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Summary of Significant Accounting Policies (Details) (USD $) | 0 Months Ended | 12 Months Ended
--- | --- | ---
May 20, 2013 | Dec. 31, 2014 registrant | Dec. 31, 2013 | Dec. 31, 2012
Summary of significant accounting policies |  |  |  |
Related Party Transaction, Amounts of Transaction |  | $ 2,700,000 us-gaap_RelatedPartyTransactionAmountsOfTransaction | $ 2,600,000 us-gaap_RelatedPartyTransactionAmountsOfTransaction | $ 2,400,000 us-gaap_RelatedPartyTransactionAmountsOfTransaction
Basis of Presentation: |  |  |  |
Number of registrants filing combined report |  | 2 awr_NumberOfRegistrantsFilingCombinedReport |  |
Stock split ratio | 2 us-gaap_StockholdersEquityNoteStockSplitConversionRatio1 |  |  |
Impairment of Long-Lived Assets |  |  |  |
Impairment of long-lived assets |  | 0 us-gaap_ImpairmentOfLongLivedAssetsHeldForUse |  | 416,000 us-gaap_ImpairmentOfLongLivedAssetsHeldForUse
Goodwill |  |  |  |
Goodwill arose from acquisition of subcontractor's business |  | 1,100,000 awr_GoodwillAcquiredInPriorPeriod |  |
Sales and Use Taxes: |  |  |  |
Non-income tax assessments accounted on a gross basis |  | 16,722,000 us-gaap_TaxesExcludingIncomeAndExciseTaxes | 15,865,000 us-gaap_TaxesExcludingIncomeAndExciseTaxes | 15,381,000 us-gaap_TaxesExcludingIncomeAndExciseTaxes
Military Utility Privatization Subsidiaries |  |  |  |
Summary of significant accounting policies |  |  |  |
Period of Fixed Price Contracts to Maintain Water Systems at Various Military Bases |  | 50 years |  |
GSWC |  |  |  |
Related Party Transactions |  |  |  |
Balance outstanding |  | 0 us-gaap_NotesReceivableRelatedPartiesCurrent / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember | 500,000 us-gaap_NotesReceivableRelatedPartiesCurrent / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember |
Property and Depreciation |  |  |  |
Aggregate composite rate for depreciation (as a percent) |  | 3.20%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember | 3.40%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember | 3.70%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember
Depreciation on transportation equipment |  | 678,000 awr_PublicUtilitiesPropertyPlantAndEquipmentDepreciationOnTransportationEquipment / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember | 877,000 awr_PublicUtilitiesPropertyPlantAndEquipmentDepreciationOnTransportationEquipment / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember | 1,800,000 awr_PublicUtilitiesPropertyPlantAndEquipmentDepreciationOnTransportationEquipment / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember
Estimated useful lives of utility plant, as authorized by the CPUC |  |  |  |
Generation |  | 40 years |  |
Interest |  |  |  |
Amount recorded in AFUDC |  | 24,000 us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedInterest / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember | 270,000 us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedInterest / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember | 299,000 us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedInterest / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember
Weighted cost of capital (as a percent) |  | 8.64%awr_WeightedCostOfCapitalPercent / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember |  |
Alternative-Revenue Programs |  |  |  |
Number of months within which expected additional revenue collection is recorded |  | 24 months |  |
Advances for Construction and Contributions in aid of Constructions |  |  |  |
Period for refund of advances for construction |  | 40 years |  |
Fair Value of Financial Instruments |  |  |  |
Long-term debt-GSWC |  | 417,057,000 us-gaap_LongTermDebtFairValue / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember |  |
Sales and Use Taxes: |  |  |  |
Franchise fees billed to customers and recorded as operating revenue |  | 3,700,000 us-gaap_CostOfReimbursableExpense / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember | 3,600,000 us-gaap_CostOfReimbursableExpense / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember | 3,400,000 us-gaap_CostOfReimbursableExpense / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember
