Quarterly report pursuant to Section 13 or 15(d)

Equity (Details)

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Equity (Details) (USD $)
 0 Months Ended 9 Months Ended 0 Months Ended 9 Months Ended 0 Months Ended
Mar. 19, 2013
Sep. 30, 2013
Sep. 30, 2012
Apr. 22, 2013
Series J Preferred Stock
Mar. 19, 2013
Corporate Office Properties, L.P.
Sep. 30, 2013
Corporate Office Properties, L.P.
Sep. 30, 2012
Corporate Office Properties, L.P.
Jul. 16, 2013
Common shares issued to public under at-the-market program
Jul. 16, 2013
Common shares issued to public under at-the-market program
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 $ 55,000,000 $ 84,800,000   $ 84,750,000 $ 55,000,000    
Issuance costs associated with redeemed preferred shares       2,900,000          
Shares issued to the public 4,485,000       4,485,000     1,500,000 1,500,000
Shares issued to the public (in dollars per share) $ 26.34                
Shares issued to the public (in dollars) 118,100,000 117,961,000 165,662,000     117,961,000 165,662,000 38,500,000  
Issuance of stock, weighted average price per share               $ 26.05  
Payments of Stock Issuance Costs               586,000  
At Market Stock, Offering Program Established, Remaining Capacity (in dollars)               $ 110,900,000  
Number of operating partnerships units converted into common shares (in units)   310,889 94,550            
Number of common shares for each converted common unit (in shares)   1