Annual report pursuant to Section 13 and 15(d)

Real Estate Investments And Accumulated Depreciation (Schedule Of Changes In Rental Properties And Accumulated Depreciation) (Details)

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Real Estate Investments And Accumulated Depreciation (Schedule Of Changes In Rental Properties And Accumulated Depreciation) (Details) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Real Estate Investments And Accumulated Depreciation [Abstract]      
Rental Properties, Balance at beginning of year $ 5,129,933us-gaap_RealEstateGrossAtCarryingValue $ 5,379,436us-gaap_RealEstateGrossAtCarryingValue $ 5,279,770us-gaap_RealEstateGrossAtCarryingValue
Rental Properties, Additions 193,005us-gaap_RealEstateOtherAdditions 317,994us-gaap_RealEstateOtherAdditions 296,079us-gaap_RealEstateOtherAdditions
Rental Properties, Rental property held for sale   (107,205)cli_RealEstateCostOfRealEstateHeldForSale (84,716)cli_RealEstateCostOfRealEstateHeldForSale
Rental Properties, Properties sold (331,181)us-gaap_RealEstateCostOfRealEstateSold (256,335)us-gaap_RealEstateCostOfRealEstateSold (34,563)us-gaap_RealEstateCostOfRealEstateSold
Rental Properties, Impairment charge   (149,030)us-gaap_RealEstateOtherDeductions (20,573)us-gaap_RealEstateOtherDeductions
Rental Properties, Retirements/disposals (33,578)cli_RealEstateRetirementsOrDisposals (54,927)cli_RealEstateRetirementsOrDisposals (56,561)cli_RealEstateRetirementsOrDisposals
Rental Properties, Balance at end of year 4,958,179us-gaap_RealEstateGrossAtCarryingValue 5,129,933us-gaap_RealEstateGrossAtCarryingValue 5,379,436us-gaap_RealEstateGrossAtCarryingValue
Accumulated Depreciation, Balance at beginning of year 1,400,988us-gaap_RealEstateAccumulatedDepreciation 1,478,214us-gaap_RealEstateAccumulatedDepreciation 1,409,163us-gaap_RealEstateAccumulatedDepreciation
Accumulated Depreciation, Depreciation expense 143,278us-gaap_SECScheduleIIIRealEstateAccumulatedDepreciationDepreciationExpense 155,846us-gaap_SECScheduleIIIRealEstateAccumulatedDepreciationDepreciationExpense 157,175us-gaap_SECScheduleIIIRealEstateAccumulatedDepreciationDepreciationExpense
Accumulated Depreciation, Rental property held for sale   (35,594)cli_RealEstateAccumulatedDepreciationRealEstateHeldForSale (23,852)cli_RealEstateAccumulatedDepreciationRealEstateHeldForSale
Accumulated Depreciation, Properties sold (96,383)us-gaap_RealEstateAccumulatedDepreciationRealEstateSold (104,196)us-gaap_RealEstateAccumulatedDepreciationRealEstateSold (10,026)us-gaap_RealEstateAccumulatedDepreciationRealEstateSold
Accumulated Depreciation, Impairment charge   (38,353)us-gaap_RealEstateAccumulatedDepreciationOtherDeductions 2,058us-gaap_RealEstateAccumulatedDepreciationOtherDeductions
Accumulated Depreciation, Retirements/disposals (33,578)cli_RealEstateAccumulatedDepreciationRetirementsOrDisposals (54,929)cli_RealEstateAccumulatedDepreciationRetirementsOrDisposals (56,304)cli_RealEstateAccumulatedDepreciationRetirementsOrDisposals
Accumulated Depreciation, Balance at end of year $ 1,414,305us-gaap_RealEstateAccumulatedDepreciation $ 1,400,988us-gaap_RealEstateAccumulatedDepreciation $ 1,478,214us-gaap_RealEstateAccumulatedDepreciation