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Equity - COPLP and Subsidiaries (Details) - USD ($) $ / shares in Units, $ in Thousands |  |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Jun. 27, 2017 | Jan. 21, 2017 | Dec. 31, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Preferred Stock |  |  |  |  |  |
Stock redeemed or called during period value |  |  |  |  | $ 172,500 | $ 26,583
Preferred units in COPLP |  |  |  | $ 8,800 | $ 8,800 |
Common Shares |  |  |  |  |  |
Number of common shares for each converted common unit (in shares) |  |  |  | 1 |  |
Number of operating partnerships units converted into common shares (in units) |  |  |  | 1,904,615 | 339,513 | 87,000
Redemption of preferred shares |  |  |  | $ 339 |  |
Dividends declared per common share (in dollars per share) |  |  |  | $ 1.1 | $ 1.10 | $ 1.10
2016 ATM Program [Member] |  |  |  |  |  |
Common Shares |  |  |  |  |  |
Shares issued to the public |  |  |  | 992,000 | 591,000 | 3,700,000
Issuance of stock, weighted average price per share (in dollars per share) |  |  | $ 29.56 | $ 30.46 | $ 33.84 | $ 29.56
Payments of stock issuance costs |  |  |  | $ 500 | $ 300 | $ 900
Net proceeds from issuance of shares after underwriting discounts and commissions but before offering expenses |  |  |  | $ 29,800 | $ 19,700 | $ 109,100
Common Shares [Member] | 2016 ATM Program [Member] |  |  |  |  |  |
Common Shares |  |  |  |  |  |
Shares issued to the public |  |  | 3,700,000 | 992,000 | 591,000 |
Issuance of stock, weighted average price per share (in dollars per share) |  |  | $ 29.56 | $ 30.46 | $ 33.84 | $ 29.56
Payments of stock issuance costs |  |  | $ 900 | $ 500 | $ 300 |
Net proceeds from issuance of shares after underwriting discounts and commissions but before offering expenses |  |  | 109,100 | $ 29,800 | $ 19,700 |
Common Shares [Member] | Forward Equity Sale Agreement [Member] |  |  |  |  |  |
Common Shares |  |  |  |  |  |
Shares issued to the public |  |  |  | 5,900,000 | 1,700,000 |
Net proceeds from issuance of shares after underwriting discounts and commissions but before offering expenses |  |  |  | $ 172,500 | $ 50,000 |
Series K Preferred Shares [Member] |  |  |  |  |  |
Preferred Stock |  |  |  |  |  |
Annual dividend yield |  | 5.60% |  |  |  |
Issuance costs associated with redeemed preferred shares |  |  | 17 |  |  |
Series L [Member] |  |  |  |  |  |
Preferred Stock |  |  |  |  |  |
Annual dividend yield | 7.375% |  |  |  |  |
Issuance costs associated with redeemed preferred shares |  |  |  |  | 6,800 |
Corporate Office Properties, L.P. [Member] |  |  |  |  |  |
Preferred Stock |  |  |  |  |  |
Stock redeemed or called during period value |  |  |  |  | $ 172,500 | $ 26,583
Common Shares |  |  |  |  |  |
Number of common shares for each converted common unit (in shares) |  |  |  | 1 |  |
Number of operating partnerships units converted into common shares (in units) |  |  |  | 1,900,000 | 339,513.000 | 87,000
Redemption of preferred shares |  |  |  | $ 339 |  |
Dividends declared per common share (in dollars per share) |  |  |  | $ 1.1 | $ 1.10 | $ 1.10
Corporate Office Properties, L.P. [Member] | Common Shares [Member] |  |  |  |  |  |
Common Shares |  |  |  |  |  |
Stock redeemed or called during period (in units/ shares) |  |  |  | 13,377 |  |
Redemption of preferred shares |  |  |  | $ 339 |  |
Corporate Office Properties, L.P. [Member] | Common Units [Member] |  |  |  |  |  |
Common Shares |  |  |  |  |  |
Percentage ownership in operating partnership |  |  |  | 98.80% | 96.90% |
Stock redeemed or called during period (in units/ shares) |  |  |  | 13,377 |  |
Redemption of preferred shares |  |  |  | $ 339 |  |
Corporate Office Properties, L.P. [Member] | Conversion of Series I preferred units [Member] |  |  |  |  |  |
Preferred Stock |  |  |  |  |  |
Annual dividend yield |  |  |  | 7.50% |  |
Limited partners' capital account, units issued |  |  |  | 352,000 |  |
Preferred units in COPLP |  |  |  | $ 8,800 |  |
Preferred stock, liquidation preference per share |  |  |  | $ 25 |  |
Annual cumulative preferred return increment frequency |  |  |  | 5 years |  |
Common units conversion basis units issuable |  |  |  | 0.5 |  |
Corporate Office Properties, L.P. [Member] | Series K Preferred Shares [Member] |  |  |  |  |  |
Preferred Stock |  |  |  |  |  |
Annual dividend yield |  | 5.60% |  |  |  |
Preferred stock, redemption price per share (in dollars per share) |  | $ 50.00 |  |  |  |
Stock redeemed or called during period value |  | $ 26,600 |  |  |  |
Issuance costs associated with redeemed preferred shares |  |  | $ 17 |  |  |
Corporate Office Properties, L.P. [Member] | Series L [Member] |  |  |  |  |  |
Preferred Stock |  |  |  |  |  |
Annual dividend yield | 7.375% |  |  |  |  |
Preferred stock, redemption price per share (in dollars per share) | $ 25.00 |  |  |  |  |
Stock redeemed or called during period value | $ 172,500 |  |  |  |  |
Issuance costs associated with redeemed preferred shares |  |  |  |  | $ 6,800 |

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