Quarterly report pursuant to Section 13 or 15(d)

Cover

v3.21.2
Cover - shares
 9 Months Ended
Sep. 30, 2021
Oct. 22, 2021
Cover [Abstract]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Sep. 30, 2021  
Document Transition Report false  
Entity File Number 1-14023  
Entity Registrant Name CORPORATE OFFICE PROPERTIES TRUST  
Entity Incorporation, State or Country Code MD  
Entity Tax Identification Number 23-2947217  
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  
Title of 12(b) Security Common Shares of beneficial interest, $0.01 par value  
Trading Symbol OFC  
Security Exchange Name NYSE  
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 Common Stock, Shares Outstanding   112,324,851
Entity Central Index Key 0000860546  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2021  
Document Fiscal Period Focus Q3