Fair Value Disclosures [Abstract] Increase (decrease) in fair value: Changes In Fair Value [Abstract] Changes in Fair Value [Abstract] Recognized in earnings Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net Recognized in other comprehensive income Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax Total Increase Decrease In Fair Value Of Interest Rate Swaps Net Increase / (decrease) in fair value of interest rate swaps, net. Quarterly Financial Information Disclosure [Abstract] Interim Results (Unaudited) Quarterly Financial Information [Text Block] Income Statement [Abstract] Revenue Revenues [Abstract] Base rent Operating Leases, Income Statement, Minimum Lease Revenue Expense recoveries Tenant Reimbursements Percentage rent Operating Leases, Income Statement, Percentage Revenue Other Other Real Estate Revenue Total revenue Revenues Operating expenses Costs and Expenses [Abstract] Property operating expenses Direct Costs of Leased and Rented Property or Equipment Provision for credit losses Provision for Loan and Lease Losses Real estate taxes Real Estate Tax Expense Interest expense and amortization of deferred debt costs Noncash Interest Expense Accretion And Amortization Of Deferred Finance Fees Noncash Interest Expense Accretion And Amortization Of Deferred Finance Fees Depreciation and amortization of deferred leasing costs Cost of Services, Depreciation and Amortization General and administrative General and Administrative Expense Acquisition related costs Acquisition Costs, Period Cost Predevelopment expenses Other Operating Expenses Other Operating Expenses Total operating expenses Costs and Expenses Operating income Operating Income (Loss) Change in fair value of derivatives Gains on sales of properties Gain (Loss) on Sale of Properties, Net of Applicable Income Taxes Net income (loss) Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Income attributable to noncontrolling interests Net Income (Loss) Attributable to Noncontrolling Interest Net income attributable to Saul Centers, Inc. Net Income (Loss) Attributable to Parent Preferred dividends Preferred Stock Dividends, Income Statement Impact Net income available to common stockholders Net Income (Loss) Available to Common Stockholders, Basic Per share net income available to common stockholders Earnings Per Share [Abstract] Basic (in usd per share) Earnings Per Share, Basic Diluted (in usd per share) Earnings Per Share, Diluted Noncontrolling Interest [Abstract] Noncontrolling Interests - Holders of Convertible Limited Partnership Units in the Operating Partnership Noncontrolling Interest Disclosure [Text Block] Leases [Abstract] Base rent (including straight-line rent) Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Series C Preferred Stock Series C Preferred Stock [Member] Class of Stock [Line Items] Class of Stock [Line Items] Income attributable to noncontrolling interests Depositary shares outstanding (in shares) Preferred Stock, Depositary Shares Outstanding Preferred Stock, Depositary Shares Outstanding Depository shares to cumulative redeemable preferred stock ratio Depository Shares To Redeemable Preferred Stock Ratio Depository Shares to Redeemable Preferred Stock Ratio Dividend rate on preferred stock Preferred Stock, Dividend Rate, Percentage Liquidation preference (in usd per share) Preferred Stock, Liquidation Preference Per Share Annual dividend on depositary shares (in usd per share) Depository Shares Dividends Per Share Depository Shares Dividends per Share Percentage of redeemable preferred stock Preferred Stock Redemption Percentage Of Originally Issued Shares Preferred Stock Redemption, Percentage of Originally Issued Shares Segment Reporting [Abstract] Business Segments Schedule of Segment Reporting Information, by Segment [Table Text Block] Changes in Fair Value of Swaps Derivative Instruments, Gain (Loss) [Table Text Block] Accounting Policies [Abstract] Allowance for Doubtful Accounts Receivable [Roll Forward] Allowance for Doubtful Accounts Receivable [Roll Forward] Beginning Balance Allowance for Doubtful Accounts Receivable Provision for Credit Losses Provision for Other Losses Charge-offs Allowance for Doubtful Accounts Receivable, Write-offs Ending Balance Number of reportable business segments Number of Reportable Segments Future contractual payments under noncancelable leases Lessee, Operating Lease, Disclosure [Table Text Block] Equity [Abstract] Dividends [Table] Dividends [Table] Dividends [Table] Dividends [Axis] Dividends [Axis] Dividends [Domain] Dividends [Domain] October 31 Dividend Payment One [Member] Dividend Payment 1st [Member] July 31 Dividend Payment Two [Member] Dividend Payment 2nd [Member] April 30 Dividend Payment Three [Member] Dividend Payment 3rd [Member] January 31 Dividend Payment Four [Member] Dividend Payment 4th [Member] Dividends [Line Items] Dividends [Line Items] Dividends [Line Items] Preferred Stockholders Payments of Ordinary Dividends, Preferred Stock and Preference Stock Common Stockholders Payments of Ordinary Dividends, Common Stock Limited Partnership Unitholders Dividends Paid To Noncontrolling Interests Dividends Paid To Noncontrolling Interests Common Stock Shares Issued (in shares) Stock Issued During Period, Shares, Dividend Reinvestment Plan Discounted Share Price (in usd per share) Dividends Reinvested In Common Stock Price Per Share Dividends Reinvested in Common Stock, Price Per Share Limited Partnership Units Issued (in shares) Limited Partner's Units Issued During Period, Units, Dividend Reinvestment Plan Limited Partner's Units Issued During Period, Units, Dividend Reinvestment Plan Average Unit Price (in usd per share) Limited Partner's Dividend Reinvestment Plan, Average Unit Price Limited Partner's Dividend Reinvestment Plan, Average Unit Price Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Operating Segments Operating Segments [Member] Corporate Corporate, Non-Segment [Member] Business Segments [Axis] Segments [Axis] Segment [Domain] Segments [Domain] Shopping Centers Shopping Centers [Member] Shopping Centers [Member] Mixed-Use Properties Mixed Use Properties [Member] Mixed-Use Properties [Member] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Revenue Expenses Cost of Real Estate Revenue Income from real estate Gross Profit Interest expense and amortization of deferred debt costs General and administrative Subtotal Segment Reporting Information Operating Income Loss Before Depreciation