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Properties, net (Details 3) (USD $) | 12 Months Ended | 0 Months Ended
--- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 23, 2013
Dispositions |  |  |  |
Gain on early extinguishment of debt | $ (9,552,000)us-gaap_GainsLossesOnExtinguishmentOfDebt | $ (27,030,000)us-gaap_GainsLossesOnExtinguishmentOfDebt | $ (943,000)us-gaap_GainsLossesOnExtinguishmentOfDebt |
Non-operating Properties |  |  |  |
Dispositions |  |  |  |
Gain on Disposition | 5,600,000 ofc_GainOnSaleOfPropertiesSold / ofc_RealEstatePropertyDisposalAxis = ofc_NonOperatingPropertiesMember |  |  |
Sale price of non-operating properties | 28,300,000 ofc_TransactionValueofNonoperatingPropertyDispositions / ofc_RealEstatePropertyDisposalAxis = ofc_NonOperatingPropertiesMember | 3,500,000 ofc_TransactionValueofNonoperatingPropertyDispositions / ofc_RealEstatePropertyDisposalAxis = ofc_NonOperatingPropertiesMember |  |
Secured Debt | December 2013 Portfolio Conveyance |  |  |  |
Dispositions |  |  |  |
Debt settled through the surrender of real estate assets |  |  |  | 146,500,000 ofc_CarryingValueOfDebtSettledThroughSurrenderOfRealEstateAssets / us-gaap_DebtInstrumentAxis = us-gaap_SecuredDebtMember / ofc_RealEstatePropertyDisposalAxis = ofc_December2013PortfolioConveyanceMember
Gain on early extinguishment of debt |  |  |  | 67,800,000 us-gaap_GainsLossesOnExtinguishmentOfDebt / us-gaap_DebtInstrumentAxis = us-gaap_SecuredDebtMember / ofc_RealEstatePropertyDisposalAxis = ofc_December2013PortfolioConveyanceMember
Secured Debt | Fair value measurement on a nonrecurring basis | December 2013 Portfolio Conveyance |  |  |  |
Dispositions |  |  |  |
Fair value of real estate disposed in settlement of debt |  |  |  | 74,000,000 ofc_RealEstateDispositionSatisfactionOfDebt / us-gaap_DebtInstrumentAxis = us-gaap_SecuredDebtMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsNonrecurringMember / ofc_RealEstatePropertyDisposalAxis = ofc_December2013PortfolioConveyanceMember
Operating properties |  |  |  |
Dispositions |  |  |  |
Number of Buildings Disposed | 8 ofc_NumberofPropertiesDisposed / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember | 31 ofc_NumberofPropertiesDisposed / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember |  |
Total Rentable Square Feet | 302,958 us-gaap_AreaOfRealEstateProperty / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember | 2,345,000 us-gaap_AreaOfRealEstateProperty / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember |  |
Transaction Value of Operating Property Dispositions | 28,835,000 ofc_TransactionValueofOperatingPropertyDispositions / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember | 293,301,000 ofc_TransactionValueofOperatingPropertyDispositions / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember |  |
Gain on Disposition | 5,093,000 ofc_GainOnSaleOfPropertiesSold / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember | 2,671,000 ofc_GainOnSaleOfPropertiesSold / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember |  |
Operating properties | 4969 and 4979 Mercantile Rd |  |  |  |
Dispositions |  |  |  |
Number of Buildings Disposed | 2 ofc_NumberofPropertiesDisposed / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_Number4969and4979MercantileRdMember |  |  |
Total Rentable Square Feet | 96,721 us-gaap_AreaOfRealEstateProperty / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_Number4969and4979MercantileRdMember |  |  |
Transaction Value of Operating Property Dispositions | 5,960,000 ofc_TransactionValueofOperatingPropertyDispositions / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_Number4969and4979MercantileRdMember |  |  |
Gain on Disposition | 2,124,000 ofc_GainOnSaleOfPropertiesSold / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_Number4969and4979MercantileRdMember |  |  |
Operating properties | 9930 and 9940 Franklin Square |  |  |  |
Dispositions |  |  |  |
Number of Buildings Disposed | 2 ofc_NumberofPropertiesDisposed / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_Number9930and9940FranklinSquareMember |  |  |
Total Rentable Square Feet | 71,992 us-gaap_AreaOfRealEstateProperty / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_Number9930and9940FranklinSquareMember |  |  |
Transaction Value of Operating Property Dispositions | 10,475,000 ofc_TransactionValueofOperatingPropertyDispositions / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_Number9930and9940FranklinSquareMember |  |  |
