Equity Commonwealth (EQC) 10-Q 3 Nov 16 2016 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2016	Oct. 27, 2016
Document and Entity Information
Entity Registrant Name	Equity Commonwealth
Entity Central Index Key	803,649
Document Type	10-Q
Document Period End Date	Sep. 30, 2016
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		125,532,523
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q3

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Real estate properties:
Land	$ 293,225	$ 389,410
Buildings and improvements	2,642,588	3,497,942
Total real estate properties, at cost, gross	2,935,813	3,887,352
Accumulated depreciation	(751,882)	(898,939)
Total real estate properties, at cost, net	2,183,931	2,988,413
Properties held for sale	13,463	0
Acquired real estate leases, net	52,017	88,760
Cash and cash equivalents	2,405,174	1,802,729
Restricted cash	36,755	32,245
Rents receivable, net of allowance for doubtful accounts of $4,515 and $7,715, respectively	150,728	174,676
Other assets, net	123,699	144,341
Total assets	4,965,767	5,231,164
LIABILITIES AND SHAREHOLDERS’ EQUITY
Senior unsecured debt, net	1,313,267	1,450,606
Mortgage notes payable, net	243,993	246,510
Liabilities related to properties held for sale	667	0
Accounts payable and accrued expenses	87,003	123,587
Assumed real estate lease obligations, net	2,140	4,296
Rent collected in advance	21,529	27,340
Security deposits	8,128	10,338
Total liabilities	1,676,727	1,862,677
Preferred shares of beneficial interest, $0.01 par value: 50,000,000 shares authorized;
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
Series E preferred shares; 7 1/4% cumulative redeemable on or after May 15, 2016; 0 and 11,000,000 shares issued and outstanding, respectively, aggregate liquidation preference $0 and $275,000, respectively	0	265,391
Common shares of beneficial interest, $0.01 par value: 350,000,000 shares authorized; 125,532,523 and 126,349,914 shares issued and outstanding, respectively	1,255	1,263
Additional paid in capital	4,402,927	4,414,611
Cumulative net income	2,554,343	2,333,709
Cumulative other comprehensive loss	(1,117)	(3,687)
Cumulative common distributions	(3,111,868)	(3,111,868)
Cumulative preferred distributions	(675,763)	(650,195)
Total shareholders’ equity	3,289,040	3,368,487
Total liabilities and shareholders’ equity	$ 4,965,767	$ 5,231,164

CONDENSED CONSOLIDATED BALANCE3

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2016	Dec. 31, 2015
Rents receivable, allowance for doubtful accounts	$ 4,515	$ 4,515	$ 7,715
Common shares of beneficial interest, par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01
Common shares of beneficial interest, shares authorized (in shares)	350,000,000	350,000,000	350,000,000
Common shares of beneficial interest, shares issued (in shares)	125,532,523	125,532,523	126,349,914
Common shares of beneficial interest, shares outstanding (in shares)	125,532,523	125,532,523	126,349,914
Series D
Preferred shares of beneficial interest, par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01
Preferred shares of beneficial interest, shares authorized (in shares)	50,000,000	50,000,000	50,000,000
Preferred shares, dividend yield	6.50%	6.50%	6.50%
Preferred shares of beneficial interest, shares issued (in shares)	4,915,196	4,915,196	4,915,196
Preferred shares, of beneficial interest, shares outstanding (in shares)	4,915,196	4,915,196	4,915,196
Preferred shares, aggregate liquidation preference	$ 122,880	$ 122,880	$ 122,880
Series E
Preferred shares of beneficial interest, par value (in dollars per share)	$ 0	$ 0	$ 0.01
Preferred shares of beneficial interest, shares authorized (in shares)	0	0	50,000,000
Preferred shares, dividend yield		0.00%	7.25%
Preferred shares of beneficial interest, shares issued (in shares)	0	0	11,000,000
Preferred shares, of beneficial interest, shares outstanding (in shares)	0	0	11,000,000
Preferred shares, aggregate liquidation preference	$ 0	$ 0	$ 275,000

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Revenues:
Rental income	$ 92,722	$ 125,459	$ 324,345	$ 457,128
Tenant reimbursements and other income	21,910	33,749	72,789	118,829
Total revenues	114,632	159,208	397,134	575,957
Expenses:
Operating expenses	49,313	73,571	157,964	261,128
Depreciation and amortization	29,184	40,522	102,766	156,858
General and administrative	13,277	16,249	38,766	43,718
Loss on asset impairment	0	0	43,736	17,162
Total expenses	91,774	130,342	343,232	478,866
Operating income	22,858	28,866	53,902	97,091
Interest and other income	3,013	637	7,184	4,813
Interest expense (including net amortization of debt discounts, premiums and deferred financing fees of $948, $171, $2,880 and $23, respectively)	(21,427)	(25,111)	(65,074)	(82,926)
(Loss) gain on early extinguishment of debt	0	(3,887)	(118)	6,111
Foreign currency exchange loss	0	(9,809)	(5)	(8,953)
Gain on sale of properties	82,169	39,793	225,210	42,953
Income before income taxes	86,613	30,489	221,099	59,089
Income tax expense	(225)	(23)	(465)	(2,377)
Net income	86,388	30,466	220,634	56,712
Preferred distributions	(1,997)	(6,981)	(15,959)	(20,943)
Excess fair value of consideration paid over carrying value of preferred shares	0	0	(9,609)	0
Net income attributable to Equity Commonwealth common shareholders	$ 84,391	$ 23,485	$ 195,066	$ 35,769
Weighted average common shares outstanding — basic (in shares)	125,533	128,739	125,627	129,386
Weighted average common shares outstanding — diluted (in shares)	126,568	129,878	127,009	130,093
Earnings per common share attributable to Equity Commonwealth common shareholders:
Basic (in USD per share)	$ 0.67	$ 0.18	$ 1.55	$ 0.28
Diluted (in USD per share)	$ 0.67	$ 0.18	$ 1.54	$ 0.27

CONDENSED CONSOLIDATED STATEME5

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Amortization of debt discounts, premiums and deferred financing fees	$ 948	$ 171	$ 2,880	$ 23

CONDENSED CONSOLIDATED STATEME6

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 86,388	$ 30,466	$ 220,634	$ 56,712
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on derivative instruments and other assets	1,117	821	2,570	(843)
Foreign currency translation adjustments	0	0	0	48,917
Total comprehensive income	$ 87,505	$ 31,287	$ 223,204	$ 104,786

CONDENSED CONSOLIDATED STATEME7

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 220,634	$ 56,712
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation	79,128	117,239
Net amortization of debt discounts, premiums and deferred financing fees	2,880	23
Straight line rental income	(12,384)	(3,512)
Amortization of acquired real estate leases	18,289	28,386
Other amortization	11,219	17,224
Share-based compensation	13,871	11,765
Loss on asset impairment	43,736	17,162
Loss (gain) on early extinguishment of debt	118	(6,111)
Foreign currency exchange loss	5	8,953
Net gain on sale of properties	(225,210)	(42,953)
Change in assets and liabilities:
Restricted cash	(6,119)	(6,275)
Rents receivable and other assets	(20,474)	(46,607)
Accounts payable and accrued expenses	(5,303)	(5,769)
Rent collected in advance	(3,912)	(6,112)
Security deposits	234	1,298
Cash provided by operating activities	116,712	141,423
CASH FLOWS FROM INVESTING ACTIVITIES:
Real estate improvements	(92,106)	(43,396)
Principal payments received from direct financing lease	0	5,717
Proceeds from sale of properties, net	1,034,403	1,425,590
Proceeds from sale of securities	0	27,068
Decrease (increase) in restricted cash	1,609	(3,238)
Cash provided by investing activities	943,906	1,411,741
CASH FLOWS FROM FINANCING ACTIVITIES:
Purchase and retirement of common shares	(25,563)	(87,983)
Redemption of preferred shares	(275,000)	0
Payments on borrowings	(141,591)	(142,868)
Deferred financing fees	(52)	(7,143)
Distributions to preferred shareholders	(15,959)	(20,943)
Cash used in financing activities	(458,165)	(258,937)
Effect of exchange rate changes on cash	(8)	(9,581)
Increase in cash and cash equivalents	602,445	1,284,646
Cash and cash equivalents at beginning of period	1,802,729	364,516
Cash and cash equivalents at end of period	2,405,174	1,649,162
SUPPLEMENTAL CASH FLOW INFORMATION:
Interest paid	69,373	93,598
Taxes paid	103	5,853
NON-CASH INVESTING ACTIVITIES:
Increase (decrease) in capital expenditures recorded as liabilities	$ 3,191	$ (9,753)

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2016
Organization, Consolidation and Presentation of Financial Statements [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, 2015. 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 Pronouncement

Recent Accounting Pronouncements	9 Months Ended
	Sep. 30, 2016
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements In August 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (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. Early adoption is permitted, including adoption in an interim period. We are currently in the process of evaluating the impact, if any, the adoption of this ASU will have on our condensed consolidated financial statements. 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 condensed consolidated financial statements. In March 2016, the FASB issued ASU 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, which simplifies several aspects of the accounting for employee share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. This update is effective for annual periods beginning after December 15, 2016, and interim periods within those annual periods, but early adoption is permitted. We are currently in the process of evaluating the impact the adoption of this ASU will have on our condensed consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases, which amends the existing accounting standards for lease accounting, including requiring lessees to recognize most leases on their balance sheets. The ASU also requires lessees or lessors to capitalize only initial direct costs of leases. This update is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years, but early adoption is permitted. We are currently in the process of evaluating the impact the adoption of this ASU will have on our condensed consolidated financial statements. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers, which provides guidance for revenue recognition. This update is effective for interim and annual reporting periods beginning after December 15, 2017. We are currently in the process of evaluating the impact, if any, the adoption of this ASU will have on our condensed consolidated financial statements. In April 2015, the FASB issued ASU No. 2015-03, Simplifying the Presentation of Debt Issuance Costs. This standard amends existing guidance to require the presentation of debt issuance costs in the balance sheet as a deduction from the carrying amount of the related debt liability instead of as a deferred charge. It is effective for annual reporting periods beginning after December 15, 2015, but early adoption is permitted. We adopted this standard on January 1, 2016 and made the following reclassifications to the prior years' consolidated balance sheet to conform to the current year's presentation (in thousands): Balance Sheet as of December 31, 2015 Originally Reported Effect of Change As Adjusted Other assets, net 157,549 (13,208 ) 144,341 Senior unsecured debt, net 1,460,592 (9,986 ) 1,450,606 Mortgage notes payable, net 249,732 (3,222 ) 246,510 In April 2014, the FASB issued ASU No. 2014-08, Presentation of Financial Statements (Topic 205) and Property, Plant, and Equipment (Topic 360): Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity, or ASU 2014-08. ASU 2014-08 changes the criteria for reporting a discontinued operation. Under the new pronouncement, a disposal of a part of an organization that has a major effect on its operations and financial results is a discontinued operation. We adopted ASU 2014-08 on January 1, 2015, and determined that our 2016 dispositions, 2015 dispositions and properties held for sale as of September 30, 2016 do not individually represent a strategic shift, as defined by the standard, that has or will have a major effect on our operations and financial results. As a result, the 2016 and 2015 dispositions and properties held for sale have not been presented as discontinued operations in the statements of operations.

