Schedule of Rental Revenue Lessor, Operating Lease, Lease Income [Table Text Block] Lessor, Operating Lease, Lease Income [Table Text Block] Recognition of right-of-use asset and lease liability Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Buildings and improvements Investment Building and Building Improvements Preferred shares, dividend yield Preferred Stock, Dividend Rate, Percentage Common shares of beneficial interest, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Summary of Marketable Securities Debt Securities, Available-for-sale [Table Text Block] Noncontrolling Interest [Table] Noncontrolling Interest [Table] Earnings per common share attributable to Equity Commonwealth common shareholders: Earnings Per Share, Basic [Abstract] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Accounting Policies [Abstract] Net income attributable to noncontrolling interests Net Income (Loss) Attributable To Noncontrolling Interest, Diluted Net Income (Loss) Attributable To Noncontrolling Interest, Diluted Concentration Risk Type [Domain] Concentration Risk Type [Domain] CASH FLOWS FROM INVESTING ACTIVITIES: Net Cash Provided by (Used in) Investing Activities [Abstract] Estimated future compensation expense for unvested shares Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Basic (in dollars per share) Income (Loss) from Continuing Operations, Per Basic Share Schedule of Fair Value and Carrying Value of Financial Instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Provision for income taxes Income Tax Expense (Benefit), Continuing Operations, by Jurisdiction [Abstract] Share-based Payment Arrangement [Abstract] Proceeds from sale of marketable securities Proceeds From Sale Of Marketable Securities Proceeds From Sale Of Marketable Securities Noncontrolling Interest Noncontrolling Interest Disclosure [Text Block] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Percentage of equity interests in fee simple owner sold Disposal Group, Not Discontinued Operation, Percentage Of Equity Interests In Fee Simple Owner Sold Disposal Group, Not Discontinued Operation, Percentage Of Equity Interests In Fee Simple Owner Sold Additional Paid in Capital Additional Paid-in Capital [Member] Depreciation Depreciation Distributions payable Dividends Payable Other revenue Parking [Member] Common shares of beneficial interest, shares outstanding (in shares) Common Stock, Shares, Outstanding Real Estate Properties [Domain] Real Estate Properties [Domain] Repurchase and retirement of common shares Payments for Repurchase of Common Stock Concentration Risk Type [Axis] Concentration Risk Type [Axis] Number of renewal options of lease arrangement Lessee, Operating Lease, Number Of Renewals Lessee, Operating Lease, Number Of Renewals Debt Instrument [Axis] Debt Instrument [Axis] Expenses: Costs and Expenses [Abstract] Preferred shares, of beneficial interest, shares outstanding (in shares) Preferred Stock, Shares Outstanding Accumulated depreciation Real Estate Investment Property, Accumulated Depreciation Restricted shares and time-based LTIP Units Restricted Stock And Time-Based Long Term Incentive Plan Units [Member] Restricted Stock And Time-Based Long Term Incentive Plan Units [Member] Uncertain tax position as part of income tax provision Unrecognized Tax Benefits, Period Increase (Decrease) Expected term Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Statement [Table] Statement [Table] Amounts recognized in cumulative other comprehensive income (Loss) by component AOCI Attributable to Parent, Net of Tax [Roll Forward] Change in assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Diluted (in dollars per share) Income (Loss) from Continuing Operations, Per Diluted Share Common shares available for issuance (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Number of real estate properties secured by mortgage Number of Real Estate Properties Secured by Mortgage Represents the number of properties secured by mortgage notes. Preferred Shares Preferred Stock [Member] Cumulative net income Retained Earnings (Accumulated Deficit) Indebtedness Debt Disclosure [Text Block] Investments, Debt and Equity Securities [Abstract] Number of Buildings Number of Buildings Sold This element represents the number of buildings sold or agreed to be sold by the entity. Mortgage notes Mortgages [Member] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Loss on asset impairment Asset Impairment Charges Distributions to preferred shareholders Payments of Ordinary Dividends, Preferred Stock and Preference Stock Document Quarterly Report Document Quarterly Report CASH FLOWS FROM OPERATING ACTIVITIES: Net Cash Provided by (Used in) Operating Activities [Abstract] RSUs and market-based LTIP units Restricted Stock Units (RSUs) And Market-Based Long Term Incentive Plan Units [Member] Restricted Stock Units (RSUs) And Market-Based Long Term Incentive Plan Units [Member] Number of real estate properties Number of Real Estate Properties Disposal Group Classification [Axis] Disposal Group Classification [Axis] Senior unsecured debt and mortgage note payable Long-term Debt, Fair Value Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Variable lease payments Variable Lease, Income SUPPLEMENTAL CASH FLOW INFORMATION: Supplemental Cash Flow Information [Abstract] Weighted average common shares outstanding — basic (in shares) Weighted average number of common shares outstanding — basic (in shares) Weighted Average Number of Shares Outstanding, Basic 2022 Lessor, Operating Lease, Payments to be Received, Four Years Customer [Domain] Customer [Domain] Risk-free rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Name of Property [Domain] Name of Property [Domain] Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] CASH FLOWS FROM FINANCING ACTIVITIES: Net Cash Provided by (Used in) Financing Activities [Abstract] Compensation expense Share-based Payment Arrangement, Expense ASSETS Assets [Abstract] Noncontrolling interest, weighted average ownership percentage by parent Noncontrolling Interest, Weighted Average Ownership Percentage By Parent Noncontrolling Interest, Weighted Average Ownership Percentage By Parent Organization, Consolidation and Presentation of Financial Statements [Abstract] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Preferred shares of beneficial interest, shares authorized (in shares) Preferred Stock, Shares Authorized Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Loss on asset impairment Loss on Asset Impairment Loss on Asset Impairment Loss on early extinguishment of debt Loss on early extinguishment of debt Gain (Loss) on Extinguishment of Debt Document Fiscal Year Focus Document Fiscal Year Focus Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] Shareholders' Equity Stockholders' Equity Note Disclosure [Text Block] Number of trustees in board of trustees Number of Trustees in Board of Trustees Number of Trustees in Board of Trustees Stock repurchase program, period in force Stock Repurchase Program, Period in Force Unrealized gain on marketable securities Unrealized gain on marketable securities Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax Distributed Earnings Distributed Earnings Title of Individual [Axis] Title of Individual [Axis] Scenario [Axis] Scenario [Axis] Interest paid Interest Paid, Excluding Capitalized Interest, Operating Activities Subsequent Event Type [Domain] Subsequent Event Type [Domain] Series D preferred shares; 6 1/2% cumulative convertible; 4,915,196 shares issued and outstanding, aggregate liquidation preference of $122,880 Convertible, Preferred Stock, Value Dollar value of issued convertible preferred stock, whether issued at par value, no par or stated value, that may be exchanged into common shares or other types of securities at the owner's option as long as it is in accordance with the issuer's terms. Convertible preferred stock possess conversion and redemption features. The stock has redemption features that are outside the control of the issuer. Contributions Noncontrolling Interest, Increase from Subsidiary Equity Issuance Gross Sales Price Real Estate Aggregate Sales Price The element represents the aggregate sales price excluding mortgage debt repayments and closing costs, of real estate properties sold or agreed to be sold by the entity. Entity Current Reporting Status Entity Current Reporting Status Preferred shares of beneficial interest, shares issued (in shares) Preferred Stock, Shares Issued Marketable securities Available-for-sale Securities Entity Emerging Growth Company Entity Emerging Growth Company Cumulative Net Income Retained Earnings [Member] Senior unsecured notes, net Senior Notes Dividend declared (in dollars per share) Preferred Stock, Dividends Per Share, Declared Cash provided by investing activities Net Cash Provided by (Used in) Investing Activities Segment Information Segment Reporting Disclosure [Text Block] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Effect of anti-dilutive securities (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Restricted cash Restricted Cash and Cash Equivalents Statement of Financial Position [Abstract] Tenant improvements Tenant Improvements Renewal term of lease arrangement Lessee, Operating Lease, Renewal Term Real Estate Properties [Line Items] Real Estate Properties [Line Items] Adjustment for noncontrolling interest Noncontrolling Interest, Period Increase (Decrease) Schedule of Issued and Outstanding Units Share-based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity [Table Text Block] Schedule of Computation of Basic and Diluted Earnings Per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Share-based compensation Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture Summary of Assumptions and Fair Values for RSUs Granted in the Period Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Increase (Decrease) in Stockholders' Equity Increase (Decrease) in Stockholders' Equity [Roll Forward] Entity Address, State or Province Entity Address, State or Province Total equity Balance as of beginning of period Balance as of end of period Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Noncontrolling interest Stockholders' Equity Attributable to Noncontrolling Interest Rents receivable and other assets Increase (Decrease) in Rents Receivable and Other Assets The net change during the reporting period in rent receivables and other operating assets which is not otherwise defined in the taxonomy. Debt Disclosure [Abstract] Vesting in three years Share-based Payment Arrangement, Tranche One [Member] Common Stock, OP Units, and LTIP Units Common Stock, Long Term Incentive Plan Units, And Operating Partnership Units [Member] Common Stock, Long Term Incentive Plan Units, And Operating Partnership Units [Member] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Principal Balance Reported Value Measurement [Member] Shareholders' equity: Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Recent Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] State and local Deferred State and Local Income Tax Expense (Benefit) Net income attributable to Equity Commonwealth common shareholders Net Income (Loss) Available to Common Stockholders, Basic Document Transition Report Document Transition Report Document Information [Table] Document Information [Table] Total rents Revenue Benchmark [Member] Share-based compensation arrangement (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Vesting [Domain] Vesting [Domain] Fair value of assets and liabilities Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Document Information [Line Items] Document Information [Line Items] Operating expenses Operating Expenses Cash, cash equivalents, and restricted cash at beginning of period Cash, cash equivalents, and restricted cash at end of period Total cash, cash equivalents, and restricted cash shown in the statements of cash flows Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Disposal Group Classification [Domain] Disposal Group Classification [Domain] Related Party Transaction [Line Items] Related Party Transaction [Line Items] LTIP Units LTIP Units Long Term Incentive Plan Units [Member] Long Term Incentive Plan Units [Member] Share-based compensation Share-based Payment Arrangement, Noncash Expense Square footage (in sqft) Area of Real Estate Property Proceeds from maturity of marketable securities Proceeds From Maturity Of Marketable Securities Proceeds From Maturity Of Marketable Securities Other comprehensive income, net of tax: Other Comprehensive Income (Loss), Net of Tax [Abstract] Unrealized gain on derivative instruments Unrealized gain on derivative instruments Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax Noncontrolling Interest Noncontrolling Interest [Member] Net income attributable to noncontrolling interest Net Income (Loss) Attributable to Noncontrolling Interest Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Anti-dilutive securities: Antidilutive Securities Excluded from Computation of Earnings Per Share, Basic and Diluted [Abstract] Antidilutive Securities Excluded from Computation of Earnings Per Share, Basic and Diluted [Abstract] Amounts recognized in cumulative other comprehensive income (Loss) Accumulated Other Comprehensive Income (Loss) [Line Items] Entity Address, City or Town Entity Address, City or Town NON-CASH INVESTING ACTIVITIES: Noncash Investing Items [Abstract] Noncash Investing Items [Abstract] Entity Filer Category Entity Filer Category Denominator for earnings per common share - basic and diluted: Earnings Per Share, Basic and Diluted, Other Disclosures [Abstract] Percentage of revenue from office properties (more than) Percentage of Real Estate Properties Considered as Office Properties Represents the percentage of real estate properties considered as office properties. Unrealized Loss on Marketable Securities AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member] Lease termination period term Lessee, Operating Lease, Option To Terminate, Termination Term Lessee, Operating Lease, Option To Terminate, Termination Term Income Tax Disclosure [Abstract] Subsequent Event [Table] Subsequent Event [Table] Total comprehensive income attributable to Equity Commonwealth Comprehensive Income (Loss), Net of Tax, Attributable to Parent Statement Statement [Line Items] Number of reportable segments Number of Reportable Segments Entity Registrant Name Entity Registrant Name Share Repurchase Program [Domain] Share Repurchase Program [Domain] Stock repurchase program, authorized amount (up to) Stock Repurchase Program, Authorized Amount Equity Commonwealth 2015 Omnibus Incentive Plan Equity Commonwealth 2015 Omnibus Incentive Plan [Member] Equity