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Income Taxes: (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Effective income tax rate      
Deferred Tax Liabilities Related to Repair-And-Maintenance Deductions     $ 30.8awr_DeferredTaxLiabilitiesRelatedtoRepairAndMaintenanceDeductions
GSWC      
Effective income tax rate      
ETRs (as a percent) 41.10%us-gaap_EffectiveIncomeTaxRateContinuingOperations
/ dei_LegalEntityAxis
= awr_GoldenStateWaterCompanyMember
37.90%us-gaap_EffectiveIncomeTaxRateContinuingOperations
/ dei_LegalEntityAxis
= awr_GoldenStateWaterCompanyMember