Name:	cwt_LongTermPurchaseCommitmentMinimumQuantityRequiredToBePurchasedByThirdParties
Namespace Prefix:	cwt_
Data Type:	xbrli:integerItemType
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Sets forth the number of units of goods that must be purchased under the terms of the prior agreement.

No definition available.

Name:	cwt_LongTermPurchaseCommitmentMinimumQuantityRequiredToBePurchasedUnderPriorAgreement
Namespace Prefix:	cwt_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Represents the number of third parties obligated to purchase treated water each year under separate agreements.

No definition available.

Name:	cwt_LongTermPurchaseCommitmentNumberOfThirdPartiesHavingSeparateAgreement
Namespace Prefix:	cwt_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Payments For Other Commitments

No definition available.

Name:	cwt_PaymentsForOtherCommitments
Namespace Prefix:	cwt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Cost of water purchased, may include any water related assessment. If water is bought on a unit volume basis, would also be considered as commodity costs.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.2)
-URI https://asc.fasb.org/extlink&oid=126953954&loc=SL114868664-224227

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Number of units of goods that must be purchased within the specified time period of the agreement to avoid penalties or unfavorable effects on pricing, among other adverse consequences.

No definition available.

Name:	us-gaap_LongTermPurchaseCommitmentMinimumQuantityRequired
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Payments of cash to suppliers for goods and services during the current period.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 17
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3367-108585

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 17
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3367-108585

Name:	us-gaap_PaymentsToSuppliers
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount of purchase arrangement to be paid after fifth fiscal year following current fiscal year. Includes, but is not limited to, recorded and unrecorded purchase obligations, long-term purchase commitment, and short-term purchase commitment. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

No definition available.

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

Amount of purchase arrangement to be paid in fifth fiscal year following current fiscal year. Includes, but is not limited to, recorded and unrecorded purchase obligations, long-term purchase commitment, and short-term purchase commitment. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

No definition available.

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

Amount of purchase arrangement to be paid in fourth fiscal year following current fiscal year. Includes, but is not limited to, recorded and unrecorded purchase obligations, long-term purchase commitment, and short-term purchase commitment. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

No definition available.

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

Amount of purchase arrangement to be paid in next fiscal year following current fiscal year. Includes, but is not limited to, recorded and unrecorded purchase obligations, long-term purchase commitment, and short-term purchase commitment. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

No definition available.

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

Amount of purchase arrangement to be paid in second fiscal year following current fiscal year. Includes, but is not limited to, recorded and unrecorded purchase obligations, long-term purchase commitment, and short-term purchase commitment. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

No definition available.

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

Amount of purchase arrangement to be paid in third fiscal year following current fiscal year. Includes, but is not limited to, recorded and unrecorded purchase obligations, long-term purchase commitment, and short-term purchase commitment. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

No definition available.

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

- References

No definition available.

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

Amount of the recorded obligation to transfer funds in the future for fixed or minimum amounts or quantities of goods or services at fixed or minimum prices (for example, as in take-or-pay contracts or throughput contracts).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 440
-SubTopic 10
-Section 50
-Paragraph 6
-URI https://asc.fasb.org/extlink&oid=123406679&loc=d3e25383-109308

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

The minimum number of units that must be purchased, in connection with an unconditional purchase obligation that has not been recognized for financial reporting purposes.

No definition available.

Name:	us-gaap_UnrecordedUnconditionalPurchaseObligationMinimumQuantityRequired
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

Cost incurred related to water production and may include cost of treatment plants, pumps, pipes and reservoir, purchased water, power and pump taxes as well as the cost of reducing water leakage.

Name:	us-gaap_WaterProductionCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Name:	us-gaap_OtherCommitmentsAxis=us-gaap_SupplyCommitmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

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

Name:	srt_StatementScenarioAxis=srt_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_SupplyCommitmentAxis=cwt_KernCountyWaterAgencyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_SupplyCommitmentAxis=cwt_StocktonEastWaterDistrictMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_SupplyCommitmentAxis=cwt_SantaClaraWaterDistrictMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_GuaranteeObligationsByNatureAxis=us-gaap_GuaranteeTypeOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: