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Properties, Net (Details 4) ft² in Thousands | Mar. 31, 2018 ft² Property
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Newly constructed properties placed in service |
Construction, Redevelopment and Dispositions |
Square footage of real estate properties (in square feet) | ft² | 74
Number of real estate properties | Property | 1
Newly redeveloped properties placed in service |
Construction, Redevelopment and Dispositions |
Square footage of real estate properties (in square feet) | ft² | 11
Number of real estate properties | Property | 1
Properties under construction or contractually committed for construction |
Construction, Redevelopment and Dispositions |
Square footage of real estate properties (in square feet) | ft² | 597
Number of real estate properties | Property | 6
Properties under or approved for redevelopment |
Construction, Redevelopment and Dispositions |
Square footage of real estate properties (in square feet) | ft² | 22
Number of real estate properties | Property | 1

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- Definition Area of a real estate property. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | num:areaItemType
Balance Type: | na
Period Type: | instant

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- Definition The number of real estate properties owned as of the balance sheet date. + References No definition available. + Details
Name: | us-gaap_NumberOfRealEstateProperties
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_RealEstatePropertiesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RealEstatePropertiesAxis=ofc_PropertiesUnderConstructionOrContractuallyCommitedForConstructionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RealEstatePropertiesAxis=ofc_PropertiesUnderorApprovedforRedevelopmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |