Cash paid during the year for: Supplemental Cash Flow Information [Abstract] Actuarial (gain)/loss Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) Vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period State Current State and Local Tax Expense (Benefit) Unamortized investment tax credit Deferred Tax Assets, Tax Credit Carryforwards, General Business Consolidated Entities [Axis] Consolidated Entities [Axis] Income Tax Statutory Rate Reconciliation [Abstract] Effective Income Tax Rate Reconciliation, Amount [Abstract] Refunds (Collections) Adjustments Balancing and Memorandum Revenue Account, Refunds (Collections) Balancing and Memorandum Revenue Account, Refunds (Collections) Preferred stock, shares outstanding (in shares) Preferred Stock, Shares Outstanding Merger related expenses Business Combination, Acquisition Related Costs Other intangibles Other Intangible Assets [Member] Stockholders’ equity: Stockholders' Equity, Number of Shares, Par Value and Other Disclosures [Abstract] Security Exchange Name Security Exchange Name Forfeited (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Major Property Class [Domain] Major Property Class [Domain] Company-funded Payments to Acquire Water Systems Using Company Funds Payments to Acquire Water Systems Using Company Funds Adjustment to pension benefit plans, net of taxes of $264 in 2021, $(324) in 2020 and $22 in 2019 Adjustment to pension benefit plans, net of taxes Adjustment to pension benefit plans, net of taxes Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax and Reclassification Adjustment, Attributable to Parent Current liabilities Liability, Defined Benefit Plan, Current Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Assets leased or available for lease Property, Plant, and Equipment, Lessor Asset under Operating Lease, after Accumulated Depreciation Number of shares available for issuance (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant 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 3.00% Senior Notes, Series N 3.00% Senior Notes, Series N [Member] 3.00% Senior Notes, Series N Rental income Operating Lease, Lease Income 2023 Long-Term Debt, Maturity, Year Two Intangibles Deferred Tax Liabilities, Intangible Assets Goodwill, measurement period adjustments Goodwill, Purchase Accounting Adjustments Schedule of Regulatory Assets [Table] Schedule of Regulatory Assets [Table] Charged to expense SEC Schedule, 12-09, Valuation Allowances and Reserves, Additions, Charge to Cost and Expense 2.47% Senior Notes, Series 2020 2.47% Senior Notes, Series 2020 [Member] 2.47% Senior Notes, Series 2020 Subsequent Event Type [Domain] Subsequent Event Type [Domain] Deferred income taxes Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Amortization of Intangible Assets Amortization of Intangible Assets Other intangible assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill Debt securities Defined Benefit Plan, Debt Security [Member] Increase related to tax positions taken during a prior year Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions Total liabilities assumed, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Liabilities Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Liabilities 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] Regulatory assets and deferred charges, less current portion, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Regulatory Assets and Deferred Charges, Net Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Regulatory Assets and Deferred Charges, Net Business Combination and Asset Acquisition [Abstract] Cash and Cash Equivalents, and Restricted Cash Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block] Business Acquisition [Axis] Business Acquisition [Axis] Accrued interest Increase (Decrease) in Interest Payable, Net Increase (decrease) in taxes attributable to: Increase (Decrease) in Tax Expense [Abstract] Increase (Decrease) in Tax Expense [Abstract] 3.51% Senior Notes, Due March 2050 3.51% Senior Notes, Due March 2050 [Member] 3.51% Senior Notes, Due March 2050 Award Type [Domain] Award Type [Domain] Future Amortization of Intangible Assets Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract] Local Phone Number Local Phone Number Market gains Defined Benefit Plan, Amortization of Gain (Loss) Schedule of Investments [Line Items] Schedule of Investments [Line Items] Debt premium, net Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Unearned Premiums Reserve Distribution to noncontrolling interest Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Price per share (usd per share) Shares Issued, Price Per Share Retained Earnings Retained Earnings [Member] MWRAM Monterey WRAM [Member] Monterey WRAM Utility Plant [Domain] Utility Plant [Domain] Performance-based and market-based restricted stock awards vested (in shares) Restricted Stock Awards, Performance-based, Vested Balance Restricted Stock Awards, Performance-based, Vested Balance Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Ownership percentage in Acequia Water Supply Corporation Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage Capital expenditures incurred but not yet paid Capital Expenditures Incurred but Not yet Paid Property, Plant and Equipment Public Utility Property, Plant, and Equipment [Table Text Block] Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer —Basic (in dollars per share) Earnings Per Share, Basic At The Market Offering At The Market Offering [Member] At The Market Offering Public Utilities General Disclosures Public Utilities General Disclosures [Table Text Block] Cash received from acquisition Cash Acquired from Acquisition Nonvested, beginning balance (in shares) Nonvested, ending balance (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number 2022 Long-Term Debt, Maturity, Year One Share-based compensation from investment in subsidiaries Share-Based Compensation From Investment in Subsidiaries Share-Based Compensation From Investment in Subsidiaries Unamortized debt issuance costs Unamortized Debt Issuance Expense Interest on long-term debt, mortgage and other interest expense Interest Expense, Debt Restricted net assets, subsidiaries, percent of consolidated assets Restricted Net Assets, Subsidiaries, Percent Of Consolidated Assets Restricted Net Assets, Subsidiaries, Percent Of Consolidated Assets Valuation and Qualifying Accounts and Reserves SEC Schedule, 12-09, Schedule of Valuation and Qualifying Accounts Disclosure [Text Block] Number of subsidiaries that are primary beneficiaries Variable Interest Entity, Primary Beneficiary, Number Of Subsidiaries Variable Interest Entity, Primary Beneficiary, Number Of Subsidiaries Cumulative Effect, Period of Adoption, Adjustment Cumulative Effect, Period of Adoption, Adjustment [Member] Noncurrent assets Assets for Plan Benefits, Defined Benefit Plan Schedule of Investments [Table] Schedule of Investments [Table] Net deferred tax liabilities Deferred Tax Liabilities, Net Less restricted cash, end of year Restricted Cash and Cash Equivalents Utility plant Deferred Tax Liabilities, Property, Plant and Equipment CEMA CEMA [Member] CEMA Entity Voluntary Filers Entity Voluntary Filers Payments SEC Schedule, 12-09, Valuation Allowances and Reserves, Increase (Decrease) Adjustment Defined Benefit Plan, Plan Assets, Category [Domain] Defined Benefit Plan, Plan Assets, Category [Domain] Plan Name [Axis] Plan Name [Axis] Fixed income Fixed Income Funds [Member] Long-term debt Long-term Debt Quoted Prices in Active Markets for Identical Assets (Level 1) Fair Value, Inputs, Level 1 [Member] Investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Goodwill, Impairment Loss Goodwill, Impairment Loss Lease Term, Option Two Lease Term, Option Two [Member] Lease Term, Option Two Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] State