Quarterly report pursuant to Section 13 or 15(d)

Commitments And Contingencies (Departure Of Executive Officers) (Narrative) (Details)

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Commitments And Contingencies (Departure Of Executive Officers) (Narrative) (Details) (USD $)
 3 Months Ended 6 Months Ended 0 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Sep. 30, 2014
May 11, 2015
item
Dec. 31, 2014
Commitments And Contingencies [Line Items]          
Severance benefits $ 23,800,000us-gaap_SeveranceCosts1 $ 11,000,000us-gaap_SeveranceCosts1      
Restricted stock units vested 37,392us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod        
Accounts payable, accrued expenses and other liabilities 134,462,000us-gaap_AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent       126,971,000us-gaap_AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent
Employee Severance [Member]          
Commitments And Contingencies [Line Items]          
Accounts payable, accrued expenses and other liabilities 11,600,000us-gaap_AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent
/ us-gaap_RestructuringCostAndReserveAxis
= us-gaap_EmployeeSeveranceMember 		      11,600,000us-gaap_AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent
/ us-gaap_RestructuringCostAndReserveAxis
= us-gaap_EmployeeSeveranceMember
Messr Lefkowitz [Member]          
Commitments And Contingencies [Line Items]          
Severance benefits 3,400,000us-gaap_SeveranceCosts1
/ us-gaap_TitleOfIndividualAxis
= cli_MessieurLefkowitzMember 		       
Stock options vested 11,457us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares
/ us-gaap_TitleOfIndividualAxis
= cli_MessieurLefkowitzMember 		       
Restricted stock units vested 68,667us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
/ us-gaap_TitleOfIndividualAxis
= cli_MessieurLefkowitzMember 		       
Period for continuation of health insurance 48 months        
Messr Thomas [Member]          
Commitments And Contingencies [Line Items]          
Severance benefits 3,100,000us-gaap_SeveranceCosts1
/ us-gaap_TitleOfIndividualAxis
= cli_MessieurThomasMember 		       
Stock options vested 33,605us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares
/ us-gaap_TitleOfIndividualAxis
= cli_MessieurThomasMember 		       
Restricted stock units vested 41,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
/ us-gaap_TitleOfIndividualAxis
= cli_MessieurThomasMember 		       
Period for continuation of health insurance 48 months        
Consulting payment     300,000us-gaap_ProfessionalFees
/ us-gaap_TitleOfIndividualAxis
= cli_MessieurThomasMember 		   
Scenario, Forecast [Member] | Messr Hersh [Member]          
Commitments And Contingencies [Line Items]          
Severance benefits       8,000,000us-gaap_SeveranceCosts1
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember
/ us-gaap_TitleOfIndividualAxis
= cli_MessieurHershMember 		 
Restricted stock units vested       210,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember
/ us-gaap_TitleOfIndividualAxis
= cli_MessieurHershMember 		 
Period for continuation of health insurance       48 months  
Cash payment       504,000cli_EmployeeTerminationAgreementCashPayment
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember
/ us-gaap_TitleOfIndividualAxis
= cli_MessieurHershMember 		 
Termination payment multiplier       210,000cli_EmployeeTerminationAgreementMultiplier
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember
/ us-gaap_TitleOfIndividualAxis
= cli_MessieurHershMember 		 
Shares issued       41,811us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember
/ us-gaap_TitleOfIndividualAxis
= cli_MessieurHershMember 		 
Deferred retirement compensation contribution       $ 2,311,792cli_EmployeeTerminationAgreementDeferredRetirementCompensationContribution
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember
/ us-gaap_TitleOfIndividualAxis
= cli_MessieurHershMember 		 
Total Stockholder Return Based Awards [Member]          
Commitments And Contingencies [Line Items]          
Restricted stock units vested 357us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
/ us-gaap_AwardTypeAxis
= cli_TotalStockholderReturnBasedAwardsMember 		       
Shares issued 45,062us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross
/ us-gaap_AwardTypeAxis
= cli_TotalStockholderReturnBasedAwardsMember 		       
Total Stockholder Return Based Awards [Member] | Scenario, Forecast [Member]          
Commitments And Contingencies [Line Items]          
Restricted stock units vested       675us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
/ us-gaap_AwardTypeAxis
= cli_TotalStockholderReturnBasedAwardsMember
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember 		 
Shares issued       41,811us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross
/ us-gaap_AwardTypeAxis
= cli_TotalStockholderReturnBasedAwardsMember
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember 		 
Total Stockholder Return Based Awards [Member] | Scenario, Forecast [Member] | Messr Hersh [Member]          
Commitments And Contingencies [Line Items]          
Restricted stock units vested       675us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
/ us-gaap_AwardTypeAxis
= cli_TotalStockholderReturnBasedAwardsMember
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember
/ us-gaap_TitleOfIndividualAxis
= cli_MessieurHershMember