Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Statement of Cash Flows [Abstract] Statement [Table] Statement [Table] Related Party Transaction [Axis] Related Party Transaction [Axis] Related Party Transaction [Domain] Related Party Transaction [Domain] Development fees Development Fees [Member] Development fees. Related Party [Axis] Related Party [Axis] Related Party [Domain] Related Party [Domain] Vornado Affiliated Entity [Member] Statement [Line Items] Statement [Line Items] Liability for real estate additions due to Vornado Non Cash Additions To Real Estate Non-cash additions to real estate included in accounts payable and accrued expenses. Unusual or Infrequent Items, or Both [Abstract] COVID-19 Pandemic Unusual or Infrequent Items, or Both, Disclosure [Text Block] Fair Value Disclosures [Abstract] Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Investment Type [Axis] Investment Type [Axis] Investments [Domain] Investments [Domain] Marketable securities Marketable Securities [Member] Marketable Securities [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Measurement Frequency [Domain] Measurement Frequency [Domain] Recurring Fair Value, Recurring [Member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Level 1 Fair Value, Inputs, Level 1 [Member] Level 2 Fair Value, Inputs, Level 2 [Member] Level 3 Fair Value, Inputs, Level 3 [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Assets, fair value Investments, Fair Value Disclosure Related Party Transactions [Abstract] Related Party Transactions Related Party Transactions Disclosure [Text Block] Statement of Stockholders' Equity [Abstract] Dividends per common share (in usd per share) Common Stock, Dividends, Per Share, Cash Paid Investments, Debt and Equity Securities [Abstract] Marketable Securities Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Debt Disclosure [Abstract] Summary of Outstanding Mortgages Payable Schedule of Long-term Debt Instruments [Table Text Block] Mortgages Payable Mortgage Notes Payable Disclosure [Text Block] SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate Schedule [Table] SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate Schedule [Table] Collaborative Arrangement and Arrangement Other than Collaborative [Axis] Collaborative Arrangement and Arrangement Other than Collaborative [Axis] Collaborative Arrangement and Arrangement Other than Collaborative [Domain] Collaborative Arrangement and Arrangement Other than Collaborative [Domain] Participation Agreement Participation Agreement [Member] Participation agreement. Name of Property [Axis] Name of Property [Axis] Name of Property [Domain] Name of Property [Domain] Rego Park II Rego Park 2 Property [Member] Rego park II. 731 Lexington Avenue Lexington Avenue Property [Member] 731 Lexington avenue. Real Estate, Type of Property [Axis] Real Estate, Type of Property [Axis] Real Estate [Domain] Real Estate [Domain] Retail Space Retail Site [Member] Office Space Office Building [Member] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Mortgages Mortgages [Member] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] LIBOR London Interbank Offered Rate (LIBOR) [Member] SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] Mortgages payable, net of deferred debt issuance costs Notes Payable Basis spread over LIBOR Debt Instrument, Basis Spread on Variable Rate Interest rate (in percentage) Debt Instrument, Interest Rate, Effective Percentage Maturity date Debt Instrument, Maturity Date Loan participation balance Participating Mortgage Loans, Participation Liabilities, Amount Proceeds from notes payable Proceeds from Notes Payable Mortgages payable, net of loan participation Notes Payable, Net Notes Payable, Net Debt instrument, description of variable rate basis Debt Instrument, Description of Variable Rate Basis Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization Nature of Operations [Text Block] Loss Contingencies [Table] Loss Contingencies [Table] Insurance Type and Tier Identifier [Axis] Insurance Type and Tier Identifier [Axis] Type and Tier Identifier [Domain] Type and Tier Identifier [Domain] General Liability General Liability [Member] Disease Coverage Disease Coverage [Member] Disease Coverage [Member] Schedule Of Insurance Type And Tier Identifier [Axis] Schedule Of Insurance Type And Tier Identifier [Axis] Schedule Of Insurance Type And Tier Identifier [Axis] Types And Tier Identifier [Domain] Types And Tier Identifier [Domain] Types And Tier Identifier [Domain] All Risk Property and Rental Value All Risk Property And Rental Value [Member] All risk property and rental value. Terrorism Coverage Including NBCR Terrorism Coverage Including NBCR [Member] Terrorism coverage including NBCR. NBCR NBCR [Member] NBCR. Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] FNSIC Fifty Ninth Street Insurance Company LLC [Member] Fifty ninth street insurance company LLC. Scenario [Axis] Scenario [Axis] Scenario [Domain] Scenario [Domain] Forecast Forecast [Member] Tenant Occupant Tenant Occupant [Member] Tenant occupant. Paramus Paramus Property [Member] Paramus property. Rego Park I Rego Park 1 Property [Member] Rego park 1. Real Estate Property Occupant [Axis] Real Estate Property Occupant [Axis] Real Estate Property Occupant [Axis] Real Estate Property Occupant [Domain] Real Estate Property Occupant [Domain] Real Estate Property Occupant [Domain] IKEA Ikea [Member] IKEA. Sears Sears [Member] Sears [Member] Statistical Measurement [Axis] Statistical Measurement [Axis] Statistical Measurement [Domain] Statistical Measurement [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Estimated Future Damages Estimated Future Damages [Member] Estimated Future Damages [Member] Loss Contingencies [Line Items] Loss Contingencies [Line Items] Insurance maximum coverage per occurrence Insurance Maximum Coverage Per Incident Insurance maximum coverage limit per incident. Insurance maximum coverage per property Insurance Maximum Coverage Per Property Insurance Maximum Coverage Per Property. Insurance maximum coverage in aggregate Insurance Maximum Coverage In Aggregate Insurance maximum coverage limit in aggregate. Insurance coverage end date Insurance Coverage End Date Insurance coverage end date. Insurance deductible Insurance Deductible The deductible owed by our wholly owned insurance subsidiary in the event of a covered loss. Self insured responsibility Self Insured Responsibility The percentage of the covered portion of a loss above the deductible for which our wholly owned insurance subsidiary is responsible for covered losses. Federal government responsibility Federal Government Responsibility The percentage of the covered portion of a loss above the deductible for which the Federal Government is responsible for covered losses. Area of land (in acres) Area of Land Lease purchase option amount Property Purchase Option Exercisable By Lessee Lease with purchase option to be exercised by lessee. Purchase option not exercised amount included in triple net rent over remainder of lease Purchase Option Not Exercised Amount Included In Triple Net Rent Over Remainder Of Lease The amount to be amortized over the remainder of the lease term if the purchase option is not exercised. Fixed interest rate on the debt Debt Instrument, Interest Rate, Stated Percentage Triple-net rent, annual amount Triple Net Rent Annual Amount Triple-net rent, annual amount Purchase option exercised, net cash proceeds from sale of land Purchase Option Exercised Proceeds From Sale Of Land Held For Use The cash inflow from the sale of land held for use in case the purchase option is exercised by lessee. Purchase option exercised, gain on sale of land Gain (Loss) on Disposition of Real Estate, Discontinued Operations Lease term range as Lessor Leases Of Lessor Rental Term Range Approximate rental term range for all outstanding leases to tenants in retail centers and office buildings. Debt instrument maturity date Loan amortization period Loan Amortization Period In the event the tenant does not exercise its purchase option, the period over which the tenant's debt service portion of its rent must be sufficient to fully amortize the loan on the property Area of property (in sqft.) Area of Real Estate Property Number of fires Number Of Fires Number of fires. Loss contingency, damages sought, value Loss Contingency, Damages Sought, Value Reasonably possible losses Loss Contingency, Estimate of Possible Loss Real property transfer tax Real Estate Tax Expense Additional real property transfer tax expense Additional Real Estate Transfer Tax Additional Real Estate Transfer Tax Real property transfer tax interest Real Estate Tax Expense Interest Real Estate Tax Expense Interest Standby letters of credit, outstanding Letters of Credit Outstanding, Amount Earnings Per Share [Abstract] Earnings Per Share Earnings Per Share [Text Block] Accounting Standards Update and Change in Accounting Principle [Abstract] Recently Issued Accounting Literature Accounting Standards Update and Change in Accounting Principle [Text Block] Share-based Payment Arrangement [Abstract] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] 2016 Omnibus Stock Plan 2016 Omnibus Stock Plan [Member] 2016 Omnibus Stock Plan [Member] Title of Individual [Axis] Title of Individual [Axis] Title of Individual [Domain] Title of Individual [Domain] Director Director [Member] Newly Appointed Director Newly Appointed Director [Member] Newly Appointed Director [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Non option equity instruments granted per director (in shares) Share Based Compensation Arrangement By Share Based Payment Award Non Option Equity Instruments Granted Per Director Number of restricted stock units granted to each of the members of the board of directors during the period. Non option equity instruments market