taxes, net of federal income tax benefit Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount Connecticut Innovations Revenue Bonds, fixed rate Connecticut Innovations Revenue Bonds [Member] Connecticut Innovations Revenue Bonds [Member] Entity Small Business Entity Small Business Performance-based and market-based restricted stock awards issued (in shares) Restricted Stock Awards, Performance-based, Issued, Intrinsic Value Restricted Stock Awards, Performance-based, Issued, Intrinsic Value Increase related to tax positions taken during the current year Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions Finite-Lived Intangible Assets [Line Items] Finite-Lived Intangible Assets [Line Items] Asset Retirement Obligations Asset Retirement Obligation [Policy Text Block] Consolidation Policy Consolidation, Subsidiaries or Other Investments, Consolidated Entities, Policy [Policy Text Block] Public Utilities, General Disclosures [Line Items] Public Utilities, General Disclosures [Line Items] Commitments Commitments Disclosure [Text Block] Long-term borrowings held as restricted cash Proceeds from Issuance of Long-Term Debt Held As Restricted Cash Proceeds from Issuance of Long-Term Debt Held As Restricted Cash Reserve for litigation and claims: SEC Schedule, 12-09, Reserve, Legal [Member] Capacity Agreement Capacity Agreement [Member] Capacity Agreement [Member] Capitalization and Liabilities Liabilities and Equity [Abstract] Unrecognized tax benefits that would impact effective tax rate Unrecognized Tax Benefits that Would Impact Effective Tax Rate Accounts payable and other current liabilities Increase (Decrease) in Accounts Payable SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Table] SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Table] 2019 WCMA 2019 WCMA [Member] 2019 WCMA [Member] Lower Colorado River Authority Lower Colorado River Authority [Member] Lower Colorado River Authority [Member] Entity Interactive Data Current Entity Interactive Data Current Thereafter Long-Term Debt, Maturity, after Year Five Proceeds to subsidiaries for notes receivable Payments For Note Receivables From Subsidiary Payments For Note Receivables From Subsidiary State revolving fund loans State Revolving Fund Loans [Member] State Revolving Fund Loans [Member] 2025 Finite-Lived Intangible Asset, Expected Amortization, Year Four California franchise tax Deferred Tax Assets, State Taxes Organization and Operations Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Income tax Income Taxes Receivable, Current Minimum volume of water to be purchased (in million gallons) Long-term Purchase Commitment, Minimum Volume Required, Next Twelve Months Long-term Purchase Commitment, Minimum Volume Required, Next Twelve Months Schedule of Future Minimum Rental Payments to be Received Lessor, Operating Lease, Payment to be Received, Fiscal Year Maturity [Table Text Block] 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 Subsidiaries Subsidiaries [Member] Balance at beginning of year Balance at end of year Unrecognized Tax Benefits Income Tax Authority [Domain] Income Tax Authority [Domain] Total deferred tax assets Deferred Tax Assets, Gross Pension non-service cost Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Address, State or Province Entity Address, State or Province Outstanding, beginning balance (in dollars per share) Outstanding, ending balance (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Weighted Average Grant Date Fair Value Refunds of advances for construction Repayments of Advances for Construction 2022 Lessor, Operating Lease, Payment to be Received, Year One Current liabilities: Liabilities, Current [Abstract] Capitalization, long-term debt and equity Capitalization, Long-term Debt and Equity 2024 Advances for Construction, Estimated Refunds, Year Three Advances for Construction, Estimated Refunds, Year Three Administrative and general General and Administrative Expense Other assets, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Noncurrent Assets Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Noncurrent Assets Major components of depreciable plant and equipment [Abstract] Property, Plant and Equipment, Net, by Type [Abstract] Executive Supplemental Retirement Plan Supplemental Employee Retirement Plan [Member] Accounting Policies [Abstract] Accounting Policies [Abstract] 2025 Defined Benefit Plan, Expected Future Benefit Payment, Year Four Amortization period for taxes paid relating to advances and contributions Advances for Construction, Deferred Taxes, Amortization Period Advances for Construction, Deferred Taxes, Amortization Period Federal Current Federal Tax Expense (Benefit) Document Transition Report Document Transition Report Common stock, $0.001 par value; authorized 70,000,000 shares in 2021 and 2020; issued and outstanding 30,181,348 shares in 2021 and 28,556,605 shares in 2020 Common Stock, Value, Issued (Decrease) Increase in accrued payables for construction costs capitalized Noncash Change in Accrued Payables Noncash Change in Accrued Payables Period for recognition of compensation cost Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Nonvested, beginning balance (in dollars per share) Nonvested, ending balance (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Kennebec Water District Kennebec Water District [Member] Kennebec Water District [Member] Funded status at end of year Defined Benefit Plan, Funded (Unfunded) Status of Plan Business Combinations Business Combination Disclosure [Text Block] Incentive Plan Incentive Plan [Member] Incentive Plan [Member] Union Member Union Member [Member] Union Member [Member] ICFR Auditor Attestation Flag ICFR Auditor Attestation Flag Product Concentration Risk Product Concentration Risk [Member] Legal Entity [Axis] Legal Entity [Axis] Class of Stock [Axis] Class of Stock [Axis] Water Water [Member] Water Recognized actuarial loss Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment Depreciable plant and equipment Total 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] Income Tax Contingency [Line Items] Income Tax Contingency [Line Items] 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] Income Tax Authority [Axis] Income Tax Authority [Axis] Net proceeds from stock offering Sale of Stock, Consideration Received on Transaction Property flow-through Effective Income Tax Rate Reconciliation, Nondeductible Expense, Depreciation, Amount Entity [Domain] Entity [Domain] Revenue from contracts with customers Revenue from Contract with Customer, Excluding Assessed Tax Intercompany receivables Intercompany Receivables, Current Intercompany Receivables, Current 2026 Advances for Construction, Estimated Refunds, Year Five Advances for Construction, Estimated Refunds, Year Five Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Equity [Abstract] Equity [Abstract] Other (expense) income: Other Nonoperating Income (Expense) [Abstract] Segment and Non-Tariffed Businesses Reporting Segment Reporting Disclosure [Text Block] Administrative expenses paid Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Other Change Regulatory Asset [Axis] Regulatory Asset [Axis] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Document Fiscal Year Focus Document Fiscal Year Focus Additional Paid-in Capital Additional Paid-in Capital [Member] Total regulatory assets, net Regulatory Assets Lease Term, Option One Lease Term, Option One [Member] Lease Term, Option One 2027 - 2031 Defined Benefit Plan, Expected Future Benefit Payment, after Year Five for Next Five Years Common stock, dividends per share, paid (usd per share) Common Stock, Dividends, Per Share, Cash Paid Utility plant: Public Utilities, Property, Plant and Equipment, Net [Abstract] Change in net deferred tax liabilities Deferred