Current Liability Schedule of earnings per share Repayment of first mortgage bonds Lease liability Amount related to lease liability. State Revolving Trust Note, due May 1, 2025 [Member] Refers to state revolving trust note. Subsequent Event Type [Axis] Document And Entity Information [Abstract]. Document And Entity Information [Abstract] Commitments and Contingencies Disclosure [Abstract] Nonredeemable Preferred Stock $4.75 Series [Member] Preferred shares that are not redeemable before liquidation of the entity. Preferred shares may provide a preferential dividend to the dividend on common stock and may take precedence over common stock in the event of a liquidation. Preferred shares typically represent an ownership interest in the company. Series 2018A [Member] Series 2018A [Member] Accumulated Deferred Income Taxes General Plant General Plant [Member] Incremental common shares attributable to $8.00 series preferred shares, shares Incremental common shares attributable to $8.00 series preferred shares, shares Collateralized debt obligation backed by, for example, but not limited to, pledge, mortgage or other lien on the entity''s assets. 4.45%, Amortizing Secured Note, due April 20, 2040 [Member] AND OTHER ASSETS: Deferred Charges And Other Assets [Abstract]. Increase (Decrease) in Accrued Taxes Payable Accrued Taxes Equity Components [Axis] Regulatory Accounting Maximum borrowing capacity, construction loan The maximum borrowing capacity for the construction loan as outlined in the closed agreement. Borrowings will take place when construction on a qualifying project is substantially complete. Entity File Number Amount of forfeitures of unearned compensation. Forfeited Untreated Refers to cost of untreated water during the period. Decreased deferred income tax expense Entity a Voluntary Filer Commitment of purchase of untreated water Water Treatment [Member] Water Treatment Increase (Decrease) in Prepaid Expense Prepayments 2020 Regulatory Agency [Axis] Debt Instrument, Unamortized Discount Less: Unamortized Debt Expense Acquisition premiums Acquisition premiums ASSETS Allowance for Funds Used During Construction (AFUDC) Increase (Decrease) in Other Operating Assets Unbilled Revenues First Mortgage Bonds - Series PP [Member] Loan secured by real property that has a first (highest) lien on such property in the event of default by the borrower. Net Income Net Income Entity Tax Identification Number The grant-date value of unearned compensation. Granted Granted Unearned Compensation Operations and Maintenance Costs incurred and are directly related to operations and maintenance. Issuance of Common Stock Amended filed increase in annual operating revenue All Long-term Debt [Member] All Long-term Debt [Member] Common stock granted and issued under plan First Mortgage Bonds - Series VV [Member] Loan secured by real property that has a first (highest) lien on such property in the event of default by the borrower. City Area Code CASH FLOWS FROM INVESTING ACTIVITIES: Convertible Preferred Stock $8.00 Series [Member] Refers to series of convertible prederred stock. Convertible Preferred Stock1 [Member] Entity Interactive Data Current Collateralized debt obligation backed by, for example, but not limited to, pledge, mortgage or other lien on the entity''s assets. Amortizing Secured Note, due August 25, 2030 [Member] Consolidation Items [Axis] Materials & Supplies Increase (Decrease) in Raw Materials, Packaging Materials and Supplies Inventories Adjusted Earnings Applicable to Common Stock Defined Benefit Plan, Expected Future Benefit Payment, Year Three 2022 Common Stock Issuance Expense Payments of Stock Issuance Costs Retirement Plan Type [Axis] Present Value of Lease Payments Increase (decrease) in annual rate per capita cost of covered healthcare benefits, next year Depreciation Cost, Depreciation and Amortization State Revolving Trust Note, due February 1, 2036 [Member] State Revolving Trust Note, due February 1, 2036 [Member] Public Utility [Axis] Stockholders' Equity, Other Common Stock Expenses Entity Filer Category Equity Securities [Member] Tax Year 2016 [Member] Liabilities, Current TOTAL CURRENT LIABILITIES Business Segments [Axis] Segments [Axis] Shares repurchased in the period General NET CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES Net Cash Provided by (Used in) Financing Activities Statement of Cash Flows [Abstract] UTILITY PLANT: DSIC rate increase The amount of a distribution system improvement charge rate increase. Minimum treated water purchase commitment The description of minimum treated water purchase commitment. Income Tax at Statutory Rate Notes Payable Document Type $7.00 Series Preferred Dividend Amount of paid and unpaid cash, stock, and paid-in-kind (PIK) dividends declared convertible $7.00 preferred stock. Discretionary contributions Entity Address, Address Line Two Non-utility Assets - Net Refers to amount of non utility fixed assets as of the balance sheet date. Increase (decrease) in deferred revenue for the period. Unearned Revenue & Advanced Service Fees Construction Advances and Contributions-Net Disclosure of accounting poliy for revenues. Revenues Cash and Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] First Mortgage Bonds [Member] First Mortgage Bonds [Member] Accounts Payable Increase (Decrease) in Accounts Payable Increase in base rates revenue per year Increase in base rates revenue per year Schedule of Segment Reporting Information, by Segment [Table] Delaware Public Service Commission [Member] Delaware Public Service Commission [Member]. Current portion of lease liabilities. Less Current Portion Stock Award - Board Of Directors Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation Effect on Projected Benefit Obligation - Decrease Inter-segment Elimination [Member] NET CASH USED IN INVESTING ACTIVITIES Net Cash Provided by (Used in) Investing