value Share Based Compensation Arrangement By Share Based Payment Award Non Option Equity Instruments Market Value Share Based Compensation Arrangement By Share Based Payment Award Non Option Equity Instruments Market Value Non option equity instruments grant date fair value per grant Share Based Compensation Arrangement By Share Based Payment Award Non Option Equity Instruments Grant Date Fair Value Per Grant Share based compensation arrangement by share based payment award non option equity instruments grant date fair value per grant. Non option equity instruments grant date fair value total Share Based Compensation Arrangement By Share Based Payment Award Non Option Equity Instruments Grant Date Fair ValueTotal Share Based Compensation Arrangement By Share Based Payment Award Non Option Equity Instruments Grant Date Fair Value Total Additional non option equity instruments granted per director (in shares) Share Based Compensation Arrangement By Share Based Payment Award Additional Non Option Equity Instruments Granted Per Director Share Based Compensation Arrangement By Share Based Payment Award Additional Non Option Equity Instruments Granted Per Director Additional non option equity instruments market value Share Based Compensation Arrangement By Share Based Payment Award Additional Non Option Equity Instruments Market Value Share Based Compensation Arrangement By Share Based Payment Award Additional Non Option Equity Instruments Market Value Additional non option equity instruments grant date fair value total Share Based Compensation Arrangement By Share Based Payment Award Additional Non Option Equity Instruments Grant Date Fair Value Total Share Based Compensation Arrangement By Share Based Payment Award Additional Non Option Equity Instruments Grant Date Fair Value Total Non option equity instruments, outstanding, number (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number Shares available for future grant under the plan (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Fair Value Measurements Fair Value Disclosures [Text Block] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Company management fees Company Management Fees [Member] Company management fees. Leasing fees Leasing Fees [Member] Leasing fees. Property management, cleaning, engineering and security fees Property Management Fees [Member] Property management fees and payments for cleaning, engineering and security services. Related Party Transaction [Line Items] Related Party Transaction [Line Items] Fees to related party Related Party Transaction, Expenses from Transactions with Related Party Net income Net Income (Loss) Attributable to Parent Weighted average shares outstanding - basic and diluted (in shares) Weighted Average Number of Shares Outstanding, Basic and Diluted Net income per common share - basic and diluted (in usd per share) Earnings Per Share, Basic and Diluted Revenue from Contract with Customer [Abstract] Fixed lease revenues Operating Lease, Lease Income, Lease Payments Variable lease revenues Operating Lease, Variable Lease Income Lease revenues Operating Lease, Lease Income Basis of Presentation Basis of Accounting [Text Block] Number of properties in greater New York City metropolitan area (property) Number of Real Estate Properties Summary of Fees to Vornado Schedule of Related Party Transactions [Table Text Block] Number of reportable segments Number of Reportable Segments Statement of Financial Position [Abstract] ASSETS Assets [Abstract] Real estate, at cost: Real Estate Investment Property, at Cost [Abstract] Land Land Buildings and leasehold improvements Buildings and Improvements, Gross Development and construction in progress Development in Process Total Real Estate Investment Property, at Cost Accumulated depreciation and amortization Real Estate Investment Property, Accumulated Depreciation Real estate, net Real Estate Investment Property, Net Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Restricted cash Restricted Cash and Cash Equivalents Marketable securities Marketable Securities Tenant and other receivables Accounts Receivable, after Allowance for Credit Loss Receivable arising from the straight-lining of rents Deferred Rent Receivables, Net Deferred leasing costs, net, including unamortized leasing fees to Vornado of $30,771 and $32,374, respectively Deferred Costs, Leasing, Net Other assets Other Assets Total assets Assets LIABILITIES AND EQUITY Liabilities and Equity [Abstract] Amounts due to Vornado Due to Related Parties Accounts payable and accrued expenses Accounts Payable and Accrued Liabilities Other liabilities Other Liabilities Total liabilities Liabilities Commitments and contingencies Commitments and Contingencies Preferred stock: $1.00 par value per share; authorized, 3,000,000 shares; issued and outstanding, none Preferred Stock, Value, Issued Common stock: $1.00 par value per share; authorized, 10,000,000 shares; issued, 