Income Taxes:	6 Months Ended
Jun. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes: On December 22, 2017, the Tax Act was signed into federal law. The provisions of this major tax reform were generally effective January 1, 2018. Among its significant provisions, the Tax Act reduced the federal corporate income tax rate from 35% to 21% and eliminated bonus depreciation for regulated utilities. AWR's effective tax rate (“ETR”) was 21.2% and 38.6% for the three months ended June 30, 2018 and 2017, respectively, and was 20.4% and 37.4% for the six months ended June 30, 2018 and 2017, respectively. GSWC's ETR was 23.6% and 39.8% for the three months ended June 30, 2018 and 2017, respectively, and was 21.9% and 38.8% for the six months ended June 30, 2018 and 2017, respectively. Both decreases were due primarily to the reduction in the federal corporate income tax rate. AWR's ETR differed from the new federal statutory rate primarily as a result of the differences between GSWC's ETR and the new federal statutory rate. These differences resulted primarily from: (i) state taxes, (ii) permanent differences including the excess tax benefits from share-based payments, which were reflected in the income statements and resulted in a reduction to income tax expense during the three and six months ended June 30, 2018 and 2017, (iii) differences between book and taxable income that are treated as flow-through adjustments in accordance with regulatory requirements (principally from plant, rate-case, and compensation expenses), and (iv) commencement of the amortization of the excess deferred income tax liability brought about by the lower federal corporate income tax rate. There were no material updates to the excess deferred income tax liability balance during the three and six months ended June 30, 2018 in accordance with Staff Accounting Bulletin 118.

Income Taxes:

On December 22, 2017, the Tax Act was signed into federal law. The provisions of this major tax reform were generally effective January 1, 2018. Among its significant provisions, the Tax Act reduced the federal corporate income tax rate from 35% to 21% and eliminated bonus depreciation for regulated utilities. AWR's effective tax rate (“ETR”) was 21.2% and 38.6% for the three months ended June 30, 2018 and 2017, respectively, and was 20.4% and 37.4% for the six months ended June 30, 2018 and 2017, respectively. GSWC's ETR was 23.6% and 39.8% for the three months ended June 30, 2018 and 2017, respectively, and was 21.9% and 38.8% for the six months ended June 30, 2018 and 2017, respectively. Both decreases were due primarily to the reduction in the federal corporate income tax rate.

AWR's ETR differed from the new federal statutory rate primarily as a result of the differences between GSWC's ETR and the new federal statutory rate. These differences resulted primarily from: (i) state taxes, (ii) permanent differences including the excess tax benefits from share-based payments, which were reflected in the income statements and resulted in a reduction to income tax expense during the three and six months ended June 30, 2018 and 2017, (iii) differences between book and taxable income that are treated as flow-through adjustments in accordance with regulatory requirements (principally from plant, rate-case, and compensation expenses), and (iv) commencement of the amortization of the excess deferred income tax liability brought about by the lower federal corporate income tax rate. There were no material updates to the excess deferred income tax liability balance during the three and six months ended June 30, 2018 in accordance with Staff Accounting Bulletin 118.