Activities Amortizing Secured Note, due December 20, 2021 [Member] State Revolving Trust Note, due July 1, 2028 [Member] Refers to state revolving trust note. Benfit plan, Cash contributions Effect on Current Year Service and Interest Cost - Decrease Defined Benefit Plan, Effect of One Percentage Point Decrease on Service and Interest Cost Components Entity Reporting Status Current Average Outstanding Common Stock, Shares Outstanding Public Utilities, Property, Plant and Equipment, Plant in Service TOTAL Shares Forfeited, shares NJ Water Supply Authority [Member] Financial Instrument [Axis] Organization, Summary of Significant Accounting Policies and Recent Developments Quarterly Financial Information Disclosure [Abstract] Proceeds from Issuance of Common Stock Collateralized debt obligation backed by, for example, but not limited to, pledge, mortgage or other lien on the entity''s assets. Amortizing Secured Note, due September 19, 2031 [Member] Net Operating Loss Carryforwards Mutual Funds [Member] Maximum number of shares authorized for grant Number of shares authorized for grant, unissued Organization Number of Reportable Segments Schedule of regulatory assets Title of 12(b) Security Loan secured by real property that has a first (highest) lien on such property in the event of default by the borrower. First Mortgage Bonds - Series WW [Member] Accumulated Amortization Accumulated amortization on ROU. RightOfUseAssetsAccumulatedAmortization Delaware State Revolving Fund [Member] Delaware State Revolving Fund. Current Fiscal Year End Date Entity Shell Company Interest Capitalized Total Lease Payments Operating Leases, Future Minimum Payments Due Entity Public Float Issuance of shares under the DRP Dividend Reinvestment & Common Stock Purchase Plan Description of 401(k) Preferred Stock TOTAL PREFERRED STOCK Total Income Tax Expense Income Taxes Income taxes Paid Debt Instrument [Axis] Increase (Decrease) in Accounts Receivable Accounts Receivable Provision for Deferred Income Taxes and ITC Deferred income tax benefits Short-term Debt [Abstract] New Jersey Board Of Public Utilities [Member]. New Jersey Board Of Public Utilities [Member] Discretionary contributions, percent Percentage employer discretionary contribution to a defined contribution plan. Business Segment Data Refers to state revolving trust note. State Revolving Trust Note, due December 1, 2026 [Member] Interest expense Investment Type [Axis] Schedule of Segment Reporting Information, by Segment Cash, Cash Equivalents and Restricted Cash, Ending Restricted Cash and Cash Equivalents Cash, Cash Equivalents and Restricted Cash, Beginning Commitment And Contingencies [Table]. Commitment And Contingencies [Table] Purchase commitment expiration date of contract The expiration date of a long-term purchase commitment. Restricted stock plan Refes to purchase of wastewater utility assets. Purchase of the wastewater utility assets 2020 Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months CASH FLOWS FROM FINANCING ACTIVITIES: Non-Current Lease Liability Documents Incorporated By Reference Text Block Operating loss carry-forward Rate Cases, Tank Painting, and Other [Member] Rate Cases, Storm Costs, Tank Painting, and Other Amortization period Loan secured by real property that has a first (highest) lien on such property in the event of default by the borrower. First Mortgage Bonds - Series LL [Member] Minimum [Member] Employee Benefit Plans Increase (Decrease) in Obligation, Pension and Other Postretirement Benefits State Revolving Trust Note, due July 1, 2031 [Member] Refers to state revolving trust note. 2022 Long-term Debt, Maturities, Repayments of Principal in Year Three Employee Benefit Plans Noncurrent Liability Interest 2023 Residential Residential operating revenues. 2008 Restricted Stock Plan [Member] Regulatory Assets [Line Items] Tax Act Effective Income Tax Rate Reconciliation, Tax Credit, Other, Amount Number of hours required to participate in contribution plan Number of hours required to participate in contribution plan Investment Tax Credits Convertible preferred stock converted, value Conversion of Convertible Preferred Stock Totals Total amount of benefit payments. Regulatory Assets Percent of voting interest held. Percent voting interest Prepayments Loan secured by real property that has a first (highest) lien on such property in the event of default by the borrower. First Mortgage Bonds - Series KK [Member] Restricted Stock Award, Net - Employees Defined Benefit Plan, Amortization of Gain (Loss) Amortization of Net Actuarial Loss Loan secured by real property that has a first (highest) lien on such property in the event of default by the borrower. First Mortgage Bonds - Series Z [Member] Amortizing Secured Note 5.69%, due January 20, 2030 [Member] Collateralized debt obligation backed by, for example, but not limited to, pledge, mortgage or other lien on the entity''s assets. Less: Current Portion of Long-term Debt Long-term Debt, Current Maturities Fair value of vested restricted shares Convertible Preferred Stock $7.00 Series Other Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Amount The period remaining for recovery of costs in the rates we charge customers. Remaining recovery period Loan to RGRME Wholesale municipal revenue. Wholesale Shares Granted, Value, Share-based Payment Arrangement, Forfeited Shares Forefeited Preferred Dividend Preferred Stock Dividend Requirements Description of application request seeking increase in base rates Service Cost Retirement Benefits [Abstract] Discount and compensation rates Matching contributions, percent Series 2019B [Member] Series 2019B [Member] Employee Benefit Plans Pension and Other Postretirement Benefits Disclosure [Text Block] CASH FLOWS FROM OPERATING ACTIVITIES: Effect on Projected Benefit Obligation - Increase Entity Incorporation State Country Code Lines of credit