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Cover Page - USD ($) $ in Billions	12 Months Ended
Cover Page - USD ($) $ in Billions	Dec. 31, 2019	Feb. 06, 2020	Jun. 28, 2019
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
Document Transition Report	false
Entity File Number	1-9317
Entity Registrant Name	EQUITY COMMONWEALTH
Entity Incorporation, State or Country Code	MD
Entity Tax Identification Number	04-6558834
Entity Address, Address Line One	Two North Riverside Plaza, Suite 2100
Entity Address, City or Town	Chicago
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60606
City Area Code	(312)
Local Phone Number	646-2800
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 3.9
Entity Common Stock, Shares Outstanding (in shares)		122,009,257
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Certain Information required by Items 10, 11, 12, 13 and 14 of Part III of this Annual Report on Form 10-K is incorporated herein by reference to the definitive Proxy Statement for the 2020 Annual Meeting of Shareholders, or the definitive Proxy Statement, which Equity Commonwealth intends to file no later than 120 days after the end of its fiscal year ended December 31, 2019.
Entity Central Index Key	0000803649
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Common Shares of Beneficial Interest
Document Information [Line Items]
Title of 12(b) Security	Common Shares of Beneficial Interest
Trading Symbol	EQC
Security Exchange Name	NYSE
6.50% Series D Cumulative Convertible Preferred Shares of Beneficial Interest
Document Information [Line Items]
Title of 12(b) Security	6.50% Series D Cumulative Convertible Preferred Shares of Beneficial Interest
Trading Symbol	EQCpD
Security Exchange Name	NYSE