And Amortization Segment Reporting Information, Operating Income (Loss) before Depreciation and Amortization Depreciation and amortization of deferred leasing costs Acquisition related costs Predevelopment expenses Gain on sale of property Capital investment Payments to Acquire Property, Plant, and Equipment Total assets Assets Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Formation, and Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Real Estate [Abstract] Schedule of Finite-Lived Intangible Assets [Table] Schedule of Finite-Lived Intangible Assets [Table] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Lease acquisition costs Lease Acquisition Costs [Member] Lease Acquisition Costs [Member] Above market leases Above Market Leases [Member] Finite-Lived Intangible Assets [Line Items] Finite-Lived Intangible Assets [Line Items] 2018 Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months 2019 Finite-Lived Intangible Assets, Amortization Expense, Year Two 2020 Finite-Lived Intangible Assets, Amortization Expense, Year Three 2021 Finite-Lived Intangible Assets, Amortization Expense, Year Four 2022 Finite-Lived Intangible Assets, Amortization Expense, Year Five Thereafter Finite-Lived Intangible Assets, Amortization Expense, after Year Five Total Finite-Lived Intangible Assets, Net Below market leases Below Market Lease, Net, Amortization Income, Fiscal Year Maturity [Abstract] 2018 Below Market Lease, Amortization Income, Next Twelve Months 2019 Below Market Lease, Amortization Income, Year Two 2020 Below Market Lease, Amortization Income, Year Three 2021 Below Market Lease, Amortization Income, Year Four 2022 Below Market Lease, Amortization Income, Year Five Thereafter Below Market Lease, Amortization Income, after Year Five Total Below Market Lease, Net Statement of Financial Position [Abstract] Assets Assets [Abstract] Real estate investments Real Estate Investments, Net [Abstract] Land Land Buildings and equipment Investment Building and Building Improvements Construction in progress Development in Process Total Purchase Price Real Estate Investment Property, at Cost Accumulated depreciation Real Estate Investment Property, Accumulated Depreciation Real estate investments, net Real Estate Investment Property, Net Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Accounts receivable and accrued income, net Accounts and Notes Receivable, Net Deferred leasing costs, net Deferred Costs, Leasing, Net Prepaid expenses, net Prepaid Expense Other assets Other Assets Total assets Liabilities Liabilities [Abstract] Mortgage notes payable Secured Debt Revolving credit facility payable Long-term Line of Credit Construction loan payable Construction Loan Dividends and distributions payable Dividends Payable Accounts payable, accrued expenses and other liabilities Accounts Payable Accrued Expenses And Other Liabilities Accounts payable, accrued expenses and other liabilities Deferred income Deferred Revenue Total liabilities Liabilities Equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Preferred stock, 1,000,000 shares authorized: Preferred Stock [Abstract] Preferred Stock [Abstract] Series C Cumulative Redeemable, 72,000 shares issued and outstanding Preferred Stock, Value, Issued Common stock, $0.01 par value, 40,000,000 shares authorized, 22,123,128 and 21,704,359 shares issued and outstanding, respectively Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital Accumulated deficit Retained Earnings (Accumulated Deficit) Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Total Saul Centers, Inc. equity Stockholders' Equity Attributable to Parent Noncontrolling interests Stockholders' Equity Attributable to Noncontrolling Interest Total equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Total liabilities and equity Liabilities and Equity Nature of Operations Nature Of Operations Policy [Policy Text Block] Nature of Operations Principles of Consolidation Consolidation, Policy [Policy Text Block] Use of Estimates Use of Estimates, Policy [Policy Text Block] Real Estate Investment Properties Real Estate, Policy [Policy Text Block] Deferred Leasing Costs Deferred Charges, Policy [Policy Text Block] Construction in Progress Construction In Progress Policy [Policy Text Block] Construction In Progress Accounts Receivable and Accrued Income Receivables, Policy [Policy Text Block] Assets Held for Sale Assets Held For Sale [Policy Text Block] Assets Held for Sale, Policy Cash and Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Deferred Debt Costs Debt, Policy [Policy Text Block] Deferred Income Deferred Revenue Policy [Policy Text Block] Deferred Revenue, Policy Derivative Financial Instruments Derivatives, Policy [Policy Text Block] Revenue Recognition Revenue Recognition, Policy [Policy Text Block] Income Taxes Income Tax, Policy [Policy Text Block] Stock Based Employee Compensation, Deferred Compensation and Stock Plan for Directors Compensation Related Costs, Policy [Policy Text Block] Noncontrolling Interest Noncontrolling Interests Policy [Policy Text Block] Noncontrolling Interests, Policy Per Share Data Earnings Per Share, Policy [Policy Text Block] Legal Contingencies Commitments and Contingencies, Policy [Policy Text Block] Recently Issued Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block] Reclassifications Reclassification, Policy [Policy Text Block] Statement of Comprehensive Income [Abstract] Net income Other comprehensive income Other Comprehensive Income (Loss), Net of Tax [Abstract] Unrealized gain on cash flow hedge Total comprehensive income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Comprehensive income attributable to noncontrolling interests Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Total comprehensive income attributable to Saul Centers, Inc. Comprehensive Income (Loss), Net of Tax, Attributable to Parent Preferred dividends Total comprehensive income available to common stockholders Total Comprehensive Income Loss Available To Common Stockholders Total Comprehensive Income (Loss) Available To Common Stockholders Debt Disclosure [Abstract] Balloon Payments Longterm Debt Maturities Balloon Payments [Abstract] Long-term Debt, Maturities, Balloon Payments [Abstract] 2018 Long Term Debt Maturities Balloon Payments In Next Twelve Months Long-Term Debt, Maturities, Balloon Payments in Next Twelve Months 2019 Long-term Debt, Maturities, Balloon Payments In Year Two Long-term Debt, Maturities, Balloon