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Summary of Significant Accounting Policies (Details) | 12 Months Ended
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Dec. 31, 2017
Properties |
Period after the cessation of major construction activities for considering property as operational if leases have not commenced earlier (in years) | 1 year
Period after the cessation of major construction activities for considering property as partially operational if leases have commenced earlier (in years) | 1 year
Property, Plant and Equipment [Line Items] |
Period used recovery analysis for long-lived assets to be held and used that may be impaired (in years) | 10 years
Minimum [Member] | Buildings and building improvements [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 10 years
Minimum [Member] | Land improvements [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 10 years
Minimum [Member] | Equipment and personal property [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 3 years
Maximum [Member] | Buildings and building improvements [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 40 years
Maximum [Member] | Land improvements [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 20 years
Maximum [Member] | Equipment and personal property [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 10 years

X
- Definition Represents the period after the cessation of major construction activities for considering property as operational if leases have not commenced earlier. + References No definition available. + Details
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Namespace Prefix: | ofc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the period after the cessation of major construction activities for considering property as partially operational if leases have commenced earlier. + References No definition available. + Details
Name: | ofc_PeriodAfterCessationOfMajorConstructionActivitiesForConsideringPropertyToBePartiallyOperationalIfLeasesHaveCommencedEarlier
Namespace Prefix: | ofc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Period used for recovery analysis of long lived assets to be held and used that may be impaired. + References No definition available. + Details
Name: | ofc_PeriodusedrecoveryanalysisforPotentiallyImpairedLongLivedAssetHeldandUsed
Namespace Prefix: | ofc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_PropertyPlantAndEquipmentAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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

X
- Definition Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment. + References No definition available. + Details
Name: | us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_BuildingAndBuildingImprovementsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_LandImprovementsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=ofc_EquipmentAndPersonalPropertyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |