| Cover | Nov. 17, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Nov. 17, 2021 |
| Entity File Number | 1-14023 |
| Entity Registrant Name | CORPORATE OFFICE PROPERTIES TRUST |
| Entity Central Index Key | 0000860546 |
| Entity Tax Identification Number | 23-2947217 |
| Entity Incorporation, State or Country Code | MD |
| Entity Address, Address Line One | 6711 Columbia Gateway Drive |
| Entity Address, Address Line Two | Suite 300 |
| Entity Address, City or Town | Columbia |
| Entity Address, State or Province | MD |
| Entity Address, Postal Zip Code | 21046 |
| City Area Code | 443 |
| Local Phone Number | 285-5400 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Shares of beneficial interest, $0.01 par value |
| Trading Symbol | OFC |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
