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Regulatory Matters 6 (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
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GSWC |  |
Regulatory matters: |  |
Net regulatory assets | $ 2,042 | $ 146,281

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- Definition -- None. No documentation exists for this element. -- + References No definition available. + Details
Name: | awr_RegulatoryAssetsAndLiabilitiesLineItems
Namespace Prefix: | awr_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The net amount of all regulatory assets less all regulatory liabilities as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
Name: | us-gaap_NetRegulatoryAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
Name: | dei_LegalEntityAxis=awr_GoldenStateWaterCompanyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |