Cash paid during the period for: Supplemental Cash Flow Information [Abstract] Unrecognized actuarial loss Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) Earnings per Share Earnings Per Share, Policy [Policy Text Block] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value Hierarchy and NAV [Domain] NET INCOME Net income Net income (loss) Net Income (Loss) Attributable to Parent Consolidated Entities [Axis] Consolidated Entities [Axis] Entity Emerging Growth Company Entity Emerging Growth Company Total production expenses Water Production Costs Refunds (Collections) Adjustments Balancing and Memorandum Revenue Account, Refunds (Collections) Balancing and Memorandum Revenue Account, Refunds (Collections) Interest cost Defined Benefit Plan, Interest Cost Accrued payroll Employee-related Liabilities, Current Income Statement Location [Axis] Income Statement Location [Axis] Statistical Measurement [Domain] Statistical Measurement [Domain] Entity Address, Address Line One Entity Address, Address Line One Stockholders’ equity: Stockholders' Equity, Number of Shares, Par Value and Other Disclosures [Abstract] Maintenance Utilities Operating Expense, Maintenance Land Public Utilities, Property, Plant and Equipment, Land PRVMA PRVMA [Member] PRVMA Company-funded Payments to Acquire Water Systems Using Company Funds Payments to Acquire Water Systems Using Company Funds Additional paid-in capital Additional Paid in Capital, Common Stock Entity Filer Category Entity Filer Category Total other assets Other Assets, Noncurrent Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Business Segments [Axis] Segments [Axis] Expected return on assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Remaining shares available for issuance under the Incentive Plan (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Retirement Benefits [Abstract] Retirement Benefits [Abstract] NET CHANGE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Series N Notes 3.00% Senior Notes, Series N [Member] 3.00% Senior Notes, Series N Public Utility, Property, Plant and Equipment [Table] Public Utility, Property, Plant and Equipment [Table] Rental income Operating Lease, Lease Income Share-based compensation APIC, Share-based Payment Arrangement, Increase for Cost Recognition Schedule of Regulatory Assets [Table] Schedule of Regulatory Assets [Table] Document Fiscal Year Focus Document Fiscal Year Focus Subsequent Event Type [Domain] Subsequent Event Type [Domain] Regulatory rate filings, capital structure, equity percentage, current Regulatory Rate Filings, Capital Structure, Equity Percentage, Current Regulatory Rate Filings, Capital Structure, Equity Percentage, Current Anti-dilutive restricted common stock units excluded from computation of earnings per share (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Sale of Stock [Axis] Sale of Stock [Axis] Other balancing and memorandum accounts, net Regulatory Balancing and Memorandum Accounts, Net Regulatory Balancing and Memorandum Accounts, Net Grant date fair value of equity instruments granted (usd per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Title of Individual [Domain] Title of Individual [Domain] Unrealized gain (loss) on investment, tax OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment, Tax POSTRETIREMENT BENEFIT PLANS Liability, Defined Benefit Plan, Noncurrent Award Type [Domain] Award Type [Domain] Credit Facility [Domain] Credit Facility [Domain] ASSETS Assets [Abstract] Authorized regulatory base charge, per residential account Authorized Regulatory Base Charge, Per Residential Account Authorized Regulatory Base Charge, Per Residential Account Number of equity instruments granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period ESPP proceeds Proceeds, Issuance of Shares, Share-based Payment Arrangement, Including Option Exercised Employee Stock Purchase Plan (ESPP) Employee Stock Purchase Plan [Member] Employee Stock Purchase Plan [Member] Entity Address, City or Town Entity Address, City or Town Retained Earnings Retained Earnings [Member] Debt Instrument [Axis] Debt Instrument [Axis] Monterey WRAM Monterey WRAM [Member] Monterey WRAM Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Accrued groundwater extraction charges, purchased water and power Accrued groundwater extraction charges, purchased water and power Accrued groundwater extraction charges, purchased water and power Public utilities, property, plant and equipment, net Public Utilities, Property, Plant and Equipment, Net Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Amortization of prior service cost Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Accrued payables for additions to utility plant Capital Expenditures Incurred but Not yet Paid Other, net All others Other Regulatory Assets [Member] Other Regulatory Assets [Member] Target vesting percentage Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Entity Interactive Data Current Entity Interactive Data Current Number of subsidiaries Number of Subsidiaries Number of Subsidiaries Basic (usd per share) Earnings Per Share, Basic Public Utilities General Disclosures Public Utilities General Disclosures [Table Text Block] Accrued unbilled utility revenue Receivables, Long-term Contracts or Programs Document Type Document Type Utility Plant Depreciation Regulatory Depreciation and Amortization, Policy [Policy Text Block] 4.01% Note Due March 2041 4.01% Note Due March 2041 [Member] 4.01% Note Due March 2041 Prepaid expenses Prepaid Expense, Current Interest on long-term debt and other interest expense Interest Expense, Debt Major Streams of Revenue Disaggregation of Revenue [Table Text Block] Plan expense Stock or Unit Option Plan Expense Real estate investments Subtotal Real Estate Investment Property, at Cost Regulatory rate filings, balancing and memorandum account, requested recovery (refund) Regulatory Rate Filings, Balancing And Memorandum Account, Requested Recovery (Refund) Regulatory Rate Filings, Balancing And Memorandum Account, Requested Recovery (Refund) Entity Current Reporting Status Entity Current Reporting Status Schedule of Real Estate Investments Schedule of Real Estate Investments [Table Text Block] Tabular disclosure of real estate investments. Regulatory Assets, Net Schedule of Regulatory Assets and Liabilities [Text Block] Regulatory rate filings, requested authorization for debt issuance Regulatory Rate Filings, Requested Authorization For Debt Issuance, Amount Regulatory Rate Filings, Requested Authorization For Debt Issuance, Amount LESS RESTRICTED CASH, END OF PERIOD Restricted Cash and Cash Equivalents Current regulatory assets, net Less: current regulatory assets, net Regulatory Assets, Current CEMA CEMA [Member] CEMA Plan Name [Axis] Plan Name [Axis] Pension Pension Balancing Account [Member] Pension Balancing Account [Member] Long-term debt, book value Long-term Debt Fair Value, Inputs, Level 1 Fair Value, Inputs, Level 1 [Member] INVESTING ACTIVITIES: Net Cash Provided by (Used in) Investing Activities [Abstract] Sales agreement, holdback amount Sales Agreement, Holdback Amount Sales Agreement, Holdback Amount Document Transition Report Document Transition Report Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Total capitalization and liabilities Liabilities and Equity Public Utilities, General Disclosures [Line Items] Public Utilities, General Disclosures [Line Items] Less accumulated depreciation and amortization Public Utilities, Property, Plant and Equipment, Accumulated Depreciation Scenario [Axis] Scenario [Axis] CAPITALIZATION AND LIABILITIES Liabilities and Equity [Abstract] Regulatory rate filings, requested project replacement value Regulatory Rate Filings, Requested Project Replacement Value Regulatory Rate Filings, Requested Project Replacement Value Accounts payable and other current liabilities Increase (Decrease) in Accounts Payable Letter of Credit Sublimit Standby Letters of Credit [Member] Minimum Minimum [Member] Income tax Income Taxes Receivable, Current Other changes, net Increase (Decrease) in Other Operating Assets and Liabilities, Net Receipts of advances and contributions in aid of construction Receipts Of Advances And Contributions In Aid Of Construction Receipts Of Advances And Contributions In Aid Of Construction Unrecognized tax benefits Unrecognized Tax Benefits Pension non-service cost Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component Regulatory rate filings, requested rate increase, percent of authorized revenue, year three Regulatory Rate Filings, Requested Rate Increase, Percent of Authorized Revenue, Year Three Regulatory Rate Filings, Requested Rate Increase as Percentage of Total Revenue at Time of Request, Year Three OTHER ASSETS: Other Assets, Noncurrent [Abstract] Refunds of advances for construction Repayments of Advances for Construction Trading Symbol Trading Symbol CURRENT LIABILITIES: Liabilities, Current [Abstract] Capitalization, long-term debt and equity Capitalization, Long-term Debt and Equity Common stock issuance, net of costs Stock Issued During Period, Value, New Issues Revenue Revenue [Policy Text Block] Administrative and general General and Administrative Expense Regulatory rate filings, capital structure, equity percentage, requested Regulatory Rate Filings, Capital Structure, Equity Percentage, Requested Regulatory Rate Filings, Capital Structure, Equity Percentage, Requested Line of Credit Line of Credit [Member] Public Utility, Property, Plant and Equipment [Line Items] Public Utility, Property, Plant and Equipment [Line Items] General Rate Case No. 21-01-003 General Rate Case No. 21-01-003 [Member] General Rate Case No. 21-01-003 Dividends