Commonwealth 2015 Omnibus Incentive Plan [Member] Marketable Securities Marketable Securities, Policy [Policy Text Block] Amortization of debt discounts, premiums and deferred financing fees Amortization of Financing Costs and Discounts Continuing Operations The component of interest expense representing the noncash expenses charged against earnings in the period to allocate debt discount and premium, and the costs to issue debt and obtain financing over the related instruments excluding discontinued operations. Cumulative other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Amendment Flag Amendment Flag Cumulative preferred distributions Cumulative Preferred Stock Distributions The amount as of the balance sheet date representing cumulative distributions to preferred shareholders. Disposed of by Sale Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] City Area Code City Area Code Vesting [Axis] Vesting [Axis] Net gain on sale of properties Gain (Loss) on Sale of Properties and Gain (Loss) on Disposal of Discontinued Operation, Net of Tax This element represents the gain (loss) included in earnings related to continuing and discontinued properties resulting from the sale of a business component. This element is a noncash adjustment to net income when calculating net cash generated by operating activities using the indirect method. Entity Central Index Key Entity Central Index Key Cumulative Other Comprehensive Loss AOCI Attributable to Parent [Member] Contributions from holders of noncontrolling interest Proceeds from Noncontrolling Interests Loss on marketable securities Gain (Loss) on Sale of Investments Common shares of beneficial interest, shares authorized (in shares) Common Stock, Shares Authorized Senior unsecured debt, net Unsecured Debt Lease payments Operating Lease, Lease Income, Lease Payments Product and Service [Domain] Product and Service [Domain] Stock repurchase program, remaining authorized repurchase amount Stock Repurchase Program, Remaining Authorized Repurchase Amount Fair Value Disclosures [Abstract] Cumulative Other Comprehensive Loss Comprehensive Income (Loss) Note [Text Block] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Real estate properties: Real Estate Investment Property, Net [Abstract] Entity Shell Company Entity Shell Company Mortgage notes payable, net Secured Debt Consolidated Properties Consolidated Properties [Member] Share Repurchase Program, March 13, 2019 Share Repurchase Program, March 13, 2019 [Member] Share Repurchase Program, March 13, 2019 [Member] Net income included in continued operations Income (Loss) from Individually Significant Component Disposed of or Held-for-sale, Excluding Discontinued Operations, before Income Tax Related Person Transactions Related Party Transactions Disclosure [Text Block] Total shareholders’ equity Stockholders' Equity Attributable to Parent Conversion basis (in shares) Equity Award, Conversion Basis, Shares Equity Award, Conversion Basis, Shares Other assets, net Other Assets Exercise price (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Exercise Price Plan Name [Axis] Plan Name [Axis] Equity Component [Domain] Equity Component [Domain] Related Party Transactions [Abstract] Common Shares Common Stock [Member] Interest rate stated percentage Debt Instrument, Interest Rate, Stated Percentage Real Estate Properties Real Estate Disclosure [Text Block] Number of Properties Number Of Real Estate Properties Sold Number Of Real Estate Properties Sold 2021 Lessor, Operating Lease, Payments to be Received, Three Years Title of Individual [Domain] Title of Individual [Domain] Rental revenue Lease Income Net amortization of debt discounts, premiums and deferred financing fees Amortization of Debt Issuance Costs and Discounts Numerator for earnings per common share - basic: Net Income (Loss) Available to Common Stockholders, Basic [Abstract] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Payments on borrowings Repayments of Long-term Debt Customer [Axis] Customer [Axis] Current Fiscal Year End Date Current Fiscal Year End Date Two North Riverside Plaza Joint Venture Limited Partnership Two North Riverside Plaza Joint Venture Limited Partnership [Member] Two North Riverside Plaza Joint Venture Limited Partnership [Member] Restricted shares Restricted Stock [Member] Award Type [Domain] Award Type [Domain] Real Estate [Abstract] Granted shares value (in dollars per share) Fair value of RSUs granted (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Additional paid in capital Additional Paid in Capital, Common Stock Real estate improvements Cash Paid for Real Estate Improvements Cash paid for improvements made to real estate investments during the period. Land Land Fair Value Estimate of Fair Value Measurement [Member] Tenant Tenant [Member] Tenant [Member] Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] Amortized Cost Debt Securities, Available-for-sale, Amortized