Annual report pursuant to Section 13 and 15(d)

Investments In Unconsolidated Joint Ventures (150 Main Street, L.L.C.) (Narrative) (Details)

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Investments In Unconsolidated Joint Ventures (150 Main Street, L.L.C.) (Narrative) (Details) (USD $)
 0 Months Ended 12 Months Ended
Aug. 22, 2013
Oct. 23, 2012
Dec. 31, 2014
Aug. 22, 2013
Oct. 23, 2012
item
Schedule of Equity Method Investments [Line Items]          
Percentage of interest in venture        [1]    
150 Main St [Member]          
Schedule of Equity Method Investments [Line Items]          
Holding and distribution pattern under operating agreement     The operating agreement of Eastchester provided, among other things, for the distribution of net operating cash flow to the members, as follows:to HVLH to the extent of its accrued but unpaid preferred return of eight percent on the unrecovered allocated land value, as defined; to the members, pro rata, to the extent of their respective accrued but unpaid return of eight percent on their unrecovered capital percentages; andto the members in accordance with their ownership percentages.Net cash flows from a capital event are distributed to the members, first, in respect of unrecovered return and then unrecovered capital on a pro rata basis, with any excess in accordance with their ownership percentages.    
Eastchester Project [Member]          
Schedule of Equity Method Investments [Line Items]          
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 		  76.25%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember 		26.25%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember
Number of units   108us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember 		    108us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember
Business acquisition, cash paid $ 4,900,000us-gaap_PaymentsToAcquireBusinessesGross
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember 		$ 2,100,000us-gaap_PaymentsToAcquireBusinessesGross
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember 		     
Third party ownership percentage     8.00%cli_ThirdPartyOwnershipPercent
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember 		   
Total project costs     50,000,000cli_EstimatedCostOfProject
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember 		   
Project costs incurred     13,900,000cli_ProjectCostsIncurred
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember 		   
Holding period gain (loss) 0us-gaap_VentureCapitalGainsLossesNet
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember 		       
Amount of project costs funded by members     21,200,000cli_AmountOfProjectCostsFundedByMembers
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember 		   
Eastchester Project [Member] | JMP Eastchester, L.L.C. [Member]          
Schedule of Equity Method Investments [Line Items]          
Third party ownership percentage   26.25%cli_ThirdPartyOwnershipPercent
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember
/ dei_LegalEntityAxis
= cli_JMPEastchesterLLCMember 		    26.25%cli_ThirdPartyOwnershipPercent
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember
/ dei_LegalEntityAxis
= cli_JMPEastchesterLLCMember
Eastchester Project [Member] | Hudson Valley Land Holdings, L.L.C. [Member]          
Schedule of Equity Method Investments [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 		  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 return on unrecovered capital     8.00%cli_PercentageReturnOnUnrecoveredCapital
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember
/ dei_LegalEntityAxis
= cli_HudsonValleyLandHoldingsLLCMember 		   
Eastchester Project [Member] | Parent Company [Member]          
Schedule of Equity Method Investments [Line Items]          
Amount of project costs funded by members     20,900,000cli_AmountOfProjectCostsFundedByMembers
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember 		   
Eastchester Project [Member] | Construction Loan [Member] | 150 Main St [Member]          
Schedule of Equity Method Investments [Line Items]          
Maximum borrowing capacity     $ 28,800,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_BusinessAcquisitionAxis
= cli_EastchesterProjectMember
/ dei_LegalEntityAxis
= cli_OneHundredFiftyMainStreetMember
/ us-gaap_ShortTermDebtTypeAxis
= cli_ConstructionLoanMember 		   
[1] Company's effective ownership % represents the Company's entitlement to residual distributions after payments of priority returns, where applicable.