Real Estate Properties

Real Estate Properties	9 Months Ended
	Sep. 30, 2016
Real Estate [Abstract]
Real Estate Properties	Real Estate Properties During the nine months ended September 30, 2016 and 2015 , we made improvements, excluding tenant-funded improvements, to our properties totaling $88.5 million and $ 46.7 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 Accounting Standards Codification (Codification) as held for sale on our condensed consolidated balance sheets. As of December 31, 2015, we had no properties classified as held for sale. As of September 30, 2016 , we classified the following property as held for sale (dollars in thousands): Asset Date Sold Number of Number of Square Footage Gross Sales Price 7800 Shoal Creek Boulevard October 2016 1 4 151,917 $ 29,210 Summarized balance sheet information for the property classified as held for sale is as follows (in thousands): September 30, 2016 Real estate properties $ 12,952 Other assets, net 511 Properties held for sale $ 13,463 Accounts payable and accrued expenses $ 337 Rent collected in advance 19 Security deposits 311 Liabilities related to properties held for sale $ 667 Property Dispositions: During the nine months ended September 30, 2016 , we sold the following properties (dollars in thousands): Asset Date Sold Number of Number of Square Footage Gross Sales Price Gain (Loss) on Sale Properties Executive Park February 2016 1 9 427,443 $ 50,865 $ 16,531 3330 N Washington Boulevard March 2016 1 1 55,719 11,250 5,455 111 East Kilbourn Avenue March 2016 1 1 373,669 60,500 14,677 1525 Locust Street April 2016 1 1 98,009 17,700 8,956 633 Ahua Street April 2016 1 1 93,141 29,000 15,963 Lakewood on the Park May 2016 1 2 180,558 37,100 13,616 Leased Land June 2016 1 7 — 48,450 15,914 9110 East Nichols Avenue June 2016 1 1 143,958 17,200 642 111 River Street (1) July 2016 1 1 566,215 235,000 78,240 Sky Park Centre July 2016 1 2 63,485 13,700 4,745 Raintree Industrial Park July 2016 1 12 563,182 11,500 (653 ) 8701 N Mopac August 2016 1 1 121,901 21,500 8,394 Portfolios of properties 812 San Antonio Street May 2016 1 1 59,321 1601 Rio Grande Street May 2016 1 1 56,219 Downtown Austin portfolio 2 2 115,540 $ 32,600 $ 20,584 785 Schilinger Road South June 2016 1 1 72,000 401 Vine Street June 2016 1 1 53,980 633 Frazier Drive June 2016 1 1 150,000 9840 Gateway Boulevard North June 2016 1 1 72,000 3003 South Expressway 281 June 2016 1 1 150,000 1331 North Center Parkway June 2016 1 1 53,980 Movie theater portfolio 6 6 551,960 $ 109,100 $ 30,595 128 Crews Drive July 2016 1 1 185,600 111 Southchase Boulevard July 2016 1 1 168,087 1043 Global Avenue July 2016 1 1 450,000 South Carolina industrial portfolio 3 3 803,687 $ 30,000 $ 7,244 100 East Wisconsin Avenue August 2016 1 1 435,067 111 Monument Circle August 2016 1 2 1,121,764 101-115 W. Washington Street August 2016 1 1 634,058 North Point Office Complex August 2016 1 2 873,335 Midwest portfolio 4 6 3,064,224 $ 416,900 $ (15,808 ) 27 56 7,222,691 $ 1,142,365 $ 225,095 (1) Property sale represented a leasehold interest. During the year ended December 31, 2015, we disposed of 91 properties ( 135 buildings) and one land parcel with a combined 18.9 million square feet for an aggregate gross sales price of $2.0 billion , excluding closing costs.

Real Estate Mortgages Receivabl

Real Estate Mortgages Receivable	9 Months Ended
	Sep. 30, 2016
Mortgage Loans on Real Estate [Abstract]
Real Estate Mortgages Receivable	Real Estate Mortgages Receivable As of September 30, 2016 and December 31, 2015 , we had total real estate mortgages receivable with an aggregate carrying value of $8.1 million included in other assets in our condensed consolidated balance sheets. We provided mortgage financing totaling $7.7 million at 6.0% per annum in connection with our sale of three suburban office and industrial properties ( 18 buildings) in January 2013 in Dearborn, MI; this real estate mortgage requires monthly interest payments and matures on January 24, 2023 . We also provided mortgage financing totaling $0.4 million at 6.0% per annum in connection with our sale of a suburban office property in Salina, NY in April 2012. This real estate mortgage requires monthly interest payments and matures on April 30, 2019 . We monitor the payment history of the borrowers and have determined that no allowance for losses related to these real estate mortgages receivable was necessary at September 30, 2016 , and December 31, 2015 .

Indebtedness

Indebtedness	9 Months Ended
	Sep. 30, 2016
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 0.075% 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 125 basis points as of September 30, 2016 . As of September 30, 2016 , the interest rate payable on borrowings under our revolving credit facility was 1.78% . As of September 30, 2016 , we had no balance outstanding and $750.0 million available under our revolving credit facility and the facility fee as of September 30, 2016 was 0.25% . Our term loans currently bear interest at a rate of LIBOR plus a spread, which was 140 and 180 basis points for the 5 -year and 7 -year term loan, respectively, as of September 30, 2016 . As of September 30, 2016 , the interest rates for the amounts outstanding under our 5 -year term loan and 7 -year term loan were 1.93% and 2.33% , respectively. As of September 30, 2016 , 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 September 30, 2016 , 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 September 30, 2016 , we had senior unsecured notes of $925.0 million (excluding net discounts and unamortized deferred financing fees) maturing from 2017 through 2042. On February 16, 2016, we redeemed at par $139.1 million of our 6.25% senior unsecured notes due 2016 and recognized a loss on early extinguishment of debt of $0.1 million from the write-off of an unamortized discount and unamortized deferred financing fees for the nine months ended September 30, 2016 . Mortgage Notes Payable: At September 30, 2016 , five of our properties ( 8 buildings) with an aggregate net book value of $293.3 million had secured mortgage notes totaling $244.0 million (including net premiums and unamortized deferred financing fees) maturing from 2017 through 2026.

Shareholders' Equity

Shareholders' Equity	9 Months Ended
	Sep. 30, 2016
Stockholders' Equity Note [Abstract]
Shareholders' Equity	Shareholders’ Equity Common Share Issuances: See Note 10 for information regarding equity issuances related to share-based compensation. Common Share Repurchases: On August 24, 2015, our Board of Trustees approved a common share repurchase plan, which authorizes the repurchase of up to $100.0 million of our outstanding common shares over the twelve month period following the date of authorization. On September 14, 2015, our Board of Trustees authorized the repurchase of up to an additional $100.0 million of our outstanding common shares over the twelve month period following the date of authorization. On March 17, 2016, 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 nine months ended September 30, 2016 , we purchased and retired 983,789 of our common shares at a weighted average price of $25.94 per share, for a total of $25.5 million . Since the inception of the common share repurchase plan through September 30, 2016 , we have purchased and retired a total of 4,394,089 of our common shares at a weighted average price of $25.80 per share, for a total of $113.4 million . In August and September 2016, the first two share repurchase authorizations, of which $86.6 million was not utilized, expired. The $150.0 million of remaining authorization available under our share repurchase program as of September 30, 2016 is scheduled to expire in March 2017. Preferred Share Redemption: On May 15, 2016, we redeemed all of our 11,000,000 outstanding series E preferred shares at a price of $25.00 per share, for a total of $275.0 million , plus any accrued and unpaid dividends. The redemption payment occurred on May 16, 2016 (the first business day following the redemption date). We recorded $9.6 million related to the excess fair value of consideration paid over the carrying value of the preferred shares as a reduction to net income attributable to common shareholders for the nine months ended September 30, 2016 . Preferred Share Distributions: In 2016, our Board of Trustees declared distributions on our series D preferred shares and series E cumulative redeemable preferred shares to date as follows: Declaration Date Record Date Payment Date Series D Dividend Per Share Series E Dividend Per Share January 26, 2016 February 5, 2016 February 16, 2016 $ 0.40625 $ 0.453125 April 15, 2016 April 25, 2016 May 16, 2016 $ 0.40625 $ 0.453125 July 11, 2016 July 29, 2016 August 15, 2016 $ 0.40625 $ — October 10, 2016 October 28, 2016 November 15, 2016 $ 0.40625 $ —

Cumulative Other Comprehensive

Cumulative Other Comprehensive Loss	9 Months Ended
	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Cumulative Other Comprehensive Loss	Cumulative Other Comprehensive Loss The following tables present the amounts recognized in cumulative other comprehensive loss for the three and nine months ended September 30, 2016 (in thousands): Unrealized Loss on Derivative Instruments Balance as of July 1, 2016 $ (2,234 ) Other comprehensive income before reclassifications 23 Amounts reclassified from cumulative other comprehensive loss to net income 1,094 Net current period other comprehensive income 1,117 Balance as of September 30, 2016 $ (1,117 ) Unrealized Loss on Derivative Instruments Balance as of January 1, 2016 $ (3,687 ) Other comprehensive loss before reclassifications (748 ) Amounts reclassified from cumulative other comprehensive loss to net income 3,318 Net current period other comprehensive income 2,570 Balance as of September 30, 2016 $ (1,117 ) The following table presents reclassifications out of cumulative other comprehensive loss for the three and nine months ended September 30, 2016 (in thousands): Amounts Reclassified from Cumulative Other Comprehensive Loss to Net Income Details about Cumulative Other Comprehensive Loss Components Three Months Ended September 30, 2016 Nine Months Ended September 30, 2016 Affected Line Items in the Statement of Operations Interest rate swap contracts $ 1,094 $ 3,318 Interest expense

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2016
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. In prior periods, we were subject to Australian taxes. Our provision for income taxes consists of the following (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2016 2015 2016 2015 Current: State $ 225 $ 90 $ 465 $ 270 Federal — — — 525 Foreign — (67 ) — 2,337 225 23 465 3,132 Deferred: Foreign — — — (755 ) — — — (755 ) Income tax expense $ 225 $ 23 $ 465 $ 2,377

Derivative Instruments

Derivative Instruments	9 Months Ended
	Sep. 30, 2016
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 related to 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 minimize 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 mitigate this risk, we only enter into derivative financial instruments with counterparties with high credit ratings or 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 periodically use interest rate swaps, caps, or other similar instruments as part of our interest rate risk management strategy. Interest rate swaps designated as cash flow hedges involve the receipt of variable-rate amounts from a counterparty in exchange for us making fixed-rate payments over the life of the agreements without exchange of the underlying notional amount. 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 2016, 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 $0.7 million will be reclassified from cumulative other comprehensive loss as an increase to interest expense. We have interest rate swap agreements to manage our interest rate risk exposure on $168.1 million of mortgage debt due 2019, which require interest at a spread over LIBOR . The interest rate swap agreements utilized by us qualify as cash flow hedges and effectively modify our exposure to interest rate risk by converting our floating interest rate debt to a fixed interest rate basis for this loan through December 1, 2016, thus reducing the impact of interest rate changes on future 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 September 30, 2016 , we had the following outstanding interest rate derivatives that were designated as cash flow hedges of interest rate risk: Interest Rate Derivative Number of Instruments Notional Amount (in thousands) Interest rate swap 2 $ 168,103 Interest rate cap 1 $ 400,000 The table below presents the fair value of our derivative financial instruments as well as their classification on the condensed consolidated balance sheets as of September 30, 2016 and December 31, 2015 (amounts in thousands): Fair Value as of Interest Rate Derivative Designated as Hedging Instrument Balance Sheet Location September 30, December 31, Pay-fixed swaps Accounts payable and accrued expenses $ (707 ) $ (3,687 ) Interest rate cap Other assets $ 112 $ — 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 and nine months ended September 30, 2016 and 2015 (amounts in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2016 2015 2016 2015 Amount of gain (loss) recognized in cumulative other comprehensive loss $ 23 $ (418 ) $ (748 ) $ (1,378 ) Amount of loss reclassified from cumulative other comprehensive loss into interest expense 1,094 1,239 3,318 3,698 Credit-risk-related Contingent Features Our agreements with each of our derivative counterparties contain a provision providing that if we default or are capable of being declared in default on any of our indebtedness, we could also be declared in default on our derivative obligations. As of September 30, 2016 , the fair value of derivatives in a net liability position including accrued interest but excluding any adjustment for nonperformance risk related to these agreements was $1.1 million . As of September 30, 2016 , we have not posted any collateral related to these agreements and were not in breach of any agreement provisions. If we had breached any of these provisions, we could have been required to settle our obligations under the agreements at their aggregate termination value of $1.1 million at September 30, 2016 .

Share-Based Compensation

Share-Based Compensation	9 Months Ended
	Sep. 30, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	Share-Based Compensation Equity Commonwealth 2015 Omnibus Incentive Plan On January 26, 2016, the Board of Trustees approved an amendment to the 2015 Omnibus Incentive Plan (as amended, the 2015 Incentive Plan) to allow the Compensation Committee (Committee) to authorize in an award agreement a transfer of all or a part of certain equity awards not for value to a “family member” (as defined in the 2015 Incentive Plan). 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. 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 will be forfeited. 2016 Equity Award Activity On June 16, 2016, in accordance with the Company’s compensation plan for independent Trustees, the Committee awarded each of the nine independent Trustees $0.1 million in restricted shares as part of their compensation for the 2016-2017 year of service on the Board of Trustees. These awards equated to 3,463 shares per Trustee, for a total of 31,167 shares, valued at $28.88 per share, the closing price of our common shares on the New York Stock Exchange (NYSE) on that day. These shares vest one year after the date of the award. On January 26, 2016, the Committee approved a grant of 136,623 restricted common shares and 277,386 RSUs at target 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 2015. The restricted shares are service based awards and vest over a four -year period. The restricted shares were granted on January 26, 2016 and were valued at $26.93 per share, the closing price of our common shares on the NYSE on that day. The RSUs are market based awards with a service condition and recipients may earn the RSU grants based on the Company’s total shareholder return (TSR) relative to the TSR's for the constituent REITs that comprise the NAREIT Office Index for the performance period of January 26, 2016 - January 26, 2019. Following the end of the performance period on January 26, 2019, the number of earned awards will be determined. The earned awards vest in two tranches with 50% of the earned award vesting on January 26, 2019 and the remaining 50% of the earned award vesting on January 26, 2020, subject to the grant recipient’s continued employment. Compensation expense for the RSU awards was determined using a Monte Carlo simulation model and is being recognized ratably from the grant date to the vesting date of each tranche. During the nine months ended September 30, 2016 , due to employee departures, 539 restricted shares were forfeited with an average price per share value at grant date of $26.82 , and 1,094 RSUs were forfeited with an average per share fair value at grant date of $38.72 . 2015 Equity Award Activity On June 16, 2015, in accordance with the Company’s compensation plan for independent Trustees, the Committee awarded each of the nine independent Trustees $0.1 million in restricted shares as part of their compensation for the 2015-2016 year of service on the Board of Trustees. These awards equated to 3,843 shares per Trustee, for a total of 34,587 shares, valued at $26.02 per share, the closing price of our common shares on the NYSE on that day. These shares vested one year after the date of the award. On January 28, 2015, the Committee approved a grant of 126,319 restricted common shares and 256,467 RSUs at target 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 2014. The restricted shares are service based awards and vest over a four -year period. The restricted shares were granted on January 28, 2015 and were valued at $26.58 per share, the closing price of our common shares on the NYSE on that day. The RSUs are market based awards with a service condition and recipients may earn the RSU grants based on the Company’s total shareholder return (TSR) relative to the TSR's for the constituent REITs that comprise the NAREIT Office Index for the performance period of January 28, 2015 - January 28, 2018. Following the end of the performance period on January 28, 2018, the number of earned awards will be determined. The earned awards vest in two tranches with 50% of the earned award vesting on January 28, 2018 and the remaining 50% of the earned award vesting on January 28, 2019, subject to the grant recipient’s continued employment. Compensation expense for the RSU awards was determined using a Monte Carlo simulation model and is being recognized ratably from the grant date to the vesting date of each tranche. During the nine months ended September 30, 2015, 8,115 restricted shares were forfeited with an average per share fair value at grant date of $26.64 , and 16,475 RSUs were forfeited with an average per share fair value at grant date of $20.50 . Outstanding Equity Awards As of September 30, 2016 , the estimated future compensation expense for all unvested restricted share grants was $14.1 million . Compensation expense for the restricted share 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 is approximately 2.3 years. As of September 30, 2016 , the estimated future compensation expense for all unvested RSUs was $22.2 million . The weighted average period over which the future compensation expense will be recorded for the RSUs is approximately 2.2 years. The assumptions and fair values for the RSUs granted for the nine months ended September 30, 2016 are included in the following table on a per share basis. 2016 Fair value of RSUs granted $ 38.80 Expected term (years) 4 Expected volatility — Expected dividend yield 1.86 % Risk-free rate 1.07 % During the three months ended September 30, 2016 and 2015 , we recorded $4.9 million and $3.7 million , respectively, and during the nine months ended September 30, 2016 and 2015 , we recorded $13.9 million and $11.8 million , respectively, of compensation expense, net of forfeitures, in general and administrative expense for grants to our Board of Trustees and the Company's employees related to our Plan. At September 30, 2016 , 2,358,464 common shares remain available for issuance under the Plan.

Fair Value of Assets and Liabil

Fair Value of Assets and Liabilities	9 Months Ended
	Sep. 30, 2016
Fair Value Disclosures [Abstract]
Fair Value of Assets and Liabilities	Fair Value of Assets and Liabilities The table below presents certain of our assets and liabilities measured at fair value during 2016 , categorized by the level of inputs used in the valuation of each asset and liability (dollars in thousands): Fair Value at September 30, 2016 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: Effective portion of interest rate swap contracts $ (707 ) $ — $ (707 ) $ — Effective portion of interest rate cap contract 112 — 112 — Effective Portion of Interest Rate Swap and Cap Contracts The fair value of our interest rate swap and cap contracts is determined using the net discounted cash flows of each 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 derivatives fall within level 2 of the fair value hierarchy, the credit valuation adjustments associated with our derivatives utilize level 3 inputs, such as estimates of current credit spreads, to evaluate the likelihood of default by us and the counterparties. As of September 30, 2016 , we have assessed the significance of the impact of the credit valuation adjustments on the overall valuation of our derivative positions and have determined that the credit valuation adjustments are not significant to the overall valuation of our derivatives. As a result, we have determined that our derivative valuations in their entirety are classified as level 2 inputs in the fair value hierarchy. Derivative Liability On July 31, 2014, our shareholders voted to approve the reimbursement of verified expenses incurred by Related Fund Management, LLC and Corvex Management LP (Related/Corvex) (see Note 14 for additional information). Approximately $16.7 million was paid during the year ended December 31, 2014. Up to $8.4 million was to be reimbursed only if the average closing price of our common shares was at least $26.00 (as adjusted for any share splits or share dividends) during the one year period after the date on which the reimbursement was approved by shareholders, and up to $8.4 million was to be reimbursed only if the average closing price of our common shares was at least $26.00 (as adjusted for any share splits or share dividends) during the one year period between the first and second anniversaries of the date on which the reimbursement was approved by shareholders. The average closing price of our common shares was at least $26.00 during both the first and second one year periods after the date on which the reimbursement was approved by shareholders, and as a result, in August 2016 and 2015 we paid an $8.2 million final payment and $8.4 million , respectively, to Related/Corvex. Prior to the payment of the reimbursement in August 2016, the potential future reimbursement of $8.4 million for the second one year period represented a derivative instrument as codified in ASC 815 Derivatives and Hedging which required the potential future reimbursement to be recorded at fair value at each reporting date. The fair value of the derivative liability as of September 30, 2016 and December 31, 2015 was $0 and $7.2 million , respectively. We recognized (income) expense of $(0.1) million and $1.0 million for the three and nine months ended September 30, 2016 , respectively, which was recorded in general and administrative expenses in our condensed consolidated statement of operations for such periods. Properties Held and Used As part of our disposition plan, and pursuant to our accounting policy, in 2016, 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 disposition plan and current estimates of market value, 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 second quarter, we recorded an impairment charge related to 111 Monument Circle, 101-115 W. Washington Street and 100 East Wisconsin Avenue of $43.7 million for the nine months ended September 30, 2016 in accordance with our impairment analysis procedures. We determined these impairments based on third party offer prices and independent third party broker information, which are level 2 inputs according to the fair value hierarchy established in ASC 820. We reduced the aggregate carrying value of these properties from $308.6 million to their estimated fair value of $264.9 million . These properties were sold in August 2016 (see Note 3 for additional information). We evaluated each of our properties and determined there were no additional valuation adjustments necessary at September 30, 2016 . Financial Instruments In addition to the assets and liabilities described in the above table, our financial instruments include our cash and cash equivalents, real estate mortgages receivable, restricted cash, senior unsecured debt and mortgage notes payable. At September 30, 2016 and December 31, 2015, the fair value of these additional financial instruments were not materially different from their carrying values, except as follows (in thousands): September 30, 2016 December 31, 2015 Carrying Amount Fair Value Carrying Amount Fair Value Senior unsecured debt and mortgage notes payable, net $ 1,557,260 $ 1,618,274 $ 1,697,116 $ 1,749,211 The fair values of our senior notes and 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). Our cash and cash equivalents consists of cash maintained in time deposits, depository accounts and money market accounts. From time-to-time we may also invest in various U.S. government securities. We continually monitor the credit ratings of the financial institutions holding our deposits to minimize our exposure to credit risk. Throughout the year, we have cash balances in excess of federally insured limits deposited with various financial institutions. We do not believe we are exposed to any significant credit risk on cash and cash equivalents. Other financial instruments that potentially subject us to concentrations of credit risk consist principally of rents receivable; however, as of September 30, 2016 , no single tenant of ours is responsible for more than 5.5% of our total annualized rents. Our derivative financial instruments, including interest rate swaps and cap, are entered with major financial institutions and we monitor the amount of credit exposure to any one counterparty.

