| Document and Entity Information | May 20, 2020 |
| Entity Listings [Line Items] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | May 20, 2020 |
| Entity Registrant Name | Equity Commonwealth |
| Entity Incorporation, State or Country Code | MD |
| Entity File Number | 001-09317 |
| Entity Tax Identification Number | 04-6558834 |
| Entity Address, Address Line One | TWO NORTH RIVERSIDE PLAZA |
| Entity Address, Address Line Two | 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000803649 |
| Common Stock [Member] | |
| Entity Listings [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 [Member] | |
| Entity Listings [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 |
