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Summary of Significant Accounting Policies (Details 1) | 12 Months Ended
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Dec. 31, 2017 Form
Cash and Cash Equivalents |
Maximum term until original maturity to classify cash and liquid investments as cash and cash equivalent (in months) | 3 months
Share-Based Compensation |
Number of forms of share based compensation plans | 3
Corporate Office Properties, L.P. [Member] |
Noncontrolling Interest [Abstract] |
Interests in several real estate entities owned directly by COPT | 1.00%

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- Definition Represents the maximum term until original maturity to classify cash and liquid investments as cash and cash equivalents. + References No definition available. + Details
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