Earnings Per Common Share

Earnings Per Common Share	9 Months Ended
	Sep. 30, 2016
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 September 30, Nine Months Ended September 30, 2016 2015 2016 2015 Numerator for earnings per common share - basic and diluted: Net income $ 86,388 $ 30,466 $ 220,634 $ 56,712 Preferred distributions (1,997 ) (6,981 ) (15,959 ) (20,943 ) Excess fair value of consideration paid over carrying value of preferred shares — — (9,609 ) — Numerator for net income per share $ 84,391 $ 23,485 $ 195,066 $ 35,769 Denominator for earnings per common share - basic and diluted: Weighted average number of common shares outstanding - basic 125,533 128,739 125,627 129,386 Weighted average number of common shares outstanding - diluted (1) 126,568 129,878 127,009 130,093 Net income per common share attributable to Equity Commonwealth common shareholders: Basic $ 0.67 $ 0.18 $ 1.55 $ 0.28 Diluted $ 0.67 $ 0.18 $ 1.54 $ 0.27 Anti-dilutive securities: Effect of Series D preferred shares; 6 1/2% cumulative convertible (2) 2,363 2,363 2,363 2,363 (1) As of September 30, 2016 , we had granted RSUs to certain employees, officers, and the chairman of the Board of Trustees. The RSUs contain both service and market-based vesting components. None of the RSUs have vested. If the market-based vesting component was measured as of September 30, 2016 , and 2015 , 1,035 and 1,139 common shares would be issued to the RSU holders, respectively. Using a weighted average basis, 1,035 and 1,139 common shares are reflected in diluted earnings per share for the three months ended September 30, 2016 and 2015 , respectively and 1,382 and 707 common shares are reflected in diluted earnings per share for the nine months ended September 30, 2016 and 2015 , respectively. (2) The Series D preferred shares are excluded from the diluted earnings per share calculation because including the Series D preferred shares would also require that the preferred distributions be added back to net income, resulting in anti-dilution during the periods presented.

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2016
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. Due to significant dispositions, during the fourth quarter of 2015, we changed the composition of our operating segments from two reportable segments (central business district properties and suburban properties) to one reportable segment. This change was made based on the financial information reviewed and used by the chief operating decision maker to make operating decisions, assess performance, develop strategy and allocate capital resources. More than 95% of our revenues for the nine months ended September 30, 2016 are from office properties.

Related Person Transactions

Related Person Transactions	9 Months Ended
	Sep. 30, 2016
Related Party Transactions [Abstract]
Related Person Transactions	Related Person Transactions The following discussion includes a description of our related person transactions for the nine months ended September 30, 2016 and 2015 . Related Person Transactions Following the Special Meeting: Equity Group Investments and associated entities: 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 recently completed improvements to the office space utilizing the $0.7 million tenant improvement allowance provided for by 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 and nine months ended September 30, 2016 , we recognized expense of $0.2 million and $0.6 million , respectively, pursuant to the 20 th /21 st Floor Office Lease and the related storage space. We had a license agreement with Equity Group Investments, a private investment firm (Equity Group), to use office space on the sixth floor at Two North Riverside Plaza. The license fee included the non-exclusive use of additional areas on the sixth floor (such as conference rooms and common areas), certain administrative services (such as mail room services and reception desk staffing), office equipment, office furniture, supplies, licensee’s share of building operating expenses and real estate taxes and access to one parking space. Mr. Zell, our Chairman, is the Chairman and Chief Executive Officer of Equity Group, and Mr. Helfand, our President and Chief Executive Officer, is the Co-President of Equity Group. The license agreement was terminated as of December 30, 2015. During the three and nine months ended September 30, 2015 , we recognized expense of $46,000 and $0.1 million , respectively, pursuant to the license agreement. We had a sublease with Equity Residential Management, L.L.C. to occupy office space on the tenth floor of Two North Riverside Plaza. Equity Residential Management, L.L.C. leases the space from Two North Riverside Plaza Joint Venture Limited Partnership. The sublease agreement was terminated as of December 30, 2015. During the three and nine months ended September 30, 2015 , we recognized expense of $0.1 million and $0.3 million , respectively, pursuant to the tenth floor office sublease. Related/Corvex: On July 31, 2014, at the reconvened session of our 2014 annual meeting of shareholders, our shareholders voted to approve the reimbursement of approximately $33.5 million of verified expenses incurred by Related/Corvex since February 2013 in connection with their consent solicitations to remove our former Trustees and elect the new Board of Trustees and to engage in related litigation. Approximately $16.7 million was paid during the year ended December 31, 2014. Up to $8.4 million was to be reimbursed only if the average closing price of our common shares was at least $26.00 (as adjusted for any share splits or share dividends) during the one year period after the date on which the reimbursement was approved by shareholders, and up to $8.4 million was to be reimbursed only if the average closing price of our common shares was at least $26.00 (as adjusted for any share splits or share dividends) during the one year period between the first and second anniversaries of the date on which the reimbursement was approved by shareholders. The average closing price of our common shares was at least $26.00 during both the first and second one year periods after the date on which the reimbursement was approved by shareholders, and as a result, in August 2016 and 2015 we paid an $8.2 million final payment and $8.4 million , respectively, to Related/Corvex. Transactions with Prior Related Persons: Certain related person transactions, and their approvals, relate to Reit Management & Research LLC (RMR) and RMR Australia Asset Management Pty Ltd (together, Former Manager) or occurred prior to the election of our new Board of Trustees at the special meeting of shareholders held on May 23, 2014 (Special Meeting) and the appointment of our current executive officers following the Special Meeting, as described below. Termination and Cooperation Agreement: On September 30, 2014, we entered into a termination and cooperation agreement (Cooperation Agreement) with Former Manager. Under the terms of the agreement, the existing business and property management agreements with RMR terminated effective September 30, 2014. Pursuant to the Cooperation Agreement, through February 28, 2015, Former Manager agreed to use best efforts to assist us in the transition of our management and operations. We paid Former Manager $1.2 million per month for transition services from October 1, 2014 to February 28, 2015, which included continued management and other services for the Australian assets pursuant to the Australian Management Agreement. Beginning March 1, 2015, we agreed to pay Former Manager $0.1 million per month until we no longer required such services or until the Australia Management Agreement was terminated, which was terminated in the third quarter of 2015, effective October 31, 2015. There is no future obligation to pay any fees to Former Manager.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2016
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events In October 2016, we sold one property ( four buildings), with 151,917 square feet for $29.2 million , excluding closing costs. This property was classified as held for sale as of September 30, 2016 (see Note 3). In October 2016, we purchased a parcel of land adjacent to our Research Park property in Austin, Texas for $2.8 million . On November 1, 2016, we delivered notice of our intent to redeem at par our $250 million 6.25% senior unsecured notes due 2017 on December 15, 2016. The notes will be redeemed for cash at a price equal to 100% of the principal amount of the notes plus any accrued and unpaid interest up to, but excluding, the redemption date.

Basis of Presentation (Policies

Basis of Presentation (Policies)	9 Months Ended
	Sep. 30, 2016
Organization, Consolidation and Presentation of Financial Statements [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, 2015. 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 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (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. Early adoption is permitted, including adoption in an interim period. We are currently in the process of evaluating the impact, if any, the adoption of this ASU will have on our condensed consolidated financial statements. 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 condensed consolidated financial statements. In March 2016, the FASB issued ASU 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, which simplifies several aspects of the accounting for employee share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. This update is effective for annual periods beginning after December 15, 2016, and interim periods within those annual periods, but early adoption is permitted. We are currently in the process of evaluating the impact the adoption of this ASU will have on our condensed consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases, which amends the existing accounting standards for lease accounting, including requiring lessees to recognize most leases on their balance sheets. The ASU also requires lessees or lessors to capitalize only initial direct costs of leases. This update is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years, but early adoption is permitted. We are currently in the process of evaluating the impact the adoption of this ASU will have on our condensed consolidated financial statements. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers, which provides guidance for revenue recognition. This update is effective for interim and annual reporting periods beginning after December 15, 2017. We are currently in the process of evaluating the impact, if any, the adoption of this ASU will have on our condensed consolidated financial statements. In April 2015, the FASB issued ASU No. 2015-03, Simplifying the Presentation of Debt Issuance Costs. This standard amends existing guidance to require the presentation of debt issuance costs in the balance sheet as a deduction from the carrying amount of the related debt liability instead of as a deferred charge. It is effective for annual reporting periods beginning after December 15, 2015, but early adoption is permitted. We adopted this standard on January 1, 2016 and made the following reclassifications to the prior years' consolidated balance sheet to conform to the current year's presentation (in thousands): Balance Sheet as of December 31, 2015 Originally Reported Effect of Change As Adjusted Other assets, net 157,549 (13,208 ) 144,341 Senior unsecured debt, net 1,460,592 (9,986 ) 1,450,606 Mortgage notes payable, net 249,732 (3,222 ) 246,510 In April 2014, the FASB issued ASU No. 2014-08, Presentation of Financial Statements (Topic 205) and Property, Plant, and Equipment (Topic 360): Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity, or ASU 2014-08. ASU 2014-08 changes the criteria for reporting a discontinued operation. Under the new pronouncement, a disposal of a part of an organization that has a major effect on its operations and financial results is a discontinued operation. We adopted ASU 2014-08 on January 1, 2015, and determined that our 2016 dispositions, 2015 dispositions and properties held for sale as of September 30, 2016 do not individually represent a strategic shift, as defined by the standard, that has or will have a major effect on our operations and financial results. As a result, the 2016 and 2015 dispositions and properties held for sale have not been presented as discontinued operations in the statements of operations.