Cost Measurement Basis [Axis] Measurement Basis [Axis] Share-Based Compensation Share-based Payment Arrangement [Text Block] General and Administrative Expense General and Administrative Expense [Member] Square Footage (in sqft) Area of Real Estate Property Disposed Area of Real Estate Property Disposed 1735 Market Street Market Street Philadelphia PA 1735 [Member] Represents information pertaining to 1735 Market Street, Philadelphia, PA. Income Statement Location [Axis] Income Statement Location [Axis] Common Shares of Beneficial Interest Common Shares Common Class A [Member] Cash used in financing activities Net Cash Provided by (Used in) Financing Activities Independent Trustee Independent Trustee [Member] Independent Trustee [Member] Cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Gain on sale of properties, net Gain on Sale Gain (Loss) on Sale of Properties Proceeds from sale of real estate mortgage receivable Proceeds from Sale and Collection of Mortgage Notes Receivable Weighted average period over which compensation expense will be recorded Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Insurance proceeds received Proceeds from Insurance Settlement, Investing Activities Debt Instrument [Line Items] Debt Instrument [Line Items] Subsequent event Subsequent Event [Member] Real estate improvements SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Improvements Noncontrolling interest, ownership percentage by parent Noncontrolling Interest, Ownership Percentage by Parent Cumulative Common Distributions Cumulative Common Distributions [Member] This element represents cumulative common distributions member. Expected volatility Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Common stock, conversion basis (in shares) Common Stock, Conversion Basis, Shares Common Stock, Conversion Basis, Shares Name of Property [Axis] Name of Property [Axis] Numerator for net income per share - diluted Net Income (Loss) Available to Common Stockholders, Diluted Assets, fair value Assets, Fair Value Disclosure Thereafter Lessor, Operating Lease, Payments to be Received, Thereafter Statement of Stockholders' Equity [Abstract] Stockholders' Equity Note [Abstract] Rent collected in advance Advance Rent Cover page. 2019 Lessor, Operating Lease, Payments to be Received, Remainder of Fiscal Year Total liabilities Liabilities Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Trading Symbol Trading Symbol Accrued capital expenditures Capital Expenditures Incurred but Not yet Paid Comprehensive income attributable to the noncontrolling interest Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Document Period End Date Document Period End Date Rents receivable Accounts Receivable, after Allowance for Credit Loss Share Repurchase Program [Axis] Share Repurchase Program [Axis] Reclassification pursuant to change in accounting principle Cumulative Effect of New Accounting Principle in Period of Adoption Series D preferred shares; 6 1/2% cumulative convertible (in shares) Incremental Common Shares Attributable to Dilutive Effect of Conversion of Preferred Stock Common shares of beneficial interest, $0.01 par value: 350,000,000 shares authorized; 121,924,199 and 121,572,155 shares issued and outstanding, respectively Common Stock, Value, Issued Real Estate Property Ownership [Axis] Real Estate Property Ownership [Axis] Unrealized gain on derivative instruments Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification and Tax Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Distributions Dividends Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Subsequent Events Subsequent Events [Text Block] Scenario [Domain] Scenario [Domain] RSUs at target Restricted Stock Units (RSUs), Target [Member] Restricted Stock Units (RSUs), Target [Member] Compensation expense, accelerated vesting due to a staffing reduction Share-based Payment Arrangement, Accelerated Cost Distributions declared per common share (in dollars per share) Common stock, dividend declared (in dollars per share) Common Stock, Dividends, Per Share, Declared Schedule of Future Minimum Lease Payments, Excluding Tenant Reimbursement Revenue, Scheduled to be Received Lessor, Operating Lease, Payments to be Received, Maturity [Table Text Block] Fair value of financial instruments Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Revenues: Revenues [Abstract] Total assets Assets Total real estate properties, at cost, gross Real Estate Investment Property, at Cost Schedule of Declared Distributions Dividends Declared [Table Text Block] 600 108th Avenue NE 600 108th Avenue NE [Member] 600 108th Avenue NE [Member] Estimated Fair Value Debt Securities, Available-for-sale Net income Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Summary of Properties Sold and Income Statement Information for Properties Disposed of Disposal Groups, Including Discontinued Operations [Table