Income Taxes:	3 Months Ended
Mar. 31, 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 income tax rate (“ETR”) was 19.2% and 35.1% for the three months ended March 31, 2018 and 2017, respectively, and GSWC's ETR was 19.2% and 36.9% for the three months ended March 31, 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 tax 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 months ended March 31, 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 tax rate. There were no material updates to the excess deferred income tax liability balance during the three months ended March 31, 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 income tax rate (“ETR”) was 19.2% and 35.1% for the three months ended March 31, 2018 and 2017, respectively, and GSWC's ETR was 19.2% and 36.9% for the three months ended March 31, 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 tax 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 months ended March 31, 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 tax rate. There were no material updates to the excess deferred income tax liability balance during the three months ended March 31, 2018 in accordance with Staff Accounting Bulletin 118.