Tax Liabilities, Period Increase (Decrease) Deferred Tax Liabilities, Period Increase (Decrease) Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Forfeitures and Expirations Collective bargaining agreement percent of wage increase for 2022 Collective Bargaining Agreement, Wage Increase, Percent, Year Three Collective Bargaining Agreement, Wage Increase, Percent, Year Three Service connections Public Utilities, Service Connections Public Utilities, Service Connections Borrowings from lines of credit Proceeds from Lines of Credit Stock-based compensation Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-based Payment Arrangement, Amount Other, net Other Nonoperating Income (Expense) Fair value of long-term debt Long-term Debt, Fair Value Number of service connections from acquisition Public Utilities, Acquisition, Service Connections Public Utilities, Acquisition, Service Connections Construction in progress Public Utilities, Property, Plant and Equipment, Construction Work in Progress Regulatory Assets [Line Items] Regulatory Assets [Line Items] Maximum Maximum [Member] Share-based Payment Arrangement [Abstract] Share-based Payment Arrangement [Abstract] Accounts receivable and accrued unbilled utility revenue Increase (Decrease) in Receivables Award Type [Axis] Award Type [Axis] Financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] 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] City Area Code City Area Code Restricted cash Restricted Cash and Cash Equivalents, Current Total assets acquired, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Assets Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Assets Performance-based and market-based restricted stock awards outstanding (in shares) Restricted Stock Awards, Performance-based, Outstanding Balance Restricted Stock Awards, Performance-based, Outstanding Balance Purchase commitment period Long-term Purchase Commitment, Period Goodwill and Intangible Assets Disclosure [Abstract] Goodwill and Intangible Assets Disclosure [Abstract] Other Other Assets, Miscellaneous, Noncurrent Utility Plant Intangible Assets Intangible Assets Disclosure [Text Block] Public Utilities, Regulatory Proceeding [Axis] Public Utilities, Regulatory Proceeding [Axis] Cost of capital memorandum accounts Cost of capital [Member] Cost of capital [Member] Total operating expense Operating expense Utilities Operating Expense Land Land Aggregate principal amount Debt Instrument, Face Amount Net periodic pension cost Net periodic benefit cost Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Restricted Stock Units (RSUs) Restricted Stock Units (RSUs) [Member] Schedule of Recognized Identified Assets Acquired and Liabilities Assumed Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block] Opening balance, SJWNE, LLC SEC Schedule, 12-09, Valuation Allowances and Reserves, Additions, Charge to Other Account Condensed Financial Statements [Table] Condensed Financial Statements [Table] 3.89% Note Due March 2041 3.89% Note Due March 2041 [Member] 3.89% Note Due March 2041 Business Acquisition [Line Items] Business Acquisition [Line Items] Total deferred tax liabilities Deferred Tax Liabilities, Gross Deferred income taxes, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Deferred Income Taxes Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Deferred Income Taxes Equity securities Defined Benefit Plan, Equity Securities [Member] Income Statement [Abstract] Income Statement [Abstract] Entity Registrant Name Entity Registrant Name SJW Corp. and SJWTX, Inc. SJW Corp. and SJWTX, Inc. [Member] SJW Corp. and SJWTX, Inc. [Member] Lines of Credit Short-term Debt [Text Block] Office buildings and other structures Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment Accounts written off SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction Shares issuable under the plan upon exercise of outstanding 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. Plan participants contributions Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant Deferrals by executives and non-employee directors Deferred Compensation Arrangement With Individual, Deferral Amount Deferred Compensation Arrangement With Individual, Deferral Amount Provision for income taxes Cumulative effect of change in accounting principle, taxes Income tax expense (benefit) Income Tax Expense (Benefit) 2024 Defined Benefit Plan, Expected Future Benefit Payment, Year Three Customers, net of allowances for uncollectible accounts of $4,600 and $3,891 in 2021 and 2020, respectively Accounts Receivable, after Allowance for Credit Loss, Current Groundwater extraction charges Groundwater Extraction Charges Groundwater Extraction Charges Entity Tax Identification Number Entity Tax Identification Number 3.10% Senior Notes, Series 2021B 3.10% Senior Notes, Series 2021B [Member] 3.10% Senior Notes, Series 2021B Investments Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Assets Change in plan assets Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] Document Fiscal Period Focus Document Fiscal Period Focus Service area from acquisition Public Utilities, Acquisition, Service Area Public Utilities, Acquisition, Service Area Total current assets Assets, Current Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Regulatory assets, net not earning a return Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided Share-Based Compensation Share-based Payment Arrangement [Policy Text Block] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract] SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract] Advances for Construction and Contributions in Aid of Construction Advances for Construction and Contributions in Aid of Construction, Policy [Policy Text Block] Disclosure of accounting policy for advances for construction and contributions in aid of construction. Current portion of long-term debt Current portion Long-term Debt, Current Maturities Estimated service lives of assets Public Utilities, Property, Plant and Equipment, Common, Useful Life Long-Lived Tangible Asset [Domain] Long-Lived Tangible Asset [Domain] 4.11% Note Due March 2041 4.11% Note Due March 2041 [Member] 4.11% Note Due March 2041 Other regulatory mechanisms, net Regulatory Mechanisms, Other, Net Regulatory Mechanisms, Other, Net Revenue Benchmark Revenue Benchmark [Member] Long-term purchase commitment, minimum area required (in acre-feet of water) Long-term Purchase Commitment, Minimum Acre Feet Required Long-term Purchase Commitment, Minimum Acre Feet Required Equity Component [Domain] Equity Component [Domain] Outstanding, beginning balance (in shares) Outstanding ending balance (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number Kendall West Utility and Bandera East Utility Kendall West Utility and Bandera East Utility [Member] Kendall West Utility and Bandera East Utility Defined Benefit Plan, Plan Assets, Category [Axis] Defined Benefit Plan, Plan Assets, Category [Axis] Tax receivable and accrued taxes Increase (Decrease) in Accrued Taxes Payable Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan Share-based Payment Arrangement, Cost by Plan [Table Text Block] Schedule of Allocation of Plan Assets Schedule of Allocation of Plan Assets [Table Text Block] Counterparty Name [Domain] Counterparty Name [Domain] Connecticut and Maine Connecticut and Maine [Member] Connecticut and Maine [Member] Income before income taxes Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Significant Observable Inputs (Level 2) Fair Value, Inputs, Level 2 [Member] Adjustment to pension benefit plans, taxes Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax, Attributable to Parent Advances for construction Contract with Customer, Liability, Noncurrent Auditor Location Auditor Location Segment Reporting [Abstract] Segment