Share-Based Compensation and Other Compensation Matters (Tables)  | 
9 Months Ended | |||||||||||||||||||||
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Sep. 30, 2016  | ||||||||||||||||||||||
| Disclosure of Compensation Related Costs, Share-based Payments [Abstract] | ||||||||||||||||||||||
| Schedule of payouts for defined performance under performance-based awards of share-based compensation | 
 The number of PSUs earned (“earned PSUs”) at the end of the performance period will be determined based on the percentile rank of COPT’s total shareholder return relative to a peer group of companies, as set forth in the following schedule: 
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- Definition Schedule of payouts for defined performance under performance-based awards of share-based compensation No definition available. 
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- References No definition available. 
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