Recent Accounting Pronounceme24

Recent Accounting Pronouncements (Tables)	9 Months Ended
	Sep. 30, 2016
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
New Accounting Pronouncement	We adopted this standard on January 1, 2016 and made the following reclassifications to the prior years' consolidated balance sheet to conform to the current year's presentation (in thousands): Balance Sheet as of December 31, 2015 Originally Reported Effect of Change As Adjusted Other assets, net 157,549 (13,208 ) 144,341 Senior unsecured debt, net 1,460,592 (9,986 ) 1,450,606 Mortgage notes payable, net 249,732 (3,222 ) 246,510

Real Estate Properties (Tables)

Real Estate Properties (Tables)	9 Months Ended
	Sep. 30, 2016
Real Estate [Abstract]
Summary of Properties Held for Sale and Balance Sheet Information for all Properties Classified as Held for sale	As of September 30, 2016 , we classified the following property as held for sale (dollars in thousands): Asset Date Sold Number of Number of Square Footage Gross Sales Price 7800 Shoal Creek Boulevard October 2016 1 4 151,917 $ 29,210 Summarized balance sheet information for the property classified as held for sale is as follows (in thousands): September 30, 2016 Real estate properties $ 12,952 Other assets, net 511 Properties held for sale $ 13,463 Accounts payable and accrued expenses $ 337 Rent collected in advance 19 Security deposits 311 Liabilities related to properties held for sale $ 667
Summary of Properties Sold and Income Statement Information for Properties Disposed of	During the nine months ended September 30, 2016 , we sold the following properties (dollars in thousands): Asset Date Sold Number of Number of Square Footage Gross Sales Price Gain (Loss) on Sale Properties Executive Park February 2016 1 9 427,443 $ 50,865 $ 16,531 3330 N Washington Boulevard March 2016 1 1 55,719 11,250 5,455 111 East Kilbourn Avenue March 2016 1 1 373,669 60,500 14,677 1525 Locust Street April 2016 1 1 98,009 17,700 8,956 633 Ahua Street April 2016 1 1 93,141 29,000 15,963 Lakewood on the Park May 2016 1 2 180,558 37,100 13,616 Leased Land June 2016 1 7 — 48,450 15,914 9110 East Nichols Avenue June 2016 1 1 143,958 17,200 642 111 River Street (1) July 2016 1 1 566,215 235,000 78,240 Sky Park Centre July 2016 1 2 63,485 13,700 4,745 Raintree Industrial Park July 2016 1 12 563,182 11,500 (653 ) 8701 N Mopac August 2016 1 1 121,901 21,500 8,394 Portfolios of properties 812 San Antonio Street May 2016 1 1 59,321 1601 Rio Grande Street May 2016 1 1 56,219 Downtown Austin portfolio 2 2 115,540 $ 32,600 $ 20,584 785 Schilinger Road South June 2016 1 1 72,000 401 Vine Street June 2016 1 1 53,980 633 Frazier Drive June 2016 1 1 150,000 9840 Gateway Boulevard North June 2016 1 1 72,000 3003 South Expressway 281 June 2016 1 1 150,000 1331 North Center Parkway June 2016 1 1 53,980 Movie theater portfolio 6 6 551,960 $ 109,100 $ 30,595 128 Crews Drive July 2016 1 1 185,600 111 Southchase Boulevard July 2016 1 1 168,087 1043 Global Avenue July 2016 1 1 450,000 South Carolina industrial portfolio 3 3 803,687 $ 30,000 $ 7,244 100 East Wisconsin Avenue August 2016 1 1 435,067 111 Monument Circle August 2016 1 2 1,121,764 101-115 W. Washington Street August 2016 1 1 634,058 North Point Office Complex August 2016 1 2 873,335 Midwest portfolio 4 6 3,064,224 $ 416,900 $ (15,808 ) 27 56 7,222,691 $ 1,142,365 $ 225,095 (1) Property sale represented a leasehold interest.

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2016
Stockholders' Equity Note [Abstract]
Schedule of Declared Distributions	In 2016, our Board of Trustees declared distributions on our series D preferred shares and series E cumulative redeemable preferred shares to date as follows: Declaration Date Record Date Payment Date Series D Dividend Per Share Series E Dividend Per Share January 26, 2016 February 5, 2016 February 16, 2016 $ 0.40625 $ 0.453125 April 15, 2016 April 25, 2016 May 16, 2016 $ 0.40625 $ 0.453125 July 11, 2016 July 29, 2016 August 15, 2016 $ 0.40625 $ — October 10, 2016 October 28, 2016 November 15, 2016 $ 0.40625 $ —

Cumulative Other Comprehensiv27

Cumulative Other Comprehensive Loss (Tables)	9 Months Ended
	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule of Amounts Recognized in Cumulative Other Comprehensive Loss	The following tables present the amounts recognized in cumulative other comprehensive loss for the three and nine months ended September 30, 2016 (in thousands): Unrealized Loss on Derivative Instruments Balance as of July 1, 2016 $ (2,234 ) Other comprehensive income before reclassifications 23 Amounts reclassified from cumulative other comprehensive loss to net income 1,094 Net current period other comprehensive income 1,117 Balance as of September 30, 2016 $ (1,117 ) Unrealized Loss on Derivative Instruments Balance as of January 1, 2016 $ (3,687 ) Other comprehensive loss before reclassifications (748 ) Amounts reclassified from cumulative other comprehensive loss to net income 3,318 Net current period other comprehensive income 2,570 Balance as of September 30, 2016 $ (1,117 )
Schedule of Reclassifications Out of Cumulative Other Comprehensive Loss	The following table presents reclassifications out of cumulative other comprehensive loss for the three and nine months ended September 30, 2016 (in thousands): Amounts Reclassified from Cumulative Other Comprehensive Loss to Net Income Details about Cumulative Other Comprehensive Loss Components Three Months Ended September 30, 2016 Nine Months Ended September 30, 2016 Affected Line Items in the Statement of Operations Interest rate swap contracts $ 1,094 $ 3,318 Interest expense

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Schedule of Provision for Income Taxes	Our provision for income taxes consists of the following (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2016 2015 2016 2015 Current: State $ 225 $ 90 $ 465 $ 270 Federal — — — 525 Foreign — (67 ) — 2,337 225 23 465 3,132 Deferred: Foreign — — — (755 ) — — — (755 ) Income tax expense $ 225 $ 23 $ 465 $ 2,377

Derivative Instruments (Tables)

Derivative Instruments (Tables)	9 Months Ended
	Sep. 30, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Outstanding Interest Rate Derivatives Designated as Cash Flow Hedges of Interest Rate Risk	As of September 30, 2016 , we had the following outstanding interest rate derivatives that were designated as cash flow hedges of interest rate risk: Interest Rate Derivative Number of Instruments Notional Amount (in thousands) Interest rate swap 2 $ 168,103 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 instruments as well as their classification on the condensed consolidated balance sheets as of September 30, 2016 and December 31, 2015 (amounts in thousands): Fair Value as of Interest Rate Derivative Designated as Hedging Instrument Balance Sheet Location September 30, December 31, Pay-fixed swaps Accounts payable and accrued expenses $ (707 ) $ (3,687 ) Interest rate cap Other assets $ 112 $ —
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 and nine months ended September 30, 2016 and 2015 (amounts in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2016 2015 2016 2015 Amount of gain (loss) recognized in cumulative other comprehensive loss $ 23 $ (418 ) $ (748 ) $ (1,378 ) Amount of loss reclassified from cumulative other comprehensive loss into interest expense 1,094 1,239 3,318 3,698

Share-Based Compensation (Table

Share-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2016
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of Assumptions and Fair Values for Restricted Stock Units Granted in the Period	The assumptions and fair values for the RSUs granted for the nine months ended September 30, 2016 are included in the following table on a per share basis. 2016 Fair value of RSUs granted $ 38.80 Expected term (years) 4 Expected volatility — Expected dividend yield 1.86 % Risk-free rate 1.07 %

Fair Value of Assets and Liab31

Fair Value of Assets and Liabilities (Tables)	9 Months Ended
	Sep. 30, 2016
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value	The table below presents certain of our assets and liabilities measured at fair value during 2016 , categorized by the level of inputs used in the valuation of each asset and liability (dollars in thousands): Fair Value at September 30, 2016 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: Effective portion of interest rate swap contracts $ (707 ) $ — $ (707 ) $ — Effective portion of interest rate cap contract 112 — 112 —
Schedule of Fair Value and Carrying Value of Financial Instruments	At September 30, 2016 and December 31, 2015, the fair value of these additional financial instruments were not materially different from their carrying values, except as follows (in thousands): September 30, 2016 December 31, 2015 Carrying Amount Fair Value Carrying Amount Fair Value Senior unsecured debt and mortgage notes payable, net $ 1,557,260 $ 1,618,274 $ 1,697,116 $ 1,749,211

Earnings Per Common Share (Tabl

Earnings Per Common Share (Tables)	9 Months Ended
	Sep. 30, 2016
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 September 30, Nine Months Ended September 30, 2016 2015 2016 2015 Numerator for earnings per common share - basic and diluted: Net income $ 86,388 $ 30,466 $ 220,634 $ 56,712 Preferred distributions (1,997 ) (6,981 ) (15,959 ) (20,943 ) Excess fair value of consideration paid over carrying value of preferred shares — — (9,609 ) — Numerator for net income per share $ 84,391 $ 23,485 $ 195,066 $ 35,769 Denominator for earnings per common share - basic and diluted: Weighted average number of common shares outstanding - basic 125,533 128,739 125,627 129,386 Weighted average number of common shares outstanding - diluted (1) 126,568 129,878 127,009 130,093 Net income per common share attributable to Equity Commonwealth common shareholders: Basic $ 0.67 $ 0.18 $ 1.55 $ 0.28 Diluted $ 0.67 $ 0.18 $ 1.54 $ 0.27 Anti-dilutive securities: Effect of Series D preferred shares; 6 1/2% cumulative convertible (2) 2,363 2,363 2,363 2,363 (1) As of September 30, 2016 , we had granted RSUs to certain employees, officers, and the chairman of the Board of Trustees. The RSUs contain both service and market-based vesting components. None of the RSUs have vested. If the market-based vesting component was measured as of September 30, 2016 , and 2015 , 1,035 and 1,139 common shares would be issued to the RSU holders, respectively. Using a weighted average basis, 1,035 and 1,139 common shares are reflected in diluted earnings per share for the three months ended September 30, 2016 and 2015 , respectively and 1,382 and 707 common shares are reflected in diluted earnings per share for the nine months ended September 30, 2016 and 2015 , respectively. (2) The Series D preferred shares are excluded from the diluted earnings per share calculation because including the Series D preferred shares would also require that the preferred distributions be added back to net income, resulting in anti-dilution during the periods presented.

