Quarterly report pursuant to Section 13 or 15(d)

Equity (Details)

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Equity (Details) (USD $)
 0 Months Ended 6 Months Ended 0 Months Ended 6 Months Ended
Mar. 19, 2013
Jun. 30, 2013
Jun. 30, 2012
Apr. 22, 2013
Series J Preferred Stock
Mar. 19, 2013
Corporate Office Properties, L.P.
Jun. 30, 2013
Corporate Office Properties, L.P.
Jun. 30, 2012
Corporate Office Properties, L.P.
Class of Stock [Line Items]              
Dividend rate       7.625%      
Redemption price per share       $ 25      
Stock redeemed or called during period, value   $ 84,750,000   $ 84,800,000   $ 84,750,000  
Issuance costs associated with redeemed preferred shares       2,900,000      
Common Shares              
Shares issued to the public 4,485,000       4,485,000    
Shares issued to the public (in dollars per share) $ 26.34            
Public Offering, Proceeds After Underwriter Discounts But Before Offering Expenses $ 118,100,000 $ 117,913,000 $ 165,665,000     $ 117,913,000 $ 165,665,000
Number of operating parterships units converted into common shares (in units)   279,019 54,550        
Number of common shares for each converted common unit (in shares)   1