Income Taxes:	3 Months Ended
Mar. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes: AWR's consolidated effective tax rate (“ETR”) was 35.1% for the three months ended March 31, 2017 as compared to 36.4% for the three months ended March 31, 2016. GSWC's ETR was 36.9% for the three months ended March 31, 2017 as compared to 37.7% for the three months ended March 31, 2016. For the three months ended March 31, 2017, the ETR was affected by the adoption of the new accounting standard update for share-based payments (see Note 1). Under the new guidance, the tax effects related to share-based payments are recorded through the income statement. Previously, tax benefits in excess of compensation cost ("windfalls") and tax deficiencies ("shortfalls") were recorded directly to equity. AWR and GSWC adopted the guidance effective January 1, 2017 and, therefore, all excess tax benefits resulting from share-based payments during the three months ended March 31, 2017 were reflected in the income statements, which resulted in a reduction to income tax expense for AWR and GSWC of approximately $412,000 and $374,000, respectively. For the three months ended March 31, 2017 and 2016, the ETR at the AWR consolidated level also fluctuated as a result of certain permanent differences recorded at AWR (parent) and ASUS and its subsidiaries, as well as state taxes recorded at AWR (parent) and ASUS and its subsidiaries (where the amounts of state taxes vary among the jurisdictions in which they operate). For the three months ended March 31, 2017 and 2016, GSWC's ETR also deviated from the statutory rate due to state tax and differences between book and taxable income that are treated as flow-through adjustments in accordance with regulatory requirements (principally plant-, rate-case- and compensation-related items). As a regulated utility, GSWC treats certain temporary differences as flow-through adjustments in computing its income tax provision consistent with the income tax approach approved by the CPUC for ratemaking purposes. Flow-through adjustments increase or decrease tax expense in one period, with an offsetting decrease or increase occurring in another period. Giving effect to these temporary differences as flow-through adjustments typically results in a greater variance between the ETR and the statutory federal income tax rate in any given period than would otherwise exist if GSWC were not required to account for its income taxes as a regulated enterprise. Changes in Tax Law: In December 2015, the Protecting Americans From Tax Hikes Act of 2015 extended bonus depreciation for qualifying property through 2019. For 2015 through 2017, bonus depreciation was extended at a 50% rate. For 2018 and 2019, bonus depreciation will be phased down to 40% and 30%, respectively. Although the change in law reduces AWR’s current taxes payable over these years, it does not reduce its total income tax expense or ETR.

Income Taxes:

AWR's consolidated effective tax rate (“ETR”) was 35.1% for the three months ended March 31, 2017 as compared to 36.4% for the three months ended March 31, 2016. GSWC's ETR was 36.9% for the three months ended March 31, 2017 as compared to 37.7% for the three months ended March 31, 2016. For the three months ended March 31, 2017, the ETR was affected by the adoption of the new accounting standard update for share-based payments (see Note 1). Under the new guidance, the tax effects related to share-based payments are recorded through the income statement. Previously, tax benefits in excess of compensation cost ("windfalls") and tax deficiencies ("shortfalls") were recorded directly to equity. AWR and GSWC adopted the guidance effective January 1, 2017 and, therefore, all excess tax benefits resulting from share-based payments during the three months ended March 31, 2017 were reflected in the income statements, which resulted in a reduction to income tax expense for AWR and GSWC of approximately $412,000 and $374,000, respectively.

For the three months ended March 31, 2017 and 2016, the ETR at the AWR consolidated level also fluctuated as a result of certain permanent differences recorded at AWR (parent) and ASUS and its subsidiaries, as well as state taxes recorded at AWR (parent) and ASUS and its subsidiaries (where the amounts of state taxes vary among the jurisdictions in which they operate). For the three months ended March 31, 2017 and 2016, GSWC's ETR also deviated from the statutory rate due to state tax and differences between book and taxable income that are treated as flow-through adjustments in accordance with regulatory requirements (principally plant-, rate-case- and compensation-related items). As a regulated utility, GSWC treats certain temporary differences as flow-through adjustments in computing its income tax provision consistent with the income tax approach approved by the CPUC for ratemaking purposes. Flow-through adjustments increase or decrease tax expense in one period, with an offsetting decrease or increase occurring in another period. Giving effect to these temporary differences as flow-through adjustments typically results in a greater variance between the ETR and the statutory federal income tax rate in any given period than would otherwise exist if GSWC were not required to account for its income taxes as a regulated enterprise.

Changes in Tax Law:

In December 2015, the Protecting Americans From Tax Hikes Act of 2015 extended bonus depreciation for qualifying property through 2019. For 2015 through 2017, bonus depreciation was extended at a 50% rate. For 2018 and 2019, bonus depreciation will be phased down to 40% and 30%, respectively. Although the change in law reduces AWR’s current taxes payable over these years, it does not reduce its total income tax expense or ETR.