Recent Accounting Pronounceme33

Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other assets, net	$ 123,699	$ 144,341
Senior unsecured notes, net	925,000
Mortgage notes payable, net	$ 243,993	246,510
ASU 2015-03
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other assets, net		144,341
Senior unsecured notes, net		1,450,606
Mortgage notes payable, net		246,510
ASU 2015-03 | Originally Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other assets, net		157,549
Senior unsecured notes, net		1,460,592
Mortgage notes payable, net		249,732
ASU 2015-03 | Effect of Change
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other assets, net		(13,208)
Senior unsecured notes, net		(9,986)
Mortgage notes payable, net		$ (3,222)

Real Estate Properties - Narrat

Real Estate Properties - Narrative (Details) $ in Thousands	1 Months Ended	9 Months Ended		12 Months Ended
	Jan. 31, 2013building	Sep. 30, 2016USD ($)ft²building	Sep. 30, 2015USD ($)	Dec. 31, 2015USD ($)ft²land_parcelbuildingproperty
Real Estate Properties [Line Items]
Real estate improvements | $		$ 88,500	$ 46,700
Number of properties held for sale | property				0
Number of buildings sold | building	18
Disposed of by Sale
Real Estate Properties [Line Items]
Number of properties sold | property				91
Number of buildings sold | building		56		135
Number of land parcels | land_parcel				1
Square Footage (in sqft) | ft²		7,222,691		18,900,000
Gross sales price | $		$ 1,142,365		$ 2,000,000

Real Estate Properties - Summar

Real Estate Properties - Summary of Properties Held for Sale (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2016USD ($)ft²buildingproperty	Dec. 31, 2015property
Real Estate Properties [Line Items]
Number of Properties		0
Held-for-sale | 7800 Shoal Creek Boulevard
Real Estate Properties [Line Items]
Number of Properties	1
Number of Buildings | building	4
Square Footage (in sqft) | ft²	151,917
Gross Sales Price | $	$ 29,210

Real Estate Properties - Summ36

Real Estate Properties - Summary of Balance Sheet Information for all Properties Classified as Held for sale (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Liabilities related to properties held for sale	$ 667	$ 0
Held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate properties	12,952
Other assets, net	511
Properties held for sale	13,463
Accounts payable and accrued expenses	337
Rent collected in advance	19
Security deposits	311
Liabilities related to properties held for sale	$ 667

Real Estate Properties - Summ37

Real Estate Properties - Summary of Properties Sold (Details) $ in Thousands

1 Months Ended

3 Months Ended

9 Months Ended

12 Months Ended

Aug. 31, 2016USD ($)ft²buildingproperty

Jul. 31, 2016USD ($)ft²buildingproperty

Jun. 30, 2016USD ($)ft²buildingproperty

May 31, 2016USD ($)ft²buildingproperty

Apr. 30, 2016USD ($)ft²buildingproperty

Mar. 31, 2016USD ($)ft²buildingproperty

Feb. 29, 2016USD ($)ft²buildingproperty

Jan. 31, 2013buildingproperty

Sep. 30, 2016USD ($)

Sep. 30, 2015USD ($)

Sep. 30, 2016USD ($)ft²buildingproperty

Sep. 30, 2015USD ($)

Dec. 31, 2015USD ($)ft²building

Real Estate Properties [Line Items]

Number of Properties | property

3

Number of Buildings | building

18

Gain (Loss) on Sale

$ 82,169

$ 39,793

$ 225,210

$ 42,953

Disposed of by Sale

Real Estate Properties [Line Items]

Number of Properties | property

27

Number of Buildings | building

56

135

Square Footage (in sqft) | ft²

7,222,691

18,900,000

Gross Sales Price

$ 1,142,365

$ 2,000,000

Gain (Loss) on Sale

$ 225,095

Disposed of by Sale | Executive Park

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

9

Square Footage (in sqft) | ft²

427,443

Gross Sales Price

$ 50,865

Gain (Loss) on Sale

$ 16,531

Disposed of by Sale | 3330 N Washington Boulevard

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

1

Square Footage (in sqft) | ft²

55,719

Gross Sales Price

$ 11,250

Gain (Loss) on Sale

$ 5,455

Disposed of by Sale | 111 East Kilbourn Avenue

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

1

Square Footage (in sqft) | ft²

373,669

Gross Sales Price

$ 60,500

Gain (Loss) on Sale

$ 14,677

Disposed of by Sale | 1525 Locust Street

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

1

Square Footage (in sqft) | ft²

98,009

Gross Sales Price

$ 17,700

Gain (Loss) on Sale

$ 8,956

Disposed of by Sale | 633 Ahua Street

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

1

Square Footage (in sqft) | ft²

93,141

Gross Sales Price

$ 29,000

Gain (Loss) on Sale

$ 15,963

Disposed of by Sale | Lakewood on the Park

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

2

Square Footage (in sqft) | ft²

180,558

Gross Sales Price

$ 37,100

Gain (Loss) on Sale

$ 13,616

Disposed of by Sale | Leased Land

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

7

Square Footage (in sqft) | ft²

0

Gross Sales Price

$ 48,450

Gain (Loss) on Sale

$ 15,914

Disposed of by Sale | 9110 East Nichols Avenue

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

1

Square Footage (in sqft) | ft²

143,958

Gross Sales Price

$ 17,200

Gain (Loss) on Sale

$ 642

Disposed of by Sale | 111 River Street(1)

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

1

Square Footage (in sqft) | ft²

566,215

Gross Sales Price

$ 235,000

Gain (Loss) on Sale

$ 78,240

Disposed of by Sale | Sky Park Centre

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

2

Square Footage (in sqft) | ft²

63,485

Gross Sales Price

$ 13,700

Gain (Loss) on Sale

$ 4,745

Disposed of by Sale | Raintree Industrial Park

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

12

Square Footage (in sqft) | ft²

563,182

Gross Sales Price

$ 11,500

Gain (Loss) on Sale

$ (653)

Disposed of by Sale | 8701 N Mopac

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

1

Square Footage (in sqft) | ft²

121,901

Gross Sales Price

$ 21,500

Gain (Loss) on Sale

$ 8,394

Disposed of by Sale | 812 San Antonio Street

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

1

Square Footage (in sqft) | ft²

59,321

Disposed of by Sale | 1601 Rio Grande Street

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

1

Square Footage (in sqft) | ft²

56,219

Disposed of by Sale | Downtown Austin portfolio

Real Estate Properties [Line Items]

Number of Properties | property

2

Number of Buildings | building

2

Square Footage (in sqft) | ft²

115,540

Gross Sales Price

$ 32,600

Gain (Loss) on Sale

$ 20,584

Disposed of by Sale | 785 Schilinger Road South

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

1

Square Footage (in sqft) | ft²

72,000

Disposed of by Sale | 401 Vine Street

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

1

Square Footage (in sqft) | ft²

53,980

Disposed of by Sale | 633 Frazier Drive

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

1

Square Footage (in sqft) | ft²

150,000

Disposed of by Sale | 9840 Gateway Boulevard North

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

1

Square Footage (in sqft) | ft²

72,000

Disposed of by Sale | 3003 South Expressway 281

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

1

Square Footage (in sqft) | ft²

150,000

Disposed of by Sale | 1331 North Center Parkway

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

1

Square Footage (in sqft) | ft²

53,980

Disposed of by Sale | Movie theater portfolio

Real Estate Properties [Line Items]

Number of Properties | property

6

Number of Buildings | building

6

Square Footage (in sqft) | ft²

551,960

Gross Sales Price

$ 109,100

Gain (Loss) on Sale

$ 30,595

Disposed of by Sale | 128 Crews Drive

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

1

Square Footage (in sqft) | ft²

185,600

Disposed of by Sale | 111 Southchase Boulevard

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

1

Square Footage (in sqft) | ft²

168,087

Disposed of by Sale | 1043 Global Avenue

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

1

Square Footage (in sqft) | ft²

450,000

Disposed of by Sale | South Carolina industrial portfolio

Real Estate Properties [Line Items]

Number of Properties | property

3

Number of Buildings | building

3

Square Footage (in sqft) | ft²

803,687

Gross Sales Price

$ 30,000

Gain (Loss) on Sale

$ 7,244

Disposed of by Sale | 100 East Wisconsin Avenue

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

1

Square Footage (in sqft) | ft²

435,067

Disposed of by Sale | 111 Monument Circle

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

2

Square Footage (in sqft) | ft²

1,121,764

Disposed of by Sale | 101-115 W. Washington Street

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

1

Square Footage (in sqft) | ft²

634,058

Disposed of by Sale | North Point Office Complex

Real Estate Properties [Line Items]

Number of Properties | property

1

Number of Buildings | building

2

Square Footage (in sqft) | ft²

873,335

Disposed of by Sale | Midwest portfolio

Real Estate Properties [Line Items]

Number of Properties | property

4

Number of Buildings | building

6

Square Footage (in sqft) | ft²

3,064,224

Gross Sales Price

$ 416,900

Gain (Loss) on Sale

$ (15,808)

Real Estate Mortgages Receiva38

Real Estate Mortgages Receivable - Narrative (Details)	1 Months Ended
	Jan. 31, 2013USD ($)buildingproperty	Apr. 30, 2012USD ($)	Sep. 30, 2016USD ($)	Dec. 31, 2015USD ($)
Mortgage Loans on Real Estate [Abstract]
Total real estate mortgage receivable included in other assets, carrying value			$ 8,100,000	$ 8,100,000
Mortgage financing related to sale of suburban property	$ 7,700,000	$ 400,000
Interest rate on real estate mortgage receivable, percent	6.00%	6.00%
Number of properties sold or agreed to be sold | property	3
Number of buildings sold | building	18
Allowance for mortgage receivables			$ 0	$ 0

Indebtedness - Narrative (Detai

Indebtedness - Narrative (Details)	Sep. 30, 2016USD ($)buildingproperty	Feb. 16, 2016USD ($)	Sep. 30, 2016USD ($)buildingproperty	Sep. 30, 2015USD ($)	Sep. 30, 2016USD ($)optionbuildingproperty	Sep. 30, 2015USD ($)	Dec. 31, 2015USD ($)
Debt Instrument [Line Items]
Senior unsecured notes, net	$ 925,000,000		$ 925,000,000		$ 925,000,000
Loss on early extinguishment of debt			0	$ (3,887,000)	(118,000)	$ 6,111,000
Real estate properties, net	2,183,931,000		2,183,931,000		2,183,931,000		$ 2,988,413,000
Mortgage notes payable, net	243,993,000		243,993,000		$ 243,993,000		$ 246,510,000
Revolving credit facility
Debt Instrument [Line Items]
Interest rate payable percentage					1.78%
Amount outstanding	0		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					1.25%
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%
Unsecured revolving credit facility | Revolving credit facility
Debt Instrument [Line Items]
Maximum borrowing capacity	750,000,000		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		$ 750,000,000
Commitment fee percentage	0.25%
Unsecured revolving credit facility | Letter of credit
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 100,000,000		100,000,000		100,000,000
Loan facility, 5-year term
Debt Instrument [Line Items]
Term loan amount outstanding	200,000,000		200,000,000		$ 200,000,000
Interest accrual rate					1.93%
Loan facility, 5-year term | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate					1.40%
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, 5-year term | Revolving credit facility
Debt Instrument [Line Items]
Debt instrument, term					5 years
Loan facility, 7-year term
Debt Instrument [Line Items]
Term loan amount outstanding	200,000,000		200,000,000		$ 200,000,000
Interest accrual rate					2.33%
Loan facility, 7-year term | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate					1.80%
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%
Loan facility, 7-year term | Revolving credit facility
Debt Instrument [Line Items]
Debt instrument, term					7 years
Senior Notes 6.25% Due 2016
Debt Instrument [Line Items]
Amount of debt, redeemed, defeased, or prepaid		$ 139,100,000
Interest rate stated percentage		6.25%
Loss on early extinguishment of debt					$ (100,000)
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		$ 1,150,000,000
Mortgage notes
Debt Instrument [Line Items]
Number of real estate properties secured by mortgage | property	5		5		5
Number of buildings secured by mortgage | building	8		8		8
Real estate properties, net	$ 293,300,000		$ 293,300,000		$ 293,300,000
Mortgage notes payable, net	$ 244,000,000		$ 244,000,000		$ 244,000,000

Shareholders' Equity - Narrativ

Shareholders' Equity - Narrative (Details)	May 15, 2016USD ($)$ / sharesshares	Sep. 30, 2016USD ($)authorization	Sep. 30, 2016USD ($)	Sep. 30, 2015USD ($)	Sep. 30, 2016USD ($)$ / sharesshares	Sep. 30, 2015USD ($)	Sep. 30, 2016USD ($)$ / sharesshares	Mar. 17, 2016USD ($)	Sep. 14, 2015USD ($)	Aug. 24, 2015USD ($)
Class of Stock [Line Items]
Number of expired stock repurchase programs | authorization		2
Stock repurchase program, amount not utilized		$ 86,600,000	$ 86,600,000		$ 86,600,000		$ 86,600,000
Excess fair value of consideration paid over carrying value of preferred shares			0	$ 0	$ 9,609,000	$ 0
Common Shares
Class of Stock [Line Items]
Stock repurchase program, authorized amount (up to)										$ 100,000,000
Stock repurchase program, additional authorized amount (up to)								$ 150,000,000	$ 100,000,000
Number of shares repurchased (in shares) | shares					983,789		4,394,089
Treasury stock acquired, average cost per share (in USD per share) | $ / shares					$ 25.94		$ 25.80
Stock repurchased and retired during period, value					$ 25,500,000		$ 113,400,000
Remaining authorized repurchase amount		$ 150,000,000	$ 150,000,000		$ 150,000,000		$ 150,000,000
Series E
Class of Stock [Line Items]
Stock repurchased during period, shares | shares	11,000,000
Redemption price per share (in USD per share) | $ / shares	$ 25
Preferred stock, redemption amount	$ 275,000,000

Shareholders' Equity - Schedule

Shareholders' Equity - Schedule of Declared Distributions (Details) - $ / shares	Nov. 15, 2016	Oct. 10, 2016	Aug. 15, 2016	Jul. 11, 2016	May 16, 2016	Apr. 15, 2016	Feb. 16, 2016	Jan. 26, 2016
Series D
Class of Stock [Line Items]
Dividend declared (in USD per share)				$ 0.40625		$ 0.40625		$ 0.40625
Dividend paid (in USD per share)			$ 0.40625		$ 0.40625		$ 0.40625
Series E
Class of Stock [Line Items]
Dividend declared (in USD per share)				$ 0		$ 0.453125		$ 0.453125
Dividend paid (in USD per share)			$ 0		$ 0.453125		$ 0.453125
Subsequent event | Series D
Class of Stock [Line Items]
Dividend declared (in USD per share)		$ 0.40625
Dividend paid (in USD per share)	$ 0.40625
Subsequent event | Series E
Class of Stock [Line Items]
Dividend declared (in USD per share)		$ 0
Dividend paid (in USD per share)	$ 0

Cumulative Other Comprehensiv42

Cumulative Other Comprehensive Loss - Schedule of Amounts Recognized in Cumulative Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2016
Amounts recognized in cumulative other comprehensive income (Loss) by component
Balance as of Beginning of Period		$ (3,687)
Balance as of End of Period	$ (1,117)	(1,117)
Unrealized Loss on Derivative Instruments
Amounts recognized in cumulative other comprehensive income (Loss) by component
Balance as of Beginning of Period	(2,234)	(3,687)
Other comprehensive income (loss) before reclassifications	23	(748)
Amounts reclassified from cumulative other comprehensive loss to net income	1,094	3,318
Net current period other comprehensive income	1,117	2,570
Balance as of End of Period	$ (1,117)	$ (1,117)

Cumulative Other Comprehensiv43

Cumulative Other Comprehensive Loss - Schedule of Reclassifications Out of Cumulative Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Reclassifications out of cumulative other comprehensive income (Loss)
Interest expense	$ 21,427	$ 25,111	$ 65,074	$ 82,926
Amounts Reclassified from Cumulative Other Comprehensive Loss to Net Income | Interest rate swap contracts
Reclassifications out of cumulative other comprehensive income (Loss)
Interest expense	$ 1,094		$ 3,318

Income Taxes - Schedule of Prov

Income Taxes - Schedule of Provision for Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Current:
State	$ 225	$ 90	$ 465	$ 270
Federal	0	0	0	525
Foreign	0	(67)	0	2,337
Current income tax expense (benefit)	225	23	465	3,132
Deferred:
Foreign	0	0	0	(755)
Deferred income tax expense (benefit)	0	0	0	(755)
Income tax expense	$ 225	$ 23	$ 465	$ 2,377

Derivative Instruments - Narrat

Derivative Instruments - Narrative (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Mar. 04, 2016
Derivative [Line Items]
Aggregate termination value	$ 1,100
Interest rate swap
Derivative [Line Items]
Fair value of derivatives in a net liability position	1,100
Interest rate cap | LIBOR
Derivative [Line Items]
Derivative, cap interest rate, percent		2.50%
Cash flow hedging | Designated as hedging instrument
Derivative [Line Items]
Estimated gain (loss) reclassification from OCI to income	(700)
Cash flow hedging | Designated as hedging instrument | Interest rate swap
Derivative [Line Items]
Amount of hedged item	$ 168,100
Derivative, variable interest rate	LIBOR
Notional amount	$ 168,103
Cash flow hedging | Designated as hedging instrument | Interest rate cap
Derivative [Line Items]
Notional amount	$ 400,000

Derivative Instruments - Schedu

Derivative Instruments - Schedule of Outstanding Interest Rate Derivatives Designated as Cash Flow Hedges of Interest Rate Risk (Details) - Cash flow hedging - Designated as hedging instrument $ in Thousands	Sep. 30, 2016USD ($)financial_instrument
Interest rate swap
Derivative [Line Items]
Number of Instruments | financial_instrument	2
Notional Amount (in thousands) | $	$ 168,103
Interest rate cap
Derivative [Line Items]
Number of Instruments | financial_instrument	1
Notional Amount (in thousands) | $	$ 400,000

Derivative Instruments - Sche47

Derivative Instruments - Schedule of Fair Value of Derivative Financial Instruments (Details) - Cash flow hedging - Designated as hedging instrument - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Interest rate swap | Accounts payable and accrued expenses
Derivatives, Fair Value [Line Items]
Interest Rate Derivative Designated as Hedging Instrument	$ (707)	$ (3,687)
Interest rate cap | Other Assets
Derivatives, Fair Value [Line Items]
Interest Rate Derivative Designated as Hedging Instrument	$ 112	$ 0

Derivative Instruments - Sche48

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		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in cumulative other comprehensive loss	$ 23	$ (418)	$ (748)	$ (1,378)
Amount of loss reclassified from cumulative other comprehensive loss into interest expense	$ 1,094	$ 1,239	$ 3,318	$ 3,698

Share-Based Compensation - Narr

Share-Based Compensation - Narrative (Details) $ / shares in Units, $ in Millions	Jun. 16, 2016USD ($)trustee$ / sharesshares	Jan. 26, 2016$ / sharesshares	Jun. 16, 2015USD ($)trustee$ / sharesshares	Jan. 28, 2015$ / sharesshares	Sep. 30, 2016USD ($)shares	Sep. 30, 2015USD ($)	Sep. 30, 2016USD ($)tranche$ / sharesshares	Sep. 30, 2015USD ($)$ / sharesshares
Share award plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares available for issuance (in shares)					2,358,464		2,358,464
Share award plan | General and Administrative Expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense | $					$ 4.9	$ 3.7	$ 13.9	$ 11.8
Restricted shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of equity awards granted (in shares)		136,623		126,319
Vesting period					4 years
Granted shares value (in dollars per share) | $ / shares		$ 26.93		$ 26.58
Shares forfeited in period							539	8,115
Weighted average grant date fair value (in USD per share) | $ / shares							$ 26.82	$ 26.64
Estimated future compensation expense for unvested shares | $					$ 14.1		$ 14.1
Weighted average period over which compensation expense will be recorded							2 years 3 months 18 days
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of equity awards granted (in shares)		277,386		256,467
Granted shares value (in dollars per share) | $ / shares							$ 38.80
Number of tranches | tranche							2
Shares forfeited in period							1,094	16,475
Weighted average grant date fair value (in USD per share) | $ / shares							$ 38.72	$ 20.50
Estimated future compensation expense for unvested shares | $					$ 22.2		$ 22.2
Weighted average period over which compensation expense will be recorded							2 years 2 months 12 days
Restricted stock units | Vesting in three years
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percent							50.00%
Restricted stock units | Vesting in four years
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percent							50.00%
Independent Trustee | Restricted shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of trustees to whom common shares granted | trustee	9		9
Stock issued during period, value, share-based compensation, gross | $	$ 0.1		$ 0.1
Grants in period per employee (in shares)	3,463		3,843
Number of equity awards granted (in shares)	31,167		34,587
Vesting period	1 year		1 year
Granted shares value (in dollars per share) | $ / shares	$ 28.88		$ 26.02

