Equity Commonwealth (EQC) 10-Q/A 8 May 18 2018 Q1 Quarterly report (amended) Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	May 03, 2018
Document and Entity Information
Entity Registrant Name	Equity Commonwealth
Entity Central Index Key	803,649
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)		124,457,073
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Real estate properties:
Land	$ 146,700	$ 191,775
Buildings and improvements	1,100,524	1,555,836
Total real estate properties, at cost, gross	1,247,224	1,747,611
Accumulated depreciation	(379,862)	(450,718)
Total real estate properties, at cost, net	867,362	1,296,893
Assets held for sale	38,882	97,688
Acquired real estate leases, net	3,621	23,847
Cash and cash equivalents	2,837,671	2,351,693
Marketable securities	247,879	276,928
Restricted cash	6,995	8,897
Rents receivable, net of allowance for doubtful accounts of $5,137 and $4,771, respectively	55,910	93,436
Other assets, net	78,986	87,563
Total assets	4,137,306	4,236,945
LIABILITIES AND EQUITY
Senior unsecured debt, net	646,246	815,984
Mortgage notes payable, net	32,281	32,594
Liabilities related to properties held for sale	1,153	1,840
Accounts payable and accrued expenses	42,007	69,220
Assumed real estate lease obligations, net	503	1,001
Rent collected in advance	9,225	11,076
Security deposits	4,412	4,735
Total liabilities	735,827	936,450
Shareholders' equity:
Common shares of beneficial interest, $0.01 par value: 350,000,000 shares authorized; 121,457,073 and 124,217,616 shares issued and outstanding, respectively	1,214	1,242
Additional paid in capital	4,295,772	4,380,313
Cumulative net income	2,785,760	2,596,259
Cumulative other comprehensive loss	(2,106)	(95)
Cumulative common distributions	(3,111,868)	(3,111,868)
Cumulative preferred distributions	(687,745)	(685,748)
Total shareholders’ equity	3,400,290	3,299,366
Noncontrolling interest	1,189	1,129
Total equity	3,401,479	3,300,495
Total liabilities and equity	4,137,306	4,236,945
Series D
Shareholders' equity:
Series D preferred shares; 6 1/2% cumulative convertible; 4,915,196 shares issued and outstanding, aggregate liquidation preference of $122,880	119,263	119,263
Total equity	$ 119,263	$ 119,263

CONDENSED CONSOLIDATED BALANCE3

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Rents receivable, allowance for doubtful accounts	$ 5,137	$ 4,771
Common shares of beneficial interest, par value (in dollars per share)	$ 0.01	$ 0.01
Common shares of beneficial interest, shares authorized (in shares)	350,000,000	350,000,000
Common shares of beneficial interest, shares issued (in shares)	121,457,073	124,217,616
Common shares of beneficial interest, shares outstanding (in shares)	121,457,073	124,217,616
Series D
Preferred shares of beneficial interest, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred shares of beneficial interest, shares authorized (in shares)	50,000,000	50,000,000
Preferred shares, dividend yield	6.50%	6.50%
Preferred shares of beneficial interest, shares issued (in shares)	4,915,196	4,915,196
Preferred shares, of beneficial interest, shares outstanding (in shares)	4,915,196	4,915,196
Preferred shares, aggregate liquidation preference	$ 122,880	$ 122,880
Common shares of beneficial interest, shares issued (in shares)	4,915,196	4,915,196

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues:
Rental income	$ 43,549	$ 80,205
Tenant reimbursements and other income	15,039	19,346
Total revenues	58,588	99,551
Expenses:
Operating expenses	24,599	41,087
Depreciation and amortization	13,903	26,915
General and administrative	13,339	12,078
Loss on asset impairment	12,087	1,286
Total expenses	63,928	81,366
Operating (loss) income	(5,340)	18,185
Interest and other income, net	5,780	4,372
Interest expense (including net amortization of debt discounts, premiums and deferred financing fees of $801 and $713, respectively)	(10,115)	(15,014)
Loss on early extinguishment of debt	(4,867)	0
Gain on sale of properties, net	205,211	16,454
Income before income taxes	190,669	23,997
Income tax expense	(3,007)	(175)
Net income	187,662	23,822
Net income attributable to noncontrolling interest	(63)	(8)
Net income attributable to Equity Commonwealth	187,599	23,814
Preferred distributions	(1,997)	(1,997)
Net income attributable to Equity Commonwealth common shareholders	$ 185,602	$ 21,817
Weighted average common shares outstanding — basic (in shares)	123,867	124,047
Weighted average common shares outstanding — diluted (in shares)	127,097	125,150
Earnings per common share attributable to Equity Commonwealth common shareholders:
Basic (in dollars per share)	$ 1.50	$ 0.18
Diluted (in dollars per share)	$ 1.48	$ 0.17
Distributed Earnings	$ 0	$ 1,997

CONDENSED CONSOLIDATED STATEME5

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Amortization of debt discounts, premiums and deferred financing fees	$ 801	$ 713

CONDENSED CONSOLIDATED STATEME6

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 187,662	$ 23,822
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on derivative instruments	117	(153)
Unrealized loss on marketable securities	(226)	(641)
Total comprehensive income	187,553	23,028
Comprehensive income attributable to the noncontrolling interest	(63)	(8)
Total comprehensive income attributable to Equity Commonwealth	$ 187,490	$ 23,020

CONSOLIDATED STATEMENTS OF SHAR

CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - 3 months ended Mar. 31, 2018 - USD ($) $ in Thousands	Total	Series D	Cumulative Preferred Distributions	Common Shares	Cumulative Common Distributions	Additional Paid in Capital	Cumulative Net Income	Cumulative Other Comprehensive Loss	Noncontrolling Interest
Balance (in shares) at Dec. 31, 2017	124,217,616	4,915,196		124,217,616
Balance at Dec. 31, 2017	$ 3,300,495	$ 119,263	$ (685,748)	$ 1,242	$ (3,111,868)	$ 4,380,313	$ 2,596,259	$ (95)	$ 1,129
Increase (Decrease) in Stockholders' Equity
Net income	187,662						187,599		63
Unrealized gain on derivative instruments	117							117
Unrealized loss on marketable securities	(226)							(226)
Repurchase of shares (in shares)				(3,027,557)
Repurchase of shares	(89,910)			$ (30)		(89,880)
Share-based compensation (in shares)				267,014
Share-based compensation	5,338			$ 2		5,010			326
Contributions	0								0
Distributions	$ (1,997)		(1,997)
Adjustment for noncontrolling interest						329			(329)
Balance (in shares) at Mar. 31, 2018	121,457,073	4,915,196		121,457,073
Balance at Mar. 31, 2018	$ 3,401,479	$ 119,263	$ (687,745)	$ 1,214	$ (3,111,868)	$ 4,295,772	$ 2,785,760	$ (2,106)	$ 1,189

CONDENSED CONSOLIDATED STATEME8

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 187,662	$ 23,822
Adjustments to reconcile net income to cash used in operating activities:
Depreciation	11,279	21,893
Net amortization of debt discounts, premiums and deferred financing fees	801	713
Straight line rental income	(1,528)	(4,387)
Amortization of acquired real estate leases	997	2,540
Other amortization	1,628	3,055
Share-based compensation	5,338	5,226
Loss on asset impairment	12,087	1,286
Loss on marketable securities	4,987	0
Loss on early extinguishment of debt	4,867	0
Net gain on sale of properties	(205,211)	(16,454)
Change in assets and liabilities:
Rents receivable and other assets	(11,410)	(18,239)
Accounts payable and accrued expenses	(10,139)	(24,053)
Rent collected in advance	(1,786)	416
Security deposits	57	181
Cash used in operating activities	(371)	(4,001)
CASH FLOWS FROM INVESTING ACTIVITIES:
Real estate improvements	(12,761)	(19,889)
Insurance proceeds received	1,443	2,000
Proceeds from sale of properties, net	744,324	94,138
Purchase of marketable securities	0	(276,238)
Proceeds from sale of marketable securities	18,613	0
Cash provided by (used in) investing activities	751,619	(199,989)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repurchase and retirement of common shares	(89,910)	(209)
Payments on borrowings	(175,265)	(348)
Contributions from holders of noncontrolling interest	0	30
Distributions to preferred shareholders	(1,997)	(1,997)
Cash used in financing activities	(267,172)	(2,524)
Increase (decrease) in cash, cash equivalents, and restricted cash	484,076	(206,514)
Cash, cash equivalents, and restricted cash at beginning of period	2,360,590	2,101,206
Cash, cash equivalents, and restricted cash at end of period	2,844,666	1,894,692
SUPPLEMENTAL CASH FLOW INFORMATION:
Interest paid	14,631	22,285
Taxes (refunded) paid, net	(2)	335
NON-CASH INVESTING ACTIVITIES:
(Decrease) increase in capital expenditures recorded as liabilities	(103)	4,266
Total cash, cash equivalents, and restricted cash shown in the statements of cash flows	$ 2,360,590	$ 2,101,206

