Annual report pursuant to Section 13 and 15(d)

Investments In Unconsolidated Joint Ventures (Narrative) (Details)

v2.4.1.9
Investments In Unconsolidated Joint Ventures (Narrative) (Details) (USD $)
 12 Months Ended
Dec. 31, 2014
sqft
Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]    
Investments in unconsolidated joint ventures $ 247,468,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures $ 181,129,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
Area of mixed use project (in square feet) 81,500cli_AreaOfMixedUseProperty  
Percentage of interest in venture    [1]  
Management, leasing, development and other services fees 6,200,000cli_ManagementLeasingDevelopmentAndOtherServicesFees 5,800,000cli_ManagementLeasingDevelopmentAndOtherServicesFees
Accounts receivable due from unconsolidated joint ventures 1,000,000us-gaap_DueFromJointVentures 523,000us-gaap_DueFromJointVentures
Maximum exposure to loss 230,500,000us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount  
Estimated future funding commitments 116,900,000cli_VariableInterestEntityEntityEstimatedFutureFundingCommitments  
Unconsolidated Joint Venture Office Buildings [Member]    
Schedule of Equity Method Investments [Line Items]    
Number of properties 36us-gaap_NumberOfRealEstateProperties
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_UnconsolidatedJointVentureOfficeBuildingsMember 		 
Unconsolidated Joint Venture Office And Retail Buildings [Member]    
Schedule of Equity Method Investments [Line Items]    
Area of property (in square feet) 5,600,000us-gaap_AreaOfRealEstateProperty
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_UnconsolidatedJointVentureOfficeAndRetailBuildingsMember 		 
Unconsolidated Joint Venture Retail Buildings [Member]    
Schedule of Equity Method Investments [Line Items]    
Number of properties 2us-gaap_NumberOfRealEstateProperties
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_UnconsolidatedJointVentureRetailBuildingsMember 		 
Unconsolidated Joint Venture Multi-Family Properties [Member]    
Schedule of Equity Method Investments [Line Items]    
Number of properties 13us-gaap_NumberOfRealEstateProperties
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_UnconsolidatedJointVentureMultipleFamilyPropertiesMember 		 
Number of units 4,183us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_UnconsolidatedJointVentureMultipleFamilyPropertiesMember 		 
Unconsolidated Joint Venture Hotel [Member]    
Schedule of Equity Method Investments [Line Items]    
Number of units 350us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_UnconsolidatedJointVentureHotelMember 		 
Unconsolidated Joint Venture Development Projects [Member]    
Schedule of Equity Method Investments [Line Items]    
Number of units 1,731us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_UnconsolidatedJointVentureDevelopmentProjectsMember 		 
Unconsolidated Joint Venture Land Parcels [Member]    
Schedule of Equity Method Investments [Line Items]    
Number of units 2,853us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_UnconsolidatedJointVentureLandParcelsMember 		 
Unconsolidated Joint Ventures [Member]    
Schedule of Equity Method Investments [Line Items]    
Maximum borrowing capacity 477,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_UnconsolidatedJointVenturesMember 		 
Amount outstanding 238,000,000us-gaap_LineOfCredit
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_UnconsolidatedJointVenturesMember 		 
Unconsolidated Joint Ventures [Member] | Parent Company [Member]    
Schedule of Equity Method Investments [Line Items]    
Maximum borrowing capacity 93,500,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_UnconsolidatedJointVenturesMember 		 
Amount outstanding 62,600,000us-gaap_LineOfCredit
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_UnconsolidatedJointVenturesMember 		 
Minimum [Member]    
Schedule of Equity Method Investments [Line Items]    
Percentage of interest in venture 7.50%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RangeAxis
= us-gaap_MinimumMember 		 
Maximum [Member]    
Schedule of Equity Method Investments [Line Items]    
Percentage of interest in venture 85.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RangeAxis
= us-gaap_MaximumMember 		 
Variable Interest Entity [Member]    
Schedule of Equity Method Investments [Line Items]    
Investments in unconsolidated joint ventures 113,600,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember 		 
Number of VIEs 9cli_NumberOfVariableInterestEntities
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember 		 
Office [Member] | Unconsolidated Joint Venture Land Parcels [Member]    
Schedule of Equity Method Investments [Line Items]    
Area of property (in square feet) 1,400,000us-gaap_AreaOfRealEstateProperty
/ us-gaap_MajorPropertyClassAxis
= us-gaap_OfficeBuildingMember
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_UnconsolidatedJointVentureLandParcelsMember 		 
South Pier At Harborside [Member]    
Schedule of Equity Method Investments [Line Items]    
Number of units 350us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_SouthPierAtHarborsideMember 		 
Percentage of interest in venture 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_SouthPierAtHarborsideMember 		[1]  
Letter of credit $ 4,100,000cli_LineOfCreditFacilityInSupportOfDebtInstrumentFairValueOfAmountOutstanding
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_SouthPierAtHarborsideMember 		 
[1] Company's effective ownership % represents the Company's entitlement to residual distributions after payments of priority returns, where applicable.