Annual report pursuant to Section 13 and 15(d)

Investments In Unconsolidated Joint Ventures (Recent Transactions) (Narrative) (Details)

v2.4.1.9
Investments In Unconsolidated Joint Ventures (Recent Transactions) (Narrative) (Details) (USD $)
 12 Months Ended 0 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Oct. 01, 2014
Jun. 06, 2014
Sep. 02, 2014
May 21, 2014
Aug. 01, 2014
Schedule of Equity Method Investments [Line Items]                
Investments in unconsolidated joint ventures $ 247,468,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures $ 181,129,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures            
Development of rental property 25,140,000us-gaap_PaymentsToDevelopRealEstateAssets 13,772,000us-gaap_PaymentsToDevelopRealEstateAssets 60,354,000us-gaap_PaymentsToDevelopRealEstateAssets          
Internal rate of return 9.00%cli_InternalRateOfReturn              
Percentage of interest in venture    [1]              
Loan to affiliate 62,276,000us-gaap_PaymentsToAcquireLoansReceivable 16,425,000us-gaap_PaymentsToAcquireLoansReceivable            
Repayment of loans payable 83,808,000us-gaap_RepaymentsOfSecuredDebt 20,715,000us-gaap_RepaymentsOfSecuredDebt 52,318,000us-gaap_RepaymentsOfSecuredDebt          
Parent Company [Member]                
Schedule of Equity Method Investments [Line Items]                
Percentage of capital event cash flows distributed 50.00%cli_PercentageOfCapitalEventCashFlowsDistributed
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember 		             
Harborside Unit A Urban Renewal, LLC [Member]                
Schedule of Equity Method Investments [Line Items]                
Number of units 763us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember 		             
Percentage of interest in venture 85.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember 		             
Investments in unconsolidated joint ventures 34,954,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember 		          30,600,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember 		 
Capital credit receivable per developable square foot 30cli_CapitalCreditReceivablePerDevelopableSquareFoot
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember 		             
Development of rental property 19,200,000us-gaap_PaymentsToDevelopRealEstateAssets
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember 		             
Percentage of interest in venture 85.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember 		[1]              
Interest rate 5.197%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember 		[2]              
Holding and distribution pattern under operating agreement In general, the operating agreement of URL-Harborside provides that net operating cash flows are distributed first, to the members in respect of preferred return, as defined, until each member shall have received payment of the accrued and unpaid preferred return; and, thereafter, 75 percent to the Company and 25 percent to ISA.              
Harborside Unit A Urban Renewal, LLC [Member] | Construction Loan [Member]                
Schedule of Equity Method Investments [Line Items]                
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 		             
Mortgage loan, maturity date Aug. 01, 2029              
Interest rate               5.197%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= cli_ConstructionLoanMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember
Harborside Unit A Urban Renewal, LLC [Member] | Parent Company [Member]                
Schedule of Equity Method Investments [Line Items]                
Percentage of operating return on capital 75.00%cli_PercentageOfOperatingReturnOnCapital
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember 		             
Internal rate of return 18.00%cli_InternalRateOfReturn
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember 		             
Percentage of capital event cash flows distributed after initial internal rate of return reached 65.00%cli_PercentageOfCapitalEventCashFlowsDistributedAfterInitialInternalRateOfReturnReached
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember 		             
Percentage of capital event cash flows distributed 75.00%cli_PercentageOfCapitalEventCashFlowsDistributed
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember 		             
Harborside Unit A Urban Renewal, LLC [Member] | Ironstate Harborside-A, LLC [Member]                
Schedule of Equity Method Investments [Line Items]                
Investments in unconsolidated joint ventures 5,400,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ dei_LegalEntityAxis
= cli_IronstateHarborsideaLLCMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember 		             
Percentage of operating return on capital 25.00%cli_PercentageOfOperatingReturnOnCapital
/ dei_LegalEntityAxis
= cli_IronstateHarborsideaLLCMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember 		             
Percentage of capital event cash flows distributed after initial internal rate of return reached 35.00%cli_PercentageOfCapitalEventCashFlowsDistributedAfterInitialInternalRateOfReturnReached
/ dei_LegalEntityAxis
= cli_IronstateHarborsideaLLCMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember 		             
Percentage of capital event cash flows distributed 25.00%cli_PercentageOfCapitalEventCashFlowsDistributed
/ dei_LegalEntityAxis
= cli_IronstateHarborsideaLLCMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember 		             
KPG-MCG Curtis JV, LLC [Member]                
Schedule of Equity Method Investments [Line Items]                
Investments in unconsolidated joint ventures 59,911,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgMcgCurtisJvLLCMember 		[3]              
Aggregate capital credits 20,600,000cli_AggregateCapitalCredits
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgMcgCurtisJvLLCMember 		             
Percentage of interest in venture 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgMcgCurtisJvLLCMember 		[1],[3]              
Area of property (in square feet) 885,000us-gaap_AreaOfRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgMcgCurtisJvLLCMember 		[3]              
Threshold of member unreturned capital for distribution of net operating cash flows 0cli_ThresholdOfMemberUnreturnedCapitalForDistributionOfNetOperatingCashFlows
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgMcgCurtisJvLLCMember 		             
Holding and distribution pattern under operating agreement In general, the operating agreement of the Curtis Center JV provides that net cash flows from operations and capital events are distributed first, to the members, pro rata in proportion to their unreturned capital contributions, until each member's unreturned capital contributions have been reduced to zero; and, thereafter, to each member, pro rata, in accordance with their percentage interests.              