Text Block] Plan Name [Domain] Plan Name [Domain] Noncontrolling Interest [Abstract] Document Fiscal Period Focus Document Fiscal Period Focus Document Type Document Type Entity Address, Postal Zip Code Entity Address, Postal Zip Code Entity Tax Identification Number Entity Tax Identification Number 6 1/2% Series D Cumulative Convertible Preferred Shares of Beneficial Interest Series D Series D Preferred Stock [Member] Income Statement [Abstract] Current: Current Income Tax Expense (Benefit), Continuing Operations [Abstract] Loss on sale of real estate mortgage receivable Loss on Sale of Investments Taxes paid, net Income Taxes Paid, Net Amortization of acquired real estate leases Amortization of Intangible Assets Total expenses Costs and Expenses Entity Interactive Data Current Entity Interactive Data Current Dividend paid (in dollars per share) Preferred Stock, Dividends, Per Share, Cash Paid Weighted average number of common shares outstanding, dilutive adjustment (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Income tax benefit (expense) Income tax benefit (expense) Income Tax Expense (Benefit) Amortization of right-of-use asset Operating Lease, Right-Of-Use Asset, Amortization Operating Lease, Right-Of-Use Asset, Amortization Cumulative common distributions Cumulative Common Stock Distributions The amount as of the balance sheet date representing cumulative distributions to common shareholders. Common stock, cash dividends paid Dividends, Common Stock, Cash Increase in cash, cash equivalents, and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Marketable Securities Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Numerator for earnings per common share - diluted: Net Income (Loss) Available to Common Stockholders, Diluted [Abstract] Straight line rental income Straight Line Rent Schedule of Issued and Outstanding Common Shares Schedule of Common Stock Outstanding Roll Forward [Table Text Block] General and administrative General and Administrative Expense Local Phone Number Local Phone Number Number of tranches Number of Tranches Number of Tranches Related Party [Axis] Related Party [Axis] RSUs RSUs Restricted Stock Units (RSUs) [Member] Total liabilities and equity Liabilities and Equity Total comprehensive income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Entity Common Stock, Shares Outstanding (in shares) Entity Common Stock, Shares Outstanding Class of Stock [Line Items] Class of Stock [Line Items] Noncontrolling ownership interest in the Operating Trust Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners Total real estate properties, at cost, net Real estate properties, net Real Estate Investment Property, Net Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Equity Components [Axis] Equity Components [Axis] Number of equity awards granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Stock issued during period, value, restricted stock award, gross Stock Issued During Period, Value, Restricted Stock Award, Gross Award Type [Axis] Award Type [Axis] Net income per common share attributable to Equity Commonwealth common shareholders: Earnings Per Share, Basic and Diluted [Abstract] Weighted average common shares outstanding — diluted (in shares) Weighted average number of common shares outstanding — diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Consideration held in escrow Escrow Deposits Related to Property Sales Weighted average number of shares, restricted stock units, unvested (in shares) Weighted Average Number Of Shares, Restricted Stock Units, Unvested Weighted Average Number Of Shares, Restricted Stock Units, Unvested Business Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Schedule of Real Estate Properties [Table] Schedule of Real Estate Properties [Table] Cumulative Preferred Distributions Cumulative Preferred Distributions [Member] This element represents cumulative preferred distributions member. Common shares of beneficial interest, shares issued (in shares) Common Stock (in shares) Common Stock, Shares, Issued Interest and other income, net Interest and Other Income Preferred distributions Preferred Stock Dividends, Income Statement Impact Preferred shares of beneficial interest, par value (in dollars per share) Preferred Stock, Par or Stated Value Per Share Fair Value of Assets and Liabilities Derivatives and Fair Value [Text Block] Subsequent Events [Abstract] Proceeds from sale of properties, net Proceeds from Sale of Productive Assets OP Units Operating Partnership Units [Member] Operating Partnership Units [Member] Rent collected in advance Increase (Decrease) in Deferred Liabilities Vesting percent Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage Net income attributable to Equity Commonwealth Net Income (Loss) Attributable to Parent Research Park Research Park [Member] Research Park [Member] Accounts payable, accrued expenses and other Accounts Payable and