Reporting [Abstract] Useful life of intangible assets Finite-Lived Intangible Asset, Useful Life Less accumulated depreciation and amortization Real Estate Investment Property, Accumulated Depreciation Regulated Regulated Operation [Member] Beginning Balance Ending Balance Balancing and Memorandum Cost Recovery Account, Net Balancing and Memorandum Cost Recovery Account, Net Land and Building Land and Building [Member] Use of Estimates Use of Estimates, Policy [Policy Text Block] Other comprehensive income (loss), net Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Contributions in aid of construction and construction advances Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, CIAC and Advances Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, CIAC and Advances Title of 12(b) Security Title of 12(b) Security Regulation Status [Axis] Regulation Status [Axis] Common stock, shares authorized (in shares) Common Stock, Shares Authorized Unrealized gain (loss) on investment, taxes Other Comprehensive Income (Loss), Available-for-sale Securities, Tax, Portion Attributable to Parent Buildings and improvements Investment Building and Building Improvements Actuarial gain (loss), discount rate change Defined Benefit Plan Actuarial Gain (Loss), Discount Rate Change Defined Benefit Plan Actuarial Gain (Loss), Discount Rate Change Title of Individual [Axis] Title of Individual [Axis] Document Type Document Type Schedule of Nonvested Restricted Stock Units Activity Schedule of Nonvested Restricted Stock Units Activity [Table Text Block] Real Estate Investments and Nonutility Properties Public Utilities, Real Estate, Policy [Policy Text Block] Disclosure of accounting policy for public utilities real estate. Product and Service [Domain] Product and Service [Domain] 2023 Lessor, Operating Lease, Payment to be Received, Year Two Stated interest rates Debt Instrument, Interest Rate, Stated Percentage Gain on sale of Texas Water Alliance (“TWA”) Gain on sale of properties Gain (Loss) on Sale of Properties Thereafter Lessor, Operating Lease, Payment to be Received, after Year Five 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 Other long-term liabilities, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Noncurrent Liabilities Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Noncurrent Liabilities Lease renewal term Lessee, Operating Lease, Renewal Term Less net income attributable to the noncontrolling interest Net Income (Loss) Attributable to Noncontrolling Interest 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] Real estate selling expenses Real Estate Selling Expenses Real Estate Selling Expenses Revolving Credit Facility Revolving Credit Facility [Member] Power Utilities Operating Expense, Purchased Power Current liabilities, including maturities of long-term debt, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Current Liabilities Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Current Liabilities Gain on sale of real estate investments Gains (Losses) on Sales of Investment Real Estate All Other Other Segments [Member] Geographical [Axis] Geographical [Axis] Offering price per share (usd per share) Sale of Stock, Price Per Share Income tax payable Income Tax Payable, Current Income Tax Payable, Current Useful Lives Estimated Useful Lives of Plant and Equipment [Abstract] Estimated Useful Lives of Plant and Equipment [Abstract] Total assets acquired Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets SJW Corp. Corporate Segment [Member] Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities Cumulative reduction in unrecognized tax benefits, due to lapsing of statutes of limitations Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense Equity earnings from subsidiaries, net of taxes Earnings from investment in subsidiaries Equity Earnings From Subsidiaries, Net of Tax Equity Earnings From Subsidiaries, Net of Tax Expected Future Benefit Payments [Abstract] Defined Benefit Plan, Expected Future Benefit Payment [Abstract] Concentration Risk Type [Axis] Concentration Risk Type [Axis] 2024 Finite-Lived Intangible Asset, Expected Amortization, Year Three Deferred tax liabilities: Deferred Tax Liabilities, Gross [Abstract] Business Combinations Business Combinations Policy [Policy Text Block] CTWS Employees CTWS Employees [Member] CTWS Employees Document Period End Date Document Period End Date Lease Contractual Term [Axis] Lease Contractual Term [Axis] Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Fixed income Fixed Income Securities [Member] Intercompany payables Intercompany Payable, Current Intercompany Payable, Current 2025 Advances for Construction, Estimated Refunds, Year Four Advances for Construction, Estimated Refunds, Year Four Consolidated Entities [Domain] Consolidated Entities [Domain] State Deferred State and Local Income Tax Expense (Benefit) Equipment Public Utilities, Property, Plant and Equipment, Equipment Supplemental disclosure of non-cash activities: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Long-term Purchase Commitment [Line Items] Long-term Purchase Commitment [Line Items] Real estate investments, net Real Estate Investment Property, Net Contract with customer, fair value of advances Contract With Customer, Refund Liability, Fair Value Disclosure Contract With Customer, Refund Liability, Fair Value Disclosure Condensed Financial Statements, Captions [Line Items] Condensed Financial Statements, Captions [Line Items] Equity Plans Shareholders' Equity and Share-based Payments [Text Block] Refunds (Collections) Adjustments Balancing and Memorandum Cost Recovery Account, Refunds (Collections) Balancing and Memorandum Cost Recovery Account, Refunds (Collections) Other items, net Effective Income Tax Rate Reconciliation, Other Reconciling Items, Amount Repayments of long-term borrowings Repayments of Long-term Debt Other production expenses Utilities Operating Expense, Other SJW Group earnings per share Earnings Per Share [Abstract] Lease Term, Option Three Lease Term, Option Three [Member] Lease Term, Option Three Property, plant, and equipment, gross Property, Plant and Equipment, Gross Long-term debt Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Long-term Debt Operating revenue Operating revenue Revenues Current contract water rate (in USD per million of gallons) Long-term Purchase Commitment, Fixed Price Long-term Purchase Commitment, Fixed Price CTWS Credit Agreement Maturing May 2025 CTWS Credit Agreement Maturing May 2025 [Member] CTWS Credit Agreement Maturing May 2025 Operating expense: Costs and Expenses [Abstract] Number of variable interest entities Variable Interest Entities, Number Of Entities Variable Interest Entities, Number Of Entities Thereafter Advances for Construction, Estimated Refunds, After Year Five Advances for Construction, Estimated Refunds, After Year Five Regulatory assets and deferred charges, less current portion Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Regulatory Asses and Deferred Charges, net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Regulatory Asses and Deferred Charges, Net Utility plant, net, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Utility Plant, Net Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Utility Plant, Net Entity Current Reporting Status Entity Current Reporting Status Weighted-  Average Grant- Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Fair value of plan assets Fair value of assets at beginning of year Fair value of plan assets at end of year Defined Benefit Plan, Plan Assets, Amount SJWTX, Inc. SJWTX, Inc. [Member] SJWTX, Inc. [Member] Net under-collected accounts Regulatory Balancing and Memorandum Accounts, Net Under-Collected Regulatory Balancing and Memorandum Accounts,, Net Under-Collected Estimated required and discretionary