Annual report pursuant to Section 13 and 15(d)

Document and Entity Information

v2.4.0.6
Document and Entity Information (USD $)
In Billions, except Share data, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
Jan. 28, 2013
Jun. 29, 2012
Document and Entity Information [Abstract]      
Entity Registrant Name CORPORATE OFFICE PROPERTIES TRUST    
Entity Central Index Key 0000860546    
Document Type 10-K    
Document Period End Date Dec. 31, 2012    
Amendment Flag false    
Current Fiscal Year End Date --12-31    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Filer Category Large Accelerated Filer    
Entity Public Float     $ 1.7
Entity Common Stock, Shares Outstanding   81,106,909  
Document Fiscal Year Focus 2012    
Document Fiscal Period Focus FY