paid Payments of Ordinary Dividends, Common Stock Regulatory rate filings, capital structure, debt percentage, current Regulatory Rate Filings, Capital Structure, Debt Percentage, Current Regulatory Rate Filings, Capital Structure, Debt Percentage, Current Supplemental Employee Retirement Plan Supplemental Employee Retirement Plan [Member] Regulatory rate filings, rate of return, requested Regulatory Rate Filings, Rate Of Return, Requested Regulatory Rate Filings, Rate Of Return, Requested Accounting Policies [Abstract] Accounting Policies [Abstract] Common stock issuance, net of costs (in shares) Stock Issued During Period, Shares, New Issues Allowance for equity funds used during construction Public Utilities, Allowance for Funds Used During Construction, Additions Public Utilities, Regulatory Proceeding [Domain] Public Utilities, Regulatory Proceeding [Domain] Common stock, $0.001 par value; authorized 70,000,000 shares; issued and outstanding shares 29,804,927 on June 30, 2021 and 28,556,605 on December 31, 2020 Common Stock, Value, Issued Regulatory rate filings, average cost of debt rate, requested Regulatory Rate Filings, Average Cost Of Debt Rate, Requested Regulatory Rate Filings, Average Cost Of Debt Rate, Requested Change in accrued payables for construction costs capitalized Noncash Change in Accrued Payables Noncash Change in Accrued Payables Recognition period for unrecognized compensation cost Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Basis of Accounting Basis of Accounting, Policy [Policy Text Block] Performance Shares Performance Shares [Member] Approved rate increase (decrease) Public Utilities, Approved Rate Increase (Decrease), Amount COMMITMENTS AND CONTINGENCIES (See Note 12) Commitments and Contingencies Accumulated other comprehensive income Accumulated Other Comprehensive Income (Loss), Net of Tax Allowance for uncollectible accounts Accounts Receivable, Allowance for Credit Loss, Current Water supply costs Water Supply Balancing Accounts [Member] Water Supply Balancing Accounts [Member] Incentive Plan Incentive Plan [Member] Incentive Plan [Member] Debt issuance costs Payments of Debt Issuance Costs Document Period End Date Document Period End Date Other Nontrade Receivables, Current Authorized temporary surcharge, percentage Authorized Temporary Surcharge, Percentage Authorized Temporary Surcharge, Percentage Class of Stock [Axis] Class of Stock [Axis] Entity Registrant Name Entity Registrant Name Depreciable plant and equipment Public Utilities, Property, Plant And Equipment, Depreciable Plant And Equipment Public Utilities, Property, Plant And Equipment, Depreciable Plant And Equipment Cash and cash equivalents: Cash, Cash Equivalents, and Short-term Investments [Abstract] Subsidiary or Equity Method Investee, Sale of Stock by Subsidiary or Equity Investee [Table] Subsidiary or Equity Method Investee, Sale of Stock by Subsidiary or Equity Investee [Table] Net proceeds from stock offering Sale of Stock, Consideration Received on Transaction Cash Cash Payment for asset acquisition Payments to Acquire Productive Assets Estimated employer contributions for the current fiscal year Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year Revenue from contracts with customers Revenue from Contract with Customer, Excluding Assessed Tax Up-front service concession payment Increase (Decrease) In Up-Front Service Concession Payment Increase (Decrease) In Up-Front Service Concession Payment Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Equity [Abstract] Water Utility Services Reportable Segment One [Member] Reportable Segment One [Member] Notes Payable, Other Payables Notes Payable, Other Payables [Member] Common Stock Common Stock [Member] OTHER (EXPENSE) INCOME: Other Nonoperating Income (Expense) [Abstract] Segment and Non-Tariffed Business Reporting Segment Reporting Disclosure [Text Block] OPERATING INCOME Operating income (loss) Operating Income (Loss) Employer plan contributions Defined Contribution Plan, Employer Discretionary Contribution Amount REGULATORY LIABILITIES Regulatory Liability, Noncurrent Regulatory Asset [Axis] Regulatory Asset [Axis] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Stock-based compensation Share-based Payment Arrangement, Noncash Expense CASH AND CASH EQUIVALENTS, END OF PERIOD Cash and Cash Equivalents, at Carrying Value Additional Paid-in Capital Additional Paid-in Capital [Member] Depreciation Depreciation Regulatory assets Regulatory Assets Approved rate increase (decrease), step increase 1 Public Utilities, Approved Rate Increase (Decrease), Percentage, Step Increase 1 Public Utilities, Approved Rate Increase (Decrease), Percentage, Step Increase 1 Utility plant: Public Utilities, Property, Plant and Equipment, Net [Abstract] DIVIDENDS PER SHARE (usd per share) Dividends per share (usd