Business

Business	3 Months Ended
	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business	Business Equity Commonwealth (the Company) is a real estate investment trust, or REIT, formed in 1986 under the laws of the State of Maryland. Our business is the ownership and operation of real estate, primarily office buildings, throughout the United States. On November 10, 2016, the Company converted to what is commonly referred to as an umbrella partnership real estate investment trust, or UPREIT, structure. In connection with this conversion, the Company contributed substantially all of its assets to EQC Operating Trust, a Maryland real estate investment trust (the Operating Trust), and the Operating Trust assumed substantially all of the Company’s liabilities pursuant to a contribution and assignment agreement between the Company and the Operating Trust. The Company now conducts and intends to continue to conduct substantially all of its activities through the Operating Trust. The Company beneficially owned 99.97% of the outstanding shares of beneficial interest, designated as units, in the Operating Trust (OP Units) as of March 31, 2018 , and the Company is the sole trustee of the Operating Trust. As the sole trustee, the Company generally has the exclusive power under the declaration of trust of the Operating Trust to manage and conduct the business of the Operating Trust, subject to certain limited approval and voting rights of other holders of OP Units. At March 31, 2018 , our portfolio, excluding properties held for sale, consisted of 13 properties ( 22 buildings), with a combined 6.3 million square feet. As of March 31, 2018 , we had $3.1 billion of cash and cash equivalents and marketable securities.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation The accompanying condensed consolidated financial statements of EQC have been prepared without audit. Certain information and footnote disclosures required by U.S. generally accepted accounting principles, or GAAP, for complete financial statements have been condensed or omitted. We believe the disclosures made are adequate to make the information presented not misleading. However, the accompanying condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes contained in our Annual Report on Form 10-K (Annual Report) for the year ended December 31, 2017 . Capitalized terms used, but not defined in this Quarterly Report, have the same meanings as in our Annual Report. In the opinion of our management, all adjustments, which include only normal recurring adjustments considered necessary for a fair presentation, have been included. All intercompany transactions and balances with or among our subsidiaries have been eliminated. Operating results for interim periods are not necessarily indicative of the results that may be expected for the full year. Reclassifications have been made to the prior years’ financial statements to conform to the current year’s presentation. The preparation of financial statements in conformity with GAAP requires us to make estimates and assumptions that affect reported amounts. Actual results could differ from those estimates. Significant estimates in the condensed consolidated financial statements include the allowance for doubtful accounts, purchase price allocations, useful lives of fixed assets and impairment of real estate and intangible assets. Share amounts are presented in whole numbers, except where noted. Recent Accounting Pronouncements In August 2017, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities, to enable entities to better portray the economics of their risk management activities in the financial statements and enhance the transparency and understandability of hedge results. The amendments also simplify the application of hedge accounting in certain situations. This update is effective for fiscal years beginning after December 15, 2018, and for interim periods within those fiscal years. We are evaluating the impact ASU 2017-12 will have on our financial position and results of operations. In May 2017, the FASB issued ASU 2017-09 Compensation-Stock Compensation (Topic 718): Scope of Modification Accounting. ASU 2017-09 is designed to provide clarity and reduce both (1) diversity in practice and (2) cost and complexity when applying the guidance in Topic 718, to a change to the terms or conditions of a share-based payment award. ASU 2017-09 is effective for fiscal years beginning after December 15, 2017. We adopted this ASU on January 1, 2018, and the adoption did not have a material impact on our consolidated financial statements. In February 2017, the FASB issued ASU 2017-01, Clarifying the Definition of a Business, that changes the definition of a business to assist entities with evaluating when a set of transferred assets and activities is a business. This update is effective for fiscal years beginning after December 15, 2017, and for interim periods within those fiscal years. We early adopted this ASU effective January 1, 2017, and the adoption of this ASU did not have a material impact on our consolidated financial statements. In February 2017, the FASB issued ASU 2017-05 Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets. ASU 2017-05 is designed to provide guidance on how to recognize gain and losses on sales, including partial sales, of nonfinancial assets to noncustomers. We adopted this ASU on January 1, 2018 and the adoption did not have a material impact on our consolidated financial statements. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash, which amends FASB Accounting Standards Codification (ASC) Topic 230, Statements of Cash Flows, to add or clarify guidance on the classification and presentation of restricted cash in the statement of cash flows. This update is effective for fiscal years beginning after December 15, 2017, and for interim periods within those fiscal years. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments, which addresses eight specific cash flow issues with the objective of reducing the existing diversity in practice. This update is effective for fiscal years beginning after December 15, 2017, and for interim periods within those fiscal years. We early adopted both ASU 2016-18 and ASU 2016-15 for the period ended December 31, 2017 and made the following reclassifications to the prior year's condensed consolidated statement of cash flows to conform to the current year's presentation (in thousands): Statement of Cash Flows for the Three Months Ended March 31, 2017 Originally Reported Effect of Change As Adjusted Cash used in operating activities $ (2,690 ) $ (1,311 ) $ (4,001 ) Cash used in investing activities (200,923 ) 934 (199,989 ) In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which requires more timely recognition of credit losses associated with financial assets. This update is effective for fiscal years beginning after December 15, 2019, and for interim periods within those fiscal years. Early adoption is permitted for fiscal years, and interim periods within those years, beginning after December 15, 2018. We are currently in the process of evaluating the impact, if any, the adoption of this ASU will have on our consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases, which sets out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e., lessees and lessors). ASU 2016-02 requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase of the leased asset by the lessee. This classification will determine whether the lease expense is recognized based on an effective interest method or on a straight-line basis over the term of the lease. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less will be accounted for similar to existing guidance for operating leases today. ASU 2016-02 supersedes previous leasing standards. ASU 2016-02 is effective for us for reporting periods beginning after December 15, 2018, with early adoption permitted. We are still assessing the impact of adopting ASU 2016-02. For leases where we are the lessor, we expect to account for these leases using an approach that is substantially equivalent to current guidance. Additionally, under ASU 2016-02 lessors may only capitalize incremental direct leasing costs. For leases in which we are the lessee, we expect to recognize a right-of-use asset and a lease liability equal to the present value of the minimum lease payments with rent expense being recognized on a straight-line basis and the right of use asset being reduced when lease payments are made. In January 2016, the FASB issued ASU 2016-01, Financial Instruments-Overall: Recognition and Measurement of Financial Assets and Financial Liabilities, related to certain aspects of recognition, measurement, presentation, and disclosure of financial instruments. ASU 2016-01 will require entities to measure their equity investments at fair value and recognize any changes in fair value in net income, with certain exceptions, rather than other comprehensive income. This update is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. We adopted this ASU on January 1, 2018 and reclassified a $1.9 million unrealized gain from cumulative other comprehensive loss to cumulative net income on our condensed consolidated balance sheet (see Note 8). In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers. The objective of ASU 2014-09, as amended, is to establish a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and will supersede most of the existing revenue recognition guidance, including industry-specific guidance. The core principle is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In applying ASU 2014-09, companies will perform a five-step analysis of transactions to determine when and how revenue is recognized. ASU 2014-09 applies to all contracts with customers except those that are within the scope of other topics in the FASB’s ASC, and more particularly lease contracts with customers, which are a scope exception. ASU 2014-09 is effective for the first interim period within annual reporting periods beginning after December 15, 2017, with early adoption permitted. We adopted this ASU on January 1, 2018 and the adoption did not have a material impact on our consolidated financial statements.

Real Estate Properties

Real Estate Properties	3 Months Ended
	Mar. 31, 2018
Real Estate [Abstract]
Real Estate Properties	Real Estate Properties During the three months ended March 31, 2018 and 2017 , we made improvements, excluding tenant-funded improvements, to our properties totaling $12.9 million and $ 14.2 million , respectively. Properties Held For Sale: We classify all properties that meet the criteria outlined in the Property, Plant and Equipment Topic of the FASB ASC as held for sale on our condensed consolidated balance sheets. As of December 31, 2017, we classified 1600 Market Street as held for sale. This property was sold in February 2018. As of March 31, 2018 , we classified the following property as held for sale: Asset Number of Number of Square Footage 1601 Dry Creek Drive 1 1 552,865 Summarized balance sheet information for the properties classified as held for sale is as follows (in thousands): March 31, 2018 December 31, 2017 Real estate properties $ 24,786 $ 76,066 Rents receivable 7,245 13,270 Other assets, net 6,851 8,352 Assets held for sale $ 38,882 $ 97,688 Accounts payable and accrued expenses $ 1,099 $ 1,021 Rent collected in advance 1 408 Security deposits 53 411 Liabilities related to properties held for sale $ 1,153 $ 1,840 Property Dispositions: During the three months ended March 31, 2018 , we sold the following properties (dollars in thousands): Asset Date Sold Number of Number of Square Footage Gross Sales Price Gain on Sale Properties 1600 Market Street February 2018 1 1 825,968 $ 160,000 $ 54,599 600 West Chicago Avenue (1) February 2018 1 2 1,561,477 510,000 107,830 5073, 5075, & 5085 S. Syracuse Street March 2018 1 1 248,493 115,186 42,762 3 4 2,635,938 $ 785,186 $ 205,191 (1) The sale of this property did not represent a strategic shift under ASC Topic 205. However, the sale does represent an individually significant disposition. The operating results of this property are included in continued operations for all periods presented through the date of sale. Net income for this property for the three months ended March 31, 2018 and 2017 was $110.0 million and $2.7 million , respectively.

Marketable Securities

Marketable Securities	3 Months Ended
	Mar. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Marketable Securities	Marketable Securities During the quarter ended March 31, 2018 , our marketable securities consisted of United States Treasury notes and common stock. The United States Treasury notes are classified as available-for-sale and mature in 2019. Available-for-sale securities are presented on our condensed consolidated balance sheets at fair value. Changes in values of the United States Treasury notes are recognized in accumulated other comprehensive loss. On January 1, 2018 we adopted ASU 2016-01 (see Note 2) and reclassified a $1.9 million unrealized gain from cumulative other comprehensive loss to cumulative net income on our condensed consolidated balance sheet. Changes in values of common stock are recognized in interest and other income, net on the condensed consolidated statements of operations. In March 2018, we sold all common stock we held and recognized a loss of $5.0 million in interest and other income, net during the three months ended March 31, 2018 . Below is a summary of our marketable securities as of March 31, 2018 and December 31, 2017 (in thousands): March 31, 2018 December 31, 2017 Amortized Cost Unrealized Loss Estimated Fair Value Cost or Amortized Cost Unrealized Gain, Net Estimated Fair Value Marketable securities $ 249,646 $ (1,767 ) $ 247,879 $ 276,567 $ 361 $ 276,928 The unrealized losses on our United States Treasury notes were caused by interest rate increases. The contractual terms of those investments do not permit the issuer to settle the securities at a price less than the amortized cost bases of the investments. Because we do not intend to sell the investments and it is not more likely than not that we will be required to sell the investments before recovery of their amortized cost bases, which may be maturity, we do not consider those investments to be other-than-temporarily impaired at March 31, 2018.

