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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 |  |  |  |  |  |  |

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