Document and Entity Information (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Feb. 11, 2014	Jun. 30, 2013
Document and Entity Information
Entity Registrant Name	CALIFORNIA WATER SERVICE GROUP
Entity Central Index Key	0001035201
Document Type	10-K
Document Period End Date	Dec. 31, 2013
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 931.3
Entity Common Stock, Shares Outstanding		47,740,957
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	FY