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Summary of Significant Accounting Policies (Details) | 12 Months Ended
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Dec. 31, 2011 Month Y
Properties |
Period after the cessation of major construction activities for considering property as operational if leases have not commenced earlier (in years) | 1
Period after the cessation of major construction activities for considering property as partially operational if leases have commenced earlier (in years) | 1
Cash and Cash Equivalents |
Maximum term until original maturity to classify cash and liquid investments as cash and cash equivalents (in months) | 3
Buildings and building improvements |
Properties |
Estimated useful life, minimum (in years) | 10
Estimated useful life, maximum (in years) | 40
Land improvements |
Properties |
Estimated useful life, minimum (in years) | 10
Estimated useful life, maximum (in years) | 20
Equipment and personal property |
Properties |
Estimated useful life, minimum (in years) | 3
Estimated useful life, maximum (in years) | 10

X
- Definition Represents the maximum term until original maturity to classify cash and liquid investments as cash and cash equivalents. + References No definition available. + Details
Name: | ofc_MaximumTermUntilOriginalMaturityToClassifyCashAndLiquidInvestmentsAsCashAndCashEquivalents
Namespace Prefix: | ofc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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
Name: | ofc_PeriodAfterCessationOfMajorConstructionActivitiesForConsideringPropertyToBeOperationalIfLeasesHaveNotCommencedEarlier
Namespace Prefix: | ofc_
Data Type: | xbrli:integerItemType
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:integerItemType
Balance Type: | na
Period Type: | duration

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

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

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

X
- Definition The maximum useful life of long-lived, physical assets used in the normal conduct of business and not intended for resale. Examples include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software. + References No definition available. + Details
Name: | us-gaap_PropertyPlantAndEquipmentUsefulLifeMaximum
Namespace Prefix: | us-gaap_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | duration

X
- Definition The minimum useful life of long lived, physical assets used in the normal conduct of business and not intended for resale. Examples include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software. + References No definition available. + Details
Name: | us-gaap_PropertyPlantAndEquipmentUsefulLifeMinimum
Namespace Prefix: | us-gaap_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | duration