Accrued Liabilities Income before income taxes Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Operating lease, expense Operating Lease, Expense Adjustments to reconcile net income to cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Entity Small Business Entity Small Business Entity File Number Entity File Number Customer concentration Customer Concentration Risk [Member] Ownership [Axis] Ownership [Axis] Rental revenue Operating Lease, Lease Income Scenario, Forecast Forecast [Member] Other amortization Amortization of Deferred Leasing Fees RSUs at maximum Restricted Stock Units (RSUs), Maximum [Member] Restricted Stock Units (RSUs), Maximum [Member] Balance as of beginning of period (in shares) Balance as of end of period (in shares) Shares, Outstanding Schedule of Amounts Recognized in Cumulative Other Comprehensive Loss Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Shares paid for tax withholding for share based compensation (in shares) Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation Vesting in four years Share-based Payment Arrangement, Tranche Two [Member] Repurchase of shares Stock Repurchased During Period, Value Other comprehensive income Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Vesting period Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Product and Service [Axis] Product and Service [Axis] Depreciation and amortization Depreciation, Depletion and Amortization State and local Current State and Local Tax Expense (Benefit) Number of buildings Number of Buildings The number of buildings owned as of the balance sheet date. Total future minimum lease payments to be received Lessor, Operating Lease, Payments to be Received LIABILITIES AND EQUITY Liabilities and Equity [Abstract] Other revenue Revenue from Contract with Customer, Excluding Assessed Tax Income Taxes Income Tax Disclosure [Text Block] Ownership [Domain] Ownership [Domain] Operating Trust EQC Operating Trust [Member] EQC Operating Trust [Member] Deferred: Deferred Federal, State and Local, Tax Expense (Benefit) [Abstract] Lease term Lessee, Operating Lease, Term of Contract Segment Reporting [Abstract] Statement of Cash Flows [Abstract] Interest expense (including net amortization of debt discounts, premiums and deferred financing fees of $(55), $559, $264 and $2,005, respectively) Interest Expense Unrealized Loss Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax Class of Stock [Axis] Class of Stock [Axis] Related Party [Domain] Related Party [Domain] Earnings Per Share [Abstract] Loss on early extinguishment of debt Gains (Losses) on Early Extinguishment of Debt Amount represents the difference between the fair value of the payments made and the carrying amount of the debt classified in continuing and discontinued operations at the time of its extinguishment. Number of shares authorized (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Subsequent Event [Line Items] Subsequent Event [Line Items] Concentration risk, percent Concentration Risk, Percentage Common stock, conversion term Common Stock, Conversion Term Common Stock, Conversion Term Security Exchange Name Security Exchange Name Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Repurchase of shares (in shares) Stock Repurchased and Retired During Period, Shares Preferred shares, aggregate liquidation preference Preferred Stock, Aggregate Liquidation Preference The aggregate liquidation preference (or restrictions) of preferred stock that has a preference in involuntary liquidation. Considerably in excess of the par or stated value of the shares. Entity Address, Address Line One Entity Address, Address Line One OP Units and LTIP Units Long Term Incentive Plan Units And Operating Partnership Units [Member] Long Term Incentive Plan Units And Operating Partnership Units [Member] Share-based compensation (in shares) Restricted share, time-based LTIP Unit grants and vested restricted stock units, net of forfeitures (in shares) Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture 2023 Lessor, Operating Lease, Payments to be Received, Five Years Noncontrolling Interest [Line Items] Noncontrolling Interest [Line Items] Statement of Comprehensive Income [Abstract] Total revenues Revenues Distributions to common shareholders Payments of Ordinary Dividends, Common Stock Earnings Per Common Share Earnings Per Share [Text Block] Accounts payable, accrued expenses and other Increase (Decrease) in Accounts Payable and Accrued Liabilities Class of Stock [Domain] Class of Stock [Domain] NON-CASH FINANCING ACTIVITIES: Noncash Financing Items [Abstract] Noncash Financing Items Repurchase of shares (in shares) Repurchase of shares (in shares) Stock Repurchased During Period, Shares 2020 Lessor, Operating Lease, Payments to be Received, Two Years Schedule of Provision for Income Taxes Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Title of 12(b) Security Title of 12(b) Security