Indebtedness

Indebtedness	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Indebtedness	Indebtedness Unsecured Revolving Credit Facility and Term Loan: We are party to a credit agreement pursuant to which the lenders agreed to provide a $750.0 million unsecured revolving credit facility, a $200.0 million 5 -year term loan facility, and a $200.0 million 7 -year term loan facility. The revolving credit facility has a scheduled maturity date of January 28, 2019, which maturity date may be extended for up to two additional periods of six months at our option subject to satisfaction of certain conditions and the payment of an extension fee of 7.5 basis points of the aggregate amount available under the revolving credit facility. The 5 -year term loan and the 7 -year term loan have scheduled maturity dates of January 28, 2020 and January 28, 2022, respectively. The credit agreement permits us to utilize up to $100.0 million of the revolving credit facility for the issuance of letters of credit. Amounts outstanding under the credit agreement generally may be prepaid at any time without premium or penalty, subject to certain exceptions. We have the right to request increases in the aggregate maximum amount of borrowings available under the revolving credit facility and term loans up to an additional $1.15 billion , subject to certain conditions. Borrowings under the 5 -year term loan and 7 -year term loan will, subject to certain exceptions, bear interest at a LIBOR rate plus a margin of 90 to 180 basis points for the 5 -year term loan and 140 to 235 basis points for the 7 -year term loan, in each case depending on our credit rating. Borrowings under the revolving credit facility will, subject to certain exceptions, bear interest at a rate equal to, at our option, either a LIBOR rate or a base rate plus a margin of 87.5 to 155 basis points for LIBOR rate advances and 0 to 55 basis points for base rate advances, in each case depending on our credit rating. In addition, we are required to pay a facility fee of 12.5 to 30 basis points, depending on our credit rating, on the borrowings available under the revolving credit facility, whether or not utilized. Borrowings under our revolving credit facility currently bear interest at LIBOR plus a spread, which was 105 basis points as of March 31, 2018 . As of March 31, 2018 , the interest rate payable on borrowings under our revolving credit facility was 2.93% . As of March 31, 2018 , we had no balance outstanding and $750.0 million available under our revolving credit facility and the facility fee as of March 31, 2018 was 20 basis points. Our term loans currently bear interest at a rate of LIBOR plus a spread, which was 115 and 155 basis points for the 5 -year and 7 -year term loan, respectively, as of March 31, 2018 . As of March 31, 2018 , the interest rates for the amounts outstanding under our 5 -year term loan and 7 -year term loan were 3.03% and 3.43% , respectively. As of March 31, 2018 , we had $200.0 million outstanding under each of our 5 -year and 7 -year term loans. Debt Covenants: Our public debt indenture and related supplements and our credit agreement contain a number of financial and other covenants, including covenants that restrict our ability to incur indebtedness or to make distributions under certain circumstances and require us to maintain financial ratios and a minimum net worth. At March 31, 2018 , we believe we were in compliance with all of our respective covenants under our public debt indenture and related supplements and our credit agreement. Senior Unsecured Notes: At March 31, 2018 , we had senior unsecured notes of $250.0 million (excluding net discounts and unamortized deferred financing fees) maturing in 2020. On March 7, 2018, we redeemed at par all $175.0 million of our 5.75% senior unsecured notes due 2042 and recognized a loss on early extinguishment of debt of $4.9 million from the write off of unamortized deferred financing fees. Mortgage Notes Payable: At March 31, 2018 , two of our properties with an aggregate net book value of $51.9 million had secured mortgage notes totaling $32.3 million (including net premiums and unamortized deferred financing fees) maturing from 2021 through 2026.

Shareholders' Equity

Shareholders' Equity	3 Months Ended
	Mar. 31, 2018
Stockholders' Equity Note [Abstract]
Shareholders' Equity	Shareholders’ Equity Common Share Issuances: See Note 11 for information regarding equity issuances related to share-based compensation. Common Share Repurchases: On March 15, 2017, our Board of Trustees authorized the repurchase of up to $150.0 million of our outstanding common shares over the twelve month period following the date of authorization. In March 2018, this share repurchase authorization, of which $81.0 million was not utilized, expired. On March 14, 2018, our Board of Trustees authorized the repurchase of up to an additional $150.0 million of our outstanding common shares over the twelve month period following the date of authorization. During the three months ended March 31, 2018 , we repurchased and retired 2,970,209 of our common shares, at a weighted average price of $29.67 per share, for a total investment of $88.1 million , of which $69.0 million was under the March 2017 authorization and $19.1 million was under the March 2018 authorization. The $130.9 million of remaining authorization available under our share repurchase program as of March 31, 2018 is scheduled to expire on March 14, 2019. During the three months ended March 31, 2018 and 2017 , certain of our employees surrendered 57,348 and 6,694 common shares owned by them, respectively, to satisfy their statutory tax withholding obligations in connection with the vesting of such common shares. Preferred Share Distributions: In 2018 , our Board of Trustees declared distributions on our series D preferred shares to date as follows: Declaration Date Record Date Payment Date Series D Dividend Per Share January 12, 2018 January 30, 2018 February 15, 2018 $ 0.40625 April 11, 2018 April 27, 2018 May 15, 2018 $ 0.40625

Noncontrolling Interest

Noncontrolling Interest	3 Months Ended
	Mar. 31, 2018
Noncontrolling Interest [Abstract]
Noncontrolling Interest	Noncontrolling Interest Noncontrolling interest represents the portion of the units in the Operating Trust not beneficially owned by the Company. An operating partnership unit (OP Unit) and a share of our common stock have essentially the same economic characteristics. Distributions with respect to OP Units will generally mirror distributions with respect to the Company’s common shares. Unitholders (other than the Company) generally have the right, commencing six months from the date of issuance of such OP Units, to cause the Operating Trust to redeem their OP Units in exchange for cash or, at the option of the Company, common shares of the Company on a one -for-one basis. As sole trustee, the Company will have the sole discretion to elect whether the redemption right will be satisfied by the Company in cash or the Company’s common shares. As a result, the Noncontrolling interest is classified as permanent equity. As of March 31, 2018 , the portion of the Operating Trust not beneficially owned by the Company is in the form of OP Units and LTIP Units (see Note 11 for a description of LTIP Units). LTIP Units may be subject to additional vesting requirements. The following table presents the changes in Equity Commonwealth’s issued and outstanding common shares and units for the three months ended March 31, 2018 : Common Shares OP Units and LTIP Units Total Outstanding at January 1, 2018 124,217,616 42,520 124,260,136 Repurchase of shares (2,970,209 ) — (2,970,209 ) Restricted share, time-based LTIP Unit grants and vested restricted stock units, net of forfeitures 209,666 — 209,666 Outstanding at March 31, 2018 121,457,073 42,520 121,499,593 Noncontrolling ownership interest in the Operating Trust 0.03 % The carrying value of the Noncontrolling interest is allocated based on the number of OP Units and LTIP Units in proportion to the number of OP Units and LTIP Units plus the number of common shares. We adjust the noncontrolling interest balance at the end of each period to reflect the noncontrolling partners’ interest in the net assets of the Operating Trust. Net income is allocated to the Noncontrolling interest in the Operating Trust based on the weighted average ownership percentage during the period. Equity Commonwealth’s weighted average ownership interest in the Operating Trust was 99.97% for the three months ended March 31, 2018 .

Cumulative Other Comprehensive

Cumulative Other Comprehensive Loss	3 Months Ended
	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Cumulative Other Comprehensive Loss	Cumulative Other Comprehensive Loss The following table presents the amounts recognized in cumulative other comprehensive loss for the three months ended March 31, 2018 (in thousands): Unrealized Loss on Derivative Instruments Unrealized Gain (Loss) on Marketable Securities Total Balance as of January 1, 2018 $ (456 ) $ 361 $ (95 ) Amounts reclassified from cumulative other comprehensive loss to cumulative net income pursuant to a change in accounting principle — (1,902 ) (1,902 ) Other comprehensive income (loss) before reclassifications 67 (226 ) (159 ) Amounts reclassified from cumulative other comprehensive loss to net income 50 — 50 Net current period other comprehensive income (loss) 117 (226 ) (109 ) Balance as of March 31, 2018 $ (339 ) $ (1,767 ) $ (2,106 ) The following table presents reclassifications out of cumulative other comprehensive loss for the three months ended March 31, 2018 (in thousands): Amounts Reclassified from Cumulative Other Comprehensive Loss to Net Income Details about Cumulative Other Comprehensive Loss Components Three Months Ended March 31, 2018 Affected Line Items in the Statement of Operations Interest rate cap contract $ 50 Interest expense

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes We have elected to be taxed as a REIT under the Internal Revenue Code of 1986, as amended, and are generally not subject to federal and state income taxes provided we distribute a sufficient amount of our taxable income to our shareholders and meet other requirements for qualifying as a REIT. We are also subject to certain state and local taxes without regard to our REIT status. Our provision for income taxes consists of the following (in thousands): Three Months Ended March 31, 2018 2017 Current: State and local $ 3,007 $ 170 Federal — 5 Income tax expense $ 3,007 $ 175 The taxable gain from sales of properties during the three months ended March 31, 2018 has fully utilized our net operating loss carryforward, and results in the tax expense recorded in the current period.

Derivative Instruments

Derivative Instruments	3 Months Ended
	Mar. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments	Derivative Instruments Risk Management Objective of Using Derivatives We are exposed to certain risks relating to our ongoing business operations, including the effect of changes in interest rates. The only risk we currently manage by using derivative instruments is our interest rate risk. We may use derivative financial instruments, including interest rate swaps, caps, options, floors and other interest rate derivative contracts, to hedge all or a portion of the interest rate risk associated with our borrowings. The principal objective of such arrangements is to reduce the risks and/or costs associated with our operating and financial structure as well as to hedge specific anticipated transactions. We do not intend to utilize derivatives for speculative or other purposes other than interest rate risk management. The use of derivative financial instruments carries certain risks, including the risk that the counterparties to these contractual arrangements are not able to perform under the agreements. To reduce this risk, we only enter into derivative financial instruments with counterparties with high credit ratings and with major financial institutions with which we and our affiliates may also have other financial relationships. We do not anticipate that any of the counterparties will fail to meet their obligations. Cash Flow Hedges of Interest Rate Risk Our objectives in using interest rate derivatives are to add stability to interest expense and to manage our exposure to interest rate movements. To accomplish this objective, we use interest rate caps as part of our interest rate risk management strategy. Interest rate caps designated as cash flow hedges involve the receipt of variable-rate amounts if interest rates rise above the cap strike rate. The effective portion of changes in the fair value of derivatives designated and that qualify as cash flow hedges is recorded in cumulative other comprehensive loss and is subsequently reclassified into earnings in the period that the hedged forecasted transaction affects earnings. During 2018, such derivatives were used to hedge the variable cash flows associated with variable-rate debt. The ineffective portion of the change in fair value of the derivatives is recognized directly in earnings. Amounts reported in cumulative other comprehensive loss related to derivatives will be reclassified to interest expense as interest payments are made on our variable-rate debt. During the next twelve months, we estimate that an additional $0.4 million will be reclassified from cumulative other comprehensive loss as an increase to interest expense. On March 4, 2016, we purchased an interest rate cap with a LIBOR strike price of 2.50% . The interest rate cap, effective April 1, 2016, has a notional amount of $400.0 million and a maturity date of March 1, 2019. As of March 31, 2018 , we had the following outstanding interest rate derivative that was designated as a cash flow hedge of interest rate risk: Interest Rate Derivative Number of Instruments Notional Amount (in thousands) Interest rate cap 1 $ 400,000 The table below presents the fair value of our derivative financial instrument as well as its classification on the condensed consolidated balance sheets as of March 31, 2018 and December 31, 2017 (amounts in thousands): Fair Value as of Interest Rate Derivative Designated as Hedging Instrument Balance Sheet Location March 31, December 31, Interest rate cap Other assets $ 84 $ 17 The table below details the location in the financial statements of the gain or loss recognized on interest rate derivatives designated as cash flow hedges for the three months ended March 31, 2018 and 2017 (amounts in thousands): Three Months Ended March 31, 2018 2017 Amount of gain (loss) recognized in cumulative other comprehensive loss $ 67 $ (154 ) Amount of loss reclassified from cumulative other comprehensive loss into interest expense 50 1 Credit-risk-related Contingent Features As of March 31, 2018 , we did not have any derivatives in a net liability position.

Share-Based Compensation

Share-Based Compensation	3 Months Ended
	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	Share-Based Compensation Recipients of the Company’s restricted shares have the same voting rights as any other common shareholder. During the period of restriction, the Company’s unvested restricted shareholders are eligible to receive dividend payments on their shares at the same rate and on the same date as any other common shareholder. The restricted shares are service based awards and vest over a four -year period. Recipients of the Company’s restricted stock units (RSUs) are entitled to receive dividends with respect to the common shares underlying the RSUs if and when the RSUs are earned, at which time the recipient will be entitled to receive an amount in cash equal to the aggregate amount of cash dividends that would have been paid in respect of the common shares underlying the recipient’s earned RSUs had such common shares been issued to the recipient on the first day of the performance period. To the extent that an award does not vest, the dividends related to unvested RSUs will be forfeited. The RSUs are market based awards with a service condition and recipients may earn RSUs based on the Company’s total shareholder return (TSR) relative to the TSRs of the companies that comprise the NAREIT Office Index over a three year performance period. Following the end of the three -year performance period, the number of earned awards will be determined. The earned awards vest in two tranches with 50% of the earned award vesting following the end of the performance period on the date the Compensation Committee of our Board of Trustees (the Committee) determines the level of achievement of the performance metric and the remaining 50% of the earned award vesting approximately one year thereafter, subject to the grant recipient’s continued employment. Compensation expense for the RSUs is determined using a Monte Carlo simulation model and is recognized ratably from the grant date to the vesting date of each tranche. LTIP Units are a class of beneficial interests in the Operating Trust that may be issued to employees, officers, or trustees of the Operating Trust, the Company or their subsidiaries (LTIP Units). Time-based LTIP Units have the same general characteristics as restricted shares and market-based LTIP Units have the same general characteristics as RSUs. Each LTIP Unit will convert automatically into an OP Unit on a one -for-one basis when the LTIP Unit becomes vested and its capital account is equalized with the per-unit capital account of the OP Units. Holders of LTIP Units generally will be entitled to receive the same per-unit distributions as the other outstanding OP Units in the Operating Trust, except that market-based LTIP Units will not participate in distributions until expiration of the applicable performance period, at which time any earned market-based LTIP Units generally will become entitled to receive a catch-up distribution for the periods prior to such time. 2018 Equity Award Activity On January 29, 2018, the Committee approved a grant of 125,409 restricted shares and 254,615 RSUs at target ( 634,628 RSUs at maximum) to the Company’s officers, certain employees and to Mr. Zell, the Chairman of our Board of Trustees, as part of their compensation for fiscal year 2017. The restricted shares granted on January 29, 2018 were valued at $29.78 per share, the closing price of our common shares on the New York Stock Exchange (NYSE) on that day. The assumptions and fair value for the RSUs granted during the three months ended March 31, 2018 are included in the following table on a per share basis. 2018 Fair value of RSUs granted $ 37.13 Expected term (years) 4 Expected volatility — Expected dividend yield 1.68 % Risk-free rate 2.26 % 2017 Equity Award Activity On January 24, 2017, the Committee approved a grant of 39,364 time-based LTIP Units, 79,924 market-based LTIP Units at target ( 199,211 market-based LTIP Units at maximum), 76,424 restricted shares and 155,168 RSUs at target ( 386,756 RSUs at maximum) to the Company’s officers, certain employees and to Mr. Zell, the Chairman of our Board of Trustees, as part of their compensation for fiscal year 2016. Outstanding Equity Awards As of March 31, 2018 , the estimated future compensation expense for all unvested restricted shares and time-based LTIP Units was $10.9 million . Compensation expense for the restricted share and time-based LTIP Unit awards is being recognized on a straight-line basis over the requisite service period for each separately vesting portion of the award. The weighted average period over which the future compensation expense will be recorded for the restricted shares and time-based LTIP units is approximately 2.3 years. As of March 31, 2018 , the estimated future compensation expense for all unvested RSUs and market-based LTIP Units was $21.1 million . The weighted average period over which the future compensation expense will be recorded for the RSUs and market-based LTIP Units is approximately 2.3 years. During the three months ended March 31, 2018 and 2017 , we recorded $5.3 million and $5.2 million , respectively, of compensation expense, net of forfeitures, in general and administrative expense for grants to our trustees and employees related to our equity compensation plans. The $5.3 million of compensation expense recorded during the three months ended March 31, 2018 includes $0.4 million of accelerated vesting due to a staffing reduction. Forfeitures are recognized as they occur. At March 31, 2018 , 868,268 shares/units remain available for issuance under the Equity Commonwealth 2015 Omnibus Incentive Plan, as amended.

Fair Value of Assets and Liabil

Fair Value of Assets and Liabilities	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value of Assets and Liabilities	Fair Value of Assets and Liabilities The table below presents assets measured at fair value during 2018 , categorized by the level of inputs used in the valuation of the assets (dollars in thousands): Fair Value at March 31, 2018 Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Description Total (Level 1) (Level 2) (Level 3) Recurring Fair Value Measurements: Interest rate cap contract $ 84 $ — $ 84 $ — Marketable securities $ 247,879 $ 247,879 $ — $ — Interest Rate Cap Contract The fair value of our interest rate cap contract is determined using the net discounted cash flows of the derivative based on the market based interest rate curve (level 2 inputs) and adjusted for our credit spread and the actual and estimated credit spreads of the counterparties (level 3 inputs). Although we have determined that the majority of the inputs used to value our derivative fall within level 2 of the fair value hierarchy, the credit valuation adjustments associated with our derivative utilize level 3 inputs, such as estimates of current credit spreads, to evaluate the likelihood of default by us and the counterparties. As of March 31, 2018 , we have assessed the significance of the impact of the credit valuation adjustments on the overall valuation of our derivative position and have determined that the credit valuation adjustments are not significant to the overall valuation of our derivative. As a result, we have determined that our derivative valuation in its entirety is classified as level 2 inputs in the fair value hierarchy. Properties Held and Used As part of our office repositioning strategy adopted by our Board of Trustees in December 2016, and pursuant to our accounting policy, in 2017, we evaluated the recoverability of the carrying values of each of the real estate assets that comprised our portfolio and determined that due to the shortening of the expected periods of ownership as a result of the office repositioning strategy and current estimates of market value less estimated costs to sell, it was necessary to reduce the net book value of a portion of the real estate assets in our portfolio to their estimated fair values. We anticipate the potential disposition of certain properties prior to the end of their remaining useful lives. As a result, in the first quarter of 2018, we recorded an impairment charge related to 777 East Eisenhower Parkway and 97 Newberry Road of $12.1 million in accordance with our impairment analysis procedures. We determined this impairment based on independent third party broker information, which are level 3 inputs according to the fair value hierarchy established in ASC 820. We reduced the aggregate carrying value of these properties from $41.8 million to their estimated fair value less estimated costs to sell of $29.7 million . We evaluated each of our properties and determined there were no additional valuation adjustments necessary at March 31, 2018 . Financial Instruments In addition to the assets described in the above table, our financial instruments include our cash and cash equivalents, real estate mortgage receivable, restricted cash, marketable securities, senior unsecured debt and mortgage notes payable. At March 31, 2018 and December 31, 2017 , the fair value of these additional financial instruments were not materially different from their carrying values, except as follows (in thousands): March 31, 2018 December 31, 2017 Carrying Amount Fair Value Carrying Amount Fair Value Senior unsecured debt and mortgage notes payable $ 681,675 $ 693,328 $ 856,940 $ 874,280 The fair values of our senior notes are based on quoted market prices (level 2 inputs) and the fair values of our mortgage notes payable are based on estimates using discounted cash flow analyses and currently prevailing interest rates adjusted by credit risk spreads (level 3 inputs). Other financial instruments that potentially subject us to concentrations of credit risk consist principally of rents receivable; however, as of March 31, 2018 , no single tenant of ours is responsible for more than 7.0% of our total annualized rents, other than one tenant that is responsible for 13.0% of our total annualized rents. Our interest rate cap counterparty is a major financial institution and we monitor the amount of our credit exposure to any one counterparty.

Earnings Per Common Share

Earnings Per Common Share	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Earnings Per Common Share	Earnings Per Common Share The following table sets forth the computation of basic and diluted earnings per share (amounts in thousands except per share amounts): Three Months Ended March 31, 2018 2017 Numerator for earnings per common share - basic: Net income $ 187,662 $ 23,822 Net income attributable to noncontrolling interest (63 ) (8 ) Preferred distributions (1,997 ) (1,997 ) Numerator for net income per share - basic $ 185,602 $ 21,817 Numerator for earnings per common share - diluted: Net income $ 187,662 $ 23,822 Preferred distributions — (1,997 ) Numerator for net income per share - diluted $ 187,662 $ 21,825 Denominator for earnings per common share - basic and diluted: Weighted average number of common shares outstanding - basic (1) 123,867 124,047 RSUs (2) 730 1,023 LTIP Units (2)(3) 136 80 OP Units (4) 1 — Series D preferred shares; 6 1/2% cumulative convertible 2,363 — Weighted average number of common shares outstanding - diluted 127,097 125,150 Net income per common share attributable to Equity Commonwealth common shareholders: Basic $ 1.50 $ 0.18 Diluted $ 1.48 $ 0.17 Anti-dilutive securities: Effect of Series D preferred shares; 6 1/2% cumulative convertible (5) — 2,363 (1) The three months ended March 31, 2018 and 2017 , includes 307 and 0 weighted-average, unvested, measured RSUs, respectively. (2) Represents weighted-average number of common shares that would have been issued if the quarter-end was the measurement date for RSUs and performance-based LTIPs. (3) Represents weighted-average time-based and performance-based LTIPs that would have been issued if the quarter-end was the measurement date for the periods shown. (4) Beneficial interests in the Operating Trust. (5) The Series D preferred shares are excluded from the diluted earnings per share calculation for the three months ended March 31, 2017 because including the Series D preferred shares would also require that the preferred distributions be added back to net income, resulting in anti-dilution.

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Segment Information	Segment Information Our primary business is the ownership and operation of office properties, and we currently have one reportable segment. More than 90% of our revenues for the three months ended March 31, 2018 are from office properties.

