Statement of Financial Position [Abstract] Rents and other receivables, allowance for doubtful accounts Allowance for Doubtful Accounts, Premiums and Other Receivables Preferred shares, par value (in dollars per share) Preferred Stock, Par or Stated Value Per Share Preferred shares, shares authorized (in shares) Preferred Stock, Shares Authorized Preferred shares, shares issued (in shares) Preferred Stock, Shares Issued Preferred shares, shares outstanding (in shares) Preferred Stock, Shares Outstanding Shares of beneficial interest, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Shares of beneficial interest, shares authorized (in shares) Common Stock, Shares Authorized Shares of beneficial interest, shares issued (in shares) Common Stock, Shares, Issued Shares of beneficial interest, shares outstanding (in shares) Common Stock, Shares, Outstanding Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative Instruments, Gain (Loss) [Table] Derivative Instruments, Gain (Loss) [Table] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Interest Rate Swap [Member] Interest Rate Swap [Member] Derivative Instruments, Gain (Loss) [Line Items] Derivative Instruments, Gain (Loss) [Line Items] Unrealized gain (loss) on interest rate hedges Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax Share-based Compensation [Abstract] Stock Based Compensation Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Real Estate [Abstract] Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] Disposal Group Classification [Axis] Disposal Group Classification [Axis] Disposal Group Classification [Domain] Disposal Group Classification [Domain] Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] Disposal Group Name [Axis] Disposal Group Name [Axis] Disposal Group Name [Domain] Disposal Group Name [Domain] 2018 Properties Sold Group [Member] Two Thousand Eighteen Properties Sold Group [Member] Two Thousand Eighteen Properties Sold Group [Member] 2017 Properties Sold Group [Member] Two Thousand Seventeen Properties Sold Group [Member] Two Thousand Seventeen Properties Sold Group [Member] Name of Property [Axis] Name of Property [Domain] Braddock Metro Center [Member] Braddock Metro Center [Member] Braddock Metro Center [Member] M Street 2445 [Member] M Street 2445 [Member] 2445 M Street [Member] Walker House [Member] Walker House [Member] Walker House [Member] Real Estate, Type of Property [Axis] Real Estate, Type of Property [Axis] Real Estate [Domain] Real Estate [Domain] Office [Member] Office [Member] Office [Member] Multifamily [Member] Multifamily [Member] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Rentable Square Feet Area of Real Estate Property Number of Units Number of Units in Real Estate Property Contract Sales Price Disposal Group, Including Discontinued Operation, Consideration Gain on Sale Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal Initial contracted sales price Disposal Group, Including Discontinued Operation, Consideration, Initial Amount Initial amount of consideration receivable per agreement for the disposal of assets and liabilities, including discontinued operation. Real estate impairment Impairment of Real Estate Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Name of Property [Axis] Name of Property [Domain] Arlington Tower [Member] Arlington Tower [Member] Arlington Tower [Member] 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] Tenant Origination Costs [Member] Tenant Origination Costs Member Tenant Origination Costs [Member] Leasing Commissions Absorption Costs [Member] Leasing Commissions Absorption Costs Member Leasing Commissions/Absorption Costs [Member] Net Lease Intangible Assets [Member] net lease intangible assets [Member] net lease intangible assets [Member] Net Lease Intangible Liability [Member] net lease intangible liability [Member] net lease intangible liability [Member] Business Acquisition [Line Items] Business Acquisition [Line Items] Asset acquisition, transaction costs capitalized Asset Acquisition, Transaction Costs Capitalized Asset Acquisition, Transaction Costs Capitalized Weighted average useful life of acquisition components Acquired Finite-lived Intangible Assets, Weighted Average Useful Life Contract purchase price contract purchase price of real estate investment property, excludes capitalized acquisition cost contract purchase price of real estate investment property, excludes capitalized acquisition cost Payments to acquire real estate Payments to Acquire Real Estate Repayments of Secured Debt Repayments of Secured Debt Payments for deposits on real estate acquisitions Payments for Deposits on Real Estate Acquisitions Other payments to acquire businesses Asset Acquisition, Credit Received Or Granted At Settlement Asset Acquisition, Credit Received Or Granted At Settlement Real Estate [Table] Real Estate [Table] Real Estate [Line Items] Real Estate [Line Items] Land Land Building Buildings and Improvements, Gross Tenant origination costs Leasehold Improvements, Gross Leasing commissions/absorption costs Finite-Lived Intangible Asset, Acquired-in-Place Leases Lease intangible assets Finite-Lived Intangible Asset, Off-market Lease, Favorable, Gross Lease intangible liabilities Off-market Lease, Unfavorable Total Real Estate Investment Property, at Cost, Net of Adjustments Real Estate Investment Property, at Cost, Net of Adjustments Organization, Consolidation and Presentation of Financial Statements [Abstract] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Taxable Reit Subsidiary [Member] Taxable Reit Subsidiary [Member] Taxable Reit Subsidiary [Member] Percentage of distribution of ordinary taxable income Percentage of Distribution of Ordinary Taxable Income Percentage of Distribution of Ordinary Taxable Income Deferred tax asset Deferred Tax Assets, Gross Deferred tax asset, net of valuation allowance Deferred Tax Assets, Net of Valuation Allowance Deferred tax liabilities, net Deferred Tax Liabilities, Net Document and Entity Information [Abstract] Document and Entity Information [Abstract] 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 Filer Category Entity Filer Category Document Type Document Type Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Entity Emerging Growth Company Entity Emerging Growth Company Entity Small Business Entity Small Business Amendment Flag Amendment Flag Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding 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] Washington Real Estate Investment Trust 2016 Omnibus Incentive Plan [Member] Washington Real Estate Investment Trust 2016 Omnibus Incentive Plan [Member] Washington Real Estate Investment Trust 2016 Omnibus Incentive Plan [Member] Award Type [Axis] Award Type [Axis] Award Type [Domain] Equity Award [Domain] Restricted Share Awards Restricted Share Awards [Member] Restricted Share Awards [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Stock based plan, aggregate number of shares authorized (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Stock based plan, period in effect (in years) Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period Percent of relative TSR evaluated relative to peer companies Stock Based Plan, LTIP TSR Metric, Percent Of Relative TSR Evaluated Relative To Peer Companies Stock Based Plan, LTIP TSR Metric, Percent Of Relative TSR Evaluated Relative To Peer Companies Percent of relative TSR evaluated relative to FTSE NAREIT Diversified Index Stock Based Plan, LTIP TSR Metric, Percent Of Relative TSR Evaluated Relative To FTSE NAREIT Diversified Index Stock Based Plan, LTIP TSR Metric, Percent Of Relative TSR Evaluated Relative To FTSE NAREIT Diversified Index Percent of absolute TSR evaluated Stock Based Plan, LTIP TSR Metric, Percent Of Absolute TSR Stock Based Plan, LTIP TSR Metric, Percent Of Absolute TSR Performance period per amendment Stock Based Plan, Performance Period, Term Stock Based Plan, Performance Period, Term Stock based compensation expense Allocated Share-based Compensation Expense Fair value of share grants vested Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value Total unvested restricted share awards (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Weighted average grant date fair value (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Total compensation costs, non-vested restricted share awards Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized Total compensation cost not yet recognized, period for recognition (in months) Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Shares of Beneficial Interest at Par Value [Member] Common Stock [Member] Additional Paid-in Capital [Member] Additional Paid-in Capital [Member] Retained Earnings [Member] Retained Earnings [Member] AOCI Attributable to Parent [Member] AOCI Attributable to Parent [Member] Parent [Member] Parent [Member] Noncontrolling Interest [Member] Noncontrolling Interest [Member] Statement [Line Items] Statement [Line Items] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Balance (in shares) Shares, Outstanding Balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Net income attributable to the controlling interests Net Income (Loss) Attributable