Payments in Year Two 2020 Long-term Debt, Maturities, Balloon Payments In Year Three Long-term Debt, Maturities, Balloon Payments in Year Three 2021 Long-term Debt, Maturities, Balloon Payments in Year Four Long-term Debt Maturities Balloon Payments in Year Four 2022 Long-term Debt, Maturities, Balloon Payments In Year Five Long-term Debt, Maturities, Balloon Payments in Year Five Thereafter Long Term Debt Maturities Balloon Payments After Year Five Long-Term Debt, Maturities, Balloon Payments after Year Five Balloon Payments Long Term Debt Balloon Payments Long-Term Debt, Balloon Payments Scheduled Principal Amortization Long-term Debt, Fiscal Year Maturity [Abstract] 2018 Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months 2019 Long-term Debt, Maturities, Repayments of Principal in Year Two 2020 Long-term Debt, Maturities, Repayments of Principal in Year Three 2021 Long-term Debt, Maturities, Repayments of Principal in Year Four 2022 Long-term Debt, Maturities, Repayments of Principal in Year Five Thereafter Long-term Debt, Maturities, Repayments of Principal after Year Five Scheduled Principal Amortization Long-term Debt Total Long Term Debt Maturities Repayments Of Principal And Balloon Payments [Abstract] Long-Term Debt, Maturities, Repayments of Principal and Balloon Payments [Abstract] 2018 Long Term Debt Maturities Repayments Of Principal And Balloon Payments In Next Twelve Months Long-Term Debt, Maturities, Repayments of Principal and Balloon Payments in Next Twelve Months 2019 Long-term Debt, Maturities, Repayments Of Principal And Balloon Payments In Year Two Long-term Debt, Maturities, Repayments of Principal and Balloon Payments in Year Two 2020 Long-term Debt, Maturities, Repayments Of Principal And Balloon Payments In Year Three Long-term Debt, Maturities, Repayments of Principal and Balloon Payments in Year Three 2021 Long-term Debt, Maturities, Repayments Of Principal And Balloon Payments In Year Four Long-term Debt, Maturities, Repayments of Principal and Balloon Payments in Year Four 2022 Long-term Debt, Maturities, Repayments Of Principal And Balloon Payments In Year Five Long-term Debt, Maturities, Repayments of Principal and Balloon Payments in Year Five Thereafter Long Term Debt Maturities Repayments Of Principal And Balloon Payments After Year Five Long-Term Debt, Maturities, Repayments of Principal and Balloon Payments after Year Five Principal amount Long-term Debt Repayments Of Principal And Balloon Payments Long-term Debt, Repayments of Principal and Balloon Payments Unamortized deferred debt costs Debt Issuance Costs, Net Net Long-term Repayments of Principal and Balloon Payments, Net of Debt Issuance Costs Long-term Repayments of Principal and Balloon Payments, Net of Debt Issuance Costs Mortgage Notes Payable, Revolving Credit Facility, Interest Expense and Amortization of Deferred Debt Costs Debt Disclosure [Text Block] Subsequent Events [Abstract] Subsequent Events Subsequent Events [Text Block] Schedule of Real Estate Properties [Table] Schedule of Real Estate Properties [Table] Real Estate Property Ownership [Axis] Real Estate Property Ownership [Axis] Real Estate Properties [Domain] Real Estate Properties [Domain] 750 N. Glebe Road Seven Fifty N Glebe Road [Member] Seven Fifty N Glebe Road [Member] 730 N. Glebe Road Seven Thirty N Glebe Road [Member] Seven Thirty N Glebe Road [Member] 726 N Glebe Road Seven Twenty Six N Glebe Road [Member] Seven Twenty Six N Glebe Road [Member] 700 N. Glebe Road Seven Hundred N Glebe Road [Member] Seven Hundred N Glebe Road [Member] Westview Pad Westview Pad [Member] Westview Pad [Member] Thruway Pad Thruway Pad [Member] Thruway Pad [Member] Beacon Center Beacon Center [Member] Beacon Center [Member] Southdale Southdale [Member] Southdale [Member] Burtonsville Town Square Burtonsville Town Square [Member] Burtonsville Town Square [Member] 2016 Acquisitions 2016 Acquisitions [Member] 2016 Acquisitions [Member] Olney Olney [Member] Olney [Member] In-place Leases Leases, Acquired-in-Place [Member] Above Market Rent Below Market Rent Below Market Leases [Member] Below Market Leases [Member] Real Estate Properties [Line Items] Real Estate Properties [Line Items] Payments to acquire real estate Payments to Acquire Real Estate Acquisition costs Real Estate Inventory, Acquisition Costs Real Estate Inventory, Acquisition Costs Area of real estate property (in square feet) Area of Real Estate Property Rent expense Operating Leases, Rent Expense, Net Mortgage loans on real estate, period increase (decrease) Mortgage Loans on Real Estate, Period Increase (Decrease) Number of properties acquired Real Estate, Number of Properties Acquired Real Estate, Number Of Properties Acquired Purchase price allocated to land Land and Land Improvements Purchase price allocated to buildings Buildings and Improvements, Gross Leasehold Interests Real Estate Investments, Other Intangible assets gross carrying amount Finite-Lived Intangible Assets, Gross Intangible assets, accumulated amortization Finite-Lived Intangible Assets, Accumulated Amortization Amortization expense Amortization of Intangible Assets Below market lease, carrying amount Below Market Lease, Gross Below market lease, accumulated amortization Below Market Lease, Accumulated Amortization Accretion income, intangible liabilities Amortization of Below Market Lease Weighted-average amortization period Finite-Lived Intangible Assets, Remaining Amortization Period Distributions Distributions Disclosure [Text Block] Distributions Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Dividend declared Dividend Declared [Member] Statement [Line Items] Statement [Line Items] Common Stock Shares Issued (in shares) Shares issued to directors (in shares) Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures Issuance of partnership units pursuant to dividend reinvestment plan (in shares) Distributions payable on preferred stock (in usd per share) Preferred Stock, Dividends Per Share, Declared Distributions payable common stock and partnership units (in usd per share) Common Stock, Dividends, Per Share, Declared Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Outstanding at January 1 (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Exercised (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Expired/Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period Outstanding December 31 (in shares) Options exercisable (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Weighted Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] Outstanding at January 1 (in usd per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Granted (in usd per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Exercised (in usd per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Expired/Forfeited (in usd per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price Outstanding December 31 (in usd per share) Exercisable at December 31 (in usd per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Intrinsic value of options exercised Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value Intrinsic value of options outstanding Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Intrinsic value of options exercisable Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Closing price (in usd per share) Share Price Weighted average remaining life of options exercisable Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Weighted average remaining life of options outstanding Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Preferred Stock Preferred Stock [Member] Common Stock Common Stock [Member] Additional Paid-in Capital Additional Paid-in Capital [Member] Accumulated Deficit Retained Earnings [Member] Accumulated Other Comprehensive (Loss) AOCI Attributable to Parent [Member] Total Saul Centers, Inc. Parent [Member] Noncontrolling Interests Noncontrolling Interest [Member] Dividend paid Dividend Paid [Member] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning balance Issuance of common stock: Common Stock Transactions [Abstract] Common Stock Transactions [Abstract] Shares issued pursuant to dividend reinvestment plan Stock Issued During Period, Value, Dividend Reinvestment Plan Shares issued due to exercise of employee stock options and issuance of directors' deferred stock Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures Issuance of partnership units pursuant to dividend reinvestment plan Limited Partner's Units Issued During Period, Value, Dividend Reinvestment Plan Limited Partner's Units Issued During Period, Value, Dividend Reinvestment Plan Change in unrealized loss on cash flow hedge Preferred stock distributions: Dividends, Preferred Stock [Abstract] Preferred stock distributions Dividends, Preferred Stock, Cash Common stock distributions Dividends, Common Stock, Cash Distributions payable common stock and distributions payable partnership units Dividends, Common Stock Ending balance Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table] Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] the 1993 Plan Stock Option Plan Nineteen Ninety Three [Member] Stock Option Plan Nineteen Ninety Three [Member] Amended 2004 Plan Amended Stock Option Plan Twenty Zero Four [Member] Amended Stock Option Plan Twenty Zero Four [Member] 2008 Options Stock Option Plan Twenty Zero Eight [Member] Stock Option Plan 2008 [Member] 2009 Options Stock Option Plan Twenty Zero Nine [Member] Stock Option Plan 2009 [Member] 2010 Options Stock Option Plan Twenty Ten [Member] Stock Option Plan 2010 [Member] 2011 Options Stock Option Plan Twenty Eleven [Member] Stock Option Plan 2011 [Member] 2012 Options Stock Option Plan Twenty Twelve [Member] Stock Option Plan 2012 [Member] 2013 Options Stock Option Plan 2013 [Member] Stock Option Plan 2013 [Member] 2014 Options Stock Option Plan Twenty Fourteen [Member] Stock Option Plan Twenty Fourteen [Member] 2015 Options Stock Option Plan Twenty Fifteen [Member] Stock Option Plan Twenty Fifteen [Member] 2016 Options 2016 Options [Member] 2016 Options [Member] 2017 Options 2017 Options [Member] 2017 Options [Member] Award Type [Axis] Award Type [Axis] Award Type [Domain] Equity Award [Domain] Stock options Employee Stock Option [Member] Incentive stock option Incentive Stock Option [Member] Incentive Stock Option [Member] Nonqualified stock options Nonqualified Stock Options [Member] Nonqualified Stock Options [Member] Title of Individual [Axis] Title of Individual [Axis] Title of Individual with Relationship to Entity [Domain] Relationship to Entity [Domain] Officer Officer [Member] Director Director [Member] Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] Authorized shares for a grant (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Options granted to purchase stocks (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures Number of individuals granted options Share Based Compensation Arrangement By Share Based Payment Award Number Of Employees Granted Awards Share Based Compensation Arrangement By Share Based Payment Award Number Of Employees Granted Awards Exercise price of options (in usd per share) Fair value stock option grant Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Fair Value Share based Compensation Arrangement by Share based Payment Award, Options, Grants in Period, Fair Value Options vested Share Based Compensation Arrangement By Share Based Payment Award Options Vested Percentage Share Based Compensation Arrangement By Share Based Payment Award Options Vested Percentage Option vesting period Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period SEC Schedule III, Real Estate and Accumulated Depreciation Disclosure [Abstract] Major Property Class [Axis] Major Property Class [Axis] Major Property Class [Domain] Major Property Class [Domain] Development Land Development Land [Member] Development Land [Member] Ashburn Village, Ashburn, VA Real Estate Property One [Member] Real Estate Property One [Member] Ashland Square Phase I, Dumfries, VA Real Estate Property Two [Member] Real Estate Property Two [Member] Beacon Center, Alexandria, VA Real Estate Property Three [Member] Real Estate Property Three [Member] BJ’s Wholesale Club, Alexandria, VA Real Estate Property Four [Member] Real Estate Property Four [Member] Boca Valley Plaza, Boca Raton, FL Real Estate Property Five [Member] Real Estate Property Five [Member] Boulevard, Fairfax, VA Real Estate Property Six [Member] Real Estate Property Six Briggs Chaney MarketPlace, Silver Spring, MD Real Estate Property Seven [Member] Real Estate Property Seven [Member] Broadlands Village, Ashburn, VA Real Estate Property Eight [Member] Real Estate Property Eight [Member] Burtonsville Town Square, Burtonsville, MD Real Estate Property Nine [Member] Real Estate Property Nine [Member] Countryside Marketplace, Sterling, VA Real Estate Property Ten [Member] Real Estate Property Ten [Member] Cranberry