per share) Common Stock, Dividends, Per Share, Cash Paid Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Approved rate increase (decrease), step increase 2 Public Utilities, Approved Rate Increase (Decrease), Percentage, Step Increase 2 Public Utilities, Approved Rate Increase (Decrease), Percentage, Step Increase 2 Regulatory rate filings, capital structure, debt percentage, requested Regulatory Rate Filings, Capital Structure, Debt Percentage, Requested Regulatory Rate Filings, Capital Structure, Debt Percentage, Requested Regulatory rate filings, return of equity rate, current Regulatory Rate Filings, Return Of Equity Rate, Current Regulatory Rate Filings, Return Of Equity Rate, Current Borrowings on line of credit Proceeds from Lines of Credit Other, net Other Nonoperating Income (Expense) Long-term debt, fair value Long-term Debt, Fair Value Rate of compensation increase Defined Benefit Plan, Rate of Compensation Increase Defined Benefit Plan, Rate of Compensation Increase Construction in progress Public Utilities, Property, Plant and Equipment, Construction Work in Progress Regulatory Assets [Line Items] Regulatory Assets [Line Items] Other current liabilities Other Liabilities, Current Maximum Maximum [Member] Share-based Payment Arrangement [Abstract] Share-based Payment Arrangement [Abstract] Legal Entity [Axis] Legal Entity [Axis] Accounts receivable and accrued unbilled utility revenue Increase (Decrease) in Receivables Chase Bank, N.A. Chase Bank, N.A. [Member] Chase Bank, N.A. [Member] Award Type [Axis] Award Type [Axis] FINANCING ACTIVITIES: Net Cash Provided by (Used in) Financing Activities [Abstract] Total Balancing and Memorandum Account [Roll Forward] Balancing and Memorandum Account [Roll Forward] Total stockholders’ equity Beginning balance Ending balance Stockholders' Equity Attributable to Parent Authorized revenue, threshold percentage Regulatory Balancing and Memorandum Accounts Review, Authorized Revenue, Threshold Percentage Threshold balance of regulatory balancing or memorandum accounts as a percentage of authorized revenue to trigger an account review. Restricted stock and deferred restricted stock Restricted Stock and Deferred Restricted Stock [Member] Restricted Stock and Deferred Restricted Stock [Member] Common stock, shares issued (shares) Common Stock, Shares, Issued Restricted cash Restricted Cash and Cash Equivalents, Current SJW Group and CLWSC SJW Group and CLWSC [Member] SJW Group and CLWSC Other Other Assets, Miscellaneous, Noncurrent Public Utilities, Regulatory Proceeding [Axis] Public Utilities, Regulatory Proceeding [Axis] Cost of capital memorandum account Cost of capital [Member] Cost of capital [Member] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Total operating expense Operating expense Utilities Operating Expense Land Land Regulatory Asset Increase (Decrease) Balancing and Memorandum Cost Recovery Account, Increase (Decrease) Balancing and Memorandum Cost Recovery Account, Increase (Decrease) Interest on long-term debt and other interest expense Interest Expense Aggregate principal amount Debt Instrument, Face Amount Net periodic benefit cost Defined Benefit Plan, Net Periodic Benefit Cost (Credit) City Area Code City Area Code Retained earnings Retained Earnings (Accumulated Deficit) Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Restricted Stock Units (RSUs) Restricted Stock Units (RSUs) [Member] Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Employee stock purchase plan (in shares) Stock Issued During Period, Shares, Employee Stock Purchase Plans 3.89% Note Due March 2041 3.89% Note Due March 2041 [Member] 3.89% Note Due March 2041 CONTRIBUTIONS IN AID OF CONSTRUCTION Contributions in Aid of Construction Water Rate Adjustment WRA [Member] WRA [Member] Income Statement [Abstract] Income Statement [Abstract] Amendment Flag Amendment Flag Repayments on line of credit Repayments of lines of credit Repayments of Lines of Credit Regulatory rate filings, requested rate increase as percentage of total revenue at time of request, year one Regulatory Rate Filings, Requested Rate Increase as Percentage of Total Revenue at Time of Request, Year One Regulatory Rate Filings, Requested Rate Increase as Percentage of Total Revenue at Time of Request, Year One Shares issuable upon exercise of Incentive Plan awards (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Shares Issuable upon Exercise Number of shares reserved for issuance under equity instrument agreements awarded that validly exist and are outstanding, including vested instruments. Provision for income taxes Provision (benefit) for income taxes Income Tax Expense (Benefit) Regulatory rate filings, requested increase in revenues Regulatory Rate Filings, Requested Increase In Revenues Regulatory Rate Filings, Requested Increase In Revenues Customers, net