employer cash contributions Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year Counterparty Name [Axis] Counterparty Name [Axis] Net regulatory assets, less current portion Net regulatory assets, less current portion Regulatory Assets, Noncurrent Tax memorandum account Tax memorandum [Member] Tax memorandum account [Member] Dividends paid Dividends Property taxes and other non-income taxes Utilities Operating Expense, Taxes Capitalized merger costs Effective Income Tax Rate Reconciliation, Other Adjustments, Merger Costs Effective Income Tax Rate Reconciliation, Other Adjustments, Merger Costs Income Taxes Income Tax, Policy [Policy Text Block] Intangible Assets Goodwill and Intangible Assets, Intangible Assets, Policy [Policy Text Block] Postretirement Benefits, Type of Deferred Compensation [Axis] Other Postretirement Benefits, Individual Contracts, Type of Deferred Compensation [Axis] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Bargaining agreements, term Bargaining Agreements, Term Bargaining Agreements, Term Cost of water to be purchased Purchase Obligation, to be Paid, Year One —Diluted (shares) Weighted Average Number of Shares Outstanding, Diluted Income Taxes Income Tax Disclosure [Text Block] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Components of Real Estate Investments [Abstract] Real Estate [Abstract] Schedule of Net Benefit Costs Schedule of Net Benefit Costs [Table Text Block] Postretirement benefit plans, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Postretirement Benefit Plans Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Postretirement Benefit Plans Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Other noncurrent assets and noncurrent liabilities Increase (Decrease) in Other Noncurrent Assets and Liabilities The increase (decrease) during the reporting period in other noncurrent operating assets and liabilities not seperately disclosed in the statement of cash flows. Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Credit Facility [Axis] Credit Facility [Axis] Entity Address, Address Line One Entity Address, Address Line One Production Expenses: Water Production Costs [Abstract] Water Production Costs [Abstract] Intercompany notes receivable Intercompany Notes Receivable, Current Intercompany Notes Receivable, Current Employee stock purchase plan Stock Issued During Period, Value, Employee Stock Purchase Plan Unrealized gain (loss) on investment, net of taxes of $68 in 2021, $247 in 2020 and $43 in 2019 Unrealized gain (loss) on investment, net of tax effect Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax, Portion Attributable to Parent Purchased water Cost of Purchased Water Current assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other Operating activities: Net Cash Provided by 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Identifiable Assets Acquired and Liabilities Assumed, Post-retirement Benefit Plans Connecticut Innovations Revenue Bonds, variable rate Connecticut Innovations Revenue Bonds, Variable Rate [Member] Connecticut Innovations Revenue Bonds, Variable Rate [Member] Investments in subsidiaries Investments In Subsidiaries Investments In Subsidiaries Mutual funds Mutual Fund [Member] Statement [Table] Statement [Table] Regulated and Unregulated Operation [Domain] Regulated and Unregulated Operation [Domain] Restricted and Deferred Restricted Stock Awards Activity Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward] Recently Adopted Accounting Principles New Accounting Pronouncements, Policy [Policy Text Block] Other Deferred Tax Assets, Other 2026 Defined Benefit Plan, Expected Future Benefit Payment, Year Five Unrecognized compensation cost Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Number of properties sold Number Of Properties Sold Number Of Properties Sold Statistical Measurement [Axis] Statistical Measurement [Axis] Notice period required for contract adjustment Notice Period Required for Contract Adjustment Notice Period Required for Contract Adjustment Subsequent Event Subsequent Event [Member] Net intangible assets Finite-Lived Intangible Assets, Net Goodwill Goodwill Cash and equivalents Defined Benefit Plan, Cash and Cash Equivalents [Member] Postretirement pensions and other medical benefits Postretirement Pensions and Other Medical Benefits [Member] Postretirement Pensions and Other Medical Benefits [Member] Tariff rate (in USD per hundred cubic feet) Long-term Purchase Commitment, Tariff Rate Long-term Purchase Commitment, Tariff Rate 2023 Advances for Construction, Estimated Refunds, Year Two Advances for Construction, Estimated Refunds, Year Two Entity [Abstract] Entity [Abstract] Entity [Abstract] Non- tariffed Unregulated Operation [Member] 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] Collective bargaining agreement percent of wage increase for 2020 Collective Bargaining Agreement, Wage Increase, Percent, Year One Collective Bargaining Agreement, Wage Increase, Percent, Year One 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] Pension and postretirement Deferred Tax Liabilities, Pension and Postretirement Benefits Deferred Tax Liabilities, Pension and Postretirement Benefits Major Supplier [Axis] Major Supplier [Axis] Major Supplier [Axis] Deferred income taxes Deferred Income Tax Expense (Benefit) Other long-term liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities CTWS Credit Agreement Maturing December 2023 CTWS Credit Agreement Maturing December 2023 [Member] CTWS Credit Agreement Maturing December 2023 Earnings Per Share Earnings Per Share, Policy [Policy Text Block] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] SJW Group net income Net income (loss) Net Income (Loss) Attributable to Parent Total production expenses Water Production Costs Net operating loss Deferred Tax Assets, Operating Loss Carryforwards Interest cost Defined Benefit Plan, Interest Cost Accrued payroll Employee-related Liabilities, Current Financial Statement Schedule Condensed Financial Information of Parent Company Only Disclosure [Text Block] Accumulated amortization of intangible assets Finite-Lived Intangible Assets, Accumulated Amortization Statistical Measurement [Domain] Statistical Measurement [Domain] Bank Owned Life Insurance Life Insurance, Corporate or Bank Owned, Amount Schedule of Maturities of Long-term Debt Schedule 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and Equipment [Table] Public Utility, Property, Plant and Equipment [Table] Share-based compensation APIC, Share-based Payment Arrangement, Increase for Cost Recognition Vested (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Vested, Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Vested, Weighted Average Grant Date Fair Value SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items] SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items] Nonutility plant Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Nonutility Plant, Net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Nonutility Plant, Net Organization, Consolidation and Presentation of Financial Statements [Abstract] Equipment Public Utilities, Property, 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Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Percentage of revenue derived from sales of water to business and residential customers Concentration Risk, Percentage ESPP proceeds Proceeds, Issuance of Shares, Share-based Payment Arrangement, Including Option Exercised Depreciable Utility Plant and Equipment Property, Plant and Equipment, Policy [Policy Text Block] Option Indexed to Issuer's Equity [Line Items] Option Indexed to Issuer's Equity [Line Items] Type of Deferred Compensation, All Types [Domain] Other Postretirement Benefits, Individual Contracts, Type of Deferred Compensation [Domain] Employee Stock Purchase Plan Employee Stock Purchase Plan [Member] Employee Stock Purchase Plan [Member] Minimum percent of delivery schedule to be purchased Long-term Purchase Commitment, Minimum Percentage Required, Next Twelve Months Long-term Purchase Commitment, Minimum Percentage Required, 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Actuarial Gain (Loss), Mortality Change Defined Benefit Plan Actuarial Gain (Loss), Mortality Change Accrued benefit cost Regulatory Liabilities, Accrued Benefit Cost Regulatory Liabilities, Accrued Benefit Cost Benefits paid Defined Benefit Plan, Plan Assets, Benefits Paid Assets Leased or Available for Lease [Abstract] Assets Leased or Available for Lease [Abstract] Assets Leased or Available for Lease [Abstract] Income Tax Contingency [Table] Income Tax Contingency [Table] Annual maximum contribution limit under Dependent Care Spending Account plan Dependent Care Spending Account, Annual Maximum Employee Contribution Dependent Care Spending Account, Annual Maximum Employee Contribution 2023 Defined Benefit Plan, Expected Future Benefit Payment, Year Two Standby Letters of Credit Standby Letters of Credit [Member] Minimum Minimum [Member] Other changes, net Increase (Decrease) in Other Operating Assets and Liabilities, Net Weighted- Average Grant- Date Fair Value Share-based 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Company Entity Emerging Growth Company Allowance for uncollectible accounts Accounts Receivable, Allowance for Credit Loss, Current Water supply costs Water Supply Balancing Accounts [Member] Water Supply Balancing Accounts [Member] Debt issuance costs Payments of Debt Issuance Costs Connecticut CONNECTICUT Other Nontrade Receivables, Current Other First Mortgage Bond First Mortgage Bonds [Member] First Mortgage Bonds [Member] Auditor Name Auditor Name Water Plant Water Plant [Member] Benefit obligations, rate of compensation increase Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase Cash Cash CTWS CTWS [Member] CTWS [Member] Up-front service concession payment Increase (Decrease) In Up-Front Service Concession Payment Increase (Decrease) In Up-Front Service Concession Payment Current: Current Income Tax Expense (Benefit), Continuing Operations [Abstract] Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract] Lessor, 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state taxes, excluding interest and penalties Unrecognized Tax Benefits, Gross Unrecognized Tax Benefits, Gross Line of credit cost of borrowing rate Line of Credit Facility, Interest Rate at Period End California Pollution Control Financing Authority Revenue Bonds California Pollution Control Financing Authority Revenue Bonds Total [Member] California Pollution Control Financing Authority Revenue Bonds Total [Member] 2022 Finite-Lived Intangible Asset, Expected Amortization, Year One Chase Bank, N.A. Chase Bank, N.A. [Member] Chase Bank, N.A. 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Number of people served from acquisition Public Utilities, Acquisition, Number of People Served Public Utilities, Acquisition, Number of People Served Sale of Stock [Domain] Sale of Stock [Domain] Concentration Risk Type [Domain] Concentration Risk Type [Domain] Actual plan asset allocations as a percent of total plan assets Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage Long-term debt, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Long-term Debt Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Long-term Debt Schedule of Segment Reporting Information, by Segment Schedule of Segment Reporting Information, by Segment [Table Text Block] Interest income on money market fund Interest Income, Money Market Deposits Long-term purchase commitment, wholesale discount (in USD per hundred cubic feet) Long-term Purchase Commitment, Wholesale Discount Long-term Purchase Commitment, Wholesale Discount Federal Deferred Federal Income Tax Expense (Benefit) Market-based RSU Market-based RSU [Member] Market-based RSU [Member] Recoveries of accounts written off SEC Schedule, 12-09, Valuation Allowances and Reserves, Addition, Recovery Proceeds from issuance of debt Proceeds from Issuance of Unsecured Debt Product and Service [Axis] Product and Service [Axis] Santa Clara Valley Water District Santa Clara Valley Water District [Member] Santa Clara Valley Water District [Member] Preferred stock, par value (usd per share) Preferred Stock, Par or Stated Value Per Share Proceeds from sale of real estate held-for-investment Proceeds from Sale of Real Estate Held-for-investment Entity Public Float Entity Public Float Documents Incorporated by Reference Documents Incorporated by Reference [Text Block] Transmission and distribution plant Public Utilities, Property, Plant and Equipment, Transmission and Distribution, Useful Life 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 Schedule of Net Funded Status Schedule of Net Funded Status [Table Text Block] Bank term loans Notes Payable to Banks [Member] Contract agreement, term Contract Agreement, Term Contract Agreement, Term Statement [Line Items] Statement [Line Items] SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain] SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain] Refunds (Collections) Adjustments Balancing and Memorandum Account, Refunds (Collections) Balancing and Memorandum Account, Refunds (Collections) Annual maximum contribution limit under Health Care Spending Account plan Health Care Spending Account, Annual Maximum Employee Contribution Health Care Spending Account, Annual Maximum Employee Contribution Category of Item Purchased [Axis] Category of Item Purchased [Axis] Gain on sale of nonutility properties Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property Master contract, negotiated term for delivery schedules Master Contract, Negotiated Term for Delivery Schedules Master Contract, Negotiated Term for Delivery Schedules Investments Investments Issuance of restricted and deferred stock units Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture Retirement Plan Type [Domain] Retirement Plan Type [Domain] Connecticut Water Company Connecticut Water Connecticut Water Company [Member] Connecticut Water Company [Member] Postretirement benefits Increase (Decrease) in Obligation, Pension and Other Postretirement Benefits Contract with customer, refund period Contract With Customer, Refund Liability, Refund Period Contract With Customer, Refund Liability, Refund Period Debt Disclosure [Abstract] Debt Disclosure [Abstract] Funded status of obligation Regulatory Assets, Funded Status of Obligation Regulatory Assets, Funded Status of Obligation Purchase price of common stock to employees under the plan, percent Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent International Union of Operating Engineers International Union of Operating Engineers [Member] International Union of Operating Engineers Long-Lived Tangible Asset [Axis] Long-Lived Tangible Asset [Axis] Subsidiary, Sale of Stock [Line Items] Subsidiary, Sale of Stock [Line Items] Real Estate Services Reportable Segment Two [Member] Reportable Segment Two [Member] Major Supplier [Domain] Major Supplier [Domain] [Domain] for Major Supplier [Axis] Lines of credit Line of Credit, Current Benefit Plans Retirement Benefits [Text Block] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Employer contributions to deferral plan Deferred Compensation Arrangement with Individual, Contributions by Employer Accrued interest, expense net of the benefit of tax deductions Unrecognized Tax Benefits, Interest on Income Taxes Accrued Document Annual Report Document Annual Report Other comprehensive (income) loss, defined benefit plan, prior service cost Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax Current