Square, Westminster, MD Real Estate Property Eleven [Member] Real Estate Property Eleven [Member] Cruse MarketPlace, Cumming, GA Real Estate Property Twelve [Member] Real Estate Property Twelve [Member] Flagship Center, Rockville, MD Real Estate Property Thirteen [Member] Real Estate Property Thirteen [Member] French Market, Oklahoma City, OK Real Estate Property Fourteen [Member] Real Estate Property Fourteen [Member] Germantown, Germantown, MD Real Estate Property Fifteen [Member] Real Estate Property Fifteen [Member] The Glen, Woodbridge, VA Real Estate Property Sixteen [Member] Real Estate Property Sixteen [Member] Great Falls Center, Great Falls, VA Real Estate Property Eighteen [Member] Real Estate Property Eighteen [Member] Hampshire Langley, Takoma, MD Real Estate Property Nineteen [Member] Real Estate Property Nineteen [Member] Hunt Club Corners, Apopka, FL Real Estate Property Twenty [Member] Real Estate Property Twenty [Member] Jamestown Place, Altamonte Springs, FL Real Estate Property Twenty One [Member] Real Estate Property Twenty One [Member] Kentlands Square I, Gaithersburg, MD Real Estate Property Twenty Two [Member] Real Estate Property Twenty Two [Member] Kentlands Square II, Gaithersburg, MD Real Estate Property Twenty Three [Member] Real Estate Property Twenty Three [Member] Kentlands Place, Gaithersburg, MD Real Estate Property Twenty Four [Member] Real Estate Property Twenty Four [Member] Lansdowne Town Center, Leesburg, VA Real Estate Property Twenty Five [Member] Real Estate Property Twenty Five [Member] Leesburg Pike Plaza, Baileys Crossroads, VA Real Estate Property Twenty Six [Member] Real Estate Property Twenty Six [Member] Lumberton Plaza, Lumberton, NJ Real Estate Property Twenty Seven [Member] Real Estate Property Twenty Seven [Member] Metro Pike Center, Rockville, MD Real Estate Property Twenty Eight [Member] Real Estate Property Twenty Eight [Member] Shops at Monocacy, Frederick, MD Real Estate Property Twenty Nine [Member] Real Estate Property Twenty Nine [Member] Northrock, Warrenton, VA Real Estate Property Thirty [Member] Real Estate Property Thirty [Member] Olde Forte Village, Ft. Washington, MD Real Estate Property Thirty One [Member] Real Estate Property Thirty One [Member] Olney, Olney, MD Real Estate Property Thirty Two [Member] Real Estate Property Thirty Two [Member] Orchard Park, Dunwoody, GA Real Estate Property Thirty Three [Member] Real Estate Property Thirty Three [Member] Palm Springs Center, Altamonte Springs, FL Real Estate Property Thirty Four [Member] Real Estate Property Thirty Four [Member] Ravenwood, Baltimore, MD Real Estate Property Thirty Five [Member] Real Estate Property Thirty Five [Member] 11503 Rockville Pike/5541 Nicholson Lane, Rockville, MD Real Estate Property Thirty Six [Member] Real Estate Property Thirty Six [Member] 1500/1580/1582/1584 Rockville Pike, Rockville, MD Real Estate Property Thirty Seven [Member] Real Estate Property Thirty Seven [Member] Seabreeze Plaza, Palm Harbor, FL Real Estate Property Thirty Eight [Member] Real Estate Property Thirty Eight [Member] Market Place at Sea Colony, Bethany Beach, DE Real Estate Property Thirty Nine [Member] Real Estate Property Thirty Nine [Member] Seven Corners, Falls Church, VA Real Estate Property Forty [Member] Real Estate Property Forty [Member] Severna Park Marketplace, Severna Park, MD Real Estate Property Forty One [Member] Real Estate Property Forty One [Member] Shops at Fairfax, Fairfax, VA Real Estate Property Forty Two [Member] Real Estate Property Forty Two [Member] Smallwood Village Center, Waldorf, MD Real Estate Property Forty Three [Member] Real Estate Property Forty Three [Member] Southdale, Glen Burnie, MD Real Estate Property Forty Four [Member] Real Estate Property Forty Four [Member] Southside Plaza, Richmond, VA Real Estate Property Forty Five [Member] Real Estate Property Forty Five [Member] South Dekalb Plaza, Atlanta, GA Real Estate Property Forty Six [Member] Real Estate Property Forty Six [Member] Thruway, Winston-Salem, NC Real Estate Property Forty Seven [Member] Real Estate Property Forty Seven [Member] Village Center, Centreville, VA Real Estate Property Forty Eight [Member] Real Estate Property Forty Eight [Member] Westview Village, Frederick, MD Real Estate Property Forty Nine [Member] Real Estate Property Forty Nine [Member] White Oak, Silver Spring, MD Real Estate Property Fifty [Member] Real Estate Property Fifty [Member] Other Buildings / Improvements Other Real Estate [Member] Other Real Estate [Member] Avenel Business Park, Gaithersburg, MD Real Estate Property Fifty One [Member] Real Estate Property Fifty One [Member] Clarendon Center, Arlington, VA (1) Real Estate Property Fifty Two [Member] Real Estate Property Fifty Two [Member] Park Van Ness, Washington, DC Park Van Ness [Member] Park Van Ness [Member] 601 Pennsylvania Ave., Washington, DC Real Estate Property Fifty Four [Member] Real Estate Property Fifty Four [Member] Washington Square, Alexandria, VA Real Estate Property Fifty Six [Member] Real Estate Property Fifty Six [Member] Ashland Square Phase II, Manassas, VA Real Estate Property Fifty Seven [Member] Real Estate Property Fifty Seven [Member] New Market, New Market, MD Real Estate Property Fifty Eight [Member] Real Estate Property Fifty Eight [Member] North Glebe Road, Arlington, VA 750/730/726 North Glebe, Arlington, VA [Member] [Member] 750/730/726 North Glebe, Arlington, VA [Member] Real Estate and Accumulated Depreciation Schedule [Axis] Real Estate and Accumulated Depreciation Schedule [Axis] Real Estate and Accumulated Depreciation Schedule [Axis] Real Estate and Accumulated Depreciation Schedule [Domain] Real Estate and Accumulated Depreciation Schedule [Domain] [Domain] for Real Estate and Accumulated Depreciation Schedule [Axis] Acquisition Date One Acquisition Date One [Member] Acquisition Date One [Member] Acquisition Date Two Acquisition Date Two [Member] Acquisition Date Two [Member] Acquisition Date Three Acquisition Date Three [Member] Acquisition Date Three [Member] Acquisition Date Four Acquisition Date Four [Member] Acquisition Date Four [Member] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Initial Basis Real Estate Investment Property Cost Initial Basis Real Estate Investment Property Cost, Initial Basis Cost capitalized subsequent to acquisition Real Estate Investment Property Cost Capitalized Subsequent To Acquisition Real Estate Investment Property Cost, Capitalized