| 
           Real Estate Joint Ventures (Details) (USD $) 
        In Thousands, unless otherwise specified  | 
        6 Months Ended | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 
           Jun. 30, 2014
 
          buillding 
         | 
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| 
           Consolidated real estate joint ventures 
         | 
        ||||||||||
| Investments in consolidated real estate joint ventures | ||||||||||
| Total Assets | $ 202,785 | [1] | ||||||||
| Pledged Assets | 115,858 | [1] | ||||||||
| Total Liabilities | 78,771 | [1] | ||||||||
| 
           LW Redstone Company, LLC 
         | 
        ||||||||||
| Investments in consolidated real estate joint ventures | ||||||||||
| Ownership (as a percent) | 85.00% | |||||||||
| Total Assets | 136,090 | [1],[2] | ||||||||
| Pledged Assets | 67,831 | [1],[2] | ||||||||
| Total Liabilities | 38,632 | [1],[2] | ||||||||
| Buildings Operated by Joint Ventures Number | 4 | [2] | ||||||||
| 
           M Square Associates, LLC 
         | 
        ||||||||||
| Investments in consolidated real estate joint ventures | ||||||||||
| Ownership (as a percent) | 50.00% | |||||||||
| Total Assets | 60,259 | [1],[3] | ||||||||
| Pledged Assets | 48,027 | [1],[3] | ||||||||
| Total Liabilities | 40,139 | [1],[3] | ||||||||
| Buildings Operated by Joint Ventures Number | 2 | [3] | ||||||||
| 
           COPT-FD Indian Head, LLC 
         | 
        ||||||||||
| Investments in consolidated real estate joint ventures | ||||||||||
| Ownership (as a percent) | 75.00% | |||||||||
| Total Assets | $ 6,436 | [1],[4] | ||||||||
          
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