to Parent Unrealized gain on interest rate hedges Other Comprehensive Income (Loss), Net of Tax Distributions to noncontrolling interests Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Dividends Dividends Stock Issued During Period, Shares, New Issues Stock Issued During Period, Shares, New Issues Stock Issued During Period, Value, New Issues Stock Issued During Period, Value, New Issues Shares issued under dividend reinvestment program (in shares) Stock Issued During Period, Shares, Dividend Reinvestment Plan Shares issued under dividend reinvestment program Stock Issued During Period, Value, Dividend Reinvestment Plan Share grants, net of forfeitures and tax withholdings (in shares) Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures Share grants, net of forfeitures and tax withholdings Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures Balance (in shares) Balance Statement of Cash Flows [Abstract] Cash flows from operating activities Net Cash Provided by (Used in) Operating Activities [Abstract] Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest 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 Depreciation, Depletion and Amortization Provision for losses on accounts receivable Provision for Doubtful Accounts Real estate impairment Impairment of Long-Lived Assets Held-for-use Gain on sale of real estate Gains (Losses) on Sales of Investment Real Estate Share-based compensation expense Share-based Compensation Deferred tax benefit Deferred Income Tax Expense (Benefit) Amortization of debt premiums, discounts and related financing costs Amortization of Debt Issuance Costs and Discounts Loss on extinguishment of debt Gain (Loss) on Extinguishment of Debt Changes in operating other assets Increase (Decrease) in Prepaid Expense and Other Assets Changes in operating other liabilities Increase (Decrease) in Accounts Payable and Accrued 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] Real estate acquisitions, net Net cash received for sale of real estate Proceeds from Sale of Real Estate Held-for-investment Capital improvements to real estate Payments for Capital Improvements Development in progress Payments to Develop Real Estate Assets Payments for (Proceeds from) Deposits on Real Estate Acquisitions Payments for (Proceeds from) Deposits on Real Estate Acquisitions Non-real estate capital improvements Payments to Acquire Productive Assets Net cash provided by (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] Line of credit borrowings, net Proceeds from (Repayments of) Lines of Credit Dividends paid Payments of Dividends Principal payments – mortgage notes payable Repayments of unsecured term loan debt Repayments of Unsecured Debt Proceeds from term loan Proceeds from (Repayments of) Other Long-term Debt Payment of financing costs Payment of Financing and Stock Issuance Costs Distributions to noncontrolling interests Payments to Noncontrolling Interests Proceeds from dividend reinvestment program Proceeds from Other Equity Net proceeds from equity issuances Proceeds from Issuance of Common Stock Payment of tax withholdings for restricted share awards Payments Related to Tax Withholding for Share-based Compensation Net cash (used in) provided by financing activities Net Cash Provided by (Used in) Financing Activities Net decrease in cash, cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Cash, cash equivalents and restricted cash at beginning of period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Cash, cash equivalents and restricted cash at end of period Supplemental disclosure of cash flow information: Supplemental Cash Flow Information [Abstract] Cash paid for interest, net of amounts capitalized Interest Paid, Excluding Capitalized Interest, Operating Activities Change in accrued capital improvements and development costs Capital Expenditures Incurred but Not yet Paid Operating partnership units issued with acquisition Business Acquisition, Equity Interest Issued or Issuable, Value Assigned Segment Reporting [Abstract] Reconciliation of Net Operating Income of Reportable Segments Schedule of Segment Reporting Information, by Segment [Table Text Block] Accounting Policies [Abstract] Fiscal Period Fiscal Period, Policy [Policy Text Block] New Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Principles of Consolidation and Basis of Presentation Consolidation, Policy [Policy Text Block] Basis of Accounting Basis of Accounting, Policy [Policy Text Block] Use of Estimates in the Financial Statements Use of Estimates, Policy [Policy Text Block] Earnings Per Share [Abstract] Computation