Related Person Transactions

Related Person Transactions	3 Months Ended
	Mar. 31, 2018
Related Party Transactions [Abstract]
Related Person Transactions	Related Person Transactions The following discussion includes a description of our related person transactions for the three months ended March 31, 2018 and 2017 . Two North Riverside Plaza Joint Venture Limited Partnership: We have a lease with Two North Riverside Plaza Joint Venture Limited Partnership, an entity associated with Mr. Zell, our Chairman, to occupy office space on the twentieth and twenty-first floors of Two North Riverside Plaza in Chicago, Illinois (20th/21st Floor Office Lease). The initial term of the lease is approximately five years, with one 5 -year renewal option. We completed improvements to the office space utilizing the $0.7 million tenant improvement allowance pursuant to the lease. In connection with the 20th/21st Floor Office Lease, we also have a lease with Two North Riverside Plaza Joint Venture Limited Partnership for storage space in the basement of Two North Riverside Plaza. The lease expires December 31, 2020; however, each party has the right to terminate on 30 days' prior written notice. During the three months ended March 31, 2018 and 2017 , we recognized expense of $0.2 million and $0.2 million , respectively, pursuant to the 20 th /21 st Floor Office Lease and the related storage space.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On April 11, 2018, we announced that our Board of Trustees declared a dividend of $0.40625 per series D preferred share, which will be paid on May 15, 2018 to shareholders of record on April 27, 2018 (see Note 6). On May 4, 2018, we redeemed at par the total $400.0 million outstanding under our 5 -year and 7 -year term loans.

Summary of Significant Accoun25

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements of EQC have been prepared without audit. Certain information and footnote disclosures required by U.S. generally accepted accounting principles, or GAAP, for complete financial statements have been condensed or omitted. We believe the disclosures made are adequate to make the information presented not misleading. However, the accompanying condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes contained in our Annual Report on Form 10-K (Annual Report) for the year ended December 31, 2017 . Capitalized terms used, but not defined in this Quarterly Report, have the same meanings as in our Annual Report. In the opinion of our management, all adjustments, which include only normal recurring adjustments considered necessary for a fair presentation, have been included. All intercompany transactions and balances with or among our subsidiaries have been eliminated. Operating results for interim periods are not necessarily indicative of the results that may be expected for the full year. Reclassifications have been made to the prior years’ financial statements to conform to the current year’s presentation. The preparation of financial statements in conformity with GAAP requires us to make estimates and assumptions that affect reported amounts. Actual results could differ from those estimates. Significant estimates in the condensed consolidated financial statements include the allowance for doubtful accounts, purchase price allocations, useful lives of fixed assets and impairment of real estate and intangible assets. Share amounts are presented in whole numbers, except where noted.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In August 2017, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities, to enable entities to better portray the economics of their risk management activities in the financial statements and enhance the transparency and understandability of hedge results. The amendments also simplify the application of hedge accounting in certain situations. This update is effective for fiscal years beginning after December 15, 2018, and for interim periods within those fiscal years. We are evaluating the impact ASU 2017-12 will have on our financial position and results of operations. In May 2017, the FASB issued ASU 2017-09 Compensation-Stock Compensation (Topic 718): Scope of Modification Accounting. ASU 2017-09 is designed to provide clarity and reduce both (1) diversity in practice and (2) cost and complexity when applying the guidance in Topic 718, to a change to the terms or conditions of a share-based payment award. ASU 2017-09 is effective for fiscal years beginning after December 15, 2017. We adopted this ASU on January 1, 2018, and the adoption did not have a material impact on our consolidated financial statements. In February 2017, the FASB issued ASU 2017-01, Clarifying the Definition of a Business, that changes the definition of a business to assist entities with evaluating when a set of transferred assets and activities is a business. This update is effective for fiscal years beginning after December 15, 2017, and for interim periods within those fiscal years. We early adopted this ASU effective January 1, 2017, and the adoption of this ASU did not have a material impact on our consolidated financial statements. In February 2017, the FASB issued ASU 2017-05 Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets. ASU 2017-05 is designed to provide guidance on how to recognize gain and losses on sales, including partial sales, of nonfinancial assets to noncustomers. We adopted this ASU on January 1, 2018 and the adoption did not have a material impact on our consolidated financial statements. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash, which amends FASB Accounting Standards Codification (ASC) Topic 230, Statements of Cash Flows, to add or clarify guidance on the classification and presentation of restricted cash in the statement of cash flows. This update is effective for fiscal years beginning after December 15, 2017, and for interim periods within those fiscal years. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments, which addresses eight specific cash flow issues with the objective of reducing the existing diversity in practice. This update is effective for fiscal years beginning after December 15, 2017, and for interim periods within those fiscal years. We early adopted both ASU 2016-18 and ASU 2016-15 for the period ended December 31, 2017 and made the following reclassifications to the prior year's condensed consolidated statement of cash flows to conform to the current year's presentation (in thousands): Statement of Cash Flows for the Three Months Ended March 31, 2017 Originally Reported Effect of Change As Adjusted Cash used in operating activities $ (2,690 ) $ (1,311 ) $ (4,001 ) Cash used in investing activities (200,923 ) 934 (199,989 ) In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which requires more timely recognition of credit losses associated with financial assets. This update is effective for fiscal years beginning after December 15, 2019, and for interim periods within those fiscal years. Early adoption is permitted for fiscal years, and interim periods within those years, beginning after December 15, 2018. We are currently in the process of evaluating the impact, if any, the adoption of this ASU will have on our consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases, which sets out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e., lessees and lessors). ASU 2016-02 requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase of the leased asset by the lessee. This classification will determine whether the lease expense is recognized based on an effective interest method or on a straight-line basis over the term of the lease. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less will be accounted for similar to existing guidance for operating leases today. ASU 2016-02 supersedes previous leasing standards. ASU 2016-02 is effective for us for reporting periods beginning after December 15, 2018, with early adoption permitted. We are still assessing the impact of adopting ASU 2016-02. For leases where we are the lessor, we expect to account for these leases using an approach that is substantially equivalent to current guidance. Additionally, under ASU 2016-02 lessors may only capitalize incremental direct leasing costs. For leases in which we are the lessee, we expect to recognize a right-of-use asset and a lease liability equal to the present value of the minimum lease payments with rent expense being recognized on a straight-line basis and the right of use asset being reduced when lease payments are made. In January 2016, the FASB issued ASU 2016-01, Financial Instruments-Overall: Recognition and Measurement of Financial Assets and Financial Liabilities, related to certain aspects of recognition, measurement, presentation, and disclosure of financial instruments. ASU 2016-01 will require entities to measure their equity investments at fair value and recognize any changes in fair value in net income, with certain exceptions, rather than other comprehensive income. This update is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. We adopted this ASU on January 1, 2018 and reclassified a $1.9 million unrealized gain from cumulative other comprehensive loss to cumulative net income on our condensed consolidated balance sheet (see Note 8). In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers. The objective of ASU 2014-09, as amended, is to establish a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and will supersede most of the existing revenue recognition guidance, including industry-specific guidance. The core principle is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In applying ASU 2014-09, companies will perform a five-step analysis of transactions to determine when and how revenue is recognized. ASU 2014-09 applies to all contracts with customers except those that are within the scope of other topics in the FASB’s ASC, and more particularly lease contracts with customers, which are a scope exception. ASU 2014-09 is effective for the first interim period within annual reporting periods beginning after December 15, 2017, with early adoption permitted. We adopted this ASU on January 1, 2018 and the adoption did not have a material impact on our consolidated financial statements.
Properties Held For Sale	We classify all properties that meet the criteria outlined in the Property, Plant and Equipment Topic of the FASB ASC as held for sale on our condensed consolidated balance sheets.
Marketable Securities	our marketable securities consisted of United States Treasury notes and common stock. The United States Treasury notes are classified as available-for-sale and mature in 2019. Available-for-sale securities are presented on our condensed consolidated balance sheets at fair value. Changes in values of the United States Treasury notes are recognized in accumulated other comprehensive loss. On January 1, 2018 we adopted ASU 2016-01 (see Note 2) and reclassified a $1.9 million unrealized gain from cumulative other comprehensive loss to cumulative net income on our condensed consolidated balance sheet. Changes in values of common stock are recognized in interest and other income, net on the condensed consolidated statements of operations.

Summary of Significant Accoun26

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
New Accounting Pronouncement, Early Adoption	We early adopted both ASU 2016-18 and ASU 2016-15 for the period ended December 31, 2017 and made the following reclassifications to the prior year's condensed consolidated statement of cash flows to conform to the current year's presentation (in thousands): Statement of Cash Flows for the Three Months Ended March 31, 2017 Originally Reported Effect of Change As Adjusted Cash used in operating activities $ (2,690 ) $ (1,311 ) $ (4,001 ) Cash used in investing activities (200,923 ) 934 (199,989 )

Real Estate Properties (Tables)

Real Estate Properties (Tables)	3 Months Ended
	Mar. 31, 2018
Real Estate [Abstract]
Disclosure of Long Lived Assets Held-for-sale	As of March 31, 2018 , we classified the following property as held for sale: Asset Number of Number of Square Footage 1601 Dry Creek Drive 1 1 552,865 Summarized balance sheet information for the properties classified as held for sale is as follows (in thousands): March 31, 2018 December 31, 2017 Real estate properties $ 24,786 $ 76,066 Rents receivable 7,245 13,270 Other assets, net 6,851 8,352 Assets held for sale $ 38,882 $ 97,688 Accounts payable and accrued expenses $ 1,099 $ 1,021 Rent collected in advance 1 408 Security deposits 53 411 Liabilities related to properties held for sale $ 1,153 $ 1,840
Summary of Properties Sold and Income Statement Information for Properties Disposed of	During the three months ended March 31, 2018 , we sold the following properties (dollars in thousands): Asset Date Sold Number of Number of Square Footage Gross Sales Price Gain on Sale Properties 1600 Market Street February 2018 1 1 825,968 $ 160,000 $ 54,599 600 West Chicago Avenue (1) February 2018 1 2 1,561,477 510,000 107,830 5073, 5075, & 5085 S. Syracuse Street March 2018 1 1 248,493 115,186 42,762 3 4 2,635,938 $ 785,186 $ 205,191 (1) The sale of this property did not represent a strategic shift under ASC Topic 205. However, the sale does represent an individually significant disposition. The operating results of this property are included in continued operations for all periods presented through the date of sale. Net income for this property for the three months ended March 31, 2018 and 2017 was $110.0 million and $2.7 million , respectively.