of allowances for uncollectible accounts of $3,866 and $3,891 on June 30, 2021 and December 31, 2020, respectively Accounts Receivable, after Allowance for Credit Loss, Current Long-term borrowings Proceeds from Issuance of Long-term Debt Equity Components [Axis] Equity Components [Axis] Groundwater extraction charges Groundwater Extraction Charges Groundwater Extraction Charges Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Total current assets Assets, Current Sale of Stock [Domain] Sale of Stock [Domain] Schedule of Segment Reporting Information, by Segment Schedule of Segment Reporting Information, by Segment [Table Text Block] Regulatory assets, net not earning a return Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided Entity File Number Entity File Number Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Market-based RSU Market-based RSU [Member] Market-based RSU [Member] Authorized WICA surcharge, percentage Authorized WICA Surcharge, Percentage Authorized WICA Surcharge, Percentage Proceeds from issuance of unsecured debt Proceeds from Issuance of Unsecured Debt Current portion of long-term debt Long-term Debt, Current Maturities Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Entity Small Business Entity Small Business Regulatory rate filings, proposed rate increase, percent of authorized revenue, year two Regulatory Rate Filings, Proposed Rate Increase, Percent of Authorized Revenue, Year Two Regulatory Rate Filings, Proposed Rate Increase, Percent of Authorized Revenue, Year Two Other regulatory mechanisms, net Regulatory Mechanisms, Other, Net Regulatory Mechanisms, Other, Net Business combinations debt premium, net Business combinations debt premium, net [Member] Business combinations debt premium, net [Member] Equity Component [Domain] Equity Component [Domain] Contributions in aid of construction Payments to Acquire Water Systems using Contributions In Aid of Construction Payments to Acquire Water Systems using Contributions In Aid of Construction Issuance of restricted and deferred stock units (in shares) Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture Notes Payable to Banks Notes Payable to Banks [Member] Tax receivable and payable, and other accrued taxes Increase (Decrease) in Accrued Taxes Payable Statement [Line Items] Statement [Line Items] Refunds (Collections) Adjustments Balancing and Memorandum Account, Refunds (Collections) Balancing and Memorandum Account, Refunds (Collections) Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Gain on sale of Texas Water Alliance Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property CTWS Plan CTWS Plan [Member] CTWS Plan [Member] Investments Investments Regulatory Rate Filings Regulatory Rate Filings [Text Block] Regulatory Rate Filings [Text Block] Issuance of restricted and deferred stock units Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture Retirement Plan Type [Domain] Retirement Plan Type [Domain] Schedule of Compensation Costs Charged to Income and Proceeds from the Exercise of Any Restricted Stock and Similar Instruments that are Recorded to Additional Paid-In Capital and Common Stock, by Award Type Share-based Payment Arrangement, Cost by Plan [Table Text Block] Connecticut Water Company Connecticut Water Company [Member] Connecticut Water Company [Member] Proceeds from sale of Texas Water Alliance Proceeds from Sale of Property Held-for-sale Postretirement benefits Increase (Decrease) in Obligation, Pension and Other Postretirement Benefits Regulatory rate filings, requested rate increase, year one Regulatory Rate Filings, Requested Rate Increase, Year One Regulatory Rate Filings, Requested Rate Increase, Year One Entity Address, State or Province Entity Address, State or Province Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Fair Value, Inputs, Level 2 Fair Value, Inputs, Level 2 [Member] Subsidiary, Sale of Stock [Line Items] Subsidiary, Sale of Stock [Line Items] ADVANCES FOR CONSTRUCTION Contract with Customer, Liability, Noncurrent Real Estate Services Reportable Segment Two [Member] Reportable Segment Two [Member] Segment Reporting [Abstract] Segment Reporting [Abstract] Entity [Domain] Entity [Domain] Line of credit Line of Credit, Current Less accumulated depreciation and amortization Real Estate Investment Property, Accumulated Depreciation Regulated Regulated Operation [Member] Benefit Plans Retirement Benefits [Text Block] Beginning Balance Ending Balance Balancing and Memorandum Cost Recovery Account, Net Balancing and Memorandum Cost Recovery Account, Net Regulatory rate filings, statutory cap reset value Regulatory Rate Filings, Statutory Cap Reset Value Regulatory Rate Filings, Statutory Cap Reset Value Entity Shell Company Entity Shell Company Local Phone Number Local Phone Number Forecast Forecast [Member] Regulatory rate