liabilities, including maturities of long-term debt Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities Advances and contributions Deferred Tax Assets, Advances and Contributions Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from advances and contributions. Issuance of common stock, net of issuance costs Proceeds from Issuance of Common Stock Total assets Assets Assets Plan Name [Domain] Plan Name [Domain] Interest Interest Paid, Excluding Capitalized Interest, Operating Activities Geographical [Domain] Geographical [Domain] Regulatory asset increase (decrease) Regulatory Asset Increase (Decrease) Balancing and Memorandum Revenue Account, Increase (Decrease) Balancing and Memorandum Revenue Account, Increase (Decrease) SJW Group Parent Company [Member] Noncontrolling Interest Noncontrolling Interest [Member] Cost to retire utility plant, net of salvage Payments for (Proceeds from) Removal Costs SJWC San Jose Water Company [Member] San Jose Water Company [Member] Schedule of Line of Credit Facilities Schedule of Line of Credit Facilities [Table Text Block] Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Cumulative Effect, Period of Adoption [Domain] Cumulative Effect, Period of Adoption [Domain] Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Tax credit carryforward Tax Credit Carryforward, Amount Utility property installed by developers Utility Property Installed by Developer Utility Property Installed by Developer Infrastructure Infrastructure [Member] Infrastructure [Member] Share-based compensation related to business combination Adjustments to Additional Paid in Capital, Share-based Compensation, Equity Award Assumed in Acquisition Adjustments to Additional Paid in Capital, Share-based Compensation, Equity Award Assumed in Acquisition Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Capitalization: Capitalization, Long-term Debt and Equity [Abstract] Lease Contractual Term [Domain] Lease Contractual Term [Domain] Section 481(a) adjustments Deferred Tax Liabilities, Change in Accounting Policy Deferred Tax Liabilities, Change in Accounting Policy —Basic (shares) Weighted Average Number of Shares Outstanding, Basic —Diluted (in dollars per share) Earnings Per Share, Diluted Segment [Domain] Segments [Domain] Weighted average shares outstanding Incremental Weighted Average Shares Attributable to Dilutive Effect [Abstract] Service cost Defined Benefit Plan, Service Cost Income taxes Income Taxes Paid, Net Deferred gain and other-property Deferred Tax Liabilities, Deferred Gain and Other-Property Related Deferred Tax Liabilities, Deferred Gain and Other-Property Related Number of people served Public Utilities, Number of People Served Public Utilities, Number of People Served South Central Texas South Central Texas [Member] South Central Texas SJW Group comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Return on capital from investments in subsidiaries Proceeds From Return On Capital From Investments In Subsidiaries Proceeds From Return On Capital From Investments In Subsidiaries Other comprehensive income: Other Comprehensive Income (Loss), Net of Tax [Abstract] Schedule of Amounts Recognized in Balance Sheet Schedule of Amounts Recognized in Balance Sheet [Table Text Block] Deferred income taxes Deferred Income Tax Liabilities, Net Public Stock Offering Public Stock Offering [Member] Public Stock Offering Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] 3.00% Senior Notes, Series O 3.00% Senior Notes, Series O [Member] 3.00% Senior Notes, Series O 3.07% Senior Notes, Series 2021A 3.07% Senior Notes, Series 2021A [Member] 3.07% Senior Notes, Series 2021A Schedule of Effective Income Tax Rate Reconciliation Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Acequia Water Supply Corporation Variable Interest Entity, Primary Beneficiary [Member] Accounts payable Accounts Payable, Current Depreciation and amortization Depreciation, Depletion and Amortization Impairment of long-lived asset Impairment, Long-Lived Asset, Held-for-Use Other intangible assets, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Intangibles SJWTX Credit Agreement SJWTX Credit Agreement [Member] SJWTX Credit Agreement [Member] SJWC Credit Agreement Maturing December 2023 SJWC Credit Agreement Maturing December 2023 [Member] SJWC Credit Agreement Maturing December 2023 Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Common stock, shares outstanding (in shares) Beginning balance (in shares) Ending balance (in shares) Common Stock, Shares, Outstanding Other assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets Pensions, postretirement benefits and stock-based compensation Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Pensions and Postretirement Benefits Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Pensions and Postretirement Benefits Regulatory Asset [Domain] Regulatory Asset [Domain] Accounts receivable: Accounts Receivable, after Allowance for Credit Loss, Current [Abstract] Entity Central Index Key Entity Central Index Key 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] Deferred tax assets: Deferred Tax Assets, Gross [Abstract] Executives and Non-employee Directors Executives and Non-employee Directors [Member] Executives and Non-employee Directors [Member] Investments, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Assets Additions to real estate investment Payments to Acquire Real Estate Reductions related to tax positions taken in a prior year Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions Customer Relationships Purchase premium customer relationships Customer Relationships [Member] Implicit rate subsidy Defined Benefit Plan, Implicit Rate Subsidy Defined Benefit Plan, Implicit Rate Subsidy Proceeds from sale of TWA, real estate investments and nonutility properties Proceeds From Sale Of Property Held-For-Sale And From Sale Of Real Estate Investments Proceeds From Sale Of Property Held-For-Sale And From Sale Of Real Estate Investments Intangible assets, customer relationships Finite-Lived Customer Relationships, Gross Other noncurrent liabilities Other Liabilities, Noncurrent Condensed Financial Information Disclosure [Abstract] Projected benefit obligation Benefit obligation at beginning of year Benefit obligation at end of year Defined Benefit Plan, Benefit Obligation Deferred gains on sales of properties Deferred Gains (Losses) on Sales of Properties Deferred Gains (Losses) on Sales of Properties Schedule of Long-term Debt Instruments Schedule of Long-term Debt Instruments [Table Text Block] Lender Name [Axis] Lender Name [Axis] Debt Instrument [Line Items] Debt Instrument [Line Items] Trading Symbol Trading Symbol Assumed equity, measurement period adjustments Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Assets Acquired and Liabilities Assumed, Net Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Assets Acquired and Liabilities Assumed, Net Regulatory asset - income tax temporary differences, net Deferred Tax Liability, Regulatory Asset, Income Tax Temporary Differences Deferred Tax Liability, Regulatory Asset, Income Tax Temporary Differences Schedule of Regulatory Asset Recorded on the Projected Benefit Obligation of the Postretirement Benefit Plans Schedule of Regulatory Asset Recorded on the Projected Benefit Obligation of the Postretirement Benefit Plans [Table Text Block] Schedule of Regulatory Asset Recorded on the Projected Benefit Obligation of the Postretirement Benefit Plans [Table Text Block] Deferred compensation arrangement with individual, by type of compensation, pension and other postretirement benefits Deferred Compensation Arrangement with Individual, by Type of Compensation, Pension and Other Postretirement Benefits [Member] Intercompany notes payable Intercompany Notes Payable, Current Intercompany Notes