5,173,450 shares; outstanding, 5,107,290 shares Common Stock, Value, Issued Additional capital Additional Paid in Capital Retained earnings Retained Earnings (Accumulated Deficit) Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Equity before treasury stock Stockholders' Equity before Treasury Stock Treasury stock: 66,160 shares, at cost Treasury Stock, Value Total equity Stockholders' Equity Attributable to Parent Total liabilities and equity Liabilities and Equity Cover [Abstract] Document Type Document Type Document Quarterly Report Document Quarterly Report Document Period End Date Document Period End Date Document Transition Report Document Transition Report Entity File Number Entity File Number Entity Registrant Name Entity Registrant Name Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Entity Tax Identification Number Entity Tax Identification Number Entity Address, Address Line One Entity Address, Address Line One Entity Address, City or Town Entity Address, City or Town Entity Address, State or Province Entity Address, State or Province Entity Address, Postal Zip Code Entity Address, Postal Zip Code City Area Code City Area Code Local Phone Number Local Phone Number Title of 12(b) Security Title of 12(b) Security Trading Symbol Trading Symbol Security Exchange Name Security Exchange Name Entity Current Reporting Status Entity Current Reporting Status Entity Interactive Data Current Entity Interactive Data Current Entity Filer Category Entity Filer Category Entity Small Business Entity Small Business Entity Emerging Growth Company Entity Emerging Growth Company Entity Shell Company Entity Shell Company Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Amendment Flag Amendment Flag Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement [Member] Portion at Fair Value Measurement [Member] Carrying Amount Reported Value Measurement [Member] Fair Value Estimate of Fair Value Measurement [Member] Assets: Cash equivalents Cash and Cash Equivalents, Fair Value Disclosure Liabilities: Liabilities [Abstract] Mortgages payable (excluding deferred debt issuance costs, net) Notes Payable, Fair Value Disclosure Financial Assets and Liabilities Measured at Fair Value Fair Value, Assets Measured on Recurring Basis [Table Text Block] Financial Assets and Liabilities Not Measured at Fair Value Fair Value, by Balance Sheet Grouping [Table Text Block] Stock-Based Compensation Share-based Payment Arrangement [Text Block] Unamortized leasing fees to Vornado Unamortized Leasing Fees To Related Party Unamortized Leasing Fees To Related Party Preferred stock: par value per share (in usd per share) Preferred Stock, Par or Stated Value Per Share Preferred stock: authorized shares (in shares) Preferred Stock, Shares Authorized Preferred stock: issued shares (in shares) Preferred Stock, Shares Issued Preferred stock: outstanding shares (in shares) Preferred Stock, Shares Outstanding Common stock: par value per share (in usd per share) Common Stock, Par or Stated Value Per Share Common stock: authorized shares (in shares) Common Stock, Shares Authorized Common stock: issued shares (in shares) Common Stock, Shares, Issued Common stock: outstanding shares (in shares) Common Stock, Shares, Outstanding Treasury stock: shares (in shares) Treasury Stock, Shares Income Statement [Abstract] Fees to Vornado Costs and Expenses, Related Party Management fees to Vornado Related Party Transaction, Selling, General and Administrative Expenses from Transactions with Related Party Schedule of Earnings Per Share, Basic and Diluted Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Product and Service [Axis] Product and Service [Axis] Product and Service [Domain] Product and Service [Domain] Parking revenue Parking [Member] Tenant services Direct Services [Member] Direct Services [Member] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Lease revenues Revenue from contract with customer Revenue from Contract with Customer, Excluding Assessed Tax Rental revenues Revenues Concentration Risk Type [Axis] Concentration Risk Type [Axis] Concentration Risk Type [Domain] Concentration Risk Type [Domain] Customer Concentration Risk Customer Concentration Risk [Member] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Revenue Revenue Benchmark [Member] Customer [Axis] Customer [Axis] Customer [Domain] Customer [Domain] Bloomberg Bloomberg [Member] Bloomberg. Rental revenues Percentage rent contributed by tenant Concentration Risk, Percentage Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Recently Issued Accounting Literature New Accounting Pronouncements, Policy [Policy Text Block] Revenue Recognition Revenue from Contract with Customer [Policy Text Block] Marketable Securities Marketable Securities, Policy [Policy Text Block] Fair Value Measurement Fair Value Measurement, Policy [Policy Text Block] CASH FLOWS FROM OPERATING ACTIVITIES Net Cash Provided by (Used in) Operating