Annual report pursuant to Section 13 and 15(d)

Investments In Unconsolidated Joint Ventures (Summary Of Unconsolidated Joint Ventures) (Details)

v2.4.1.9
Investments In Unconsolidated Joint Ventures (Summary Of Unconsolidated Joint Ventures) (Details) (USD $)
12 Months Ended 0 Months Ended
Dec. 31, 2014
Aug. 15, 2014
Mar. 20, 2013
Dec. 09, 2013
Sep. 02, 2013
Jun. 30, 2013
Dec. 31, 2013
Dec. 23, 2013
May 21, 2014
Aug. 01, 2014
Schedule of Equity Method Investments [Line Items]                    
Company's Effective Ownership %    [1]                  
Carrying Amount $ 247,468,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures           $ 181,129,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures      
Property Debt, Balance 1,673,364,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages                  
Internal rate of return 9.00%cli_InternalRateOfReturn                  
Minimum [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Company's Effective Ownership % 7.50%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
                 
Maximum [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Company's Effective Ownership % 85.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
                 
Marbella RoseGarden, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 412us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_MarbellaRoseGardenLLCMember
                 
Company's Effective Ownership % 24.27%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_MarbellaRoseGardenLLCMember
[1]                  
Carrying Amount 15,779,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_MarbellaRoseGardenLLCMember
          15,797,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_MarbellaRoseGardenLLCMember
     
Property Debt, Balance 95,000,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_MarbellaRoseGardenLLCMember
                 
Property Debt, Maturity Date 05/01/18                  
Property Debt, Interest Rate 4.99%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_MarbellaRoseGardenLLCMember
                 
RoseGarden Monaco Holdings, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 523us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoseGardenMonacoHoldingsLLCMember
                 
Company's Effective Ownership % 15.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoseGardenMonacoHoldingsLLCMember
[1]                  
Carrying Amount 2,161,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoseGardenMonacoHoldingsLLCMember
          3,201,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoseGardenMonacoHoldingsLLCMember
     
Property Debt, Balance 165,000,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoseGardenMonacoHoldingsLLCMember
                 
Property Debt, Maturity Date 02/01/21                  
Property Debt, Interest Rate 4.19%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoseGardenMonacoHoldingsLLCMember
                 
Rosewood Lafayette Holdings, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 217us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodLafayetteHoldingsLLCMember
                 
Company's Effective Ownership % 25.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodLafayetteHoldingsLLCMember
[1]                  
Carrying Amount 62,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodLafayetteHoldingsLLCMember
          857,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodLafayetteHoldingsLLCMember
     
Property Debt, Balance 38,665,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodLafayetteHoldingsLLCMember
                 
Property Debt, Maturity Date 07/01/15                  
Property Debt, Interest Rate 4.00%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodLafayetteHoldingsLLCMember
                 
PruRose Port Imperial South 15, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 236us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PruRosePortImperialSouthFifteenLLCMember
                 
Company's Effective Ownership % 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PruRosePortImperialSouthFifteenLLCMember
[1]                  
Property Debt, Balance 57,500,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PruRosePortImperialSouthFifteenLLCMember
                 
Property Debt, Maturity Date 09/01/20                  
Property Debt, Interest Rate 4.32%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PruRosePortImperialSouthFifteenLLCMember
                 
Rosewood Morristown, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 130us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
[2],[3]                  
Company's Effective Ownership % 12.50%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
[1],[2],[3]                  
Carrying Amount 6,029,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
[2],[3]           6,455,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
[2],[3]      
Property Debt, Balance 46,217,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
[2],[3],[4]                  
Note payable 975,000us-gaap_NotesPayable
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
                 
Overlook Ridge JV, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 251us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OverlookRidgeJVLLCMember
                 
Company's Effective Ownership % 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OverlookRidgeJVLLCMember
[1]                  
Property Debt, Balance 69,501,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OverlookRidgeJVLLCMember
[5]                  
Overlook Ridge JV 2C/3B, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 371us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OverlookRidgeJvTwoCAndThreeBLLCMember
[6]                  
Company's Effective Ownership % 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OverlookRidgeJvTwoCAndThreeBLLCMember
[1],[6]                  
Carrying Amount 2,524,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OverlookRidgeJvTwoCAndThreeBLLCMember
[6]                  
Property Debt, Balance 49,824,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OverlookRidgeJvTwoCAndThreeBLLCMember
[6]                  
Property Debt, Maturity Date 12/26/15 [6]                  
Property Debt, Interest Rate, LIBOR L+2.50 [6],[7]                  
Property Debt, Interest Rate, Spread Over LIBOR 2.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OverlookRidgeJvTwoCAndThreeBLLCMember
                 
Cash consideration   2,970,000us-gaap_PaymentsToAcquireBusinessesGross
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OverlookRidgeJvTwoCAndThreeBLLCMember
               
PruRose Riverwalk G, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 316us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PruRoseRiverwalkGLLCMember
[8]                  
Company's Effective Ownership % 25.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PruRoseRiverwalkGLLCMember
[1],[8]                  
Carrying Amount 955,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PruRoseRiverwalkGLLCMember
[8]           3,117,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PruRoseRiverwalkGLLCMember
[8]      
Property Debt, Balance 79,594,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PruRoseRiverwalkGLLCMember
[8]                  
Property Debt, Maturity Date 07/15/21 [8]                  
Property Debt, Interest Rate 6.00%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PruRoseRiverwalkGLLCMember
[8],[9]                  
Elmajo Urban Renewal Associates, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 355us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_ElmajoUrbanRenewalAssociatesLLCMember
[8]                  
Company's Effective Ownership % 7.50%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_ElmajoUrbanRenewalAssociatesLLCMember
[1],[8]                  
Carrying Amount             203,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_ElmajoUrbanRenewalAssociatesLLCMember
[8]      
Property Debt, Balance 81,264,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_ElmajoUrbanRenewalAssociatesLLCMember
[8]                  
Property Debt, Maturity Date 06/27/16 [8]                  
Property Debt, Interest Rate, LIBOR L+2.10 [10],[8]                  
Property Debt, Interest Rate, Spread Over LIBOR 2.10%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_ElmajoUrbanRenewalAssociatesLLCMember
                 
Crystal House Apartments Investors LLC [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 828us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CrystalHouseApartmentsInvestorsLLCMember
[11]   828us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CrystalHouseApartmentsInvestorsLLCMember
             
Company's Effective Ownership % 25.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CrystalHouseApartmentsInvestorsLLCMember
[1],[11]   25.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CrystalHouseApartmentsInvestorsLLCMember
             
Carrying Amount 27,051,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CrystalHouseApartmentsInvestorsLLCMember
[11]           26,838,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CrystalHouseApartmentsInvestorsLLCMember
[11]      
Property Debt, Balance 165,000,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CrystalHouseApartmentsInvestorsLLCMember
[11]                  
Property Debt, Maturity Date 04/01/20 [11]                  
Property Debt, Interest Rate 3.17%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CrystalHouseApartmentsInvestorsLLCMember
[11]                  
Cash consideration     30,200,000us-gaap_PaymentsToAcquireBusinessesGross
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CrystalHouseApartmentsInvestorsLLCMember
             
Percentage of interest in developable land 50.00%cli_PercentageOfInterestInDevelopableLand
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CrystalHouseApartmentsInvestorsLLCMember
  50.00%cli_PercentageOfInterestInDevelopableLand
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CrystalHouseApartmentsInvestorsLLCMember
             
Number of units available for development 295cli_NumberOfUnitsAvailableForDevelopment
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CrystalHouseApartmentsInvestorsLLCMember
  295cli_NumberOfUnitsAvailableForDevelopment
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CrystalHouseApartmentsInvestorsLLCMember
             
Number of approved units available for development 252cli_NumberOfApprovedUnitsAvailableForDevelopment
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CrystalHouseApartmentsInvestorsLLCMember
  252cli_NumberOfApprovedUnitsAvailableForDevelopment
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CrystalHouseApartmentsInvestorsLLCMember
             
Portside Master Company, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 176us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PortsideMasterCompanyLLCMember
                 
Company's Effective Ownership % 38.25%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PortsideMasterCompanyLLCMember
[1]                  
Carrying Amount 1,747,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PortsideMasterCompanyLLCMember
          3,207,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PortsideMasterCompanyLLCMember
     
Property Debt, Balance 37,093,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PortsideMasterCompanyLLCMember
                 
Property Debt, Maturity Date 12/04/15                  
Property Debt, Interest Rate, LIBOR L+2.50 [12]                  
Property Debt, Interest Rate, Spread Over LIBOR 2.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PortsideMasterCompanyLLCMember
                 
PruRose Port Imperial South 13, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 280us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PruRosePortImperialSouthThirteenLLCMember
                 
Company's Effective Ownership % 20.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PruRosePortImperialSouthThirteenLLCMember
[1]                  
Carrying Amount 1,087,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PruRosePortImperialSouthThirteenLLCMember
          2,206,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PruRosePortImperialSouthThirteenLLCMember
     
Property Debt, Balance 49,084,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PruRosePortImperialSouthThirteenLLCMember
                 
Property Debt, Maturity Date 06/27/16                  
Property Debt, Interest Rate, LIBOR L+2.15 [13]                  
Property Debt, Interest Rate, Spread Over LIBOR 2.15%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PruRosePortImperialSouthThirteenLLCMember
                 
Roseland/Port Imperial Partners, L.P. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 363us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoselandPortImperialPartnersLPMember
[14],[8]                  
Company's Effective Ownership % 20.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoselandPortImperialPartnersLPMember
[1],[14],[8]                  
Carrying Amount 1,800,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoselandPortImperialPartnersLPMember
[14],[8]           2,068,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoselandPortImperialPartnersLPMember
[14],[8]      
RoseGarden Marbella South, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 311us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoseGardenMarbellaSouthLLCMember
                 
Company's Effective Ownership % 24.27%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoseGardenMarbellaSouthLLCMember
[1]                  
Carrying Amount 11,282,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoseGardenMarbellaSouthLLCMember
          7,567,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoseGardenMarbellaSouthLLCMember
     
Property Debt, Balance 31,564,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoseGardenMarbellaSouthLLCMember
                 
Property Debt, Maturity Date 03/30/17                  
Property Debt, Interest Rate, LIBOR L+2.25 [15]                  
Property Debt, Interest Rate, Spread Over LIBOR 2.25%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoseGardenMarbellaSouthLLCMember
                 
Estuary Urban Renewal Unit B, LLC [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 227us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_EstuaryUrbanRenewalUnitBLLCMember
                 
Company's Effective Ownership % 7.50%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_EstuaryUrbanRenewalUnitBLLCMember
[1]                  
Carrying Amount             24,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_EstuaryUrbanRenewalUnitBLLCMember
     
