Income Taxes (Notes)	9 Months Ended
Income Taxes (Notes)	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income Tax Disclosure [Text Block]	Income Taxes For the three and nine months ended September 30, 2020, income tax expense was $4,578 and $9,226, respectively. Income tax expense for the three and nine months ended September 30, 2019, was $2,565 and $8,802, respectively. The effective consolidated income tax rates were 15% and 21% for the three months ended September 30, 2020 and 2019, respectively, and 16% and 23% for the nine months ended September 30, 2020, and 2019, respectively. The lower effective rates for the three and nine months ended September 30, 2020, were primarily due to flow-through tax benefits. SJW Group had unrecognized tax benefits of approximately $6,594 and $3,834 as of September 30, 2020 and December 31, 2019, respectively. SJW Group does not expect its unrecognized tax benefits to change significantly within the next 12 months. On March 27, 2020, the Coronavirus Aid, Relief, and Economic Security (“CARES”) Act was signed into law. The CARES Act includes, among other items, measures concerning income taxes. SJW Group has considered the income tax implications of the CARES Act in its estimated tax provision and does not believe it will materially impact the company’s year-end tax rate. The Internal Revenue Service has issued guidance that will determine the final disposition of the excess deferred taxes and other impacts of the Tax Cuts and Jobs Act (H.R. 1). At this time, the company has applied a reasonable interpretation of the Tax Act and continues to work with the state utility regulators to determine the final methodology for disposition of excess deferred taxes.

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.