Activities [Abstract] 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] Depreciation and amortization, including amortization of debt issuance costs Depreciation, Depletion and Amortization Straight-lining of rental income Straight Line Rent Write-off of tenant receivables Accounts Receivable, Allowance for Credit Loss, Writeoff Stock-based compensation Share-based Payment Arrangement, Noncash Expense Change in fair value of marketable securities Marketable Securities, Unrealized Gain (Loss) Dividends received in stock Investment Income, Dividend Changes in operating assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Tenant and other receivables, net Increase (Decrease) in Accounts Receivable Other assets Increase (Decrease) in Other Operating Assets Amounts due to Vornado Increase (Decrease) in Due to Related Parties Accounts payable and accrued expenses Increase (Decrease) in Accounts Payable and Accrued Liabilities Other liabilities Increase (Decrease) in Other Operating Liabilities Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities CASH FLOWS FROM INVESTING ACTIVITIES Net Cash Provided by (Used in) Investing Activities [Abstract] Construction in progress and real estate additions Payments For Capital Improvements And Construction In Process The cash outflow for acquisition of or capital improvements to properties held for investment (operating, managed, leased) or for use and the cash outflow from construction costs to date on capital projects that have not been completed and assets being constructed that are not ready to be placed into service. Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities CASH FLOWS FROM FINANCING ACTIVITIES Net Cash Provided by (Used in) Financing Activities [Abstract] Dividends paid Payments of Ordinary Dividends, Common Stock Debt issuance costs Payments of Debt Issuance Costs Proceeds from borrowing Proceeds from Issuance of Long-term Debt Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities Net increase (decrease) in cash and cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Cash and cash equivalents and restricted cash at beginning of period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Cash and cash equivalents and restricted cash at end of period RECONCILIATION OF CASH AND CASH EQUIVALENTS AND RESTRICTED CASH Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract] Cash and cash equivalents at beginning of period Restricted cash at beginning of period Cash and cash equivalents at end of period Restricted cash at end of period SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION Supplemental Cash Flow Elements [Abstract] Cash payments for interest Interest Paid, Excluding Capitalized Interest, Operating Activities NON-CASH TRANSACTIONS Noncash Investing and Financing Items [Abstract] Liability for real estate additions, including $269 and $29 for development fees due to Vornado in 2020 and 2019, respectively Write-off of fully amortized and/or depreciated assets Write Off Of Fully Amortized And Depreciated Assets This element represents written off amount of fully amortized and depreciated assets. Lease liability arising from the recognition of right-of-use asset Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Reclassification of prepaid real estate taxes to construction in progress for property in redevelopment Reclassification of Prepaid Real Estate Taxes to Construction in Progress Reclassification of Prepaid Real Estate Taxes to Construction in Progress Antidilutive securities excluded from computation of earnings per share, amount (shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Investment Holdings [Table] Investment Holdings [Table] Common Stock Common Stock [Member] Macerich Macerich [Member] Macerich interest. Investment Holdings [Line Items] Investment Holdings [Line Items] Macerich common shares (shares) Investment Owned, Balance, Shares Fair value Closing share price (in usd per share) Share Price Unusual or Infrequent Item, or Both [Table] Unusual or Infrequent Item, or Both [Table] Office Retail Residential Residential Real Estate [Member] 731 Lexington Avenue Seven Three One Lexington Avenue Property [Member] Seven Three One Lexington Avenue Property [Member] Alexander Apartment Tower Alexander Apartment Tower [Member] Alexander apartment tower. Unusual or Infrequent Item, or Both [Axis] Unusual or Infrequent Item, or Both [Axis] Unusual or Infrequent Item, or Both [Domain] Unusual or Infrequent Item, or Both [Domain] COVID-19 COVID-19 [Member] COVID-19 [Member] Unusual or Infrequent Item, or Both [Line Items] Unusual or Infrequent Item, or Both [Line Items] Rent collected, percent Rent Collected, Percent Rent Collected, Percent Rent collected & deferred, percent Rent Collected & Deferred, Percent Rent Collected & Deferred, Percent Reduction of rental revenues Write-off of rent receivable Write-off of Rent Receivable Write-off of Rent Receivable Revenue