Annual report pursuant to Section 13 and 15(d)

Real Estate Joint Ventures (Details)

v2.4.1.9
Real Estate Joint Ventures (Details) (USD $)
 12 Months Ended 0 Months Ended 12 Months Ended 0 Months Ended
Dec. 31, 2014
buillding
sqft
Sep. 17, 2013
Dec. 11, 2013
Dec. 31, 2013
Dec. 31, 2012
Property
Aug. 07, 2014
Investments in consolidated real estate joint ventures            
Investing receivables $ 52,147,000us-gaap_NotesReceivableNet     $ 53,663,000us-gaap_NotesReceivableNet    
LW Redstone Company, LLC            
Investments in consolidated real estate joint ventures            
Number of buildings operated by the joint venture 4ofc_BuildingsOperatedByJointVenturesNumber
/ dei_LegalEntityAxis
= ofc_LwRedstoneCompanyLlcMember 		         
Partner's capital account upon formation 9,000,000ofc_PartnersCapitalAccountUponFormation
/ dei_LegalEntityAxis
= ofc_LwRedstoneCompanyLlcMember 		         
Percentage of residual distributable cash flows in excess of unpaid cumulative preferred returns and return of invested capital entitled to the company 85.00%ofc_PercentageOfResidualDistributableCashFlowsEntitledInExcessOfUnpaidCumulativePreferredReturnsAndReturnOfInvestedCapital
/ dei_LegalEntityAxis
= ofc_LwRedstoneCompanyLlcMember 		         
Percentage of residual distributable cash flows in excess of unpaid cumulative preferred returns and return of invested capital entitled to the entity's partners 15.00%ofc_PercentageOfResidualDistributableCashFlowsEntitledInExcessOfUnpaidCumulativePreferredReturnsAndReturnOfInvestedCashRelatedToRealEstatePartner
/ dei_LegalEntityAxis
= ofc_LwRedstoneCompanyLlcMember 		         
Number of years following construction commencement threshold achievement before partner's interest can be purchased at fair value 5 years          
Construction commencement threshold (in square feet) 4,400,000.0ofc_ConstructionCommencementThreshold
/ dei_LegalEntityAxis
= ofc_LwRedstoneCompanyLlcMember 		         
Construction Commencement Threshold, Completed 561,000ofc_ConstructionCommencementThresholdCompleted
/ dei_LegalEntityAxis
= ofc_LwRedstoneCompanyLlcMember 		         
LW Redstone Company, LLC | Maximum            
Investments in consolidated real estate joint ventures            
Infrastructure costs anticipated to be funded by entity for reimbursement by the City of Huntsville (in dollars) 76,000,000ofc_InfrastructureCostsAnticipatedToBeFunded
/ dei_LegalEntityAxis
= ofc_LwRedstoneCompanyLlcMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember 		         
M Square Associates, LLC            
Investments in consolidated real estate joint ventures            
Number of buildings operated by the joint venture 2ofc_BuildingsOperatedByJointVenturesNumber
/ dei_LegalEntityAxis
= ofc_MSquareAssociatesLlcMember 		         
Percentage of residual amounts distributed to each member 50.00%ofc_PercentageOfResidualNetCashFlowDistributedToEachPartner
/ dei_LegalEntityAxis
= ofc_MSquareAssociatesLlcMember 		         
Consolidated real estate joint ventures            
Investments in consolidated real estate joint ventures            
Total Assets 202,948,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember 		[1]          
Encumbered Assets 115,476,000us-gaap_PledgedAssetsNotSeparatelyReportedRealEstate
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember 		[1]          
Total Liabilities 80,736,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember 		[1]          
Arundel Preserve 5, LLC            
Investments in consolidated real estate joint ventures            
Ownership (as a percent)   50.00%us-gaap_VariableInterestEntityOwnershipPercentage
/ dei_LegalEntityAxis
= ofc_ArundelPreserveLlcMember 		       
Arundel Preserve 5, LLC | Common Shares            
Investments in consolidated real estate joint ventures            
Acquisition of property and noncontrolling interest in other consolidated entity for COPLP common units (in units)   221,501us-gaap_StockIssuedDuringPeriodSharesAcquisitions
/ dei_LegalEntityAxis
= ofc_ArundelPreserveLlcMember
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_CommonStockMember 		       
Acquisition of property and noncontrolling interest in other consolidated entity for COPLP common units (in dollars)   5,200,000us-gaap_StockIssuedDuringPeriodValueAcquisitions
/ dei_LegalEntityAxis
= ofc_ArundelPreserveLlcMember
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_CommonStockMember 		       
MOR Forbes 2 LLC            
Investments in consolidated real estate joint ventures            
Ownership (as a percent)     50.00%us-gaap_VariableInterestEntityOwnershipPercentage
/ dei_LegalEntityAxis
= ofc_MorForbes2LlcMember 		     
Unconsolidated real estate joint ventures            
Investments in consolidated real estate joint ventures            
Ownership (as a percent)         20.00%us-gaap_VariableInterestEntityOwnershipPercentage
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember 		 
Number of buildings operated by the joint venture         16ofc_BuildingsOperatedByJointVenturesNumber
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember 		 
Investment balance         (6,400,000)ofc_DistributionsReceivedInExcessOfInvestmentInUnconsolidatedRealEstateJointVenture
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember 		 
Difference between carrying amount of investment and share of the equity in the joint venture         4,500,000us-gaap_EquityMethodInvestmentDifferenceBetweenCarryingAmountAndUnderlyingEquity
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember 		 
Gain on disposal       6,300,000us-gaap_EquityMethodInvestmentRealizedGainLossOnDisposal
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember 		   
