Document and Entity Information	9 Months Ended
	Sep. 30, 2018 shares
Document and Entity Information
Entity Registrant Name	CALIFORNIA WATER SERVICE GROUP
Entity Central Index Key	0001035201
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding	48,068,000
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Entity Emerging Growth Company	false
Entity Small Business	false