Organization and Operations and Basis of Presentation	9 Months Ended
Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Operations and Basis of Presentation	Organization and Operations and Basis of Presentation California Water Service Group (the Company) is a holding company that provides water utility and other related services in California, Washington, New Mexico and Hawaii through its wholly-owned subsidiaries. California Water Service Company (Cal Water), Washington Water Service Company (Washington Water), New Mexico Water Service Company (New Mexico Water), and Hawaii Water Service Company, Inc. (Hawaii Water) provide regulated utility services under the rules and regulations of their respective state’s regulatory commissions (jointly referred to herein as the Commissions). CWS Utility Services and HWS Utility Services LLC provide non-regulated water utility and utility-related services. The Company operates in one reportable segment, providing water and related utility services. Basis of Presentation The unaudited condensed consolidated interim financial information has been prepared in accordance with accounting principles generally accepted in the United States of America (GAAP) for interim financial information and in accordance with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X promulgated by the Securities and Exchange Commission (SEC) and therefore do not contain all of the information and footnotes required by GAAP and the SEC for annual financial statements. The unaudited condensed consolidated financial statements should be read in conjunction with the Company’s consolidated financial statements for the year ended December 31, 2017, included in its annual report on Form 10-K as filed with the SEC on March 1, 2018. The preparation of the Company’s unaudited condensed consolidated interim financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the balance sheet dates and the reported amounts of revenues and expenses for the periods presented. These include, but are not limited to, estimates and assumptions used in determining the Company’s regulatory asset and liability balances based upon probability assessments of regulatory recovery, revenues earned but not yet billed, asset retirement obligations, allowance for doubtful accounts, pension and other employee benefit plan liabilities, and income tax-related assets and liabilities. Actual results could differ from these estimates. In the opinion of management, the accompanying unaudited condensed consolidated interim financial statements reflect all adjustments, consisting of normal recurring transactions that are necessary to provide a fair presentation of the results for the periods covered. The results for interim periods are not necessarily indicative of the results for any future period. Due to the seasonal nature of the water business, the results for interim periods are not indicative of the results for a 12-month period. Revenue and income are generally higher in the warm, dry summer months when water usage and sales are greater. Revenue and income are generally lower in the winter months when cooler temperatures and rainfall curtail water usage and sales.

Organization and Operations and Basis of Presentation

California Water Service Group (the Company) is a holding company that provides water utility and other related services in California, Washington, New Mexico and Hawaii through its wholly-owned subsidiaries. California Water Service Company (Cal Water), Washington Water Service Company (Washington Water), New Mexico Water Service Company (New Mexico Water), and Hawaii Water Service Company, Inc. (Hawaii Water) provide regulated utility services under the rules and regulations of their respective state’s regulatory commissions (jointly referred to herein as the Commissions). CWS Utility Services and HWS Utility Services LLC provide non-regulated water utility and utility-related services.

The Company operates in one reportable segment, providing water and related utility services.

Basis of Presentation

The unaudited condensed consolidated interim financial information has been prepared in accordance with accounting principles generally accepted in the United States of America (GAAP) for interim financial information and in accordance with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X promulgated by the Securities and Exchange Commission (SEC) and therefore do not contain all of the information and footnotes required by GAAP and the SEC for annual financial statements. The unaudited condensed consolidated financial statements should be read in conjunction with the Company’s consolidated financial statements for the year ended December 31, 2017, included in its annual report on Form 10-K as filed with the SEC on March 1, 2018.

The preparation of the Company’s unaudited condensed consolidated interim financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the balance sheet dates and the reported amounts of revenues and expenses for the periods presented. These include, but are not limited to, estimates and assumptions used in determining the Company’s regulatory asset and liability balances based upon probability assessments of regulatory recovery, revenues earned but not yet billed, asset retirement obligations, allowance for doubtful accounts, pension and other employee benefit plan liabilities, and income tax-related assets and liabilities. Actual results could differ from these estimates.

In the opinion of management, the accompanying unaudited condensed consolidated interim financial statements reflect all adjustments, consisting of normal recurring transactions that are necessary to provide a fair presentation of the results for the periods covered. The results for interim periods are not necessarily indicative of the results for any future period.

Due to the seasonal nature of the water business, the results for interim periods are not indicative of the results for a 12-month period. Revenue and income are generally higher in the warm, dry summer months when water usage and sales are greater. Revenue and income are generally lower in the winter months when cooler temperatures and rainfall curtail water usage and sales.