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Properties, net (Details 4) (USD $) In Millions, unless otherwise specified | 3 Months Ended
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Mar. 31, 2015 sqft Property
Newly constructed properties placed in service |
Construction and Redevelopment Activities |
Square feet of properties placed in service | 440,000 ofc_SquareFeetofPropertiesPlacedinService / us-gaap_RealEstatePropertiesAxis = ofc_NewlyConstructedPropertiesPlacedInServiceMember
Number of real estate properties placed in service | 3 ofc_NumberOfRealEstatePropertiesPlacedInService / us-gaap_RealEstatePropertiesAxis = ofc_NewlyConstructedPropertiesPlacedInServiceMember
Properties under construction or contractually committed for construction |
Construction and Redevelopment Activities |
Number of real estate properties | 7 us-gaap_NumberOfRealEstateProperties / us-gaap_RealEstatePropertiesAxis = ofc_PropertiesUnderConstructionOrContractuallyCommitedForConstructionMember
Square footage of real estate properties (in square feet) | 1,100,000 us-gaap_AreaOfRealEstateProperty / us-gaap_RealEstatePropertiesAxis = ofc_PropertiesUnderConstructionOrContractuallyCommitedForConstructionMember
Properties under construction or contractually committed for construction | Baltimore and Washington Corridor |
Construction and Redevelopment Activities |
Number of real estate properties | 2 us-gaap_NumberOfRealEstateProperties / us-gaap_RealEstatePropertiesAxis = ofc_PropertiesUnderConstructionOrContractuallyCommitedForConstructionMember / ofc_RealEstatePropertyLocationAxis = ofc_BaltimoreAndWashingtonCorridorMember
Properties under construction or contractually committed for construction | Northern Virginia |
Construction and Redevelopment Activities |
Number of real estate properties | 4 us-gaap_NumberOfRealEstateProperties / us-gaap_RealEstatePropertiesAxis = ofc_PropertiesUnderConstructionOrContractuallyCommitedForConstructionMember / ofc_RealEstatePropertyLocationAxis = ofc_NorthernVirginiaMember
Properties under construction or contractually committed for construction | Huntsville |
Construction and Redevelopment Activities |
Number of real estate properties | 1 us-gaap_NumberOfRealEstateProperties / us-gaap_RealEstatePropertiesAxis = ofc_PropertiesUnderConstructionOrContractuallyCommitedForConstructionMember / ofc_RealEstatePropertyLocationAxis = ofc_HuntsvilleMember
Properties redeveloped |
Construction and Redevelopment Activities |
Square feet of properties placed in service | 111,000 ofc_SquareFeetofPropertiesPlacedinService / us-gaap_RealEstatePropertiesAxis = ofc_PropertiesRedevelopedMember
Properties under or approved for redevelopment |
Construction and Redevelopment Activities |
Number of real estate properties | 5 us-gaap_NumberOfRealEstateProperties / us-gaap_RealEstatePropertiesAxis = ofc_PropertiesUnderorApprovedforRedevelopmentMember
Square footage of real estate properties (in square feet) | 344,000 us-gaap_AreaOfRealEstateProperty / us-gaap_RealEstatePropertiesAxis = ofc_PropertiesUnderorApprovedforRedevelopmentMember
Properties under or approved for redevelopment | Baltimore and Washington Corridor |
Construction and Redevelopment Activities |
Number of real estate properties | 3 us-gaap_NumberOfRealEstateProperties / us-gaap_RealEstatePropertiesAxis = ofc_PropertiesUnderorApprovedforRedevelopmentMember / ofc_RealEstatePropertyLocationAxis = ofc_BaltimoreAndWashingtonCorridorMember
Properties under or approved for redevelopment | Greater Philadelphia |
Construction and Redevelopment Activities |
Number of real estate properties | 1 us-gaap_NumberOfRealEstateProperties / us-gaap_RealEstatePropertiesAxis = ofc_PropertiesUnderorApprovedforRedevelopmentMember / ofc_RealEstatePropertyLocationAxis = ofc_GreaterPhiladelphiaMember
Properties under or approved for redevelopment | St Marys County |
Construction and Redevelopment Activities |
Number of real estate properties | 1 us-gaap_NumberOfRealEstateProperties / us-gaap_RealEstatePropertiesAxis = ofc_PropertiesUnderorApprovedforRedevelopmentMember / ofc_RealEstatePropertyLocationAxis = ofc_StMarysCountyMember
Non-operating properties |
Construction and Redevelopment Activities |
Sale price of land | 18.1 us-gaap_ProceedsFromSaleOfLandHeldforinvestment / ofc_RealEstatePropertyDisposalAxis = ofc_NonOperatingPropertiesMember
Gain on sale | 4.0 ofc_GainOnSaleOfPropertiesSold / ofc_RealEstatePropertyDisposalAxis = ofc_NonOperatingPropertiesMember
Partially operational properties |
Construction and Redevelopment Activities |
Number of real estate properties | 1 us-gaap_NumberOfRealEstateProperties / ofc_RealEstatePropertiesStatusAxis = ofc_PartiallyOperationalPropertiesMember

X
- Definition Represents the total gain recognized on properties sold during the period. + References No definition available. + Details
Name: | ofc_GainOnSaleOfPropertiesSold
Namespace Prefix: | ofc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Represents the number of real estate properties placed in service during the year. + References No definition available. + Details
Name: | ofc_NumberOfRealEstatePropertiesPlacedInService
Namespace Prefix: | ofc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition The amount of square footage placed into service during the period. + References No definition available. + Details
Name: | ofc_SquareFeetofPropertiesPlacedinService
Namespace Prefix: | ofc_
Data Type: | num:areaItemType
Balance Type: | na
Period Type: | duration

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

X
- 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

X
- Definition The cash inflow from the sale of land held for investment; excludes sales of land held as inventory or productive use. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3179-108585 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_RealEstatePropertiesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | ofc_RealEstatePropertiesStatusAxis=ofc_PartiallyOperationalPropertiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ofc_RealEstatePropertyDisposalAxis=ofc_NonOperatingPropertiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_RealEstatePropertiesAxis=ofc_PropertiesRedevelopedMember
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: |