of Basic and Diluted Earnings per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] 2015 Term Loan [Member] 2015 Term Loan [Member] 2015 Term Loan [Member] 2016 Term Loan [Member] 2016 Term Loan [Member] 2016 Term Loan [Member] 2018 Term Loan [Member] 2018 Term Loan [Member] 2018 Term Loan [Member] 2018 Term Loan A [Member] 2018 Term Loan A [Member] 2018 Term Loan A [Member] 2018 Term Loan B [Member] 2018 Term Loan B [Member] 2018 Term Loan B [Member] Number of derivative instruments held Derivative, Number of Instruments Held Derivative, notional amount Derivative, Notional Amount Derivative, fixed interest rate (percent) Derivative, Fixed Interest Rate Debt instrument, face amount Debt Instrument, Face Amount Estimated derivative gain (loss) to be reclassified within twelve months Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months Fair value of derivative net asset position Derivative Assets (Liabilities), at Fair Value, Net Assets Assets [Abstract] Land Income producing property Rental Properties Net income producing property, at cost Real Estate Investment Property, at Cost Accumulated depreciation and amortization Real Estate Investment Property, Accumulated Depreciation Net income producing property Real Estate Investment Property, Net Properties under development or held for future development Development in Process Total real estate held for investment, net Real Estate Investments, Net Investment in real estate held for sale, net Real Estate Held-for-sale Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Restricted cash Restricted Cash and Cash Equivalents Rents and other receivables, net of allowance for doubtful accounts of $2,927 and $2,426, respectively Accounts and Notes Receivable, Net Prepaid expenses and other assets Prepaid Expense and Other Assets Other assets related to properties held for sale Disposal Group, Including Discontinued Operation, Other Assets, Current Total assets Assets Liabilities Liabilities [Abstract] Notes payable, net Notes Payable Mortgage notes payable, net Secured Debt Line of credit Long-term Line of Credit Accounts payable and other liabilities Accounts Payable and Accrued Liabilities Dividend payable Dividends Payable Advance rents Advance Rent Tenant security deposits Security Deposit Liability Other liabilities related to properties held for sale Disposal Group, Including Discontinued Operation, Liabilities Total liabilities Liabilities Equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Shareholders’ equity Stockholders' Equity Attributable to Parent [Abstract] Preferred shares; $0.01 par value; 10,000 shares authorized; no shares issued or outstanding Preferred Stock, Value, Issued Shares of beneficial interest, $0.01 par value; 100,000 shares authorized; 79,844 and 78,510 shares issued and outstanding, respectively Common Stock, Value, Issued Additional paid in capital Additional Paid in Capital Distributions in excess of net income Retained Earnings (Accumulated Deficit) Accumulated other comprehensive income Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax Total shareholders’ equity Stockholders' Equity Attributable to Parent Noncontrolling interests in subsidiaries Stockholders' Equity Attributable to Noncontrolling Interest Total equity Total liabilities and equity Liabilities and Equity Debt Disclosure [Abstract] Schedule of Revolving Credit Facility Schedule of Line of Credit Facilities [Table Text Block] Unsecured Lines of Credit Payable Debt Disclosure [Text Block] Fair Value Disclosures [Abstract] Fair Value Disclosures Fair Value Disclosures [Text Block] Mortgage Notes Payable Mortgage Notes Payable Disclosure [Text Block] Real estate rental revenue Revenues Net income Cash, cash equivalents and restricted cash Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Supplemental Employee Retirement Plan [Member] Supplemental Employee Retirement Plan [Member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value, Measurements, Fair Value Hierarchy [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, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Assets: Assets, Fair Value Disclosure [Abstract] SERP Other Assets, Fair Value Disclosure Interest rate swaps Derivative Asset Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Kenmore Apartments [Member] Kenmore Apartments [Member] Kenmore Apartments [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Repayment of mortgage note Net Rentable Square Feet Net Rentable Area Contract Purchase Price Derivative Instruments Derivative Instruments and Hedging Activities Disclosure [Text Block] Statement