Non-income tax assessments accounted on a gross basis |  | 15,221,000 us-gaap_TaxesExcludingIncomeAndExciseTaxes / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember | 14,072,000 us-gaap_TaxesExcludingIncomeAndExciseTaxes / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember | 13,835,000 us-gaap_TaxesExcludingIncomeAndExciseTaxes / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember
GSWC | Carrying Amount |  |  |  |
Fair Value of Financial Instruments |  |  |  |
Long-term debt-GSWC |  | 326,090,000 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember | 332,377,000 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember |
GSWC | Fair Value |  |  |  |
Fair Value of Financial Instruments |  |  |  |
Long-term debt-GSWC |  |  | 412,590,000 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember |
GSWC | Fair Value | Level 2 |  |  |  |
Fair Value of Financial Instruments |  |  |  |
Long-term debt-GSWC |  | 417,057,000 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember |  |
GSWC | Minimum |  |  |  |
Estimated useful lives of utility plant, as authorized by the CPUC |  |  |  |
Source of water supply |  | 30 years |  |
Pumping |  | 25 years |  |
Water treatment |  | 20 years |  |
Transmission and distribution |  | 25 years |  |
Other plant |  | 7 years |  |
GSWC | Maximum |  |  |  |
Estimated useful lives of utility plant, as authorized by the CPUC |  |  |  |
Source of water supply |  | 50 years |  |
Pumping |  | 40 years |  |
Water treatment |  | 35 years |  |
Transmission and distribution |  | 55 years |  |
Other plant |  | 40 years |  |
GSWC | Purchase, production, distribution and sale of water |  |  |  |
Nature of Operations: |  |  |  |
Number of customers served |  | 258,000 awr_NumberOfCustomers / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember / us-gaap_StatementBusinessSegmentsAxis = awr_WaterServiceUtilityOperationsMember |  |
GSWC | Electric |  |  |  |
Nature of Operations: |  |  |  |
Number of customers served |  | 24,000 awr_NumberOfCustomers / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember / us-gaap_StatementBusinessSegmentsAxis = awr_ElectricServiceUtilityOperationsMember |  |
American States Utility Services [Member] |  |  |  |
Sales and Use Taxes: |  |  |  |
Non-income tax assessments accounted on a gross basis |  | 490,000 us-gaap_TaxesExcludingIncomeAndExciseTaxes / dei_LegalEntityAxis = awr_AmericanStatesUtilityServicesMember | 864,000 us-gaap_TaxesExcludingIncomeAndExciseTaxes / dei_LegalEntityAxis = awr_AmericanStatesUtilityServicesMember | 717,000 us-gaap_TaxesExcludingIncomeAndExciseTaxes / dei_LegalEntityAxis = awr_AmericanStatesUtilityServicesMember
American States Utility Services [Member] | Military Utility Privatization Subsidiaries |  |  |  |
Nature of Operations: |  |  |  |
Period of fixed price contracts to operate and maintain the water and/or wastewater systems at various military bases |  | 50 years |  |
AWR |  |  |  |
Related Party Transactions |  |  |  |
Maximum borrowing capacity on line of credit |  | 100,000,000.0 us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity / dei_LegalEntityAxis = us-gaap_ParentCompanyMember |  |
AWR | Syndicated Credit Facility |  |  |  |
Related Party Transactions |  |  |  |
Maximum borrowing capacity on line of credit |  | 100,000,000.0 us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity / dei_LegalEntityAxis = us-gaap_ParentCompanyMember / us-gaap_LongtermDebtTypeAxis = awr_SyndicatedRevolvingCreditFacilityMember |  |
AWR | Promissory note |  |  |  |
Related Party Transactions |  |  |  |
Maximum borrowing capacity on debt instrument |  | 20,000,000.0 awr_DebtInstrumentMaximumBorrowingCapacity / dei_LegalEntityAxis = us-gaap_ParentCompanyMember / us-gaap_LongtermDebtTypeAxis = us-gaap_NotesPayableOtherPayablesMember |  |
Notes Receivable | AWR | Promissory note |  |  |  |
Related Party Transactions |  |  |  |
Balance outstanding |  | $ 0 us-gaap_NotesReceivableRelatedPartiesCurrent / us-gaap_BalanceSheetLocationAxis = us-gaap_NotesReceivableMember / dei_LegalEntityAxis = us-gaap_ParentCompanyMember / us-gaap_LongtermDebtTypeAxis = us-gaap_NotesPayableOtherPayablesMember |  |
Sales [Member] | GSWC | Purchase, production, distribution and sale of water |  |  |  |
Nature of Operations: |  |  |  |
Percentage of total revenues |  | 90.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / dei_LegalEntityAxis = awr_GoldenStateWaterCompanyMember / us-gaap_StatementBusinessSegmentsAxis = awr_WaterServiceUtilityOperationsMember |  |

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