Payable, Current Other Deferred Tax Liabilities, Other Depreciation expense as percentage of beginning of year balance of depreciable plant Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service Uncertain tax positions Effective Income Tax Rate Reconciliation, Uncertain Tax Positions Effective Income Tax Rate Reconciliation, Uncertain Tax Positions Unamortized debt premium, net Debt Instrument, Unamortized Premium Vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Vested, Number Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Vested, Number Reduction in delivery schedule, percent Reduction in Delivery Schedule, Percent Reduction in Delivery Schedule, Percent Line of Credit Facility [Table] Line of Credit Facility [Table] Plan participants contributions Defined Benefit Plan, Plan Assets, Contributions by Plan Participant Borrowings from subsidiaries for notes payable Proceed From Subsidiary Notes Payable Proceed From Subsidiary Notes Payable SJWC Credit Agreement SJWC Credit Agreement [Member] SJWC Credit Agreement Long-term debt, less current portion Total long-term debt, less current portion Long-term Debt, Excluding Current Maturities Compensation costs charged to income: Share-based Payment Arrangement, Expense Schedule of Regulatory Assets, Net Schedule of Regulatory Assets [Table Text Block] Regulatory asset - business combinations debt premium, net Deferred Tax Liabilities, Regulatory Asset, Debt Premium Deferred Tax Liabilities, Regulatory Asset, Debt Premium Charged to regulatory asset SEC Schedule, 12-09, Valuation Allowances And Reserves Charged To Regulatory Assets SEC Schedule, 12-09, Valuation Allowances And Reserves Charged To Regulatory Assets Long-term Purchase Commitment [Table] Long-term Purchase Commitment [Table] Beginning Balance Ending Balance Balancing and Memorandum Account, Net Balancing and Memorandum Account, Net Net income before noncontrolling interest Net income Net income before noncontrolling interest Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Increase in delivery schedule, percent Increase in Delivery Schedule, Percent Increase in Delivery Schedule, Percent Total liabilities assumed Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities Number of communities served Public Utilities, Number of Communities Served Public Utilities, Number of Communities Served Cash, cash equivalents and restricted cash, beginning of year Cash, cash equivalents and restricted cash, end of year Cash and cash equivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents 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 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 Schedule of Finite-Lived Intangible Assets Schedule of Finite-Lived Intangible Assets [Table Text Block] Impairment of Long-Lived Assets and Goodwill Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block] Pension flow-through Effective Income Tax Rate Reconciliation, Nondeductible Expense, Pensions Effective Income Tax Rate Reconciliation, Nondeductible Expense, Pensions Maine Water Company Maine Water Maine Water Company [Member] Maine Water Company [Member] Collective bargaining agreement percent of wage increase for 2021 Collective Bargaining Agreement, Wage Increase, Percent, Year Two Collective Bargaining Agreement, Wage Increase, Percent, Year Two Liabilities assumed: Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities [Abstract] Over-Allotment Option Over-Allotment Option [Member] Accrued interest Interest Payable, Current Capitalization Stockholders' Equity Note Disclosure [Text Block] 2026 Finite-Lived Intangible Asset, Expected Amortization, Year Five CLWSC Canyon Lake Water Service Company [Member] Canyon Lake Water Service Company Financial Instruments and Investments Fair Value of Financial Instruments, Policy [Policy Text Block] Auditor Firm ID Auditor Firm ID Transmission and distribution Public Utilities, Property, Plant and Equipment, Transmission and Distribution Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Change in benefit obligation Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Building and Building Improvements Building and Building Improvements [Member] Changes in operating assets and liabilities, net of acquired assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Schedule of Asset Retirement Obligations Schedule of Asset Retirement Obligations [Table Text Block] Vested (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Class of Stock [Domain] Class of Stock [Domain] Payments for business/asset acquisitions Cash purchase price Payments to Acquire Businesses, Gross SJWTX, Inc. Credit Agreement Maturing December 2023 SJWTX, Inc. Credit Agreement Maturing December 2023 [Member] SJWTX, Inc. Credit Agreement Maturing December 2023 Line Limit Line of credit facility, maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity CTWS Connecticut Water Service, Inc. [Member] Connecticut Water Service, Inc. [Member] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Actuarial gain (loss), data and other changes Defined Benefit Plan Actuarial Gain (Loss), Data And Other Changes Defined Benefit Plan Actuarial Gain (Loss), Data And Other Changes Regulatory Asset Increase (Decrease) Balancing and Memorandum Account, Increase (Decrease) Balancing and Memorandum Account, Increase (Decrease) Fair value of restricted stock awards Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested, Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested, Grant Date Fair Value Net periodic benefit cost, discount rate Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Other current assets Other Assets, Current Net periodic benefit cost, rate of compensation increase Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase Liabilities, net Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position Income tax temporary differences Deferred Income Tax Charge [Member] Revenue accounts: Balancing and Memorandum Revenue Account [Roll Forward] Balancing and Memorandum Revenue Account [Roll Forward] Income tax at federal statutory rate Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount RWA South Central Connecticut Regional Water Authority [Member] South Central Connecticut Regional Water Authority [Member] Intercompany receivables Increase (Decrease) In Intercompany Receivables, Current Increase (Decrease) In Intercompany Receivables, Current Audit Information [Abstract] Audit Information Customer advances for construction, refunded on service connections Customer Advances for Construction, Refunded on Service Connections Customer Advances for Construction, Refunded on Service Connections Balance, beginning of period Balance, end of period SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount 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 2024 Lessor, Operating Lease, Payment to be Received, Year Three Pension Plan Pension Plan [Member] Reversal of excess deferred taxes recognized in regulatory liability Effective Income Tax Rate Reconciliation, Reversal Of Excess Deferred Taxes Recognized In Regulatory Liability, Amount Effective Income Tax Rate Reconciliation, Reversal Of Excess Deferred Taxes Recognized In Regulatory Liability, Amount Concession fees Concession Fees [Member] Concession Fees [Member] Major Property Class [Axis] Major Property Class [Axis] Regulated Operations [Abstract] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Estimated Refunds of Advances for Construction [Abstract] Estimated Refunds of Advances for Construction [Abstract] Estimated Refunds of Advances for Construction [Abstract] Schedule of Finite-Lived Intangible Assets [Table] Schedule of Finite-Lived Intangible Assets [Table] SJWTX, Inc. dba Canyon Lake Water Supply Corporation Subsidiary One [Member] Subsidiary One [Member] Long-Term Debt Long-term Debt [Text Block]