Regulatory Assets and Liabilities (Details) (USD $)	3 Months Ended					6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Dec. 31, 2011	Jun. 30, 2013 Pension costs	Dec. 31, 2012 Pension costs	Jun. 30, 2013 Conservation costs	Jun. 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 proceeds used to replace damaged infrastructure	1,200,000
MTBE regulatory and other liabilities	10,600,000
Balancing account disclosures
Period considered while calculating regulatory liability						3 years
Regulatory assets							3,700,000	2,400,000
Regulatory and other liabilities				$ 6,800,000	$ 6,500,000