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Summary of Significant Accounting Policies (Details 1) | 12 Months Ended
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Dec. 31, 2014 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 | 2 ofc_NumberofDifferentFormsofShareBasedCompensation
Market concentration premium |
Useful Lifes Related To Intangible Assets and Property [Abstract] |
Finite-Lived Intangible Asset, Useful Life | 40 years
Corporate Office Properties, L.P. |
Noncontrolling Interest [Abstract] |
Interests in several real estate entities owned directly by COPT | 1.00%ofc_NoncontrollingInterestPercentageGenerallyOwnedbyParent / dei_LegalEntityAxis = us-gaap_SubsidiariesMember

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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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- Definition Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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