Property Debt, Balance 40,366,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_EstuaryUrbanRenewalUnitBLLCMember
                 
Property Debt, Maturity Date 01/25/17                  
Property Debt, Interest Rate, LIBOR L+2.10 [16]                  
Property Debt, Interest Rate, Spread Over LIBOR 2.10%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_EstuaryUrbanRenewalUnitBLLCMember
                 
RiverPark At Harrison I, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 141us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RiverparkAtHarrisonILLCMember
                 
Company's Effective Ownership % 36.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RiverparkAtHarrisonILLCMember
[1]                  
Carrying Amount 4,744,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RiverparkAtHarrisonILLCMember
          3,655,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RiverparkAtHarrisonILLCMember
     
Property Debt, Balance 21,298,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RiverparkAtHarrisonILLCMember
                 
Property Debt, Maturity Date 06/27/16                  
Property Debt, Interest Rate, LIBOR L+2.35 [17]                  
Property Debt, Interest Rate, Spread Over LIBOR 2.35%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RiverparkAtHarrisonILLCMember
                 
Capitol Place Mezz LLC [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 377us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CapitolPlaceMezzLlcMember
                 
Company's Effective Ownership % 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CapitolPlaceMezzLlcMember
[1]             50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CapitolPlaceMezzLlcMember
   
Carrying Amount 49,327,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CapitolPlaceMezzLlcMember
          46,628,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CapitolPlaceMezzLlcMember
46,500,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CapitolPlaceMezzLlcMember
   
Property Debt, Balance 73,971,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CapitolPlaceMezzLlcMember
                 
Property Debt, Maturity Date 07/01/2033                  
Property Debt, Interest Rate 4.82%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CapitolPlaceMezzLlcMember
[18]                  
Harborside Unit A Urban Renewal, LLC [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 763us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember
                 
Company's Effective Ownership % 85.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember
[1]                  
Carrying Amount 34,954,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember
              30,600,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember
 
Property Debt, Maturity Date 08/01/29                  
Property Debt, Interest Rate 5.197%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember
[19]                  
Harborside Unit A Urban Renewal, LLC [Member] | Construction Loan [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Property Debt, Interest Rate                   5.197%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= cli_ConstructionLoanMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember
Maximum borrowing capacity 192,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LongtermDebtTypeAxis
= cli_ConstructionLoanMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember
                192,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LongtermDebtTypeAxis
= cli_ConstructionLoanMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember
Amount outstanding 0us-gaap_LineOfCredit
/ us-gaap_LongtermDebtTypeAxis
= cli_ConstructionLoanMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember
                 
Maturity Aug. 01, 2029                  
Harborside Unit A Urban Renewal, LLC [Member] | Parent Company [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Internal rate of return 18.00%cli_InternalRateOfReturn
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember
                 
RoseGarden Monaco, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 300us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoseGardenMonacoLLCMember
                 
Company's Effective Ownership % 41.67%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoseGardenMonacoLLCMember
[1]                  
Carrying Amount 1,283,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoseGardenMonacoLLCMember
          1,224,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoseGardenMonacoLLCMember
     
Grand Jersey Waterfront Urban Renewal Associates, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 1,000us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_GrandJerseyWaterfrontUrbanRenewalAssociatesLLCMember
                 
Company's Effective Ownership % 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_GrandJerseyWaterfrontUrbanRenewalAssociatesLLCMember
[1]                  
Carrying Amount 337,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_GrandJerseyWaterfrontUrbanRenewalAssociatesLLCMember
          337,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_GrandJerseyWaterfrontUrbanRenewalAssociatesLLCMember
     
Red Bank Corporate Plaza, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Square Feet 92,878us-gaap_AreaOfRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RedBankCorporatePlazaLLCMember
                 
Company's Effective Ownership % 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RedBankCorporatePlazaLLCMember
[1]                  
Carrying Amount 3,963,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RedBankCorporatePlazaLLCMember
          4,046,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RedBankCorporatePlazaLLCMember
     
Property Debt, Balance 15,868,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RedBankCorporatePlazaLLCMember
                 
Property Debt, Maturity Date 05/17/16                  
Property Debt, Interest Rate 3.99375%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RedBankCorporatePlazaLLCMember
                 
Property Debt, Interest Rate, LIBOR L+3.00 [20]                  
Property Debt, Interest Rate, Spread Over LIBOR 3.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RedBankCorporatePlazaLLCMember
                 
Notional amount 13,650,000us-gaap_NotionalAmountOfNonderivativeInstruments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RedBankCorporatePlazaLLCMember
                 
12 Vreeland Associates, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Square Feet 139,750us-gaap_AreaOfRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_TwelveVreelandAssociatesLLCMember
                 
Company's Effective Ownership % 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_TwelveVreelandAssociatesLLCMember
[1]                  
Carrying Amount 5,620,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_TwelveVreelandAssociatesLLCMember
          5,514,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_TwelveVreelandAssociatesLLCMember
     
Property Debt, Balance 14,002,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_TwelveVreelandAssociatesLLCMember
                 
Property Debt, Maturity Date 07/01/23                  
Property Debt, Interest Rate 2.87%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_TwelveVreelandAssociatesLLCMember
                 
BNES Associates III [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Square Feet 106,345us-gaap_AreaOfRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_BNESAssociatesIIIMember
                 
Company's Effective Ownership % 31.25%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_BNESAssociatesIIIMember
[1]                  
Carrying Amount 1,993,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_BNESAssociatesIIIMember
          1,753,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_BNESAssociatesIIIMember
     
