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Equity (Details) - USD ($) $ / shares in Units, $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2019 | Mar. 31, 2018
Class of Stock [Line Items] |  |
Conversion of common units to common shares (in units/shares) | 5,500 | 53,817
Dividends declared per share (in usd per share) | $ 0.2750 | $ 0.275
Common Shares | Forward Equity Sale Agreement |  |
Class of Stock [Line Items] |  |
Number of shares issued | 1,600,000 |
Proceeds from common shares issued under forward equity sale agreements | $ 46.5 |
Remaining capacity under program | 0 |
Common Shares | 2018 Common Stock Issued to Public Under At-the-Market Program |  |
Class of Stock [Line Items] |  |
Aggregate gross sales price | $ 300.0 |
Corporate Office Properties, L.P. |  |
Class of Stock [Line Items] |  |
Dividends declared per share (in usd per share) | $ 0.275 | $ 0.275

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