Subsequent To Acquisition Land Buildings Total Purchase Price Accumulated Depreciation Book Value Related Debt Development land, related debt Total, related debt Secured Debt, Including Construction Loan Secured Debt, Including Construction Loan Buildings and Improvements Depreciable Lives in Years Property, Plant and Equipment, Useful Life Total real estate investments: SEC Schedule III, Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward] Balance, beginning of year Acquisitions SEC Schedule III, Real Estate, Other Acquisitions Improvements SEC Schedule III, Real Estate, Improvements Retirements SEC Schedule III, Real Estate, Other Deductions Transfers to assets held for sale SEC III, Real Estate, Transfers to Assets Held for Sale SEC III, Real Estate, Transfers to Assets Held for Sale Balance, end of year Total accumulated depreciation: SEC Schedule III, Reconciliation of Real Estate Accumulated Depreciation [Roll Forward] Balance, beginning of year Depreciation expense SEC Schedule III, Real Estate Accumulated Depreciation, Depreciation Expense Retirements SEC Schedule III, Real Estate Accumulated Depreciation, Other Deductions Transfers to assets held for sale SEC Schedule III, Real Estate Accumulated Depreciation, Transfers to Assets Held for Sale SEC Schedule III, Real Estate Accumulated Depreciation, Transfers to Assets Held for Sale Balance, end of year Property Plant and Equipment Estimated Useful Lives [Table] Property Plant And Equipment Estimated Useful Lives [Table] Property Plant and Equipment Estimated Useful Lives [Table] 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Glebe Road Glebe Road [Member] Glebe Road [Member] Other Other Property [Member] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Notes Payable [Table] Notes Payable [Table] Notes Payable [Table] Real Estate Property Name [Axis] Real Estate Property Name [Axis] Real Estate Property Name [Axis] Real Estate Property Name [Domain] Real Estate Property Name [Domain] [Domain] for Real Estate Property Name [Axis] Shops at Fairfax and Boulevard Shops at Fairfax and Boulevard [Member] Shops at Fairfax and Boulevard [Member] Northrock Northrock [Member] Northrock [Member] Variable rate loans payable Variable Rate Loans Payable [Member] Variable Rate Loans Payable [Member] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] 6.01% due February 2018 Six Point Zero One Maturing February Twenty Eighteen [Member] Six Point Zero One Maturing February Twenty Eighteen [Member] 5.88% due January 2019 Five Point Eight Eight Maturing January Twenty Nineteen [Member] Five Point Eight Eight Maturing January Twenty Nineteen [Member] 5.76% due May 2019 Five Point Seven Six Maturing May Twenty Nineteen [Member] Five Point Seven Six Maturing May Twenty Nineteen [Member] 5.62% due July 2019 Five Point Six Two Maturing July Twenty Nineteen [Member] Five Point Six Two Maturing July Twenty Nineteen [Member] 5.79% due September 2019 Five Point Seven Nine Maturing September Twenty Nineteen [Member] Five Point Seven Nine Maturing September Twenty Nineteen [Member] 5.22% due January 2020 Five Point Two Two Maturing January Twenty Twenty [Member] Five Point Two Two Maturing January Twenty Twenty [Member] 5.60% due May 2020 Five Point Six Zero Maturing May Twenty Twenty [Member] Five Point Six Zero Maturing May Twenty Twenty [Member] 5.30% due June 2020 Five Point Three Zero Maturing June Twenty Twenty [Member] Five Point Three Zero Maturing June Twenty Twenty [Member] 5.83% due July 2020 Five Point 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Twenty Four [Member] 7.35% due June 2024 Seven Point Three Five Maturing June Twenty Twenty Four [Member] Seven Point three Five Maturing June Twenty Twenty Four [Member] 7.60% due June 2024 Seven Point Six Zero Maturing June Twenty Twenty Four [Member] Seven Point Six Zero Maturing June Twenty Twenty Four [Member] 7.02% due July 2024 Seven Point Zero Two Maturing July Twenty Twenty Four [Member] Seven Point Zero Two Maturing July Twenty Twenty Four [Member] 7.45% due July 2024 Seven Point Four Five Maturing July Twenty Twenty Four [Member] Seven Point Four Five Maturing July Twenty Twenty Four [Member] 7.30% due January 2025 Seven Point Three Zero Maturing July Twenty Twenty Five [Member] Seven Point Three Zero Maturing July Twenty Twenty Five [Member] 6.18% due January 2026 Six Point One Eight Maturing January Twenty Twenty Six [Member] Six Point One Eight Maturing January Twenty Twenty Six [Member] 5.31% due April 2026 Five Point Three One Maturing April Twenty Twenty Six [Member] Five Point Three One Maturing April Twenty Twenty Six [Member] 4.30% due October 2026 Four Point Three Zero Maturing October Twenty Twenty Six [Member] Four Point Three Zero Maturing October Twenty Twenty Six [Member] 4.53% due November 2026 Four Point Five Three Maturing November Twenty Twenty Six [Member] Four Point Five Three Maturing November Twenty Twenty Six [Member] 4.70% due December 2026 Four Point Seven Zero Maturing December Twenty Twenty Six [Member] Four Point Seven Zero Maturing December Twenty Twenty Six [Member] 5.84% due May 2027 Five Point Eight Four Maturing May Twenty Twenty Seven [Member] Five Point Eight Four Maturing May Twenty Twenty Seven [Member] 4.04% due April 2028 Four Point Zero Four Maturing April Twenty Twenty Eight [Member] Four Point Zero Four Maturing April Twenty Twenty Eight [Member] 3.51% due June 2028 Three Point Five One Maturing June Twenty Twenty Eight [Member] Three Point Five One Maturing June Twenty Twenty Eight [Member] 3.99% due September 2028 Three Point Nine Nine Maturing September Twenty Twenty Eight [Member] Three Point Nine Nine Maturing September Twenty Twenty Eight [Member] 3.69% Due March 2030 Three Point Six Nine Percent Due March Twenty Thirty [Member] Three Point Six Nine Percent Due March Twenty Thirty [Member] 3.99% Due April 2030 Three Point Ninety Nine Due April Twenty Thirty [Member] Three Point Ninety Nine Due April Twenty Thirty [Member] 3.39% due January 2032 Three Point Three Nine Maturing February Twenty Thirty Two [Member] Three Point Three Nine Maturing February Twenty Thirty Two [Member] 4.88% due September 2032 Four Point Eight Eight Maturing September Twenty Thirty Two [Member] Four Point Eight Eight Maturing September Twenty Thirty Two [Member] 3.75% due December 2032 Three Point Seven Five Maturing December Twenty Thirty Two [Member] Three Point Seven Five Maturing December Twenty Thirty Two [Member] 8.00% due April 2034 Eight Percent due April 2034 [Member] Eight Percent due April 2034 [Member] Revolving credit facility Unsecured Revolving Credit Facility [Member] Unsecured Revolving Credit Facility [Member] Metro Pike Center Bank Loan Metro Pike Center Bank Loan [Member] Metro Pike Center Bank Loan [Member] Notes Payable [Line Items] Notes Payable [Line Items] Notes Payable [Line Items] Variable rate debt Loans Payable Interest rate spread on LIBOR Debt Instrument, Basis Spread on Variable Rate Scheduled maturity period Debt Instrument Maturity Period Debt Instrument Maturity Period Total notes payable Notes and Loans Payable Interest rate during period Debt Instrument, Interest Rate During Period Business Segments Segment Reporting Disclosure [Text Block] Document And Entity Information [Abstract] Document And Entity Information [Abstract] Document type Document Type Amendment flag Amendment Flag Document period end date Document Period End Date Document fiscal year focus Document Fiscal Year Focus Document fiscal period focus Document Fiscal Period Focus Trading symbol Trading Symbol Entity registrant name Entity Registrant Name Entity central index key Entity Central Index Key Current fiscal year end date Current Fiscal Year End Date Entity well-known seasoned issuer Entity Well-known Seasoned Issuer Entity current reporting status Entity Current Reporting Status Entity voluntary filers Entity Voluntary Filers Entity filer category Entity Filer Category Entity common stock, shares outstanding Entity Common Stock, Shares Outstanding Entity public float Entity Public Float Washington Square Washington Square [Member] Washington Square [Member] Broadlands Village, The Glen and Kentlands Square I Broadlands Village, The Glen and Kentlands Square I [Member] Broadlands Village, The Glen and Kentlands Square I [Member] Olde Forte Village Olde Forte Village [Member] Olde Forte Village [Member] Countryside Countryside [Member] Countryside [Member] Briggs Chancy MarketPlace Briggs Chancy MarketPlace [Member] Briggs Chancy MarketPlace [Member] Shops at Monocacy Shops at Monocacy [Member] Shops at Monocacy [Member] Boca Valley Plaza Boca Valley Plaza [Member] Boca Valley Plaza [Member] Palm Springs Center Palm Springs Center [Member] Palm Springs Center [Member] Thruway Thruway [Member] Thruway [Member] Jamestown Place Jamestown Place [Member] Jamestown Place [Member] Hunt Club Corners Hunt Club Corners [Member] Hunt Club Corners [Member] Landsowne Town Center Landsowne Town Center [Member] Landsowne Town Center [Member] Orchard Park Orchard Park [Member] Orchard Park [Member] BJs Wholesale BJs Wholesale [Member] BJ's Wholesale [Member] Great Falls Shopping Center Great Falls Shopping Center [Member] Great Falls Shopping Center [Member] Leesburg Pike Leesburg Pike [Member] Leesburg Pike [Member] Village Center Village Center [Member] Village Center [Member] White Oak Shopping Center White Oak Shopping Center [Member] White Oak Shopping Center [Member] Avenel Business Park Avenel Business Park [Member] Avenel Business Park [Member] Ashburn Village Ashburn Village [Member] Ashburn Village [Member] Ravenwood Ravenwood [Member] Ravenwood [Member] Clarendon Center Clarendon Center [Member] Clarendon Center [Member] Severna Park Market Place Severna Park Marketplace [Member] Severna Park Marketplace Kentlands Square II Kentlands Square II [Member] Kentlands Square II [Member] Cranberry Square Cranberry Square [Member] Cranberry Square [Member] Seven Corners Seven Corners [Member] Seven Corners Hampshire Langley Hampshire Langley [Member] Hampshire Langley [Member] Seabreeze Plaza Seabreeze Plaza [Member] Seabreeze Plaza [Member] Park Van Ness Metro Pike Center Metro Pike Center [Member] Metro Pike Center [Member] Principal and interest payments Debt Instrument, Periodic Payment Balloon payment to be paid Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid Amortization period Debt Instrument Amortization Periods Debt Instrument Amortization Periods Loan amount Debt Instrument, Face Amount Number of shopping centers Number Of Shopping Centers Number Of Shopping Centers Amortization of principal Long-term Debt, Maturities, Repayments of Principal, Remainder of Fiscal Year Number of notes Number Of Notes Number of Notes Fixed rate increase on note Fixed Rate Increase on Note Fixed Rate Increase on Note - Annual increase on amount due under notes payable Negative amortization Amortization of Debt Discount (Premium) Line of credit facility, maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Debt maturity extension period Debt Instrument Potential Term Extension Period Debt Instrument, Potential Term Extension Period Debt instrument fee Debt Instrument Fee Percentage Debt Instrument, Fee, Percentage Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Statement of Cash Flows [Abstract] Great Eastern Shopping Center Great Eastern Shopping Center [Member] Great Eastern Shopping 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Increase (Decrease) in Other Operating Assets Increase (decrease) in accounts payable, accrued expenses and other liabilities Increase Decrease In Accounts Payable Accrued Expenses And Other Liabilities The net change during the reporting period in the aggregate amount of accounts payable accrued expenses and other liabilities incurred but not paid. Decrease in deferred income Increase (Decrease) in Deferred Income Taxes 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] Acquisitions of real estate investments Payments to Acquire Other Real Estate Additions to real estate investments Additions to development and redevelopment projects Payments to Develop Real Estate Assets Proceeds from sale of properties Proceeds from Sale of Real Estate Held-for-investment 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] Proceeds from mortgage notes payable Proceeds from Issuance of Secured Debt Repayments on mortgage notes payable Repayments of Secured Debt Proceeds from construction loans payable Proceeds from Construction Loans Payable Proceeds from revolving credit facility Proceeds from Lines of Credit Repayments on revolving credit facility Repayments of Lines of Credit Additions to deferred debt costs Payments of Debt Issuance Costs Proceeds from the issuance of: Proceeds from Issuance or Sale of Equity [Abstract] Common stock Proceeds from Issuance of Common Stock Partnership units Proceeds from Sale of Interest in Partnership Unit