Quarterly report pursuant to Section 13 or 15(d)

Investments In Unconsolidated Joint Ventures (Summary Of Company's Equity In Earnings (Loss) Of Unconsolidated Joint Ventures) (Details)

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Investments In Unconsolidated Joint Ventures (Summary Of Company's Equity In Earnings (Loss) Of Unconsolidated Joint Ventures) (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures $ (3,529)us-gaap_IncomeLossFromEquityMethodInvestments $ (1,235)us-gaap_IncomeLossFromEquityMethodInvestments
Marbella RoseGarden, L.L.C. [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures 61us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_MarbellaRoseGardenLLCMember
(6)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_MarbellaRoseGardenLLCMember
RoseGarden Monaco Holdings, L.L.C. [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures (317)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoseGardenMonacoHoldingsLLCMember
(277)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoseGardenMonacoHoldingsLLCMember
Rosewood Lafayette Holdings, L.L.C. [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures (62)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodLafayetteHoldingsLLCMember
(216)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodLafayetteHoldingsLLCMember
Rosewood Morristown, L.L.C. [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures (94)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
(98)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RosewoodMorristownLLCMember
Overlook Ridge JV 2C/3B, L.L.C. [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures (220)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OverlookRidgeJvTwoCAndThreeBLLCMember
62us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OverlookRidgeJvTwoCAndThreeBLLCMember
PruRose Riverwalk G, L.L.C. [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures (254)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PruRoseRiverwalkGLLCMember
(538)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PruRoseRiverwalkGLLCMember
Elmajo Urban Renewal Associates, L.L.C. [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures   (112)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_ElmajoUrbanRenewalAssociatesLLCMember
Crystal House Apartments Investors LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures (10)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CrystalHouseApartmentsInvestorsLLCMember
(327)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CrystalHouseApartmentsInvestorsLLCMember
Portside Master Company, L.L.C. [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures (719)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PortsideMasterCompanyLLCMember
(213)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PortsideMasterCompanyLLCMember
PruRose Port Imperial South 13, L.L.C. [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures (225)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PruRosePortImperialSouthThirteenLLCMember
(206)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PruRosePortImperialSouthThirteenLLCMember
Roseland/Port Imperial Partners, L.P. [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures (184)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoselandPortImperialPartnersLPMember
(164)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoselandPortImperialPartnersLPMember
Estuary Urban Renewal Unit B, LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures   (15)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_EstuaryUrbanRenewalUnitBLLCMember
RiverPark At Harrison I, L.L.C. [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures (173)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RiverparkAtHarrisonILLCMember
 
Capitol Place Mezz LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures 75us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_CapitolPlaceMezzLlcMember
 
Grand Jersey Waterfront Urban Renewal Associates, L.L.C. [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures (19)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_GrandJerseyWaterfrontUrbanRenewalAssociatesLLCMember
(37)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_GrandJerseyWaterfrontUrbanRenewalAssociatesLLCMember
Red Bank Corporate Plaza, L.L.C. [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures 110us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RedBankCorporatePlazaLLCMember
99us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RedBankCorporatePlazaLLCMember
12 Vreeland Associates, L.L.C. [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures (14)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_TwelveVreelandAssociatesLLCMember
89us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_TwelveVreelandAssociatesLLCMember
BNES Associates III [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures 68us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_BNESAssociatesIIIMember
36us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_BNESAssociatesIIIMember
Hillsborough 206 Holdings, L.L.C. [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures   (5)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_HillsboroughTwoHundredSixHoldingsLLCMember
KPG-P 100 IMW JV, LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures (384)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgPOneHundredImwJvLlcMember
(653)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgPOneHundredImwJvLlcMember
Keystone-TriState [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures (1,348)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KeystoneTristateMember
 
KPG-MCG Curtis JV, LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures 196us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_KpgMcgCurtisJvLLCMember
 
Plaza VIII & IX Associates, L.L.C. [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures 86us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PlazaEightAndNineAssociatesLLCMember
102us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_PlazaEightAndNineAssociatesLLCMember
Roseland/North Retail, L.L.C. [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures (18)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoselandNorthRetailLLCMember
(24)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_RoselandNorthRetailLLCMember
South Pier At Harborside [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures (84)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_SouthPierAtHarborsideMember
398us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_SouthPierAtHarborsideMember
Stamford SM LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures   916us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_StamfordSmLlcMember
Other [Member]    
Schedule of Equity Method Investments [Line Items]    
Company's equity in earnings (loss) of unconsolidated joint ventures   $ (46)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cli_OtherJointVenturesMember