Marketable Securities (Tables)

Marketable Securities (Tables)	3 Months Ended
	Mar. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Summary of Marketable Securities	Below is a summary of our marketable securities as of March 31, 2018 and December 31, 2017 (in thousands): March 31, 2018 December 31, 2017 Amortized Cost Unrealized Loss Estimated Fair Value Cost or Amortized Cost Unrealized Gain, Net Estimated Fair Value Marketable securities $ 249,646 $ (1,767 ) $ 247,879 $ 276,567 $ 361 $ 276,928

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2018
Stockholders' Equity Note [Abstract]
Schedule of Declared Distributions	In 2018 , our Board of Trustees declared distributions on our series D preferred shares to date as follows: Declaration Date Record Date Payment Date Series D Dividend Per Share January 12, 2018 January 30, 2018 February 15, 2018 $ 0.40625 April 11, 2018 April 27, 2018 May 15, 2018 $ 0.40625

Noncontrolling Interest (Tables

Noncontrolling Interest (Tables)	3 Months Ended
	Mar. 31, 2018
Noncontrolling Interest [Abstract]
Schedule of Issued and Outstanding Common Shares	The following table presents the changes in Equity Commonwealth’s issued and outstanding common shares and units for the three months ended March 31, 2018 : Common Shares OP Units and LTIP Units Total Outstanding at January 1, 2018 124,217,616 42,520 124,260,136 Repurchase of shares (2,970,209 ) — (2,970,209 ) Restricted share, time-based LTIP Unit grants and vested restricted stock units, net of forfeitures 209,666 — 209,666 Outstanding at March 31, 2018 121,457,073 42,520 121,499,593 Noncontrolling ownership interest in the Operating Trust 0.03 %
Schedule of Issued and Outstanding Units	The following table presents the changes in Equity Commonwealth’s issued and outstanding common shares and units for the three months ended March 31, 2018 : Common Shares OP Units and LTIP Units Total Outstanding at January 1, 2018 124,217,616 42,520 124,260,136 Repurchase of shares (2,970,209 ) — (2,970,209 ) Restricted share, time-based LTIP Unit grants and vested restricted stock units, net of forfeitures 209,666 — 209,666 Outstanding at March 31, 2018 121,457,073 42,520 121,499,593 Noncontrolling ownership interest in the Operating Trust 0.03 %

Cumulative Other Comprehensiv31

Cumulative Other Comprehensive Loss (Tables)	3 Months Ended
	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule of Amounts Recognized in Cumulative Other Comprehensive Loss	The following table presents the amounts recognized in cumulative other comprehensive loss for the three months ended March 31, 2018 (in thousands): Unrealized Loss on Derivative Instruments Unrealized Gain (Loss) on Marketable Securities Total Balance as of January 1, 2018 $ (456 ) $ 361 $ (95 ) Amounts reclassified from cumulative other comprehensive loss to cumulative net income pursuant to a change in accounting principle — (1,902 ) (1,902 ) Other comprehensive income (loss) before reclassifications 67 (226 ) (159 ) Amounts reclassified from cumulative other comprehensive loss to net income 50 — 50 Net current period other comprehensive income (loss) 117 (226 ) (109 ) Balance as of March 31, 2018 $ (339 ) $ (1,767 ) $ (2,106 )
Schedule of Reclassifications Out of Cumulative Other Comprehensive Loss	The following table presents reclassifications out of cumulative other comprehensive loss for the three months ended March 31, 2018 (in thousands): Amounts Reclassified from Cumulative Other Comprehensive Loss to Net Income Details about Cumulative Other Comprehensive Loss Components Three Months Ended March 31, 2018 Affected Line Items in the Statement of Operations Interest rate cap contract $ 50 Interest expense

Income Taxes (Tables)

Income Taxes (Tables)	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Schedule of Provision for Income Taxes	Our provision for income taxes consists of the following (in thousands): Three Months Ended March 31, 2018 2017 Current: State and local $ 3,007 $ 170 Federal — 5 Income tax expense $ 3,007 $ 175

Derivative Instruments (Tables)

Derivative Instruments (Tables)	3 Months Ended
	Mar. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Outstanding Interest Rate Derivatives Designated as Cash Flow Hedges of Interest Rate Risk	As of March 31, 2018 , we had the following outstanding interest rate derivative that was designated as a cash flow hedge of interest rate risk: Interest Rate Derivative Number of Instruments Notional Amount (in thousands) Interest rate cap 1 $ 400,000
Schedule of Fair Value of Derivative Financial Instruments	The table below presents the fair value of our derivative financial instrument as well as its classification on the condensed consolidated balance sheets as of March 31, 2018 and December 31, 2017 (amounts in thousands): Fair Value as of Interest Rate Derivative Designated as Hedging Instrument Balance Sheet Location March 31, December 31, Interest rate cap Other assets $ 84 $ 17
Schedule of Gain or Loss Recognized on Interest Rate Derivatives Designated as Cash Flow Hedges	The table below details the location in the financial statements of the gain or loss recognized on interest rate derivatives designated as cash flow hedges for the three months ended March 31, 2018 and 2017 (amounts in thousands): Three Months Ended March 31, 2018 2017 Amount of gain (loss) recognized in cumulative other comprehensive loss $ 67 $ (154 ) Amount of loss reclassified from cumulative other comprehensive loss into interest expense 50 1

Share-Based Compensation (Table

Share-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Assumptions and Fair Values for RSUs Granted in the Period	The assumptions and fair value for the RSUs granted during the three months ended March 31, 2018 are included in the following table on a per share basis. 2018 Fair value of RSUs granted $ 37.13 Expected term (years) 4 Expected volatility — Expected dividend yield 1.68 % Risk-free rate 2.26 %

Fair Value of Assets and Liab35

Fair Value of Assets and Liabilities (Tables)	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Schedule of Assets Measured at Fair Value	The table below presents assets measured at fair value during 2018 , categorized by the level of inputs used in the valuation of the assets (dollars in thousands): Fair Value at March 31, 2018 Using Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Description Total (Level 1) (Level 2) (Level 3) Recurring Fair Value Measurements: Interest rate cap contract $ 84 $ — $ 84 $ — Marketable securities $ 247,879 $ 247,879 $ — $ —
Schedule of Fair Value and Carrying Value of Financial Instruments	At March 31, 2018 and December 31, 2017 , the fair value of these additional financial instruments were not materially different from their carrying values, except as follows (in thousands): March 31, 2018 December 31, 2017 Carrying Amount Fair Value Carrying Amount Fair Value Senior unsecured debt and mortgage notes payable $ 681,675 $ 693,328 $ 856,940 $ 874,280

Earnings Per Common Share (Tabl

Earnings Per Common Share (Tables)	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Schedule of Computation of Basic and Diluted Earnings Per Share	The following table sets forth the computation of basic and diluted earnings per share (amounts in thousands except per share amounts): Three Months Ended March 31, 2018 2017 Numerator for earnings per common share - basic: Net income $ 187,662 $ 23,822 Net income attributable to noncontrolling interest (63 ) (8 ) Preferred distributions (1,997 ) (1,997 ) Numerator for net income per share - basic $ 185,602 $ 21,817 Numerator for earnings per common share - diluted: Net income $ 187,662 $ 23,822 Preferred distributions — (1,997 ) Numerator for net income per share - diluted $ 187,662 $ 21,825 Denominator for earnings per common share - basic and diluted: Weighted average number of common shares outstanding - basic (1) 123,867 124,047 RSUs (2) 730 1,023 LTIP Units (2)(3) 136 80 OP Units (4) 1 — Series D preferred shares; 6 1/2% cumulative convertible 2,363 — Weighted average number of common shares outstanding - diluted 127,097 125,150 Net income per common share attributable to Equity Commonwealth common shareholders: Basic $ 1.50 $ 0.18 Diluted $ 1.48 $ 0.17 Anti-dilutive securities: Effect of Series D preferred shares; 6 1/2% cumulative convertible (5) — 2,363 (1) The three months ended March 31, 2018 and 2017 , includes 307 and 0 weighted-average, unvested, measured RSUs, respectively. (2) Represents weighted-average number of common shares that would have been issued if the quarter-end was the measurement date for RSUs and performance-based LTIPs. (3) Represents weighted-average time-based and performance-based LTIPs that would have been issued if the quarter-end was the measurement date for the periods shown. (4) Beneficial interests in the Operating Trust. (5) The Series D preferred shares are excluded from the diluted earnings per share calculation for the three months ended March 31, 2017 because including the Series D preferred shares would also require that the preferred distributions be added back to net income, resulting in anti-dilution

Business (Details)

Business (Details) ft² in Millions, $ in Billions	Mar. 31, 2018USD ($)ft²buildingproperty
Noncontrolling Interest [Line Items]
Cash, cash equivalents, and short-term investments | $	$ 3.1
Consolidated Properties
Noncontrolling Interest [Line Items]
Number of real estate properties | property	13
Number of buildings | building	22
Square footage (in sqft) | ft²	6.3
Operating Trust
Noncontrolling Interest [Line Items]
Noncontrolling interest, ownership percentage by parent	99.97%

Summary of Significant Accoun38

Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018
New Accounting Pronouncement, Early Adoption [Line Items]
Cash used in operating activities	$ (371)	$ (4,001)
Cash used in investing activities	$ 751,619	(199,989)
Accounting Standards Update 2016-18 and Accounting Standards Update 2016-15
New Accounting Pronouncement, Early Adoption [Line Items]
Cash used in operating activities		(4,001)
Cash used in investing activities		(199,989)
Accounting Standards Update 2016-01 | Cumulative other comprehensive loss
New Accounting Pronouncement, Early Adoption [Line Items]
Cumulative effect of new accounting principle in period of adoption			$ (1,902)
Accounting Standards Update 2016-01 | Cumulative net income
New Accounting Pronouncement, Early Adoption [Line Items]
Cumulative effect of new accounting principle in period of adoption			$ 1,902
Originally Reported | Accounting Standards Update 2016-18 and Accounting Standards Update 2016-15
New Accounting Pronouncement, Early Adoption [Line Items]
Cash used in operating activities		(2,690)
Cash used in investing activities		(200,923)
Effect of Change | Accounting Standards Update 2016-18 and Accounting Standards Update 2016-15
New Accounting Pronouncement, Early Adoption [Line Items]
Cash used in operating activities		(1,311)
Cash used in investing activities		$ 934

Real Estate Properties - Narrat

Real Estate Properties - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Real Estate [Abstract]
Real estate improvements	$ 12.9	$ 14.2

Real Estate Properties - Summar

Real Estate Properties - Summary of Properties Held for Sale (Details) - Subsequent event - Held-for-sale - 1601 Dry Creek Drive	1 Months Ended
	May 31, 2018ft²buildingproperty
Real Estate Properties [Line Items]
Number of Properties | property	1
Number of Buildings | building	1
Square Footage (in sqft) | ft²	552,865

