs	Dec. 31, 2012 Pension costs	Sep. 30, 2013 Conservation costs	Sep. 30, 2013 Pension costs	Dec. 31, 2012 Pension costs
Regulatory Assets and Liabilities
Portion of litigation proceeds received by Cal Water to replace infrastructure damaged by the gasoline additive Methyl tert-butyl ether (MTBE)			$ 34,200,000
Reclassification from other long-term liabilities to Contributions in Aid of Construction		22,400,000
Amount of net proceeds used to replace damaged infrastructure	800,000
MTBE regulatory and other liabilities	9,800,000
Balancing account disclosures
Period considered while calculating regulatory liability						3 years
Regulatory assets							2,300,000	2,400,000
Regulatory and other liabilities				$ 7,700,000	$ 6,500,000