Annual report pursuant to Section 13 and 15(d)

Significant Accounting Policies (Narrative) (Details)

v2.4.1.9
Significant Accounting Policies (Narrative) (Details) (USD $)
 3 Months Ended 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Jan. 06, 2014
Dec. 31, 2011
Jan. 06, 2015
Significant Accounting Policies [Line Items]                
Capitalized development and construction salaries and other related costs     $ 3,100,000cli_CapitalizedDevelopmentConstructionSalariesAndOtherRelatedExpenses $ 4,400,000cli_CapitalizedDevelopmentConstructionSalariesAndOtherRelatedExpenses $ 3,800,000cli_CapitalizedDevelopmentConstructionSalariesAndOtherRelatedExpenses      
Construction, tenant improvement, and development in-progress 62,800,000us-gaap_ConstructionInProgressGross 40,800,000us-gaap_ConstructionInProgressGross 62,800,000us-gaap_ConstructionInProgressGross 40,800,000us-gaap_ConstructionInProgressGross        
Maximum period after cessation of major construction activity that projects are considered complete     1 year          
Threshold of investment value for discontinuation of equity method accounting 0cli_ThresholdOfInvestmentValueForDiscontinuationOfEquityMethodAccounting   0cli_ThresholdOfInvestmentValueForDiscontinuationOfEquityMethodAccounting          
Amortization of deferred financing costs     3,274,000us-gaap_AmortizationOfFinancingCosts 3,172,000us-gaap_AmortizationOfFinancingCosts 2,669,000us-gaap_AmortizationOfFinancingCosts      
Writeoff of unamortized deferred financing costs     12,000us-gaap_WriteOffOfDeferredDebtIssuanceCost 156,000us-gaap_WriteOffOfDeferredDebtIssuanceCost 593,000us-gaap_WriteOffOfDeferredDebtIssuanceCost      
Deferred leasing costs     3,840,000us-gaap_AmortizationOfDeferredLeasingFees 4,223,000us-gaap_AmortizationOfDeferredLeasingFees 4,354,000us-gaap_AmortizationOfDeferredLeasingFees      
Deferred tax asset 14,400,000us-gaap_DeferredTaxAssetsValuationAllowance   14,400,000us-gaap_DeferredTaxAssetsValuationAllowance          
Income taxes, material adjustment amount     0cli_MaterialAdjustmentAmount          
Common stock, shares outstanding 89,076,578us-gaap_CommonStockSharesOutstanding 88,247,591us-gaap_CommonStockSharesOutstanding 89,076,578us-gaap_CommonStockSharesOutstanding 88,247,591us-gaap_CommonStockSharesOutstanding   87,928,002us-gaap_CommonStockSharesOutstanding    
Common units outstanding 11,083,876cli_CommonUnitsOutstanding 11,864,775cli_CommonUnitsOutstanding 11,083,876cli_CommonUnitsOutstanding 11,864,775cli_CommonUnitsOutstanding 12,141,836cli_CommonUnitsOutstanding 11,864,775cli_CommonUnitsOutstanding 12,197,122cli_CommonUnitsOutstanding  
Distributions payable, record date Jan. 06, 2015 Jan. 06, 2014            
Common stock dividends and common unit distributions per share $ 0.15cli_CommonStockDividendsAndCommonUnitDistributionsPerShare $ 0.30cli_CommonStockDividendsAndCommonUnitDistributionsPerShare            
Dividends paid per common share     $ 0.90us-gaap_CommonStockDividendsPerShareCashPaid $ 1.50us-gaap_CommonStockDividendsPerShareCashPaid $ 1.80us-gaap_CommonStockDividendsPerShareCashPaid      
Dividends paid, percent representing ordinary income     77.00%cli_CommonStockDividendsPerSharePaidPercentRepresentingOrdinaryIncome 53.00%cli_CommonStockDividendsPerSharePaidPercentRepresentingOrdinaryIncome 75.00%cli_CommonStockDividendsPerSharePaidPercentRepresentingOrdinaryIncome      
Dividends paid, percent representing return of capital to shareholders     23.00%cli_CommonStockDividendsPerSharePaidPercentRepresentingReturnOfCapitalToStockholders 33.00%cli_CommonStockDividendsPerSharePaidPercentRepresentingReturnOfCapitalToStockholders 25.00%cli_CommonStockDividendsPerSharePaidPercentRepresentingReturnOfCapitalToStockholders      
Dividends paid, percent representing capital gain       14.00%cli_CommonStockDividendsPerSharePaidPercentRepresentingCapitalGain        
Restricted stock expense     8,139,000us-gaap_RestrictedStockExpense 2,387,000us-gaap_RestrictedStockExpense 3,642,000us-gaap_RestrictedStockExpense      
Common stock dividends and common unit distributions payable, date Jan. 14, 2015 Jan. 15, 2014            
Difference between other comprehensive income and net income     0cli_DifferenceBetweenOtherComprehensiveIncomeAndNetIncomeLoss 0cli_DifferenceBetweenOtherComprehensiveIncomeAndNetIncomeLoss 0cli_DifferenceBetweenOtherComprehensiveIncomeAndNetIncomeLoss      
Accumulated other comprehensive income 0us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax 0us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax 0us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax 0us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax        
Executive Officer [Member]                
Significant Accounting Policies [Line Items]                
Restricted stock expense     $ 5,824,000us-gaap_RestrictedStockExpense
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= us-gaap_ExecutiveOfficerMember 		         
Subsequent Event [Member]                
Significant Accounting Policies [Line Items]                
Common stock, shares outstanding               88,866,652us-gaap_CommonStockSharesOutstanding
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Common units outstanding               11,083,876cli_CommonUnitsOutstanding
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