Real Estate Properties - Summ41

Real Estate Properties - Summary of Balance Sheet Information for all Properties Classified as Held for sale (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Liabilities related to properties held for sale	$ 1,153	$ 1,840
Held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate properties	24,786	76,066
Rents receivable	7,245	13,270
Other assets, net	6,851	8,352
Assets held for sale	38,882	97,688
Accounts payable and accrued expenses	1,099	1,021
Rent collected in advance	1	408
Security deposits	53	411
Liabilities related to properties held for sale	$ 1,153	$ 1,840

Real Estate Properties - Summ42

Real Estate Properties - Summary of Properties Sold (Details) $ in Thousands	1 Months Ended		3 Months Ended
	Mar. 31, 2018USD ($)ft²buildingproperty	Feb. 28, 2018USD ($)ft²buildingproperty	Mar. 31, 2018USD ($)ft²buildingproperty	Mar. 31, 2017USD ($)
Real Estate Properties [Line Items]
Gain on Sale			$ 205,211	$ 16,454
Disposed of by Sale
Real Estate Properties [Line Items]
Number of Properties | property			3
Number of Buildings | building			4
Square Footage (in sqft) | ft²			2,635,938
Gross Sales Price			$ 785,186
Gain on Sale			205,191
Net income included in continued operations			$ 110,000	$ 2,700
Disposed of by Sale | 1600 Market Street
Real Estate Properties [Line Items]
Number of Properties | property		1
Number of Buildings | building		1
Square Footage (in sqft) | ft²		825,968
Gross Sales Price		$ 160,000
Gain on Sale		$ 54,599
Disposed of by Sale | 600 West Chicago Avenue
Real Estate Properties [Line Items]
Number of Properties | property		1
Number of Buildings | building		2
Square Footage (in sqft) | ft²		1,561,477
Gross Sales Price		$ 510,000
Gain on Sale		$ 107,830
Disposed of by Sale | 5073, 5075, & 5085 S. Syracuse Street
Real Estate Properties [Line Items]
Number of Properties | property	1
Number of Buildings | building	1
Square Footage (in sqft) | ft²	248,493
Gross Sales Price	$ 115,186
Gain on Sale	$ 42,762

Marketable Securities (Details)

Marketable Securities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Recognized loss on sale of common stock included in interest and other income	$ 5,000
Estimated Fair Value	247,879		$ 276,928
Marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	249,646		276,567
Unrealized Loss	(1,767)
Unrealized Gain, Net			361
Estimated Fair Value	$ 247,879		$ 276,928
Accounting Standards Update 2016-01 | Cumulative other comprehensive loss
Schedule of Available-for-sale Securities [Line Items]
Cumulative effect of new accounting principle in period of adoption		$ (1,902)
Accounting Standards Update 2016-01 | Cumulative net income
Schedule of Available-for-sale Securities [Line Items]
Cumulative effect of new accounting principle in period of adoption		$ 1,902

Indebtedness - Narrative (Detai

Indebtedness - Narrative (Details)	Mar. 31, 2018USD ($)property	Mar. 07, 2018USD ($)	Mar. 31, 2018USD ($)optionproperty	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)
Debt Instrument [Line Items]
Senior unsecured notes, net	$ 250,000,000		$ 250,000,000
Loss on early extinguishment of debt			4,867,000	$ 0
Real estate properties, net	867,362,000		867,362,000		$ 1,296,893,000
Mortgage notes payable, net	32,281,000		32,281,000		$ 32,594,000
Loan facility, 5-year term
Debt Instrument [Line Items]
Term loan amount outstanding	200,000,000		$ 200,000,000
Interest accrual rate			3.03%
Loan facility, 5-year term | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate			1.15%
Loan facility, 5-year term | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate			0.90%
Loan facility, 5-year term | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate			1.80%
Loan facility, 7-year term
Debt Instrument [Line Items]
Term loan amount outstanding	200,000,000		$ 200,000,000
Interest accrual rate			3.43%
Loan facility, 7-year term | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate			1.55%
Loan facility, 7-year term | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate			1.40%
Loan facility, 7-year term | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate			2.35%
Revolving credit facility and term loans
Debt Instrument [Line Items]
Additional increases in maximum amount of borrowings available	$ 1,150,000,000		$ 1,150,000,000
6.65% Senior Unsecured Notes Due 2018
Debt Instrument [Line Items]
Debt redeemed at par		$ 175,000,000
Debt instrument, interest rate		5.75%
Loss on early extinguishment of debt		$ 4,900,000
Mortgage notes
Debt Instrument [Line Items]
Number of real estate properties secured by mortgage | property	2		2
Real estate properties, net	$ 51,900,000		$ 51,900,000
Mortgage notes payable, net	32,300,000		$ 32,300,000
Revolving credit facility
Debt Instrument [Line Items]
Interest rate payable percentage			2.93%
Amount outstanding	0		$ 0
Revolving credit facility | Minimum
Debt Instrument [Line Items]
Commitment fee percentage			0.125%
Revolving credit facility | Maximum
Debt Instrument [Line Items]
Commitment fee percentage			0.30%
Revolving credit facility | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate			1.05%
Revolving credit facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate			0.875%
Revolving credit facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate			1.55%
Revolving credit facility | Base rate | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate			0.00%
Revolving credit facility | Base rate | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate			0.55%
Revolving credit facility | Unsecured revolving credit facility
Debt Instrument [Line Items]
Maximum borrowing capacity	750,000,000		$ 750,000,000
Debt instrument, number of extension options | option			2
Debt instrument, extension option term			6 months
Debt instrument, extension option fee, percent			0.075%
Amount available for borrowing	$ 750,000,000		$ 750,000,000
Commitment fee percentage	0.20%
Revolving credit facility | Loan facility, 5-year term
Debt Instrument [Line Items]
Term loan amount outstanding	$ 200,000,000		$ 200,000,000
Debt instrument, term			5 years
Revolving credit facility | Loan facility, 7-year term
Debt Instrument [Line Items]
Term loan amount outstanding	200,000,000		$ 200,000,000
Debt instrument, term			7 years
Letter of credit | Unsecured revolving credit facility
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 100,000,000		$ 100,000,000

Shareholders' Equity - Narrativ

Shareholders' Equity - Narrative (Details) - USD ($)	Mar. 14, 2018	Mar. 15, 2017	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2017
Class of Stock [Line Items]
Stock repurchase program, period in force	12 months
Common Shares
Class of Stock [Line Items]
Stock repurchase program, authorized amount (up to)		$ 150,000,000
Stock repurchase program, period in force		12 months
Stock repurchase program, amount not utilized			$ 81,000,000
Stock repurchase program, additional authorized amount (up to)	$ 150,000,000
Stock repurchased and retired during period (in shares)				2,970,209
Stock repurchased and retired during period, price per share (in dollars per share)				$ 29.67
Stock repurchased and retired during period, value	$ 19,100,000	$ 69,000,000		$ 88,100,000
Stock repurchase program, remaining authorized repurchase amount			$ 130,900,000	$ 130,900,000
Number of shares surrendered to satisfy tax withholding obligations (in shares)				57,348	6,694

Shareholders' Equity - Schedule

Shareholders' Equity - Schedule of Declared Distributions (Details) - Series D - $ / shares	May 15, 2018	Apr. 27, 2018	Apr. 11, 2018	Feb. 15, 2018	Jan. 30, 2018
Class of Stock [Line Items]
Dividend declared (in dollars per share)					$ 0.40625
Dividend paid (in dollars per share)				$ 0.40625
Subsequent event
Class of Stock [Line Items]
Dividend declared (in dollars per share)		$ 0.40625	$ 0.40625
Dividend paid (in dollars per share)	$ 0.40625

Noncontrolling Interest (Detail

Noncontrolling Interest (Details)	3 Months Ended
	Mar. 31, 2018shares
Noncontrolling Interest [Abstract]
Common stock, conversion term	6 months
Common stock, conversion basis (in shares)	1
Operating Trust
Noncontrolling Interest [Line Items]
Noncontrolling interest, ownership percentage by parent	99.97%

Noncontrolling Interest - Commo

Noncontrolling Interest - Common Shares and Units Activity (Details)	3 Months Ended
	Mar. 31, 2018shares
Increase (Decrease) in Stockholders' Equity
Ownership percentage by noncontrolling owners	0.03%
Common Shares
Increase (Decrease) in Stockholders' Equity
Outstanding, beginning balance (in shares)	124,217,616
Repurchase of shares (in shares)	(2,970,209)
Restricted share, time-based LTIP Unit grants and vested restricted stock units, net of forfeitures (in shares)	209,666
Outstanding, ending balance (in shares)	121,457,073
OP Units and LTIP Units | Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity
Outstanding, beginning balance (in shares)	42,520
Repurchase of shares (in shares)	0
Restricted share, time-based LTIP Unit grants and vested restricted stock units, net of forfeitures (in shares)	0
Outstanding, ending balance (in shares)	42,520
Common Class A, LTIP Units, and OP Units
Increase (Decrease) in Stockholders' Equity
Outstanding, beginning balance (in shares)	124,260,136
Repurchase of shares (in shares)	(2,970,209)
Restricted share, time-based LTIP Unit grants and vested restricted stock units, net of forfeitures (in shares)	209,666
Outstanding, ending balance (in shares)	121,499,593

Cumulative Other Comprehensiv49

Cumulative Other Comprehensive Loss - Schedule of Amounts Recognized in Cumulative Other Comprehensive Income (Loss) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)
Amounts recognized in cumulative other comprehensive income (Loss) by component
Balance as of beginning of period	$ (95)
Amounts reclassified from cumulative other comprehensive loss to cumulative net income pursuant to a change in accounting principle	(1,902)
Other comprehensive (loss) income before reclassifications	(159)
Amounts reclassified from cumulative other comprehensive loss to net income	50
Net current period other comprehensive income (loss)	(109)
Balance as of end of period	(2,106)
Unrealized Loss on Derivative Instruments
Amounts recognized in cumulative other comprehensive income (Loss) by component
Balance as of beginning of period	(456)
Amounts reclassified from cumulative other comprehensive loss to cumulative net income pursuant to a change in accounting principle	0
Other comprehensive (loss) income before reclassifications	67
Amounts reclassified from cumulative other comprehensive loss to net income	50
Net current period other comprehensive income (loss)	117
Balance as of end of period	(339)
Unrealized Gain (Loss) on Marketable Securities
Amounts recognized in cumulative other comprehensive income (Loss) by component
Balance as of beginning of period	361
Amounts reclassified from cumulative other comprehensive loss to cumulative net income pursuant to a change in accounting principle	(1,902)
Other comprehensive (loss) income before reclassifications	(226)
Amounts reclassified from cumulative other comprehensive loss to net income	0
Net current period other comprehensive income (loss)	(226)
Balance as of end of period	$ (1,767)

