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Summary of Significant Accounting Policies Narrative (Details)	12 Months Ended
	Dec. 31, 2014
Acequia Water Supply Corporation [Member]
Public Utilities General Disclosures [Line Items]
Ownership percentage in Acequia Water Supply Corporation	25.00%us-gaap_VariableInterestEntityOwnershipPercentage / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Minimum [Member]
Public Utilities General Disclosures [Line Items]
Service area in square miles	240sjw_PublicUtilitiesServiceArea / us-gaap_RangeAxis = us-gaap_MinimumMember
Sales [Member] | Product Concentration Risk [Member]
Public Utilities General Disclosures [Line Items]
Percentage of revenue derived from sales of water to business and residential customers	93.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_ProductConcentrationRiskMember
San Jose Water Company [Member]
Public Utilities General Disclosures [Line Items]
Number of people served	1,000,000sjw_PublicUtilitiesNumberOfPeopleServed / dei_LegalEntityAxis = us-gaap_SubsidiariesMember
SJWTX,Inc. dba Canyon Lake Water Supply Corporation [Member]
Public Utilities General Disclosures [Line Items]
Number of people served	36,000sjw_PublicUtilitiesNumberOfPeopleServed / dei_LegalEntityAxis = sjw_SubsidiaryOneMember
444 West Santa Clara Street, L.P. [Member]
Public Utilities General Disclosures [Line Items]
Limited partership interest percentage	70.00%us-gaap_LimitedLiabilityCompanyLLCOrLimitedPartnershipLPMembersOrLimitedPartnersOwnershipInterest / dei_LegalEntityAxis = us-gaap_PartnershipInterestMember

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+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 21

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13537-108611



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-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592



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-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13531-108611



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The number of units or percentage investment held by one or more members or limited partners of the LLC or LP.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 272

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Percentage of the Variable Interest Entity's (VIE) voting interest owned by (or beneficial interest in) the reporting entity (directly or indirectly).

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-Publisher FASB

-Name Accounting Standards Codification

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