Recognition Revenue from Contract with Customer [Text Block] Mortgage payable gross Notes Payable Gross Notes payable gross. Deferred debt issuance costs, net of accumulated amortization of $16,605 and $14,362, respectively Debt Issuance Costs, Net Notes payable Deferred debt issuance costs, accumulated amortization Accumulated Amortization, Debt Issuance Costs Statement of Comprehensive Income [Abstract] Other comprehensive (loss) income: Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent [Abstract] Change in fair value of interest rate cap Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax Comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] Components of Lease Revenue Operating Lease, Lease Income [Table Text Block] Vornado Vornado [Member] Vornado [Member] Ownership [Axis] Ownership [Axis] Ownership [Domain] Ownership [Domain] Alexander's Inc. Alexander's Inc. [Member] Alexander's Inc. [Member] Property Management Fees Management, property management, cleaning, engineering and security fees Management Property Management Cleaning Engineering And Security Fees [Member] Management property management cleaning and security fees. Office and Retail Space Office And Retail Space [Member] Office And Retail Space [Member] Common Area Common Area [Member] Common area. Noncontrolling interest, ownership percentage by noncontrolling owners Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners Management fee agreement value Management Fee Agreement Value The amount of management fee paid to related party to manage corporate activities. Property management fee agreement percentage of income Property Management Fee, Percent Fee Property management fee agreement, price per square foot Property Management Fee Agreement, Price Per Square Foot Property Management Fee Agreement, Price Per Square Foot Property management fee agreement value Property Management Fee Agreement Value Annual amount paid to related party as property management fees. Property management fee escalation percentage per annum Property Management Fee Escalation Percentage Per Annum Annual increase in the amount paid to related party as property management fees. Development fee as percentage of development costs Development Fee Percentage Percentage of development costs that the related party will receive as per the Development agreement. Lease fee percentage of rent one to ten years Lease Fee Percentage Of Rent One To Ten Years Percentage of rent payable to related party for leasing services for the first ten years of the lease. Lease fee percentage of rent eleven to twenty years Lease Fee Percentage Of Rent Eleven To Twenty Years Percentage of rent payable to related party for leasing services for the eleventh through twentieth years of the lease. Lease fee percentage of rent twenty first to thirty years Lease Fee Percentage Of Rent Twenty First To Thirty Years Percentage of rent payable to related party for leasing services for the twenty-first through thirtieth years of the lease. Percentage increase lease fee if broker used Percentage Increase Lease Fee If Broker Used Percentage of increase in leasing services payable to related party if a real estate broker is used Percentage commissions on sale of assets under fifty million Percentage Commissions On Sale Of Assets Under Fifty Million Percentage of gross proceeds under $50,000,000 from the sale of any assets, payable to related party. Asset sale commission threshold Asset Sale Commission Threshold Asset sale commission threshold. Percentage commissions on sale of assets over fifty million Percentage Commissions On Sale Of Assets Over Fifty Million Percentage of gross proceeds over $50,000,000 from the sale of any assets, payable to related party. Amounts due to related party Related Party Transaction, Due from (to) Related Party REVENUES Revenues [Abstract] EXPENSES Operating Expenses [Abstract] Operating, including fees to Vornado of $1,235, $1,371, $2,618 and $2,620 respectively Operating Costs and Expenses Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction General and administrative, including management fees to Vornado of $595 and $1,190 in each period General and Administrative Expense Total expenses Operating Expenses Interest and other income, net Interest and Other Income Interest and debt expense Interest and Debt Expense Change in fair value of marketable securities Net income Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Additional Capital Additional Paid-in Capital [Member] Retained Earnings Retained Earnings [Member] Accumulated Other Comprehensive Loss AOCI Attributable to Parent [Member] Treasury Stock Treasury Stock [Member] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning Balance, Shares Beginning Balance, Value Dividends paid Dividends, Common Stock, Cash Deferred stock unit grants Shares Granted, Value, Share-based Payment Arrangement, after Forfeiture Ending Balance, Shares Ending Balance, Value