Quarterly report pursuant to Section 13 or 15(d)

Real Estate Transactions (Narrative) (Details)

v2.4.1.9
Real Estate Transactions (Narrative) (Details) (USD $)
3 Months Ended 12 Months Ended 0 Months Ended
Mar. 31, 2015
property
Mar. 31, 2014
Dec. 31, 2014
property
Apr. 01, 2015
Real Estate Properties [Line Items]        
Purchase price of property $ 19,658,000us-gaap_PaymentsToAcquireAndDevelopRealEstate $ 14,600,000us-gaap_PaymentsToAcquireAndDevelopRealEstate    
Realized gains (losses) on disposition of rental property, net 144,000us-gaap_GainLossOnDispositionOfAssets      
Number of properties sold 1cli_NumberOfPropertiesSold   16cli_NumberOfPropertiesSold  
City Square Project [Member] | Subsequent Event [Member]        
Real Estate Properties [Line Items]        
Number of units       370us-gaap_NumberOfUnitsInRealEstateProperty
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_CitySquareProjectMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Purchase price of property       3,100,000us-gaap_PaymentsToAcquireAndDevelopRealEstate
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_CitySquareProjectMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Contingent consideration       1,250,000us-gaap_BusinessCombinationContingentConsiderationLiability
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_CitySquareProjectMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Minimum project start period       12 months
Total project costs       88,000,000cli_EstimatedCostOfProject
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_CitySquareProjectMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
1451 Metropolitan Drive [Member]        
Real Estate Properties [Line Items]        
Area of property (in square feet) 21,600us-gaap_AreaOfRealEstateProperty
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_OneThousandFourHundredFiftyOneMetropolitanDriveMember
     
Sales proceeds $ 1,100,000us-gaap_ProceedsFromSaleOfRealEstateHeldforinvestment
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= cli_OneThousandFourHundredFiftyOneMetropolitanDriveMember