KPG-MCG Curtis JV, LLC [Member] | Parent Company [Member]                
Schedule of Equity Method Investments [Line Items]                
Percentage of interest in venture 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]                
Percentage of interest in venture 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ dei_LegalEntityAxis
= cli_KeystonePropertyGroupMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgMcgCurtisJvLLCMember 		             
90-Day Loan 1 [Member] | Keystone Property Group [Member]                
Schedule of Equity Method Investments [Line Items]                
Maturity period         90 days      
Loan to affiliate         52,300,000us-gaap_PaymentsToAcquireLoansReceivable
/ dei_LegalEntityAxis
= cli_KeystonePropertyGroupMember
/ us-gaap_ShortTermDebtTypeAxis
= cli_NinetyDayLoanNumberOneMember 		     
Interest rate         3.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ dei_LegalEntityAxis
= cli_KeystonePropertyGroupMember
/ us-gaap_ShortTermDebtTypeAxis
= cli_NinetyDayLoanNumberOneMember 		     
Repayment of loans payable       52,300,000us-gaap_RepaymentsOfSecuredDebt
/ dei_LegalEntityAxis
= cli_KeystonePropertyGroupMember
/ us-gaap_ShortTermDebtTypeAxis
= cli_NinetyDayLoanNumberOneMember 		       
90-Day Loan 2 [Member] | Keystone Property Group [Member]                
Schedule of Equity Method Investments [Line Items]                
Maturity period         90 days      
Loan to affiliate         10,000,000us-gaap_PaymentsToAcquireLoansReceivable
/ dei_LegalEntityAxis
= cli_KeystonePropertyGroupMember
/ us-gaap_ShortTermDebtTypeAxis
= cli_NinetyDayLoanNumberTwoMember 		     
Interest rate         3.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ dei_LegalEntityAxis
= cli_KeystonePropertyGroupMember
/ us-gaap_ShortTermDebtTypeAxis
= cli_NinetyDayLoanNumberTwoMember 		     
Repayment of loans payable           10,000,000us-gaap_RepaymentsOfSecuredDebt
/ dei_LegalEntityAxis
= cli_KeystonePropertyGroupMember
/ us-gaap_ShortTermDebtTypeAxis
= cli_NinetyDayLoanNumberTwoMember 		   
Harborside Residential Project [Member] | Harborside Unit A Urban Renewal, LLC [Member]                
Schedule of Equity Method Investments [Line Items]                
Number of units 763us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_HarborsideResidentialProjectMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember 		             
Total project costs 320,000,000cli_EstimatedCostOfProject
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_HarborsideResidentialProjectMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember 		             
State tax credit 33,000,000us-gaap_DeferredTaxAssetsTaxCreditCarryforwards
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_HarborsideResidentialProjectMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember 		             
Harborside Residential Project [Member] | Harborside Unit A Urban Renewal, LLC [Member] | Parent Company [Member]                
Schedule of Equity Method Investments [Line Items]                
Total project costs 59,100,000cli_EstimatedCostOfProject
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_HarborsideResidentialProjectMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember 		             
Curtis Center Property [Member]                
Schedule of Equity Method Investments [Line Items]                
Percentage of interest in venture 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_CurtisCenterPropertyMember 		             
Curtis Center Property [Member] | Keystone Property Group [Member]                
Schedule of Equity Method Investments [Line Items]                
Percentage of interest in venture 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ dei_LegalEntityAxis
= cli_KeystonePropertyGroupMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_CurtisCenterPropertyMember 		             
Curtis Center Property [Member] | KPG-MCG Curtis JV, LLC [Member]                
Schedule of Equity Method Investments [Line Items]                
Investments in unconsolidated joint ventures 125,000,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_CurtisCenterPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgMcgCurtisJvLLCMember 		             
Lease period 29 years              
Curtis Center Property [Member] | KPG-MCG Curtis JV, LLC [Member] | Parent Company [Member]                
Schedule of Equity Method Investments [Line Items]                
Investments in unconsolidated joint ventures 62,500,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_CurtisCenterPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgMcgCurtisJvLLCMember 		             
Curtis Center Property [Member] | KPG-MCG Curtis JV, LLC [Member] | Keystone Property Group [Member]                
Schedule of Equity Method Investments [Line Items]                
Investments in unconsolidated joint ventures 62,500,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ dei_LegalEntityAxis
= cli_KeystonePropertyGroupMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_CurtisCenterPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgMcgCurtisJvLLCMember 		             
Land [Member] | Harborside Unit A Urban Renewal, LLC [Member] | Parent Company [Member]                
Schedule of Equity Method Investments [Line Items]                
Investments in unconsolidated joint ventures $ 5,500,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_LandMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HarborsideUnitaUrbanRenewalLLCMember 		             
[1] Company's effective ownership % represents the Company's entitlement to residual distributions after payments of priority returns, where applicable.
[2] The construction/permanent loan has a maximum borrowing amount of $192,000.
[3] 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.