Annual report pursuant to Section 13 and 15(d)

Real Estate Transactions (Impairments On Properties Held and Used) (Narrative) (Details)

v2.4.1.9
Real Estate Transactions (Impairments On Properties Held and Used) (Narrative) (Details) (USD $)
 3 Months Ended 12 Months Ended
Dec. 31, 2013
Sep. 30, 2013
Dec. 31, 2013
property
Dec. 31, 2012
Dec. 31, 2014
property
sqft
Impairments $ 62,153,000us-gaap_AssetImpairmentCharges [1],[2] $ 48,700,000us-gaap_AssetImpairmentCharges [1] $ 110,853,000us-gaap_AssetImpairmentCharges $ 9,845,000us-gaap_AssetImpairmentCharges  
Number of impaired properties     18cli_NumberOfImpairedRealEstateProperties    
Mortgage loan 746,191,000us-gaap_SecuredDebt   746,191,000us-gaap_SecuredDebt   820,910,000us-gaap_SecuredDebt
Capitalization rate     8.50%cli_FairValueInputsCapitalizationRate    
Minimum [Member]          
Discount rate     10.00%us-gaap_FairValueInputsDiscountRate
/ us-gaap_RangeAxis
= us-gaap_MinimumMember 		   
Maximum [Member]          
Discount rate     15.00%us-gaap_FairValueInputsDiscountRate
/ us-gaap_RangeAxis
= us-gaap_MaximumMember 		   
Roseland, Parsippany, Warren And Lyndhurst, New Jersey [Member]          
Number of impaired properties     9cli_NumberOfImpairedRealEstateProperties
/ us-gaap_StatementGeographicalAxis
= cli_RoselandParsippanyWarrenAndLyndhurstNewJerseyMember 		   
Area of property (in square feet) 1,300,000us-gaap_AreaOfRealEstateProperty
/ us-gaap_StatementGeographicalAxis
= cli_RoselandParsippanyWarrenAndLyndhurstNewJerseyMember 		  1,300,000us-gaap_AreaOfRealEstateProperty
/ us-gaap_StatementGeographicalAxis
= cli_RoselandParsippanyWarrenAndLyndhurstNewJerseyMember 		   
Mortgage loan 160,000,000us-gaap_SecuredDebt
/ us-gaap_StatementGeographicalAxis
= cli_RoselandParsippanyWarrenAndLyndhurstNewJerseyMember 		  160,000,000us-gaap_SecuredDebt
/ us-gaap_StatementGeographicalAxis
= cli_RoselandParsippanyWarrenAndLyndhurstNewJerseyMember 		   
Fair Lawn, New Jersey, Woodcliff Lake, New Jersey, Stamford Connecticut, And Elmsford, New York [Member]          
Area of property (in square feet)         646,000us-gaap_AreaOfRealEstateProperty
/ us-gaap_StatementGeographicalAxis
= cli_FairLawnNewJerseyWoodcliffLakeNewJerseyStamfordConnecticutAndElmsfordNewYorkMember
Number of properties sold         7cli_NumberOfPropertiesSold
/ us-gaap_StatementGeographicalAxis
= cli_FairLawnNewJerseyWoodcliffLakeNewJerseyStamfordConnecticutAndElmsfordNewYorkMember
Morris Plains And Upper Saddle River, New Jersey [Member]          
Area of property (in square feet)         550,000us-gaap_AreaOfRealEstateProperty
/ us-gaap_StatementGeographicalAxis
= cli_MorrisPlainsAndUpperSaddleRiverNewJerseyMember
Number of impaired properties being considered for repositioning         2cli_NumberOfImpairedPropertiesBeingConsideredForRepositioning
/ us-gaap_StatementGeographicalAxis
= cli_MorrisPlainsAndUpperSaddleRiverNewJerseyMember
Keystone Portfolio [Member]          
Impairments     $ 20,800,000us-gaap_AssetImpairmentCharges
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= cli_KeystonePortfolioMember 		   
Keystone Portfolio [Member] | Fair Lawn, New Jersey, Woodcliff Lake, New Jersey, Stamford Connecticut, And Elmsford, New York [Member]          
Number of properties sold         6cli_NumberOfPropertiesSold
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= cli_KeystonePortfolioMember
/ us-gaap_StatementGeographicalAxis
= cli_FairLawnNewJerseyWoodcliffLakeNewJerseyStamfordConnecticutAndElmsfordNewYorkMember
[1] Amounts for the year ended December 31, 2013 relate to impairment charges as further described in Note 3: Real Estate Transactions - Impairments on Properties Held and Used.
[2] During the quarter ended December 31, 2013, the Company identified and recorded an out-of-period adjustment to reflect a charge of $1,260,000 to correct an error in the measurement of its impairment charges on certain properties in the third quarter of 2013. In the third quarter, in measuring the impairments on these properties, the Company did not include certain tenant improvement amounts to be paid for in-place leases in its discounted cash flows used to measure fair value and, as a result, should have recognized larger impairment charges by this aggregate amount. The Company has determined that this adjustment was not material to the quarter ended December 31, 2013 or the prior interim period.