Cumulative Other Comprehensiv50

Cumulative Other Comprehensive Loss - Schedule of Reclassifications Out of Cumulative Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reclassifications out of cumulative other comprehensive income (loss)
Interest expense	$ 10,115	$ 15,014
Amounts Reclassified from Cumulative Other Comprehensive Loss to Net Income | Interest rate cap contract
Reclassifications out of cumulative other comprehensive income (loss)
Interest expense	$ 50

Income Taxes - Schedule of Prov

Income Taxes - Schedule of Provision for Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Current:
State and local	$ 3,007	$ 170
Federal	0	5
Income tax expense	$ 3,007	$ 175

Derivative Instruments - Narrat

Derivative Instruments - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2016	Mar. 04, 2016
LIBOR | Interest rate cap
Derivative [Line Items]
Derivative, cap interest rate, percent			2.50%
Notional amount		$ 400,000,000
Cash flow hedging | Designated as hedging instrument
Derivative [Line Items]
Estimated loss to be be reclassified from cumulative other comprehensive loss as an increase to interest expense	$ 400,000
Cash flow hedging | Designated as hedging instrument | Interest rate cap
Derivative [Line Items]
Notional amount	$ 400,000,000

Derivative Instruments - Schedu

Derivative Instruments - Schedule of Outstanding Interest Rate Derivatives Designated as Cash Flow Hedges of Interest Rate Risk (Details) - Interest rate cap - Cash flow hedging - Designated as hedging instrument	Mar. 31, 2018USD ($)financial_instrument
Derivative [Line Items]
Number of Instruments | financial_instrument	1
Notional Amount | $	$ 400,000,000

Derivative Instruments - Sche54

Derivative Instruments - Schedule of Fair Value of Derivative Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Interest rate cap | Cash flow hedging | Designated as hedging instrument | Other Assets
Derivatives, Fair Value [Line Items]
Interest Rate Derivative Designated as Hedging Instrument	$ 84	$ 17

Derivative Instruments - Sche55

Derivative Instruments - Schedule of Gain or Loss Recognized on Interest Rate Derivatives Designated as Cash Flow Hedges (Details) - Cash flow hedging - Designated as hedging instrument - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in cumulative other comprehensive loss	$ 67	$ (154)
Amount of loss reclassified from cumulative other comprehensive loss into interest expense	$ 50	$ 1

Share-Based Compensation - Narr

Share-Based Compensation - Narrative (Details) $ / shares in Units, $ in Millions	Jan. 29, 2018$ / sharesshares	Jan. 24, 2017shares	Mar. 31, 2018USD ($)tranche$ / sharesshares	Mar. 31, 2017USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense, accelerated vesting due to a staffing reduction | $			$ 0.4
Share award plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares available for issuance (in shares)			868,268
General and Administrative Expense | Share award plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense | $			$ 5.3	$ 5.2
Restricted shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
Number of equity awards granted (in shares)	125,409	76,424
Granted shares value (in dollars per share) | $ / shares	$ 29.78
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			3 years
Number of tranches | tranche			2
Granted shares value (in dollars per share) | $ / shares			$ 37.13
RSUs | Vesting in three years
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percent			50.00%
RSUs | Vesting in four years
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			1 year
Vesting percent			50.00%
RSUs at target
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of equity awards granted (in shares)	254,615	155,168
RSUs at maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of equity awards granted (in shares)	634,628	386,756
LTIP Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Conversion basis (in shares)			1
Time-based LTIP units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of equity awards granted (in shares)		39,364
Market-based LTIP units at target
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of equity awards granted (in shares)		79,924
Market-based LTIP units at maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of equity awards granted (in shares)		199,211
Restricted shares and time-based LTIP Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Estimated future compensation expense for unvested shares | $			$ 10.9
Weighted average period over which compensation expense will be recorded			2 years 3 months 18 days
RSUs and market-based LTIP units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Estimated future compensation expense for unvested shares | $			$ 21.1
Weighted average period over which compensation expense will be recorded			2 years 3 months 18 days

Share-Based Compensation - Summ

Share-Based Compensation - Summary of Assumptions and Fair Values for Restricted Stock Units Granted in the Period (Details) - RSUs	3 Months Ended
	Mar. 31, 2018$ / shares
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Fair value of RSUs granted (in dollars per share)	$ 37.13
Expected term	4 years
Expected volatility	0.00%
Expected dividend yield	1.68%
Risk-free rate	2.26%

Fair Value of Assets and Liab58

Fair Value of Assets and Liabilities - Schedule of Assets and Liabilities Measure at Fair Value (Details) - Recurring $ in Thousands	Mar. 31, 2018USD ($)
Marketable securities
Recurring Fair Value Measurements:
Assets, fair value	$ 247,879
Quoted Prices in Active Markets for Identical Assets (Level 1) | Marketable securities
Recurring Fair Value Measurements:
Assets, fair value	247,879
Significant Other Observable Inputs (Level 2) | Marketable securities
Recurring Fair Value Measurements:
Assets, fair value	0
Significant Unobservable Inputs (Level 3) | Marketable securities
Recurring Fair Value Measurements:
Assets, fair value	0
Interest rate cap
Recurring Fair Value Measurements:
Assets, fair value	84
Interest rate cap | Quoted Prices in Active Markets for Identical Assets (Level 1)
Recurring Fair Value Measurements:
Assets, fair value	0
Interest rate cap | Significant Other Observable Inputs (Level 2)
Recurring Fair Value Measurements:
Assets, fair value	84
Interest rate cap | Significant Unobservable Inputs (Level 3)
Recurring Fair Value Measurements:
Assets, fair value	$ 0

Fair Value of Assets and Liab59

Fair Value of Assets and Liabilities - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)
Fair value of assets and liabilities
Loss on asset impairment	$ 12,087	$ 1,286
Real estate properties, net	$ 867,362		$ 1,296,893
Total rents | Customer concentration
Fair value of assets and liabilities
Concentration risk, benchmark percentage	0.070
Total rents | Customer concentration | Tenant
Fair value of assets and liabilities
Concentration risk, percent	13.00%
Real Estate Held-for-sale | Significant Other Observable Inputs (Level 2) | Market Approach Valuation Technique
Fair value of assets and liabilities
Assets, fair value	$ 29,700
Fair Value, Measurements, Nonrecurring | Disposition Plan | Carrying Amount
Fair value of assets and liabilities
Real estate properties, net	$ 41,800

Fair Value of Assets and Liab60

Fair Value of Assets and Liabilities - Schedule of Fair Value and Carrying Value of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Carrying Amount
Fair value of financial instruments
Senior unsecured debt and mortgage notes payable	$ 681,675	$ 856,940
Fair Value
Fair value of financial instruments
Senior unsecured debt and mortgage notes payable	$ 693,328	$ 874,280

Earnings Per Common Share - Sch

Earnings Per Common Share - Schedule of Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Numerator for earnings per common share - basic:
Net income	$ 187,662	$ 23,822
Net income attributable to noncontrolling interest	(63)	(8)
Preferred distributions	(1,997)	(1,997)
Net income attributable to Equity Commonwealth common shareholders	185,602	21,817
Numerator for earnings per common share - diluted:
Net income	187,662	23,822
Preferred distributions	0	(1,997)
Numerator for net income per share - diluted	$ 187,662	$ 21,825
Denominator for earnings per common share - basic and diluted:
Weighted average number of common shares outstanding — basic (in shares)	123,867	124,047
Weighted average number of common shares outstanding — diluted (in shares)	127,097	125,150
Net income per common share attributable to Equity Commonwealth common shareholders:
Basic (in dollars per share)	$ 1.50	$ 0.18
Diluted (in dollars per share)	$ 1.48	$ 0.17
Series D
Anti-dilutive securities:
Effect of Series D preferred shares; 6 1/2% cumulative convertible (in shares)	0	2,363
Preferred shares, dividend yield	6.50%	6.50%
Series D
Denominator for earnings per common share - basic and diluted:
Series D preferred shares; 6 1/2% cumulative convertible	2,363	0
Anti-dilutive securities:
Preferred shares, dividend yield	6.50%	6.50%	6.50%
RSUs
Denominator for earnings per common share - basic and diluted:
Weighted average number of common shares outstanding, dilutive adjustment (in shares)	730	1,023
LTIP Units
Denominator for earnings per common share - basic and diluted:
Weighted average number of common shares outstanding, dilutive adjustment (in shares)	136	80
OP Units
Denominator for earnings per common share - basic and diluted:
Weighted average number of common shares outstanding, dilutive adjustment (in shares)	1	0

Earnings Per Common Share - S62

Earnings Per Common Share - Schedule of Computation of Basic and Diluted Earnings Per Share (Footnote) (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Weighted average number of shares, restricted stock units, unvested (in shares)	307	0

Segment Information - Narrative

Segment Information - Narrative (Details)	3 Months Ended
	Mar. 31, 2018segment
Segment Reporting [Abstract]
Number of reportable segments	1
Percentage of revenue from office properties (more than)	90.00%

Related Person Transactions - N

Related Person Transactions - Narrative (Details) - Two North Riverside Plaza Joint Venture Limited Partnership $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)option	Mar. 31, 2017USD ($)
Related Party Transaction [Line Items]
Lease term	5 years
Number of renewal options of lease arrangement | option	1
Renewal term of lease arrangement	5 years
Tenant improvements	$ 0.7
Lease termination period duration	30 days
Expenses from transactions with related party	$ 0.2	$ 0.2

Subsequent Events - Narrative (

Subsequent Events - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	May 15, 2018	May 04, 2018	Apr. 27, 2018	Apr. 11, 2018	Feb. 15, 2018	Jan. 30, 2018	Mar. 31, 2018
Revolving credit facility | Loan facility, 5-year term
Subsequent Event [Line Items]
Debt instrument, term							5 years
Revolving credit facility | Loan facility, 7-year term
Subsequent Event [Line Items]
Debt instrument, term							7 years
Series D
Subsequent Event [Line Items]
Dividend declared (in dollars per share)						$ 0.40625
Dividend paid (in dollars per share)					$ 0.40625
Subsequent event | Revolving credit facility | Loan facility, 5-year term
Subsequent Event [Line Items]
Debt redeemed at par		$ 400
Debt instrument, term		5 years
Subsequent event | Revolving credit facility | Loan facility, 7-year term
Subsequent Event [Line Items]
Debt instrument, term		7 years
Subsequent event | Series D
Subsequent Event [Line Items]
Dividend declared (in dollars per share)			$ 0.40625	$ 0.40625
Dividend paid (in dollars per share)	$ 0.40625