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v2.4.1.9

General - Additional Information (Details) (USD $) In Thousands, unless otherwise specified | 0 Months Ended | 12 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | --- | ---
Apr. 01, 2015 | Mar. 27, 2015 | Dec. 31, 2014 | Dec. 31, 2015 | Mar. 26, 2015 | Jan. 05, 2015
Regulatory Liabilities [Line Items] |  |  |  |  |  |
Water reduction target goal (percent) |  |  | 20.00%sjw_WaterReductionTargetGoalPercentage |  |  |
Mandatory Water Reduction, Percentage | 25.00%sjw_MandatoryWaterReductionPercentage |  |  |  |  |
Authorized Regulatory Surcharge, Gross |  | $ 1,876 sjw_AuthorizedRegulatorySurchargeGross |  |  |  |
Memorandum Account, Recovery Request |  |  |  |  | $ 9,567 sjw_MemorandumAccountRecoveryRequest | $ 976 sjw_MemorandumAccountRecoveryRequest
Scenario, Forecast [Member] |  |  |  |  |  |
Regulatory Liabilities [Line Items] |  |  |  |  |  |
Water reduction target goal (percent) |  |  |  | 30.00%sjw_WaterReductionTargetGoalPercentage / us-gaap_StatementScenarioAxis = us-gaap_ScenarioForecastMember |  |

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- Definition Authorized Regulatory Surcharge, Gross + References No definition available. + Details
Name: | sjw_AuthorizedRegulatorySurchargeGross
Namespace Prefix: | sjw_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Mandatory Water Reduction, Percentage + References No definition available. + Details
Name: | sjw_MandatoryWaterReductionPercentage
Namespace Prefix: | sjw_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition A request to the regulatory authority for authorization to refund over (under) collected amounts. + References No definition available. + Details
Name: | sjw_MemorandumAccountRecoveryRequest
Namespace Prefix: | sjw_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Water Reduction Target Goal, Percentage + References No definition available. + Details
Name: | sjw_WaterReductionTargetGoalPercentage
Namespace Prefix: | sjw_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_RegulatoryLiabilitiesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |