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Equity (Details) - USD ($) $ / shares in Units, $ in Millions | 6 Months Ended
--- | ---
Jun. 30, 2015 | Jun. 30, 2014
Class of Stock [Line Items] |  |
Number of operating partnerships units converted into common shares (in units) | 158,000 | 78,498
Common Shares |  |
Class of Stock [Line Items] |  |
Shares issued to the public (in units/ shares) | 890,241 |
Weighted average price per share of stock issued | $ 30.29 |
Net proceeds of stock issuance | $ 26.6 |
Commission costs | 0.4 |
Remaining capacity under ATM Plan | $ 84.0 |
Corporate Office Properties, L.P. | Common Shares |  |
Class of Stock [Line Items] |  |
Shares issued to the public (in units/ shares) | 890,241 | 0

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