Gain on Disposition | 2,303,000 ofc_GainOnSaleOfPropertiesSold / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_Number9930and9940FranklinSquareMember |  |  |
Operating properties | 5020, 5022, 5024 and 5026 Campbell Boulevard |  |  |  |
Dispositions |  |  |  |
Number of Buildings Disposed | 4 ofc_NumberofPropertiesDisposed / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_Number502050225024and5026CampbellBoulevardMember |  |  |
Total Rentable Square Feet | 134,245 us-gaap_AreaOfRealEstateProperty / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_Number502050225024and5026CampbellBoulevardMember |  |  |
Transaction Value of Operating Property Dispositions | 12,400,000 ofc_TransactionValueofOperatingPropertyDispositions / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_Number502050225024and5026CampbellBoulevardMember |  |  |
Gain on Disposition | 666,000 ofc_GainOnSaleOfPropertiesSold / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_Number502050225024and5026CampbellBoulevardMember |  |  |
Operating properties | 920 Elkridge Landing Road |  |  |  |
Dispositions |  |  |  |
Number of Buildings Disposed |  | 1 ofc_NumberofPropertiesDisposed / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_Number920ElkridgeLandingRoadMember |  |
Total Rentable Square Feet |  | 103,000 us-gaap_AreaOfRealEstateProperty / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_Number920ElkridgeLandingRoadMember |  |
Transaction Value of Operating Property Dispositions |  | 6,900,000 ofc_TransactionValueofOperatingPropertyDispositions / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_Number920ElkridgeLandingRoadMember |  |
Gain on Disposition |  | 0 ofc_GainOnSaleOfPropertiesSold / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_Number920ElkridgeLandingRoadMember |  |
Operating properties | 4230 Forbes Boulevard |  |  |  |
Dispositions |  |  |  |
Number of Buildings Disposed |  | 1 ofc_NumberofPropertiesDisposed / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_Number4230ForbesBoulevardMember |  |
Total Rentable Square Feet |  | 56,000 us-gaap_AreaOfRealEstateProperty / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_Number4230ForbesBoulevardMember |  |
Transaction Value of Operating Property Dispositions |  | 5,600,000 ofc_TransactionValueofOperatingPropertyDispositions / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_Number4230ForbesBoulevardMember |  |
Gain on Disposition |  | 1,507,000 ofc_GainOnSaleOfPropertiesSold / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_Number4230ForbesBoulevardMember |  |
Operating properties | December 2013 Colorado Springs Portfolio Disposition |  |  |  |
Dispositions |  |  |  |
Number of Buildings Disposed |  | 15 ofc_NumberofPropertiesDisposed / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_December2013ColoradoSpringsPortfolioDispositionMember |  |
Total Rentable Square Feet |  | 1,165,000 us-gaap_AreaOfRealEstateProperty / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_December2013ColoradoSpringsPortfolioDispositionMember |  |
Transaction Value of Operating Property Dispositions |  | 133,925,000 ofc_TransactionValueofOperatingPropertyDispositions / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_December2013ColoradoSpringsPortfolioDispositionMember |  |
Gain on Disposition |  | 1,164,000 ofc_GainOnSaleOfPropertiesSold / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_December2013ColoradoSpringsPortfolioDispositionMember |  |
Operating properties | December 2013 Portfolio Conveyance |  |  |  |
Dispositions |  |  |  |
Number of Buildings Disposed |  | 14 ofc_NumberofPropertiesDisposed / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_December2013PortfolioConveyanceMember |  |
Total Rentable Square Feet |  | 1,021,000 us-gaap_AreaOfRealEstateProperty / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_December2013PortfolioConveyanceMember |  |
Transaction Value of Operating Property Dispositions |  | 146,876,000 ofc_TransactionValueofOperatingPropertyDispositions / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_December2013PortfolioConveyanceMember |  |
Gain on Disposition |  | $ 0 ofc_GainOnSaleOfPropertiesSold / ofc_RealEstatePropertyClassificationAxis = ofc_OperatingPropertiesMember / ofc_RealEstatePropertyDisposalAxis = ofc_December2013PortfolioConveyanceMember |  |

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