Annual report pursuant to Section 13 and 15(d)

Organization And Basis Of Presentation (Details)

v2.4.1.9
Organization And Basis Of Presentation (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
sqft
state
property
Dec. 31, 2013
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 283cli_RealEstatePropertyOwnedAndInvestmentInterest  
Aggregate square feet of the property owned or investment interest 31,000,000cli_RealEstatePropertyOwnedAndInvestmentInterestArea  
Number of states where properties are located 7cli_RealEstatePropertyOwnedOrInvestmentInterestNumberOfLocation  
Consolidated joint ventures, total real estate assets $ 242.9cli_ConsolidatedJointVenturesRealEstateAssets $ 219.9cli_ConsolidatedJointVenturesRealEstateAssets
Consolidated joint ventures, mortgages 94.3cli_ConsolidatedJointVenturesMortgages 81.9cli_ConsolidatedJointVenturesMortgages
Consolidated joint ventures, other liabilities $ 15.7cli_ConsolidatedJointVenturesOtherLiabilities $ 18.3cli_ConsolidatedJointVenturesOtherLiabilities
Commercial Properties [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 264cli_RealEstatePropertyOwnedAndInvestmentInterest
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_CommercialRealEstateMember 		 
Number of tenants 2,000cli_NumberOfTenants
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_CommercialRealEstateMember 		 
Multi-Family Properties [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 19cli_RealEstatePropertyOwnedAndInvestmentInterest
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_MultipleFamilyPropertiesMember 		 
Number of units 5,484us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_MultipleFamilyPropertiesMember 		 
Office And Office/Flex Buildings [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 249cli_RealEstatePropertyOwnedAndInvestmentInterest
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_OfficeAndOfficeFlexBuildingsMember 		 
Aggregate square feet of the property owned or investment interest 30,500,000cli_RealEstatePropertyOwnedAndInvestmentInterestArea
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_OfficeAndOfficeFlexBuildingsMember 		 
Unconsolidated Joint Venture Office Buildings [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 36cli_RealEstatePropertyOwnedAndInvestmentInterest
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_UnconsolidatedJointVentureOfficeBuildingsMember 		 
Aggregate square feet of the property owned or investment interest 5,600,000cli_RealEstatePropertyOwnedAndInvestmentInterestArea
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_UnconsolidatedJointVentureOfficeBuildingsMember 		 
Industrial/Warehouse Facilities [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 6cli_RealEstatePropertyOwnedAndInvestmentInterest
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_IndustrialAndWarehouseFacilitiesMember 		 
Aggregate square feet of the property owned or investment interest 387,400cli_RealEstatePropertyOwnedAndInvestmentInterestArea
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_IndustrialAndWarehouseFacilitiesMember 		 
Unconsolidated Joint Venture Multi-Family Properties [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 13cli_RealEstatePropertyOwnedAndInvestmentInterest
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_UnconsolidatedJointVentureMultipleFamilyPropertiesMember 		 
Number of units 4,183us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_UnconsolidatedJointVentureMultipleFamilyPropertiesMember 		 
Parking/Retail [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 5cli_RealEstatePropertyOwnedAndInvestmentInterest
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_ParkingRetailMember 		 
Aggregate square feet of the property owned or investment interest 121,500cli_RealEstatePropertyOwnedAndInvestmentInterestArea
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_ParkingRetailMember 		 
Unconsolidated Joint Venture Parking/Retail Buildings [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 2cli_RealEstatePropertyOwnedAndInvestmentInterest
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_UnconsolidatedJointVentureParkingRetailBuildingsMember 		 
Aggregate square feet of the property owned or investment interest 81,500cli_RealEstatePropertyOwnedAndInvestmentInterestArea
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_UnconsolidatedJointVentureParkingRetailBuildingsMember 		 
Unconsolidated Joint Venture Hotel [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 1cli_RealEstatePropertyOwnedAndInvestmentInterest
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_UnconsolidatedJointVentureHotelMember 		 
Number of units 350us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= cli_UnconsolidatedJointVentureHotelMember 		 
Land [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 3cli_RealEstatePropertyOwnedAndInvestmentInterest
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_LandMember