Property Debt, Balance 6,756,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_BNESAssociatesIIIMember
                 
Property Debt, Maturity Date 11/01/23                  
Property Debt, Interest Rate 4.76%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_BNESAssociatesIIIMember
                 
Hillsborough 206 Holdings, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Square Feet 160,000us-gaap_AreaOfRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HillsboroughTwoHundredSixHoldingsLLCMember
                 
Company's Effective Ownership % 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HillsboroughTwoHundredSixHoldingsLLCMember
[1]                  
Carrying Amount 1,962,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HillsboroughTwoHundredSixHoldingsLLCMember
          1,962,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HillsboroughTwoHundredSixHoldingsLLCMember
     
KPG-P 100 IMW JV, LLC [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Square Feet 339,615us-gaap_AreaOfRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgPOneHundredImwJvLlcMember
                 
Company's Effective Ownership % 33.33%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgPOneHundredImwJvLlcMember
[1]                  
Carrying Amount             1,887,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgPOneHundredImwJvLlcMember
     
Property Debt, Balance 61,500,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgPOneHundredImwJvLlcMember
                 
Property Debt, Maturity Date 09/09/16                  
Property Debt, Interest Rate, LIBOR L+7.00 [21]                  
Property Debt, Interest Rate, Spread Over LIBOR 7.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgPOneHundredImwJvLlcMember
                 
Cash consideration       2,800,000us-gaap_PaymentsToAcquireBusinessesGross
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgPOneHundredImwJvLlcMember
           
Number of extension options 2cli_DebtInstrumentNumberOfExtensionOptions
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgPOneHundredImwJvLlcMember
                 
Loan extension period 1 year                  
Amount outstanding 15,800,000us-gaap_LineOfCredit
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgPOneHundredImwJvLlcMember
                 
Construction reserve 25,000,000cli_LineOfCreditFacilityConstructionReserve
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgPOneHundredImwJvLlcMember
                 
Keystone-Penn [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Square Feet 1,842,820us-gaap_AreaOfRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystonePennMember
                 
Company's Effective Ownership %                     
Property Debt, Balance 203,811,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystonePennMember
[22]                  
Keystone-Penn [Member] | Principal Balance Due August 27, 2023 [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Property Debt, Balance 127,600,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_DebtInstrumentAxis
= cli_PrincipalBalanceDueAugustTwoThousandTwentyThreeMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystonePennMember
                 
Property Debt, Maturity Date August 27, 2023                  
Property Debt, Interest Rate 5.114%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= cli_PrincipalBalanceDueAugustTwoThousandTwentyThreeMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystonePennMember
                 
Keystone-Penn [Member] | Principal Balance Due August 27, 2016 [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Property Debt, Balance 65,786,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_DebtInstrumentAxis
= cli_PrincipalBalanceDueAugustTwoThousandSixteenMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystonePennMember
                 
Property Debt, Maturity Date August 27, 2016                  
Keystone-Penn [Member] | Principal Balance Due August 27, 2016 [Member] | Minimum [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Property Debt, Interest Rate, LIBOR LIBOR+5.0                  
Property Debt, Interest Rate, Spread Over LIBOR 5.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_DebtInstrumentAxis
= cli_PrincipalBalanceDueAugustTwoThousandSixteenMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystonePennMember
                 
Keystone-Penn [Member] | Principal Balance Due August 27, 2016 [Member] | Maximum [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Property Debt, Interest Rate, LIBOR LIBOR+5.75                  
Property Debt, Interest Rate, Spread Over LIBOR 5.75%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_DebtInstrumentAxis
= cli_PrincipalBalanceDueAugustTwoThousandSixteenMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystonePennMember
                 
Keystone-Penn [Member] | Principal Balance Due August 27, 2015 [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Property Debt, Balance 10,425,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_DebtInstrumentAxis
= cli_PrincipalBalanceDueAugustTwoThousandFifteenMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystonePennMember
                 
Property Debt, Maturity Date August 27, 2015                  
Property Debt, Interest Rate, LIBOR LIBOR+6.0                  
Property Debt, Interest Rate, Spread Over LIBOR 6.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_DebtInstrumentAxis
= cli_PrincipalBalanceDueAugustTwoThousandFifteenMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystonePennMember
                 
Keystone-Penn [Member] | Principal Balance Due July 6, 2044 [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Property Debt, Maturity Date July 6, 2044                  
Keystone-TriState [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Square Feet 1,266,384us-gaap_AreaOfRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystoneTristateMember
                 
Company's Effective Ownership %                     
Carrying Amount 6,140,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystoneTristateMember
                 
Property Debt, Balance 204,843,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystoneTristateMember
[23]                  
Sale price of property, capital balance in properties in which senior pari passu interest is held 6,200,000cli_DiscontinuedOperationRealEstateSalePricePartnersCapitalInPropertiesInWhichSeniorInterestIsHeld
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystoneTristateMember
                 
Number of properties with senior pari passu interest 5cli_DiscontinuedOperationRealEstateSalePriceNumberOfPropertiesWithSeniorInterest
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystoneTristateMember
                 
Keystone-TriState [Member] | Principal Balance Due July 1, 2017 [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Property Debt, Balance 41,240,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_DebtInstrumentAxis
= cli_PrincipalBalanceDueJulyTwoThousandSeventeenMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystoneTristateMember
                 
