| Document and Entity Information | May 07, 2021 |
| Document And Entity Information [Line Items] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001593222 |
| Document Type | 8-K |
| Document Period End Date | May 7, 2021 |
| Entity Registrant Name | City Office REIT, Inc. |
| Entity Incorporation State Country Code | MD |
| Entity File Number | 001-36409 |
| Entity Tax Identification Number | 98-1141883 |
| Entity Address, Address Line One | 666 Burrard Street |
| Entity Address, Address Line Two | Suite 3210 |
| Entity Address, City or Town | Vancouver |
| Entity Address, State or Province | BC |
| Entity Address, Postal Zip Code | V6C 2X8 |
| City Area Code | (604) |
| Local Phone Number | 806-3366 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Stock [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Common Stock, $0.01 par value |
| Trading Symbol | CIO |
| Security Exchange Name | NYSE |
| Series A Preferred Stock [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 6.625% Series A Cumulative Redeemable Preferred Stock, $0.01 par value per share |
| Trading Symbol | CIO.PrA |
| Security Exchange Name | NYSE |
