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Concentration of Rental Revenue (Details) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Concentration Risk |  |  |  |  |  |
Number of regions with real estate operations which are not located in the Mid-Atlantic region of the United States | 3 ofc_ConcentrationRiskNumberOfRegionsWithRealEstateOperationsNotLocatedInMidAtlanticRegionOfUnitedStates |  |  |  |  |
Rental revenue | Tenants |  |  |  |  |  |
Concentration Risk |  |  |  |  |  |
Percentage required for qualification as major customer | 5.00%ofc_ThresholdForDisclosurePercentage / us-gaap_ConcentrationRiskByBenchmarkAxis = ofc_RentalRevenueMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember |  |  |  |  |
Number of tenants from which the entity has recognized the most rental revenue aggregated for revenue concentration disclosure | 5 ofc_ConcentrationRiskNumberOfTenantsFromWhichEntityHasRecognizedMostRentalRevenueAggregatedForRevenueConcentrationDisclosure / us-gaap_ConcentrationRiskByBenchmarkAxis = ofc_RentalRevenueMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember |  |  |  |  |
Rental revenue | Tenants | United States Government |  |  |  |  |  |
Concentration Risk |  |  |  |  |  |
Percentage of revenue | 18.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = ofc_RentalRevenueMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = ofc_UnitedStatesGovernmentMember |  | 18.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = ofc_RentalRevenueMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = ofc_UnitedStatesGovernmentMember |  | 18.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = ofc_RentalRevenueMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = ofc_UnitedStatesGovernmentMember |
Rental revenue | Tenants | Northrop Grumman Corporation |  |  |  |  |  |
Concentration Risk |  |  |  |  |  |
Percentage of revenue | 6.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = ofc_RentalRevenueMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = ofc_NorthropGrummanCorporationMember | [1] | 8.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = ofc_RentalRevenueMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = ofc_NorthropGrummanCorporationMember | [1] | 7.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = ofc_RentalRevenueMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = ofc_NorthropGrummanCorporationMember | [1]
Rental revenue | Tenants | Booz Allen Hamilton, Inc. |  |  |  |  |  |
Concentration Risk |  |  |  |  |  |
Percentage of revenue | 6.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = ofc_RentalRevenueMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = ofc_BoozAllenHamiltonIncMember |  | 6.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = ofc_RentalRevenueMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = ofc_BoozAllenHamiltonIncMember |  | 6.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = ofc_RentalRevenueMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = ofc_BoozAllenHamiltonIncMember |
Rental revenue | Tenants | Computer Sciences Corporation |  |  |  |  |  |
Concentration Risk |  |  |  |  |  |
Percentage of revenue |  |  | 5.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = ofc_RentalRevenueMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = ofc_ComputerSciencesCorporationMember | [1] | 5.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = ofc_RentalRevenueMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = ofc_ComputerSciencesCorporationMember | [1]
Rental revenue | Tenants | Five largest tenants |  |  |  |  |  |
Concentration Risk |  |  |  |  |  |
Percentage of revenue | 39.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = ofc_RentalRevenueMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = ofc_FiveLargestTenantsMember |  | 41.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = ofc_RentalRevenueMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = ofc_FiveLargestTenantsMember |  | 39.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = ofc_RentalRevenueMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = ofc_FiveLargestTenantsMember |
Construction contract revenue | United States Government |  |  |  |  |  |
Concentration Risk |  |  |  |  |  |
Percentage of revenue | 90.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = ofc_ConstructionContractRevenueMember / us-gaap_MajorCustomersAxis = ofc_UnitedStatesGovernmentMember |  | 90.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = ofc_ConstructionContractRevenueMember / us-gaap_MajorCustomersAxis = ofc_UnitedStatesGovernmentMember |  | 90.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = ofc_ConstructionContractRevenueMember / us-gaap_MajorCustomersAxis = ofc_UnitedStatesGovernmentMember |
[1] | Includes affiliated organizations and agencies and predecessor companies.

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- Definition Represents the number of regions with real estate operations which are not located in the Mid-Atlantic region of the United States. + References No definition available. + Details
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- Definition Represents the number of tenants from which the entity has recognized the most rental revenue aggregated for revenue concentration disclosure. + References No definition available. + Details
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