Property Debt, Maturity Date July 1, 2017                  
Property Debt, Interest Rate, LIBOR 4.95                  
Property Debt, Interest Rate, Spread Over LIBOR 4.95%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_DebtInstrumentAxis
= cli_PrincipalBalanceDueJulyTwoThousandSeventeenMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystoneTristateMember
                 
Keystone-TriState [Member] | Principal Balance Due September 9, 2017 [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Property Debt, Balance 70,903,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_DebtInstrumentAxis
= cli_PrincipalBalanceDueSeptemberNinthTwoThousandSeventeenMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystoneTristateMember
                 
Property Debt, Maturity Date September 9, 2017                  
Bears interest at fixed rate range, minimum 5.65%us-gaap_DebtInstrumentInterestRateEffectivePercentageRateRangeMinimum
/ us-gaap_DebtInstrumentAxis
= cli_PrincipalBalanceDueSeptemberNinthTwoThousandSeventeenMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystoneTristateMember
                 
Bears interest at fixed rate range, maximum 6.75%us-gaap_DebtInstrumentInterestRateEffectivePercentageRateRangeMaximum
/ us-gaap_DebtInstrumentAxis
= cli_PrincipalBalanceDueSeptemberNinthTwoThousandSeventeenMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystoneTristateMember
                 
Keystone-TriState [Member] | Principal Balance Due July 6, 2024 [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Property Debt, Balance 14,250,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_DebtInstrumentAxis
= cli_PrincipalBalanceDueJulyTwoThousandTwentyFourMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystoneTristateMember
                 
Property Debt, Maturity Date July 6, 2024                  
Property Debt, Interest Rate 4.88%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= cli_PrincipalBalanceDueJulyTwoThousandTwentyFourMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystoneTristateMember
                 
Keystone-TriState [Member] | Principal Balance Due July 6, 2044 [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Property Debt, Balance 63,400,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_DebtInstrumentAxis
= cli_PrincipalBalanceDueJulySixthTwoThousandFortyFourMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystoneTristateMember
                 
Property Debt, Interest Rate 4.93%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= cli_PrincipalBalanceDueJulySixthTwoThousandFortyFourMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystoneTristateMember
                 
Keystone-TriState [Member] | Principal Balance Due August 6, 2044 [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Property Debt, Balance 15,050,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_DebtInstrumentAxis
= cli_PrincipalBalanceDueAugustSixthTwoThousandFortyFourMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystoneTristateMember
                 
Property Debt, Interest Rate 4.71%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= cli_PrincipalBalanceDueAugustSixthTwoThousandFortyFourMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystoneTristateMember
                 
Keystone-TriState [Member] | Keystone Entities [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Internal rate of return 15.00%cli_InternalRateOfReturn
/ dei_LegalEntityAxis
= cli_KeystoneEntitiesMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystoneTristateMember
                 
Keystone-TriState [Member] | Parent Company [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Internal rate of return 10.00%cli_InternalRateOfReturn
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystoneTristateMember
                 
Keystone-Penn And Keystone TriState [Member] | Principal Balance Due August 6, 2044 [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Property Debt, Maturity Date August 6, 2044                  
Keystone-Penn And Keystone TriState [Member] | Parent Company [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Internal rate of return 10.00%cli_InternalRateOfReturn
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystonePennAndKeystoneTristateMember
                 
Keystone-Penn And Keystone TriState [Member] | Keystone Property Group [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Internal rate of return 15.00%cli_InternalRateOfReturn
/ dei_LegalEntityAxis
= cli_KeystonePropertyGroupMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystonePennAndKeystoneTristateMember
                 
KPG-MCG Curtis JV, LLC [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Square Feet 885,000us-gaap_AreaOfRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgMcgCurtisJvLLCMember
[24]                  
Company's Effective Ownership % 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgMcgCurtisJvLLCMember
[1],[24]                  
Carrying Amount 59,911,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgMcgCurtisJvLLCMember
[24]                  
Property Debt, Balance    [25]                  
KPG-MCG Curtis JV, LLC [Member] | Parent Company [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Company's Effective Ownership % 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgMcgCurtisJvLLCMember
                 
KPG-MCG Curtis JV, LLC [Member] | Keystone Property Group [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Company's Effective Ownership % 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ dei_LegalEntityAxis
= cli_KeystonePropertyGroupMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgMcgCurtisJvLLCMember
                 
Plaza VIII & IX Associates, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Square Feet 1,225,000us-gaap_AreaOfRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PlazaEightAndNineAssociatesLLCMember
                 
Company's Effective Ownership % 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PlazaEightAndNineAssociatesLLCMember
[1]                  
Carrying Amount 4,022,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PlazaEightAndNineAssociatesLLCMember
          3,702,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PlazaEightAndNineAssociatesLLCMember
     
Roseland/North Retail, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Square Feet 30,745us-gaap_AreaOfRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoselandNorthRetailLLCMember
[8]                  
Company's Effective Ownership % 20.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoselandNorthRetailLLCMember
[1],[8]                  
Carrying Amount 1,828,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoselandNorthRetailLLCMember
[8]           1,930,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoselandNorthRetailLLCMember
[8]      
South Pier At Harborside [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 350us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_SouthPierAtHarborsideMember
                 
Company's Effective Ownership % 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_SouthPierAtHarborsideMember
[1]                  
Property Debt, Balance 65,643,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_SouthPierAtHarborsideMember
[26]                  
Note payable 4,100,000us-gaap_NotesPayable
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_SouthPierAtHarborsideMember
                 
Bears interest at fixed rate range, minimum 6.09%us-gaap_DebtInstrumentInterestRateEffectivePercentageRateRangeMinimum
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_SouthPierAtHarborsideMember
                 
Bears interest at fixed rate range, maximum 6.62%us-gaap_DebtInstrumentInterestRateEffectivePercentageRateRangeMaximum
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_SouthPierAtHarborsideMember
                 
Maturity Aug. 01, 2020                  
Letter of credit 4,100,000cli_LineOfCreditFacilityInSupportOfDebtInstrumentFairValueOfAmountOutstanding
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_SouthPierAtHarborsideMember
                 
Stamford SM LLC [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Company's Effective Ownership % 80.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_StamfordSmLlcMember
[1],[27]                  
Carrying Amount             36,258,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_StamfordSmLlcMember
[27]      
Other [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Carrying Amount 907,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OtherJointVenturesMember
[28]           693,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OtherJointVenturesMember
[28]      
The Shops At 40 Park Property [Member] | Rosewood Morristown, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Square Feet 50,973us-gaap_AreaOfRealEstateProperty
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_ShopsAtFortyParkPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
                 
Property Debt, Balance 6,500,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_ShopsAtFortyParkPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
                 
Property Debt, Maturity Date August 2018                  
Property Debt, Interest Rate 3.63%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_ShopsAtFortyParkPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
                 
Residual ownership interest 12.50%cli_ResidualOwnershipInterest
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_ShopsAtFortyParkPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
                 
Additional borrowing capacity 1,000,000cli_MortgageLoanOnRealEstateAdditionalBorrowingCapacity
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_ShopsAtFortyParkPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
                 
Lofts At 40 Park Property [Member] | Rosewood Morristown, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 59us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_LoftsAtFortyParkPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
                 
Property Debt, Balance 1,117,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_LoftsAtFortyParkPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
                 
Property Debt, Maturity Date September 2015                  
Property Debt, Interest Rate, Spread Over LIBOR 2.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_LoftsAtFortyParkPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
                 
Indirect ownership interest 25.00%cli_IndirectOwnershipPercentage
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_LoftsAtFortyParkPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
                 
Number of stories 5cli_NumberOfStoriesInRealEstateProperty
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_LoftsAtFortyParkPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
                 
Metropolitan Property [Member] | Rosewood Morristown, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Property Debt, Balance 38,600,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_MetropolitanPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
                 
Property Debt, Maturity Date September 2020                  
Property Debt, Interest Rate 3.25%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_MetropolitanPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
                 
Port Imperial North Land [Member] | Roseland/Port Imperial Partners, L.P. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of Apartment Units 836us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_PortImperialNorthLandMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoselandPortImperialPartnersLPMember
                 
Residual ownership interest 20.00%cli_ResidualOwnershipInterest
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_PortImperialNorthLandMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoselandPortImperialPartnersLPMember
                 
Senior Loans [Member] | Quarrystone I Property [Member] | Overlook Ridge JV, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Property Debt, Balance 52,501,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_QuarrystoneIPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OverlookRidgeJVLLCMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_SeniorLoansMember
                 
Property Debt, Maturity Date March 2016                  
Property Debt, Interest Rate, Spread Over LIBOR 2.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_QuarrystoneIPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OverlookRidgeJVLLCMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_SeniorLoansMember
                 
Junior Loans [Member] | Quarrystone I Property [Member] | Rosewood Morristown, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Property Debt, Balance 17,000,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_QuarrystoneIPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_JuniorLoansMember
                 
Property Debt, Maturity Date March 2016                  
Property Debt, Interest Rate, Spread Over LIBOR 0.90%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_QuarrystoneIPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_JuniorLoansMember
                 
Letter of Credit [Member] | Quarrystone I Property [Member] | Overlook Ridge JV, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Maximum borrowing capacity 17,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_QuarrystoneIPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OverlookRidgeJVLLCMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_LetterOfCreditMember
                 
Construction Loan [Member] | Overlook Ridge JV 2C/3B, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Property Debt, Interest Rate 3.0875%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OverlookRidgeJvTwoCAndThreeBLLCMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_ConstructionLoansMember
                 
Number of extension options 2cli_DebtInstrumentNumberOfExtensionOptions
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OverlookRidgeJvTwoCAndThreeBLLCMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_ConstructionLoansMember
                 
Loan extension period 1 year                  
Maximum borrowing capacity 55,500,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OverlookRidgeJvTwoCAndThreeBLLCMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_ConstructionLoansMember
                 
Notional amount 52,000,000us-gaap_NotionalAmountOfNonderivativeInstruments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OverlookRidgeJvTwoCAndThreeBLLCMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_ConstructionLoansMember
      1,840,000us-gaap_NotionalAmountOfNonderivativeInstruments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OverlookRidgeJvTwoCAndThreeBLLCMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_ConstructionLoansMember
         
Construction Loan [Member] | PruRose Riverwalk G, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Maximum borrowing capacity 83,113,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PruRoseRiverwalkGLLCMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_ConstructionLoansMember
                 
Construction Loan [Member] | Elmajo Urban Renewal Associates, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Loan extension period 1 year                  
Extension fee 0.25%cli_DebtInstrumentExtensionFeePercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_ElmajoUrbanRenewalAssociatesLLCMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_ConstructionLoansMember
                 
Maximum borrowing capacity 91,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_ElmajoUrbanRenewalAssociatesLLCMember
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Construction Loan [Member] | Portside Master Company, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of extension options 2cli_DebtInstrumentNumberOfExtensionOptions
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= cli_PortsideMasterCompanyLLCMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_ConstructionLoansMember
                 
Maximum borrowing capacity 42,500,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
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= cli_PortsideMasterCompanyLLCMember
/ us-gaap_ShortTermDebtTypeAxis
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Construction Loan [Member] | PruRose Port Imperial South 13, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Property Debt, Interest Rate 2.79%us-gaap_DebtInstrumentInterestRateStatedPercentage
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= cli_PruRosePortImperialSouthThirteenLLCMember
/ us-gaap_ShortTermDebtTypeAxis
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Maximum borrowing capacity 73,350,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
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Construction Loan [Member] | RoseGarden Marbella South, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of extension options 2cli_DebtInstrumentNumberOfExtensionOptions
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/ us-gaap_ShortTermDebtTypeAxis
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Loan extension period 1 year                  
Maximum borrowing capacity 77,400,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
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Construction Loan [Member] | Estuary Urban Renewal Unit B, LLC [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Loan extension period 1 year                  
Extension fee 0.25%cli_DebtInstrumentExtensionFeePercentage
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Maximum borrowing capacity 57,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
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Construction Loan [Member] | RiverPark At Harrison I, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Number of extension options 2cli_DebtInstrumentNumberOfExtensionOptions
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Maximum borrowing capacity 23,400,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
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Construction Loan [Member] | Capitol Place Mezz LLC [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Maximum borrowing capacity 100,700,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
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Construction Loan Extension Number 1 [Member] | Overlook Ridge JV 2C/3B, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Extension fee 0.25%cli_DebtInstrumentExtensionFeePercentage
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Construction Loan Extension Number 1 [Member] | Portside Master Company, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Loan extension period 2 years                  
Extension fee 0.125%cli_DebtInstrumentExtensionFeePercentage
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Construction Loan Extension Number 1 [Member] | PruRose Port Imperial South 13, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Loan extension period 1 year                  
Extension fee 0.25%cli_DebtInstrumentExtensionFeePercentage
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Construction Loan Extension Number 1 [Member] | RoseGarden Marbella South, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Extension fee 0.25%cli_DebtInstrumentExtensionFeePercentage
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Construction Loan Extension Number 1 [Member] | RiverPark At Harrison I, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Extension fee 0.20%cli_DebtInstrumentExtensionFeePercentage
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Schedule of Equity Method Investments [Line Items]                    
Extension fee 0.25%cli_DebtInstrumentExtensionFeePercentage
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Schedule of Equity Method Investments [Line Items]                    
Loan extension period 2 years                  
Extension fee 0.25%cli_DebtInstrumentExtensionFeePercentage
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Construction Loan Extension Number 2 [Member] | PruRose Port Imperial South 13, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
Loan extension period 6 months                  
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Schedule of Equity Method Investments [Line Items]                    
Extension fee 0.25%cli_DebtInstrumentExtensionFeePercentage
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Schedule of Equity Method Investments [Line Items]                    
Extension fee 0.20%cli_DebtInstrumentExtensionFeePercentage
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Mezz Loan [Member] | Stamford SM LLC [Member]                    
Schedule of Equity Method Investments [Line Items]                    
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Property Debt, Maturity Date August 6, 2014                  
Mezz Loan [Member] | Stamford SM LLC [Member] | Parent Company [Member]                    
Schedule of Equity Method Investments [Line Items]                    
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Hotel [Member] | South Pier At Harborside [Member]                    
Schedule of Equity Method Investments [Line Items]                    
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Overlook Ridge Properties [Member]                    
Schedule of Equity Method Investments [Line Items]                    
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Schedule of Equity Method Investments [Line Items]                    
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LR Overlook Phase III, L.L.C. [Member]                    
Schedule of Equity Method Investments [Line Items]                    
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Schedule of Equity Method Investments [Line Items]                    
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Keystone Portfolio [Member]                    
Schedule of Equity Method Investments [Line Items]                    
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Schedule of Equity Method Investments [Line Items]                    
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Schedule of Equity Method Investments [Line Items]                    
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[1] Company's effective ownership % represents the Company's entitlement to residual distributions after payments of priority returns, where applicable.
[2] Through the joint venture, the Company also owns a 12.5 percent interest in a 50,973 square feet retail building ("Shops at 40 Park") and a 25 percent interest in a to-be-built 59-unit, five story multi-family rental development property ("Lofts at 40 Park").