of Comprehensive Income [Abstract] Unrealized gain (loss) on interest rate hedges Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax, Portion Attributable to Parent Comprehensive income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Less: Comprehensive loss attributable to noncontrolling interests Net Income (Loss) Attributable to Noncontrolling Interest Comprehensive income attributable to the controlling interests Comprehensive Income (Loss), Net of Tax, Attributable to Parent Number of reportable segments Number of Reportable Segments Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Statement, Business Segments [Axis] Segments [Axis] Segment [Domain] Segments [Domain] Office Retail Retail [Member] Corporate and Other Corporate and Other [Member] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Real estate expenses Cost of Revenue Net operating income Gross Profit Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction General and administrative General and Administrative Expense Interest expense Interest Expense Other income Other Nonoperating Income (Expense) Gain on sale of real estate Real estate impairment Income tax benefit Income Tax Expense (Benefit) Loss on extinguishment of debt Net income Less: Net loss attributable to noncontrolling interests in subsidiaries Capital expenditures capital expenditures payment for capital expenditures by segment Total assets Equity [Abstract] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Common Stock [Member] Class of Stock [Line Items] Class of Stock [Line Items] Number of separate equity distribution agreements Number Of Equity Distribution Agreements Number Of Equity Distribution Agreements Capital shares reserved for future issuances Common Stock, Capital Shares Reserved for Future Issuances, Value Common Stock, Capital Shares Reserved for Future Issuances, Value Common shares issued Shares issued, average price per share Stock Issued During Period, Weighted Average Price stock issued during period, weighted average price Proceeds from issuance of common shares Shares issued under dividend reinvestment program (in shares) Shares issued under dividend reinvestment program, weighted share price per share Stock Issued During Period, Weighted Share Price, Dividend Reinstated Plan Stock issued during period, weighted share price, Dividend Reinstated Plan Value of shares issued under dividend reinvestment program Schedule of Real Estate Properties [Table] Schedule of Real Estate Properties [Table] The Trove [Member] The Trove [Member] The Trove [Member] Riverside Developments [Member] Riverside Developments [Member] Riverside Developments [Member] Spring Vally Retail Center [Member] Spring Vally Retail Center [Member] Spring Vally Retail Center [Member] Real Estate Properties [Line Items] Real Estate Properties [Line Items] Net income Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Allocation of earnings to unvested restricted share awards Undistributed Earnings (Loss) Allocated to Participating Securities, Basic Net Income (Loss) Attributable to Parent, Diluted Net Income (Loss) Attributable to Parent, Diluted Weighted average shares outstanding - basic (in shares) Weighted Average Number of Shares Outstanding, Basic Operating partnership units Incremental Common Shares Attributable to Operating Partnership Units Incremental Common Shares Attributable to Operating Partnership Units Employee restricted share awards Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Weighted average shares outstanding - diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Basic net income attributable to the controlling interests per common share (in dollars per share) Earnings Per Share, Basic Diluted net income attributable to the controlling interests per common share (in dollars per share) Earnings Per Share, Diluted Line of Credit Facility [Table] Line of Credit Facility [Table] Line of Credit Facility [Axis] Lender Name [Axis] Line of Credit Facility, Lender [Domain] Line of Credit Facility, Lender [Domain] Credit facility 2018 [Member] credit facility 2018 [Member] credit facility 2018 [Member] Credit facility 2015 [Member] credit facility 2015 [Member] credit facility 2015 [Member] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Line of Credit Line of Credit [Member] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] LIBOR [Member] London Interbank Offered Rate (LIBOR) [Member] Base Rate [Member] Base Rate [Member] Federal Funds Effective Swap Rate [Member] Federal Funds Effective Swap Rate [Member] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum [Member] Minimum [Member] Maximum [Member] Maximum [Member] Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Committed capacity Line of Credit Facility, Maximum Borrowing Capacity Debt instrument, term Debt Instrument, Term Debt instrument, maturity date Debt Instrument, Maturity Date Number of extensions allowed line of credit facility, number of extensions allowed line of credit facility, number of extensions allowed Term of extension Line Of Credit, Extension, Term Line Of Credit, Extension, Term Basis spread on variable rate (percent) Debt Instrument, Basis Spread on Variable Rate Commitment fee (percent) Line of Credit Facility, Commitment Fee Percentage Interest rate during period (percent) Line of Credit Facility, Interest Rate During Period Debt instrument variable rate (percent) Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate Proceeds from term loan Proceeds from Issuance of Debt Schedule of Fair Value of Derivatives Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Schedule of Derivative Gains and Losses Recognized in Other Comprehensive Income Schedule of Derivative Instruments, Effect on Other Comprehensive Income (Loss) [Table Text Block] Square footage of office property sold Shareholders' Equity Stockholders' Equity Note Disclosure [Text Block] Committed capacity Borrowings outstanding Unused and available Line of Credit Facility, Remaining Borrowing Capacity Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Prepaid Expenses and Other Assets [Member] Prepaid Expenses and Other Current Assets [Member] Accounts Payable and Other Liabilities [Member] Accounts Payable and Accrued Liabilities [Member] Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Aggregate Notional Amount Asset Derivatives Liability Derivatives Derivative Liability Income Statement [Abstract] Revenue Revenues [Abstract] Expenses Costs and Expenses [Abstract] Depreciation and amortization General and administrative Operating expenses Operating Expenses Other operating income Gain (Loss) on Disposition of Assets [Abstract] Real estate operating income Operating Income (Loss) Other (expense) income Nonoperating Income (Expense) [Abstract] Loss on extinguishment of debt Total other income (expense) Nonoperating Income (Expense) Net income attributable to the controlling interests Basic net income per share: Earnings Per Share, Basic [Abstract] Diluted net income per share: Earnings Per Share, Diluted [Abstract] Weighted average shares outstanding - diluted (in shares) Dividends declared per share (in dollars per share) Common Stock, Dividends, Per Share, Cash Paid Financial Assets and Liabilities Measured at Fair Value Fair Value Measurement and Measurement Inputs, Recurring and Nonrecurring [Text Block] Financial Assets and Liabilities Not Measured at Fair Value Fair Value, by Balance Sheet Grouping [Table Text Block] Line of Credit Facility, Increase (Decrease) During the Period [Roll Forward] Line of Credit Facility, Increase (Decrease), Net [Abstract] Balance at December 31, 2017 Borrowings Proceeds from Lines of Credit Repayments Repayments of Lines of Credit Balance at September 30, 2018 Nature of Business Nature of Operations [Text Block] Segment Information Segment Reporting Disclosure [Text Block] Summary of Significant Accounting Policies and Basis of Presentations Basis of Presentation and Significant Accounting Policies [Text Block] Earnings per Common Share Earnings Per Share [Text Block] Real Estate Real Estate Disclosure [Text Block] Schedule of Real Estate Property Acquired Schedule of Real Estate Property Acquired [Table Text Block] Schedule of Real Estate Property Acquired [Table Text Block] Revenue and Earnings From Acquisition Revenue and Earnings From Acquisition [Table Text Block] Revenue and Earnings From Acquisition [Table Text Block] Total Purchase Price Of Acquisitions Total Purchase Price Of Acquisitions [Table Text Block] Total Purchase Price Of Acquisitions [Table Text Block] Schedule of Properties Sold Disposal Groups, Including Discontinued Operations [Table Text Block] Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] 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 Value Reported Value Measurement [Member] Fair Value Estimate of Fair Value Measurement [Member] Cash and cash equivalents Cash and Cash Equivalents, Fair Value Disclosure Restricted cash Restricted Cash, Fair Value Disclosure Restricted Cash, Fair Value Disclosure Mortgage notes payable, net Loans Payable, Fair Value Disclosure Line of credit Lines of Credit, Fair Value Disclosure Notes payable, net Notes Payable, Fair Value Disclosure