Annual report pursuant to Section 13 and 15(d)

Investments In Unconsolidated Joint Ventures (KPG-MCG Curtis JV, LLC / Curtis Center) (Narrative) (Details)

v2.4.1.9
Investments In Unconsolidated Joint Ventures (KPG-MCG Curtis JV, LLC / Curtis Center) (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
Schedule of Equity Method Investments [Line Items]            
Percentage of interest in venture    [1]          
Carrying Amount $ 247,468,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures $ 181,129,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures        
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      
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 		         
KPG-MCG Curtis JV, LLC [Member]            
Schedule of Equity Method Investments [Line Items]            
Percentage of interest in venture 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgMcgCurtisJvLLCMember 		[1],[2]          
Carrying Amount 59,911,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgMcgCurtisJvLLCMember 		[2]          
Construction square foot 885,000us-gaap_AreaOfRealEstateProperty
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgMcgCurtisJvLLCMember 		[2]          
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] | 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 		         
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] | Curtis Center Property [Member]            
Schedule of Equity Method Investments [Line Items]            
Carrying Amount 125,000,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_CurtisCenterPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgMcgCurtisJvLLCMember 		         
Lease period 29 years          
KPG-MCG Curtis JV, LLC [Member] | Curtis Center Property [Member] | Keystone Property Group [Member]            
Schedule of Equity Method Investments [Line Items]            
Carrying Amount 62,500,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ dei_LegalEntityAxis
= cli_KeystonePropertyGroupMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_CurtisCenterPropertyMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgMcgCurtisJvLLCMember 		         
KPG-MCG Curtis JV, LLC [Member] | Curtis Center Property [Member] | Parent Company [Member]            
Schedule of Equity Method Investments [Line Items]            
Carrying Amount 62,500,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_CurtisCenterPropertyMember
/ 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 of senior unsecured notes         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 of senior unsecured notes         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
[1] Company's effective ownership % represents the Company's entitlement to residual distributions after payments of priority returns, where applicable.
[2] 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.