Annual report pursuant to Section 13 and 15(d)

Real Estate Transactions (Narrative) (Details)

v2.4.1.9
Real Estate Transactions (Narrative) (Details) (USD $)
 12 Months Ended 0 Months Ended
Dec. 31, 2014
Apr. 10, 2014
Aug. 15, 2014
Dec. 02, 2014
Aug. 22, 2013
Oct. 23, 2012
Dec. 31, 2013
Real Estate Properties [Line Items]              
Percentage of interest in venture    [1]            
Transaction costs $ 2,100,000us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts           $ 642,000us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts
Acquisition and other investment fundings handled by intermediary 44,400,000us-gaap_OtherSignificantNoncashTransactionValueOfConsiderationGiven1            
Percentage of noncontrolling interest 11.10%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners           11.90%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
Multi-Family Properties [Member]              
Real Estate Properties [Line Items]              
Number of units 5,484us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_MultipleFamilyPropertiesMember 		           
Minimum [Member]              
Real Estate Properties [Line Items]              
Percentage of interest in venture 7.50%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RangeAxis
= us-gaap_MinimumMember 		           
Maximum [Member]              
Real Estate Properties [Line Items]              
Percentage of interest in venture 85.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RangeAxis
= us-gaap_MaximumMember 		           
Andover Place [Member]              
Real Estate Properties [Line Items]              
Number of units   220us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_BusinessAcquisitionAxis
= cli_AndoverPlaceMember 		         
Cash consideration   37,700,000us-gaap_PaymentsToAcquireBusinessesGross
/ us-gaap_BusinessAcquisitionAxis
= cli_AndoverPlaceMember 		         
Overlook Ridge Properties [Member]              
Real Estate Properties [Line Items]              
Cash consideration     16,600,000us-gaap_PaymentsToAcquireBusinessesGross
/ us-gaap_BusinessAcquisitionAxis
= cli_OverlookRidgePropertiesMember 		       
Overlook Ridge Properties [Member] | Multi-Family Properties [Member]              
Real Estate Properties [Line Items]              
Percentage of additional interest acquired     25.00%cli_PercentageOfAdditionalInterestAcquired
/ us-gaap_BusinessAcquisitionAxis
= cli_OverlookRidgePropertiesMember
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_MultipleFamilyPropertiesMember 		       
Indirect ownership interest     50.00%cli_IndirectOwnershipPercentage
/ us-gaap_BusinessAcquisitionAxis
= cli_OverlookRidgePropertiesMember
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_MultipleFamilyPropertiesMember 		       
Number of properties in which additional interest was acquired during period     2cli_NumberOfPropertiesInWhichAdditionalInterestWasAcquiredDuringPeriod
/ us-gaap_BusinessAcquisitionAxis
= cli_OverlookRidgePropertiesMember
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_MultipleFamilyPropertiesMember 		       
Overlook Ridge Properties [Member] | Consolidated Land [Member]              
Real Estate Properties [Line Items]              
Percentage of interest in developable land 100.00%cli_PercentageOfInterestInDevelopableLand
/ us-gaap_BusinessAcquisitionAxis
= cli_OverlookRidgePropertiesMember
/ us-gaap_RealEstatePropertiesAxis
= us-gaap_ConsolidatedPropertiesMember 		  100.00%cli_PercentageOfInterestInDevelopableLand
/ us-gaap_BusinessAcquisitionAxis
= cli_OverlookRidgePropertiesMember
/ us-gaap_RealEstatePropertiesAxis
= us-gaap_ConsolidatedPropertiesMember 		       
Loans assumed     23,000,000us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLongTermDebt
/ us-gaap_BusinessAcquisitionAxis
= cli_OverlookRidgePropertiesMember
/ us-gaap_RealEstatePropertiesAxis
= us-gaap_ConsolidatedPropertiesMember 		       
Overlook Ridge Properties [Member] | Minimum [Member] | Consolidated Land [Member]              
Real Estate Properties [Line Items]              
Spread over LIBOR     2.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_BusinessAcquisitionAxis
= cli_OverlookRidgePropertiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_RealEstatePropertiesAxis
= us-gaap_ConsolidatedPropertiesMember 		       
Overlook Ridge Properties [Member] | Maximum [Member] | Consolidated Land [Member]              
Real Estate Properties [Line Items]              
Spread over LIBOR     3.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_BusinessAcquisitionAxis
= cli_OverlookRidgePropertiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_RealEstatePropertiesAxis
= us-gaap_ConsolidatedPropertiesMember 		       
Conshohocken, Pennsylvania [Member]              
Real Estate Properties [Line Items]              
Cash consideration       15,300,000us-gaap_PaymentsToAcquireBusinessesGross
/ us-gaap_BusinessAcquisitionAxis
= cli_ConshohockenPennsylvaniaMember 		     
Curtis Center [Member]              
Real Estate Properties [Line Items]              
Percentage of interest in venture 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_BusinessAcquisitionAxis
= cli_CurtisCenterMember 		           
Acquisition and other investment fundings handled by intermediary 40,100,000us-gaap_OtherSignificantNoncashTransactionValueOfConsiderationGiven1
/ us-gaap_BusinessAcquisitionAxis
= cli_CurtisCenterMember 		           
Eastchester Project [Member]              
Real Estate Properties [Line Items]              
Number of units           108us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember 		 
Cash consideration         4,900,000us-gaap_PaymentsToAcquireBusinessesGross
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember 		2,100,000us-gaap_PaymentsToAcquireBusinessesGross
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember 		 
Percentage of interest in venture         76.25%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember 		26.25%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember 		 
Parent ownership percentage         76.25%us-gaap_MinorityInterestOwnershipPercentageByParent
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember 		   
Third party ownership percentage 8.00%cli_ThirdPartyOwnershipPercent
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember 		           
Holding period gain (loss)         0us-gaap_VentureCapitalGainsLossesNet
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember 		   
Total project costs 50,000,000cli_EstimatedCostOfProject
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember 		           
Project costs incurred to date 13,900,000cli_ProjectCostsIncurredToDate
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember 		           
Amount of project costs funded by members 21,200,000cli_AmountOfProjectCostsFundedByMembers
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember 		           
Parent Company [Member] | Eastchester Project [Member]              
Real Estate Properties [Line Items]              
Amount of project costs funded by members 20,900,000cli_AmountOfProjectCostsFundedByMembers
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember 		           
Hudson Valley Land Holdings, L.L.C. [Member] | Eastchester Project [Member]              
Real Estate Properties [Line Items]              
Third party ownership percentage         23.75%cli_ThirdPartyOwnershipPercent
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember
/ dei_LegalEntityAxis
= cli_HudsonValleyLandHoldingsLLCMember 		47.50%cli_ThirdPartyOwnershipPercent
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember
/ dei_LegalEntityAxis
= cli_HudsonValleyLandHoldingsLLCMember 		 
Percentage of noncontrolling interest         23.75%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember
/ dei_LegalEntityAxis
= cli_HudsonValleyLandHoldingsLLCMember 		   
150 Main Street, L.L.C. [Member] | Eastchester Project [Member] | Construction Loan [Member]              
Real Estate Properties [Line Items]              
Maximum borrowing capacity $ 28,800,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember
/ dei_LegalEntityAxis
= cli_OneHundredFiftyMainStreetLLCMember
/ us-gaap_LongtermDebtTypeAxis
= cli_ConstructionLoanMember 		           
[1] Company's effective ownership % represents the Company's entitlement to residual distributions after payments of priority returns, where applicable.