Distributions to: Payments of Dividends [Abstract] Series C preferred stockholders Common stockholders Noncontrolling interests Distributions To Noncontrolling Interest Distributions To Noncontrolling Interest Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities Net increase (decrease) in cash and cash equivalents Cash and Cash Equivalents, Period Increase (Decrease) Cash and cash equivalents, beginning of year Cash and cash equivalents, end of year Supplemental disclosure of cash flow information: Supplemental Cash Flow Information [Abstract] Cash paid for interest Interest Paid Increase (decrease) in accrued real estate investments and development costs Noncash or Part Noncash Increase (Decrease) In Accrued Real Estate Investments And Development Costs Noncash or Part Noncash Increase (Decrease) in Real Estate Investments and Development Costs Significant Accounting Policies [Table] Significant Accounting Policies [Table] Significant Accounting Policies [Table] Glebe Road Construction Loan Glebe Road Construction Loan [Member] Glebe Road Construction Loan [Member] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Revenue Sales Revenue, Services, Net [Member] Major Customers [Axis] Customer [Axis] Name of Major Customer [Domain] Customer [Domain] Giant Food Giant Food [Member] Giant Food [Member] Capital One Capital One [Member] Capital One [Member] Long Lived Assets Held-for-sale by Asset Type [Axis] Long Lived Assets Held-for-sale by Asset 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Accumulated Amortization Amortization expense deferred leasing cost Amortization of Deferred Leasing Fees Allowance for doubtful accounts receivables Accounts receivable, net representing rental income accrued Accrued Fees and Other Revenue Receivable Allowance for doubtful accounts receivables representing rental income accrued Allowance for Doubtful Accounts, Premiums and Other Receivables Number of real estate properties Net rentable area (in square feet) Net Rentable Area Real estate held-for-sale Real Estate Held-for-sale Real estate, accumulated depreciation Real estate, costs to sell and liabilities Liabilities Held-for-sale, Amount Liabilities Held-for-sale, Amount Accumulated amortization Accumulated Amortization, Debt Issuance Costs Accrued penalties and interest Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued Tax basis of the company's real estate investments SEC Schedule III, Real Estate, Federal Income Tax Basis Shares credited to deferred fee accounts (in shares) Deferred Compensation Arrangement with Individual, Shares Issued Shares issued to directors Allocated Share-based Compensation Expense Schedule of construction in progress Schedule of Construction in Progress [Table Text Block] Schedule of Construction in Progress [Table Text Block] Allowance for doubtful accounts Allowance For Doubtful Accounts [Table Text Block] Allowance for Doubtful Accounts, Table Basic and diluted shares outstanding Schedule of Weighted Average Number of Shares [Table Text Block] Real estate and accumulated depreciation SEC Schedule III, Real Estate and Accumulated Depreciation Disclosure [Text Block] Summary of results of operations for quarterly periods Quarterly Financial Information [Table Text Block] Real estate investments for federal income tax Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Scenario [Axis] Scenario [Axis] Scenario, Unspecified [Domain] Scenario, Unspecified [Domain] Scenario, Forecast Scenario, Forecast [Member] Kentlands Square II Bank Loan Kentlands Square II Bank Loan [Member] Kentlands Square II Bank Loan [Member] Burtonsville Fixed Rate Mortgage Burtonsville Fixed Rate Mortgage [Member] Burtonsville Fixed Rate Mortgage [Member] Park Van Ness Loan Park Van Ness Loan [Member] Park Van Ness Loan [Member] Washington Square 2017 Mortgage Washington Square 2017 Mortgage [Member] Washington Square 2017 Mortgage [Member] Debt Covenant Debt Covenant [Member] Debt Covenant [Member] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Unsecured Revolving Credit Facility Revolving Credit Facility Revolving Credit Facility [Member] Line of Credit Line of Credit [Member] 4.67% Construction To Permanent Loan Due 2035 Four Point Six Seven Percent Construction To Permanent Loan Due Twenty Thirty Five [Member] Four Point Six Seven Percent Construction To Permanent Loan Due Twenty Thirty Five [Member] Mortgage Notes Payable Mortgage Notes Payable [Member] Mortgage Notes Payable [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Outstanding debt Secured Debt, Other Principal amount Debt outstanding with fixed-rate Long-term Debt, Percentage Bearing Fixed Interest, Amount Debt outstanding with variable-rate Long-term Debt, Percentage Bearing Variable Interest, Amount Extension in line of credit facility period Line Of Credit Facility Potential Term Extension Period Line of Credit Facility Potential Term Extension Period Available borrowing capacity Line of Credit Facility, Remaining Borrowing Capacity Outstanding line of credit Long-term Debt, Gross Letter of credit available borrowing capacity Letter Of Credit Facilities Maximum Borrowing Capacity Letter of Credit Facilities, Maximum Borrowing Capacity Guarantor obligations, maximum exposure Guarantor Obligations, Maximum Exposure, Undiscounted Remaining loan balance Loan term Debt Instrument, Term Loan fixed interest rate Debt Instrument, 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Issuance Costs, Gross Stock Option Plan Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Fair Value of Financial Instruments Fair Value Disclosures [Text Block] Intangible assets Leases Disclosure [Table] Leases Disclosure [Table] Leases Disclosure [Table] Flagship Center Flagship Center [Member] Flagship Center [Member] Capitalized Cost By Type [Axis] Capitalized Cost By Type [Axis] Capitalized Cost By Type [Axis] Capitalized Cost By Type [Domain] Capitalized Cost By Type [Domain] Capitalized Cost By Type [Domain] 90-year Ground Leasehold Interest Ninety Year Ground Lease [Member] Ninety Year Ground Lease [Member] 99-year Ground Lease Ninety Nine Year Ground Lease [Member] Ninety Nine Year Ground Lease [Member] Leases Disclosure [Line Items] Leases Disclosure [Line Items] Leases Disclosure [Line Items] Number of properties subject to noncancelable long-term lease Lessee Leasing Arrangements, Number of Properties Under Lease Lessee Leasing Arrangements, 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