Share-Based Compensation - Summ

Share-Based Compensation - Summary of Assumptions and Fair Values for Restricted Stock Units Granted in the Period (Details) - Restricted stock units	9 Months Ended
	Sep. 30, 2016$ / 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)	$ 38.80
Expected term (years)	4 years
Expected volatility	0.00%
Expected dividend yield	1.86%
Risk-free rate	1.07%

Fair Value of Assets and Liab51

Fair Value of Assets and Liabilities - Schedule of Assets and Liabilities Measure at Fair Value (Details) - Recurring $ in Thousands	Sep. 30, 2016USD ($)
Interest rate swap
Recurring Fair Value Measurements:
Effective portion of interest rate swap contracts	$ (707)
Interest rate swap | Level 1
Recurring Fair Value Measurements:
Effective portion of interest rate swap contracts	0
Interest rate swap | Level 2
Recurring Fair Value Measurements:
Effective portion of interest rate swap contracts	(707)
Interest rate swap | Level 3
Recurring Fair Value Measurements:
Effective portion of interest rate swap contracts	0
Interest rate cap
Recurring Fair Value Measurements:
Effective portion of interest rate cap contract	112
Interest rate cap | Level 1
Recurring Fair Value Measurements:
Effective portion of interest rate cap contract	0
Interest rate cap | Level 2
Recurring Fair Value Measurements:
Effective portion of interest rate cap contract	112
Interest rate cap | Level 3
Recurring Fair Value Measurements:
Effective portion of interest rate cap contract	$ 0

Fair Value of Assets and Liab52

Fair Value of Assets and Liabilities - Narrative (Details)	1 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Aug. 31, 2016USD ($)	Aug. 31, 2015USD ($)	Sep. 30, 2016USD ($)	Sep. 30, 2015USD ($)	Sep. 30, 2016USD ($)Tenant	Sep. 30, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2015USD ($)	Jul. 31, 2014USD ($)$ / shares
Fair value of assets and liabilities
Loss on asset impairment			$ 0	$ 0	$ 43,736,000	$ 17,162,000
Number of tenants responsible for more than 4% of total annualized rents | Tenant					0
Real estate properties, net			2,183,931,000		$ 2,183,931,000			$ 2,988,413,000
Total rents | Credit concentration
Fair value of assets and liabilities
Concentration risk, percent					5.50%
General and Administrative Expense
Fair value of assets and liabilities
Change in fair value of derivatives			(100,000)		$ 1,000,000
Market Approach Valuation Technique | Real Estate Held-for-sale | Level 2
Fair value of assets and liabilities
Assets, fair value disclosure			264,900,000		264,900,000
Disposition Plan | Carrying Amount | Fair Value, Measurements, Nonrecurring
Fair value of assets and liabilities
Real estate properties, net			308,600,000		308,600,000
Derivative liability | Level 3
Fair value of assets and liabilities
Derivative liability			0		0			$ 7,200,000
Minimum
Fair value of assets and liabilities
Average closing price per common share during one year period after date (in dollars per share) | $ / shares									$ 26
Related/Corvex
Fair value of assets and liabilities
Amount of reimbursements payable to related party upon the approval of shareholders	$ 8,200,000	$ 8,400,000					$ 16,700,000
Amount of reimbursements payable to related party if specified minimum common share price maintain during the one year period after the date on which the reimbursement is approved by shareholders (up to)									$ 8,400,000
Amount of reimbursements payable to related party if specified minimum common share price maintain during the one year period between the first and second anniversaries of the date on which the reimbursement is approved by shareholders (up to)									$ 8,400,000
Derivative liability, potential reimbursement to related party contingent on stock price			$ 8,400,000		$ 8,400,000
Related/Corvex | Minimum
Fair value of assets and liabilities
Average closing price per common share during one year period after date (in dollars per share) | $ / shares									$ 26
Average closing price per common share during first and second year after date (in dollars per share) | $ / shares									$ 26

Fair Value of Assets and Liab53

Fair Value of Assets and Liabilities - Schedule of Fair Value and Carrying Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Carrying Amount
Fair value of financial instruments
Senior unsecured debt and mortgage notes payable, net	$ 1,557,260	$ 1,697,116
Fair Value
Fair value of financial instruments
Senior unsecured debt and mortgage notes payable, net	$ 1,618,274	$ 1,749,211

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		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Numerator for earnings per common share - basic and diluted:
Net income	$ 86,388	$ 30,466	$ 220,634	$ 56,712
Preferred distributions	(1,997)	(6,981)	(15,959)	(20,943)
Excess fair value of consideration paid over carrying value of preferred shares	0	0	(9,609)	0
Net income attributable to Equity Commonwealth common shareholders	$ 84,391	$ 23,485	$ 195,066	$ 35,769
Denominator for earnings per common share - basic and diluted:
Weighted average number of common shares outstanding — basic (in shares)	125,533	128,739	125,627	129,386
Weighted average number of common shares outstanding — diluted (in shares)	126,568	129,878	127,009	130,093
Net income per common share attributable to Equity Commonwealth common shareholders:
Basic (in USD per share)	$ 0.67	$ 0.18	$ 1.55	$ 0.28
Diluted (in USD per share)	$ 0.67	$ 0.18	$ 1.54	$ 0.27
Effect of Series D preferred shares; 6 1/2% cumulative convertible
Anti-dilutive securities:
Effect of Series D preferred shares; 6 1/2% cumulative convertible (in shares)	2,363	2,363	2,363	2,363
Effect of Series D preferred shares; 6 1/2% cumulative convertible
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Preferred shares, dividend yield	6.50%	6.50%	6.50%	6.50%	6.50%

Earnings Per Common Share - S55

Earnings Per Common Share - Schedule of Computation of Basic and Diluted Earnings Per Share (Footnote) (Details) - Restricted stock units - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
RSUs vested (in shares)			0
Common shares issued (in shares)	1,035,000	1,139,000	1,035,000	1,139,000
Weighted average common shares outstanding — diluted (in shares)	1,035,000	1,139,000	1,382,000	707,000

Segment Information - Narrative

Segment Information - Narrative (Details) - segment	3 Months Ended	9 Months Ended
	Dec. 31, 2015	Sep. 30, 2016
Segment Reporting [Abstract]
Number of reportable segments	2	1
Percentage of revenue from office properties (more than)		95.00%

Related Person Transactions - N

Related Person Transactions - Narrative (Details) $ / shares in Units, $ in Thousands	Mar. 01, 2015USD ($)	Aug. 31, 2016USD ($)	Aug. 31, 2015USD ($)	Sep. 30, 2016USD ($)	Sep. 30, 2015USD ($)	Feb. 28, 2015USD ($)	Sep. 30, 2016USD ($)option	Sep. 30, 2015USD ($)	Dec. 31, 2015parking_space	Dec. 31, 2014USD ($)	Jul. 31, 2014USD ($)$ / shares
Minimum
Related Party Transaction [Line Items]
Average closing price per common share during one year period after date (at least) (in dollars per share) | $ / shares											$ 26
Two North Riverside Plaza Joint Venture Limited Partnership
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				$ 700			$ 700
Lease termination period duration							30 days
Expenses from transactions with related party				$ 200			$ 600
Equity Group Investments and associated entities
Related Party Transaction [Line Items]
Expenses from transactions with related party					$ 46			$ 100
Number of parking spaces | parking_space									1
Equity Residential Management, L.L.C.
Related Party Transaction [Line Items]
Expenses from transactions with related party					$ 100			$ 300
Related/Corvex
Related Party Transaction [Line Items]
Due to related persons											$ 33,500
Amount of reimbursements payable to related party upon the approval of shareholders		$ 8,200	$ 8,400							$ 16,700
Amount of reimbursements payable to related party if specified minimum common share price maintain during the one year period after the date on which the reimbursement is approved by shareholders (up to)											8,400
Amount of reimbursements payable to related party if specified minimum common share price maintain during the one year period between the first and second anniversaries of the date on which the reimbursement is approved by shareholders (up to)											$ 8,400
Related/Corvex | Minimum
Related Party Transaction [Line Items]
Average closing price per common share during one year period after date (at least) (in dollars per share) | $ / shares											$ 26
Average closing price per common share during first and second year after date (in dollars per share) | $ / shares											$ 26
RMR and RMR Australia
Related Party Transaction [Line Items]
Monthly management transition fee	$ 100					$ 1,200

Subsequent Events - Narrative (

Subsequent Events - Narrative (Details) $ in Thousands	Nov. 01, 2016USD ($)	Oct. 31, 2016USD ($)ft²buildingproperty	Jan. 31, 2013building	Sep. 30, 2016USD ($)ft²building	Dec. 31, 2015USD ($)ft²buildingproperty
Subsequent Event [Line Items]
Number of buildings sold | building			18
Disposed of by Sale
Subsequent Event [Line Items]
Number of properties sold | property					91
Number of buildings sold | building				56	135
Property square feet | ft²				7,222,691	18,900,000
Gross sales price				$ 1,142,365	$ 2,000,000
Subsequent event | Senior notes 6.25% due 2017
Subsequent Event [Line Items]
Amount of debt intended to be redeemed	$ 250,000
Interest rate stated percentage	6.25%
Percentage of principal amount redeemed	100.00%
Subsequent event | Austin, Texas
Subsequent Event [Line Items]
Payments to acquire land		$ 2,800
Subsequent event | Disposed of by Sale
Subsequent Event [Line Items]
Number of properties sold | property		1
Number of buildings sold | building		4
Property square feet | ft²		151,917
Gross sales price		$ 29,200