Annual report pursuant to Section 13 and 15(d)

Document and Entity Information

v3.10.0.1
Document and Entity Information - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Jan. 31, 2019
Jun. 30, 2018
Entity Information [Line Items]      
Entity Registrant Name CORPORATE OFFICE PROPERTIES TRUST    
Entity Central Index Key 0000860546    
Document Type 10-K    
Document Period End Date Dec. 31, 2018    
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     $ 2,700.0
Entity Common Stock, Shares Outstanding   110,263,078  
Document Fiscal Year Focus 2018    
Document Fiscal Period Focus FY    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false    
Corporate Office Properties, L.P. [Member]      
Entity Information [Line Items]      
Entity Registrant Name CORPORATE OFFICE PROPERTIES, L.P.    
Entity Central Index Key 0001577966    
Document Type 10-K    
Document Period End Date Dec. 31, 2018    
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 Non-accelerated Filer    
Entity Public Float     $ 84.4
Document Fiscal Year Focus 2018    
Document Fiscal Period Focus FY    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false