Represents the total obligation of third parties under separate agreements.

No definition available.

Name:	cwt_LongTermPurchaseCommitmentAggregateObligationOfThirdParties
Namespace Prefix:	cwt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the amount of total treated water charge under the long-term contract.

+ References

No definition available.

+ Details

Name:	cwt_LongTermPurchaseCommitmentAggregateTreatedWaterCharge
Namespace Prefix:	cwt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the obligations for capital facilities charge and treated water charge under the long-term contract.

+ References

No definition available.

+ Details

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

- Definition

Represents the obligations per acre foot for capital facilities charge and treated water charge under the long-term contract.

+ References

No definition available.

+ Details

Name:	cwt_LongTermPurchaseCommitmentAnnualCapitalFacilitiesChargeAndTreatedWaterChargeObligationPerAcreFoot
Namespace Prefix:	cwt_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the annual cost paid to purchase water under the long-term contract.

+ References

No definition available.

+ Details

Name:	cwt_LongTermPurchaseCommitmentAnnualCost
Namespace Prefix:	cwt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Sets forth the 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, by third parties under separate agreements.

+ References

No definition available.

+ Details

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

- Definition

Sets forth the number of units of goods that must be purchased under the terms of the prior agreement.

+ References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

Represents the estimated operating cost per acre foot for treated water delivered under the long-term contract.

+ References

No definition available.

+ Details

Name:	cwt_LongTermPurchaseCommitmentTreatedWaterEstimatedOperatingCostPerAcreFoot
Namespace Prefix:	cwt_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Definition

Amount of minimum lease payments for capital leases due in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6455398&loc=d3e45280-112737

+ Details

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

- Definition

Amount of minimum lease payments for capital leases due in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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

- Definition

Amount of minimum lease payments for capital leases due in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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

- Definition

Amount of minimum lease payments for capital leases due in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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

- Definition

Amount of minimum lease payments for capital leases due in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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

- Definition

Amount of minimum lease payments for capital leases due after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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

- Details

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

- Definition

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.

+ References

No definition available.

+ Details

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

- Definition

Amount of loss contingency liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

+ Details

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

- Definition

The difference between the maximum amount of estimated loss and the amount recorded as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 05

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6395354&loc=d3e12631-108344

+ Details

Name:	us-gaap_LossContingencyRangeOfPossibleLossPortionNotAccrued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Minimum amount of purchase arrangement maturing after the fifth fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

+ References

No definition available.

+ Details

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

- Definition

Minimum amount of purchase arrangement maturing in the fifth fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

+ References

No definition available.

+ Details

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

- Definition

Minimum amount of purchase arrangement maturing in the fourth fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

+ References

No definition available.

+ Details

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

- Definition

Minimum amount of purchase arrangement maturing in the next fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

+ References

No definition available.

+ Details

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

- Definition

Minimum amount of purchase arrangement maturing in the second fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

+ References

No definition available.

+ Details

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

- Definition

Minimum amount of purchase arrangement maturing in the third fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

+ References

No definition available.

+ Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=cwt_WaterContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

COMMITMENTS AND CONTINGENCIES (Detail 2) (USD $)	12 Months Ended
COMMITMENTS AND CONTINGENCIES (Detail 2) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Capital Lease Obligations
2015	$ 1,109,000
2016	1,109,000
2017	1,109,000
2018	1,016,000
2019	1,248,000
Thereafter	6,345,000
Contingency loss recognized liability	3,200,000
Possible losses in excess of the amount accrued	1,500,000
Water Contracts
Future minimum commitments
2015	21,045,000
2016	21,116,000
2017	21,144,000
2018	23,067,000
2019	21,145,000
Thereafter	423,911,000
Santa Clara Valley Water District
Long-term purchase commitments - other disclosures
Annual cost	5,486,000	7,407,000	6,164,000
Stockton East Water District (SEWD)
Long-term purchase commitments - other disclosures
Annual cost	8,739,000	9,990,000	6,591,000
Kern County Water Agency (Agency)
Long-term purchase commitments - other disclosures
Annual cost	6,704,000	6,289,000	6,272,000
Minimum acre feet of treated water to be purchased under prior agreement	11,500
Number of other parties obligated to purchase treated water	3
Minimum acre feet of treated water to be purchased per year by other parties	32,500
Total obligation of all parties, excluding the Company	82,397,000
Total capital facilities charge and treated water charge obligation	7,744,000
Total capital facilities charge and treated water charge obligation per acre foot	378
Total treated water charge	$ 2,760,000
Portion of estimated operating cost per acre foot for treated water delivered	14
Kern County Water Agency (Agency) \| Minimum
Long-term purchase commitments - other disclosures
Minimum acre feet of treated water to be purchased per year over life of contract	19,000
Kern County Water Agency (Agency) \| Maximum
Long-term purchase commitments - other disclosures
Minimum acre feet of treated water to be purchased per year over life of contract	20,500