Condensed statements of operations for unconsolidated real estate joint venture            
Revenues       6,519,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationRevenue
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember 		7,316,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationRevenue
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember 		 
Property operating expenses       (2,818,000)ofc_EquityMethodInvestmentSummarizedFinancialInformationPropertyOperatingExpenses
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember 		(2,829,000)ofc_EquityMethodInvestmentSummarizedFinancialInformationPropertyOperatingExpenses
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember 		 
Interest expense       (10,463,000)ofc_EquityMethodInvestmentSummarizedFinancialInformationInterestExpenses
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember 		(7,672,000)ofc_EquityMethodInvestmentSummarizedFinancialInformationInterestExpenses
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember 		 
Depreciation and amortization expense       (2,067,000)ofc_EquityMethodInvestmentSummarizedFinancialInformationDepreciationAndAmortizationExpenses
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember 		(2,283,000)ofc_EquityMethodInvestmentSummarizedFinancialInformationDepreciationAndAmortizationExpenses
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember 		 
Gain on early extinguishment of debt       23,013,000ofc_EquityMethodInvestmentSummarizedFinancialInformationGainsLossesonExtinguishmentofDebt
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember 		0ofc_EquityMethodInvestmentSummarizedFinancialInformationGainsLossesonExtinguishmentofDebt
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember 		 
Net income (loss)       14,184,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLoss
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember 		(5,468,000)us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLoss
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember 		 
Unconsolidated real estate joint ventures | Nonrecourse loan guarantees of unconsolidated partnership | Nonrecourse mezzanine loan            
Investments in consolidated real estate joint ventures            
Nonrecourse mezzanine debt balance, equity method joint venture 5,600,000ofc_NonrecourseMezzanineDebtBalanceequitymethodjointventure
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember
/ us-gaap_LongtermDebtTypeAxis
= ofc_NonrecourseMezzanineLoanMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= ofc_NonrecourseLoanGuaranteesofUnconsolidatedPartnershipMember 		         
LW Redstone Company, LLC | Variable Interest Entity, Primary Beneficiary            
Investments in consolidated real estate joint ventures            
Ownership (as a percent) 85.00%us-gaap_VariableInterestEntityOwnershipPercentage
/ us-gaap_CounterpartyNameAxis
= ofc_LwRedstoneCompanyLlcMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember 		         
Total Assets 143,534,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets
/ us-gaap_CounterpartyNameAxis
= ofc_LwRedstoneCompanyLlcMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember 		[1],[2]          
Encumbered Assets 66,620,000us-gaap_PledgedAssetsNotSeparatelyReportedRealEstate
/ us-gaap_CounterpartyNameAxis
= ofc_LwRedstoneCompanyLlcMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember 		[1],[2]          
Total Liabilities 41,659,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities
/ us-gaap_CounterpartyNameAxis
= ofc_LwRedstoneCompanyLlcMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember 		[1],[2]          
M Square Associates, LLC | Variable Interest Entity, Primary Beneficiary            
Investments in consolidated real estate joint ventures            
Ownership (as a percent) 50.00%us-gaap_VariableInterestEntityOwnershipPercentage
/ us-gaap_CounterpartyNameAxis
= ofc_MSquareAssociatesLlcMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember 		         
Total Assets 59,414,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets
/ us-gaap_CounterpartyNameAxis
= ofc_MSquareAssociatesLlcMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember 		[1],[3]          
Encumbered Assets 48,856,000us-gaap_PledgedAssetsNotSeparatelyReportedRealEstate
/ us-gaap_CounterpartyNameAxis
= ofc_MSquareAssociatesLlcMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember 		[1],[3]          
Total Liabilities 39,077,000us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities
/ us-gaap_CounterpartyNameAxis
= ofc_MSquareAssociatesLlcMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember 		[1],[3]          
COPT-FD Indian Head, LLC | Variable Interest Entity, Primary Beneficiary            
Investments in consolidated real estate joint ventures            
Proceeds from real estate and real estate joint ventures           6,400,000us-gaap_ProceedsFromRealEstateAndRealEstateJointVentures
/ us-gaap_CounterpartyNameAxis
= ofc_CoptFdIndianHeadLlcMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Notes receivable from City of Huntsville            
Investments in consolidated real estate joint ventures            
Investing receivables $ 49,147,000us-gaap_NotesReceivableNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ofc_NotesReceivableFromCityOfHuntsvilleMember 		    $ 44,055,000us-gaap_NotesReceivableNet
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= ofc_NotesReceivableFromCityOfHuntsvilleMember 		   
[1] Excludes amounts eliminated in consolidation.
[2] This joint venture’s property is in Huntsville, Alabama.
[3] This joint venture’s properties are in College Park, Maryland (in the Baltimore/Washington Corridor).