Fair Value Measurement	3 Months Ended
Fair Value Measurement	Mar. 31, 2018
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENT	Fair Value Measurement The following instruments are not measured at fair value on SJW Group’s condensed consolidated balance sheets as of March 31, 2018, but require disclosure of their fair values: cash and cash equivalents, accounts receivable and accounts payable. The estimated fair value of such instruments as of March 31, 2018, approximates their carrying value as reported on the condensed consolidated balance sheets. The fair value of such financial instruments are determined using the income approach based on the present value of estimated future cash flows. There have been no changes in valuation technique during the three months ended March 31, 2018. The fair value of these instruments would be categorized as Level 2 in the fair value hierarchy, with the exception of cash and cash equivalents, which would be categorized as Level 1. The fair value of pension plan assets is discussed in Note 4. The fair value of SJW Group’s long-term debt was approximately $512,151 and $537,840 as of March 31, 2018, and December 31, 2017, respectively, and was determined using a discounted cash flow analysis, based on the current rates for similar financial instruments of the same duration and creditworthiness of the company. The book value of the long-term debt was $431,175 and $431,092 as of March 31, 2018, and December 31, 2017, respectively. The fair value of long-term debt would be categorized as Level 2 in the fair value hierarchy. As of March 31, 2018, and December 31, 2017, the fair value of the company’s investment in California Water Service Group was $3,067 and $4,535, respectively, and would be categorized as Level 1 of the fair value hierarchy. For the three months ended March 31, 2018, SJW Group recognized an unrealized loss of $667 due to the change in fair value of the company’s investment in California Water Service Group.

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.