Represents the ownership interest percentage of the parent in consolidated subsidiaries.

No definition available.

Name:	cwt_OwnershipInterestPercentageOfParentInConsolidatedSubsidiaries
Namespace Prefix:	cwt_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	dei_LegalEntityAxis=cwt_CalWaterMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=cwt_AllOtherSubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=cwt_FirstMortgageBondsLLSeriesDue2019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=cwt_FirstMortgageBondsPPPSeriesDue2040Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Condensed Consolidating Financial Statements - Additional Information (Details) - USD ($)	Sep. 30, 2018	Nov. 17, 2010	Apr. 17, 2009
Cal Water
Debt Instrument [Line Items]
Ownership interest (as a percent)	100.00%
All Other Subsidiaries
Debt Instrument [Line Items]
Ownership interest (as a percent)	100.00%
First Mortgage Bonds, 5.875% due 2019 \| Cal Water
Debt Instrument [Line Items]
Debt issued			$ 100,000,000
Interest rate			5.875%
First Mortgage Bonds, 5.500% due 2040 \| Cal Water
Debt Instrument [Line Items]
Debt issued		$ 100,000,000
Interest rate		5.50%