[3] The Company's ownership interests in this venture are subordinate to its partner's preferred capital balance and the payment of the outstanding balance remaining on a note ($975 as of December 31, 2014), and is not expected to meaningfully participate in the venture's cash flows in the near term.
[4] Property debt balance consists of: (i) a loan, collateralized by the Metropolitan at 40 Park, with a balance of $38,600 at December 31, 2014, bears interest at 3.25 percent, matures in September 2020 and is interest only through September 2015; (ii) a loan, collateralized by the Shops at 40 Park, with a balance of $6,500 at December 31, 2014, bears interest at 3.63 percent, matures in August 2018 and is interest-only through July 2015; and (iii) a loan, collateralized by the Lofts at 40 Park, with a balance of $1,117, bears interest at LIBOR plus 250 basis points and matures in September 2015. The Shops at 40 Park mortgage loan also provides for additional borrowing proceeds of $1 million based on certain preferred thresholds being achieved.
[5] Property debt balance consists of: (i) the senior loan, collateralized by the Quarrystone property, with a balance of $52,501 at December 31, 2014, bears interest at LIBOR plus 200 basis, matures in March 2016 and (ii) the junior loan, with a balance of $17,000, bears interest at LIBOR plus 90 basis points, matures in March 2016 and is collateralized by a $17,000 letter of credit provided by an affiliate of the partner.
[6] On August 15, 2014, the Company acquired the equity interests of its joint venture partner in Overlook Ridge JV 2C/3B, L.L.C. for $2.97 million and LR Overlook Phase II, L.L.C., the property-owning entity owned by Overlook Ridge JV, L.L.C., which increased its ownership to 50 percent in two operating multi-family properties. The Company also acquired the equity interests of its joint venture partner in LR Overlook Phase III, L.L.C. and Overlook Ridge, L.L.C. for $0.6 million and $12.99 million respectively, which increased its ownership to 100 percent in developable land (See Note 3: Real Estate Transactions - Acquisitions).
[7] The construction loan has a maximum borrowing amount of $55,500 and provides, subject to certain conditions, two one-year extension options with a fee of 25 basis points each. The joint venture has a swap agreement that fixes the all-in rate to 3.0875 percent per annum on an initial notional amount of $1,840, increasing to $52,000, for the period from September 3, 2013 to November 2, 2015.
[8] The Company's ownership interests in this venture are subordinate to its partner's preferred capital balance and the Company is not expected to meaningfully participate in the venture's cash flows in the near term.
[9] The construction loan with a maximum borrowing amount of $83,113 was converted to a permanent loan on December 26,2014 with a maximum borrowing amount of $80,249
[10] The construction loan has a maximum borrowing amount of $91,000 and provides, subject to certain conditions, a one-year extension option with a fee of 25 basis points.
[11] The Company also owns a 50 percent interest in a vacant land parcel to accommodate the development of approximately 295 additional units of which 252 are currently approved.
[12] The construction loan has a maximum borrowing amount of $42,500 and provides, subject to certain conditions, two two-year extension options with a fee of 12.5 basis points for the first two-year extension and 25 basis points for the second two-year extension.
[13] The construction loan has a maximum borrowing amount of $73,350 and provides, subject to certain conditions, one-year extension option followed by a six-month extension option with a fee of 25 basis points each. The joint venture has a swap agreement that fixes the all-in rate to 2.79 percent per annum on an initial notional amount of $1,620, increasing to $69,500 for the period from July 1, 2013 to January 1, 2016.
[14] The Company also owns a 20 percent residual interest in undeveloped land parcels: parcels 6, I, and J ("Port Imperial North Land") that can accommodate the development of 836 apartment units.
[15] The construction loan has a maximum borrowing amount of $77,400 and provides, subject to certain conditions, two one-year extension options with a fee of 25 basis points for each year.
[16] The construction loan has a maximum borrowing amount of $57,000 and provides, subject to certain conditions, a one-year extension option with a fee of 25 basis points.
[17] The construction loan has a maximum borrowing amount of $23,400 and provides, subject to certain conditions, two one-year extension options with a fee of 20 basis points for each year.
[18] The construction/permanent loan has a maximum borrowing amount of $100,700 with amortization starting in August 2017.
[19] The construction/permanent loan has a maximum borrowing amount of $192,000.
[20] The joint venture has a swap agreement that fixes the all-in rate to 3.99375 percent per annum on an initial notional amount of $13,650 and then adjusting in accordance with an amortization schedule, which is effective from October 17, 2011 through loan maturity.
[21] The mortgage loan has two one-year extension options, subject to certain conditions, and includes a $25 million construction escrow with a balance of $15.8 million to be drawn at December 31, 2014.
[22] Principal balance of $127,600 bears interest at 5.114 percent and matures in August 27, 2023; principal balance of $65,786 bears interest at rates ranging from LIBOR+5.0 percent to LIBOR+5.75 percent and matures in August 27, 2016; principal balance of $10,425 bears interest at LIBOR+6.0 percent matures in August 27, 2015.
[23] Principal balance of $41,240 bears interest at 4.95 percent and matures on July 1, 2017; principal balance of $70,903 bears interest at rates ranging from 5.65 percent to 6.75 percent and matures on September 9, 2017; principal balance of $14,250 bears interest at 4.88 percent and matures on July 6, 2024; principal balance of $63,400 bears interest at 4.93 percent and matures on July 6, 2044; principal balance of $15,050 bears interest at 4.71 percent and matures on August 6, 2044.
[24] Includes undivided interests in the same manner as investments in noncontrolling partnership, pursuant to ASC 970-323-25-12. See discussion in Unconsolidated Joint Venture Transactions following in this footnote.
[25] See Note 10: Mortgages, Loans Payable and Other Obligations for debt secured by interests in these assets.
[26] Balance includes: (i) mortgage loan, collateralized by the hotel property, with a balance of $61,519, bears interest at 6.15 percent and matures in November 2016, and (ii) loan with a balance of $4.1 million, bears interest at fixed rates ranging from 6.09 percent to 6.62 percent and matures in August 1, 2020. The Company posted a $4.1 million letter of credit in support of this loan, half of which is indemnified by the partner.
[27] The joint venture collected net proceeds of $47.2 million at maturity, of which the Company received its share of $37.8 million on August 6, 2014.
[28] The Company owns other interests in various unconsolidated joint ventures, including interests in assets previously owned and interest in ventures whose businesses are related to its core operations. These ventures are not expected to significantly impact the Company's operations in the near term.