filings, average cost of debt rate, current Regulatory Rate Filings, Average Cost Of Debt Rate, Current Regulatory Rate Filings, Average Cost Of Debt Rate, Current Issuance of common stock, net of issuance costs Proceeds from Issuance of Common Stock Total assets Assets Assets Regulation Status [Axis] Regulation Status [Axis] Plan Name [Domain] Plan Name [Domain] Regulatory rate filings, rate of return, current Regulatory Rate Filings, Rate Of Return, Current Regulatory Rate Filings, Rate Of Return, Current Common stock, shares authorized (shares) Common Stock, Shares Authorized Interest Interest Paid, Excluding Capitalized Interest, Operating Activities Buildings and improvements Investment Building and Building Improvements Title of Individual [Axis] Title of Individual [Axis] Regulatory Asset Increase (Decrease) Balancing and Memorandum Revenue Account, Increase (Decrease) Balancing and Memorandum Revenue Account, Increase (Decrease) Requested increase in revenues, completed infrastructure investments not currently in approved rates and surcharges Regulatory Rate Filings, Requested Increase In Revenues, Completed Infrastructure Investments Not Currently In Approved Rates And Surcharges Regulatory Rate Filings, Requested Increase In Revenues, Completed Infrastructure Investments Not Currently In Approved Rates And Surcharges Interest Rate Debt Instrument, Interest Rate, Stated Percentage Payments to retire utility plant, net of salvage Payments for (Proceeds from) Removal Costs Gain on sale of Texas Water Alliance Gain on sale of real estate investments Gain (Loss) on Sale of Properties San Jose Water Company San Jose Water Company [Member] San Jose Water Company [Member] Accrued groundwater extraction charges, purchased water and power Increase (Decrease) in Accrued Groundwater Extraction Charges, Purchased Water and Power Increase (Decrease) in Accrued Groundwater Extraction Charges, Purchased Water and Power Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Balancing and memorandum accounts, net Balancing and Memorandum Accounts [Member] Balancing and Memorandum Accounts [Member] Avon Water Company Avon Water Company [Member] Avon Water Company [Member] Revolving Credit Facility Revolving Credit Facility [Member] Power Utilities Operating Expense, Purchased Power General Significant Accounting Policies [Text Block] NET CASH PROVIDED BY OPERATING ACTIVITIES Net Cash Provided by (Used in) Operating Activities All Other Other Segments [Member] Utility property installed by developers Utility Property Installed by Developer Utility Property Installed by Developer Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Entity Tax Identification Number Entity Tax Identification Number CAPITALIZATION: Capitalization, Long-term Debt and Equity [Abstract] Basic (shares) Weighted Average Number of Shares Outstanding, Basic Diluted (usd per share) Earnings Per Share, Diluted Segment [Domain] Segments [Domain] WEIGHTED AVERAGE SHARES OUTSTANDING Weighted Average Number of Shares Outstanding Basic and Diluted [Abstract] Weighted Average Number of Shares Outstanding Basic and Diluted [Abstract] Offering price per share (usd per share) Sale of Stock, Price Per Share Regulatory rate filings, requested reduction in water bills for income-eligible customers Regulatory Rate Filings, Requested Reduction in Water Bills for Income-Eligible Customers Regulatory Rate Filings, Requested Reduction in Water Bills for Income-Eligible Customers Service cost Defined Benefit Plan, Service Cost Income taxes Income Taxes Paid, Net COMPREHENSIVE INCOME Comprehensive Income (Loss), Net of Tax, Attributable to Parent SJW Group Corporate Segment [Member] NET CASH PROVIDED BY FINANCING ACTIVITIES Net Cash Provided by (Used in) Financing Activities Regulatory rate filings, approved revenue increase Regulatory Rate Filings, Approved Revenue Increase Regulatory Rate Filings, Approved Revenue Increase Regulatory rate filings, requested rate increase, year three Regulatory Rate Filings, Requested Rate Increase, Year Three Regulatory Rate Filings, Requested Rate Increase, Year Three DEFERRED INCOME TAXES Deferred Income Tax Liabilities, Net Service-based restricted stock vesting period Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Regulatory rate filings, requested rate increase, year two Regulatory Rate Filings, Requested Rate Increase, Year Two Regulatory Rate Filings, Requested Rate Increase, Year Two Public Stock Offering Public Stock Offering [Member] Public Stock Offering Fair Value Measurement Fair Value Disclosures [Text Block] Accounts payable Accounts Payable, Current Regulatory rate filings, return of equity rate, requested Regulatory Rate Filings, Return Of Equity Rate, Requested Regulatory Rate Filings, Return Of Equity Rate, Requested General Rate Case No. 21-05-004 General Rate Case No. 21-05-004 [Member] General Rate Case No. 21-05-004 Depreciation and amortization Depreciation, Depletion and Amortization SJWTX Credit Agreement SJWTX Credit Agreement [Member] SJWTX Credit Agreement [Member] Accumulated Other Comprehensive Income AOCI Attributable to Parent [Member] Common stock, shares outstanding (shares) Beginning balance (in shares) Ending balance (in shares) Common Stock, Shares, Outstanding CTWS Employees CTWS Employees [Member] CTWS Employees Regulatory Asset [Domain] Regulatory Asset [Domain] Requested WICA surcharge increase (decrease), percentage Requested WICA Surcharge Increase (Decrease), Percentage Requested WICA Surcharge Increase (Decrease), Percentage Number of reporting units Number of Reporting Units Accounts receivable: Accounts Receivable, after Allowance for Credit Loss, Current [Abstract] Authorized regulatory surcharge, per thousand gallons Authorized Regulatory Surcharge, Per Thousand Gallons Authorized Regulatory Surcharge, Per Thousand Gallons Line of Credit Facility, Lender [Domain] Line of Credit Facility, Lender [Domain] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Unrealized gain (loss) on investment, net of tax OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax Consolidated Entities [Domain] Consolidated Entities [Domain] Approved rate increase (decrease) Public Utilities, Approved Rate Increase (Decrease), Percentage Additions to real estate investments Payments to Acquire Real Estate WICA WICA [Member] WICA Income Statement Location [Domain] Income Statement Location [Domain] Supplemental disclosure of non-cash activities: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Real estate investments, net Real Estate Investment Property, Net Equity Plans Shareholders' Equity and Share-based Payments [Text Block] OTHER NONCURRENT LIABILITIES Other Liabilities, Noncurrent Refunds (Collections) Adjustments Balancing and Memorandum Cost Recovery Account, Refunds (Collections) Balancing and Memorandum Cost Recovery Account, Refunds (Collections) Lender Name [Axis] Lender Name [Axis] Debt Instrument [Line Items] Debt Instrument [Line Items] Repayments of long-term borrowings Repayments of Long-term Debt Other production expenses Utilities Operating Expense, Other EARNINGS PER SHARE Earnings Per Share [Abstract] Property, plant, and equipment, gross Property, Plant and Equipment, Gross Document Quarterly Report Document Quarterly Report REVENUE Total revenues Revenues Potential increase in number of service connections Increase In Number Of Service Connections Increase In Number Of Service Connections Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding SJWC Credit Agreement SJWC Credit Agreement [Member] SJWC Credit Agreement OPERATING EXPENSE: Costs and Expenses [Abstract] Long-term debt, less current portion Long-term Debt, Excluding Current Maturities Number of county residences served Number Of County Residences Served Number Of County Residences Served Compensation costs charged to income: Share-based Payment Arrangement, Expense Schedule of Regulatory Assets, Net Schedule of Regulatory Assets [Table Text Block] Fair value of plan assets Defined Benefit Plan, Plan Assets, Amount Regulatory Assets and Liabilities Disclosure [Abstract] Regulatory Assets and Liabilities Disclosure [Abstract] Document Fiscal Period Focus Document Fiscal Period Focus Effective consolidated income tax rate Effective Income Tax Rate Reconciliation, Percent Beginning Balance Ending Balance Balancing and Memorandum Account, Net Balancing and Memorandum Account, Net Requested WISC surcharge increase (decrease), percentage Requested WISC Surcharge Increase (Decrease), Percentage Requested WISC Surcharge Increase (Decrease), Percentage Net regulatory assets, less current portion Total regulatory assets, net, less current portion Regulatory Assets, Noncurrent CASH, CASH EQUIVALENTS AND RESTRICTED CASH, BEGINNING OF PERIOD CASH, CASH EQUIVALENTS AND RESTRICTED CASH, END OF PERIOD Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Tax memorandum account Tax memorandum [Member] Tax memorandum account [Member] Dividends paid Dividends Shares issued in offering (in shares) Sale of Stock, Number of Shares Issued in Transaction Common stock, par value (usd per share) Common Stock, Par or Stated Value Per Share Property taxes and other non-income taxes Utilities Operating Expense, Taxes Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] CURRENT ASSETS: Assets, Current [Abstract] Other changes, net Proceeds from (Payments for) Other Financing Activities Alternative revenue programs, net Alternative Revenue Programs, Net Alternative Revenue Programs, Net Intangible assets Finite-Lived Intangible Assets, Gross Entity Central Index Key Entity Central Index Key Security Exchange Name Security Exchange Name Maine Water Company Maine Water Company [Member] Maine Water Company [Member] Diluted (shares) Weighted Average Number of Shares Outstanding, Diluted Other comprehensive income (loss), net Other Comprehensive Income (Loss), Net of Tax Income Taxes Income Tax Disclosure [Text Block] Over-Allotment Option Over-Allotment Option [Member] Accrued interest Interest Payable, Current Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Current Fiscal Year End Date Current Fiscal Year End Date Balancing and Memorandum Accounts Public Utilities Disclosure [Text Block] Capitalization Stockholders' Equity Note Disclosure [Text Block] Schedule of Net Benefit Costs Schedule of Net Benefit Costs [Table Text Block] CLWSC Canyon Lake Water Service Company [Member] Canyon Lake Water Service Company Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Credit Facility [Axis] Credit Facility [Axis] NET CASH USED IN INVESTING ACTIVITIES Net Cash Provided by (Used in) Investing Activities Changes in operating assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Production Expenses: Water Production Costs [Abstract] Water Production Costs [Abstract] Employee stock purchase plan Stock Issued During Period, Value, Employee Stock Purchase Plan Purchased water Cost of Purchased Water OPERATING ACTIVITIES: Net Cash Provided by (Used in) Operating Activities [Abstract] General and Administrative Expense General and Administrative Expense [Member] Total current liabilities Liabilities, Current Depreciation and amortization Utilities Operating Expense, Depreciation and Amortization Class of Stock [Domain] Class of Stock [Domain] Beginning Balance Ending Balance Balancing and Memorandum Revenue Account, Net Balancing and Memorandum Revenue Accounting, Net Public Utilities General Disclosures [Table] Public Utilities General Disclosures [Table] Line of credit facility, maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Regulatory Asset Increase (Decrease) Balancing and Memorandum Account, Increase (Decrease) Balancing and Memorandum Account, Increase (Decrease) Regulatory rate filings, requested authorization for capital budget, amount Regulatory Rate Filings, Requested Authorization For Capital Budget, Amount Regulatory Rate Filings, Requested Authorization For Capital Budget, Amount Requested WICA surcharge, percentage Requested WICA Surcharge, Percentage Requested WICA Surcharge, Percentage Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Title of 12(b) Security Title of 12(b) Security Statement [Table] Statement [Table] Other current assets Other Assets, Current Regulated and Unregulated Operation [Domain] Regulated and Unregulated Operation [Domain] Regulatory rate filings, return of equity rate, approved Regulatory Rate Filings, Return Of Equity Rate, Approved Regulatory Rate Filings, Return Of Equity Rate, Approved Recently Adopted Accounting Principles New Accounting Pronouncements, Policy [Policy Text Block] Unrecognized compensation costs Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Public utilities, requested rate increase (decrease), amount Public Utilities, Requested Rate Increase (Decrease), Amount Advice Letter No. 561/561A Advice Letter No. 561/561A [Member] Advice Letter No. 561/561A Statistical Measurement [Axis] Statistical Measurement [Axis] Income tax temporary differences Deferred Income Tax Charge [Member] Long-Term Liabilities and Bank Borrowings [Abstract] Long-Term Liabilities and Bank Borrowings [Abstract] Long-Term Liabilities and Bank Borrowings [Abstract] Revenue accounts: Balancing and Memorandum Revenue Account [Roll Forward] Balancing and Memorandum Revenue Account [Roll Forward] Subsequent Event Subsequent Event [Member] Cover [Abstract] Goodwill Goodwill Operating revenue Regulated Operating Revenue Postretirement pensions and other medical benefits Postretirement Pensions and Other Medical Benefits [Member] Postretirement Pensions and Other Medical Benefits [Member] Regulatory assets and liabilities excluding income tax temporary differences, net and postretirement benefits. Increase (Decrease) To Regulatory Asset And Liabilities Excluding Income Tax Temporary Differences, Net And Postretirement Benefits Increase (Decrease) To Regulatory Asset And Liabilities Excluding Income Tax Temporary Differences, Net And Postretirement Benefits Income tax payable Accrued Income Taxes, Current Non-tariffed Unregulated Operation [Member] Scenario [Domain] Scenario [Domain] Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Cost-recovery accounts: Balancing and Memorandum Cost Recovery Account [Roll Forward] Balancing and Memorandum Cost Recovery Account [Roll Forward] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Regulated Operations [Abstract] Regulated Operations [Abstract] Bank Borrowings and Long-Term Liabilities Long-term Debt [Text Block] Deferred income taxes Deferred Income Tax Expense (Benefit)