Investments In Unconsolidated Joint Ventures (Narrative) (Details) (USD $)
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]      
Investments in unconsolidated joint ventures $ 262,052,000   $ 247,468,000
Amount outstanding 42,000,000   0
Management, leasing, development and other services fees 1,600,000 504,000  
Accounts receivable due from unconsolidated joint ventures 1,200,000   1,000,000
Maximum exposure to loss 206,400,000    
Estimated future funding commitments 76,600,000    
Unconsolidated Joint Venture Office Buildings [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of properties 36    
Unconsolidated Joint Venture Office And Retail Buildings [Member]      
Schedule of Equity Method Investments [Line Items]      
Area of property (in square feet) 5,700,000    
Unconsolidated Joint Venture Retail Buildings [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of properties 2    
Unconsolidated Joint Venture Multi-Family Properties [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of properties 14    
Number of units 4,560    
Unconsolidated Joint Venture Hotel [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of units 350    
Unconsolidated Joint Venture Development Projects [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of units 1,354    
Unconsolidated Joint Venture Land Parcels [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of units 2,853    
Unconsolidated Joint Ventures [Member] | Guarantee of Indebtedness of Others [Member]      
Schedule of Equity Method Investments [Line Items]      
Maximum borrowing capacity 477,000,000    
Amount outstanding 250,700,000    
Unconsolidated Joint Ventures [Member] | Parent Company [Member] | Guarantee of Indebtedness of Others [Member]      
Schedule of Equity Method Investments [Line Items]      
Maximum borrowing capacity 82,800,000    
Amount outstanding 51,900,000    
Minimum [Member]      
Schedule of Equity Method Investments [Line Items]      
Percentage of interest in venture 7.50%    
Maximum [Member]      
Schedule of Equity Method Investments [Line Items]      
Percentage of interest in venture 85.00%    
Variable Interest Entity [Member]      
Schedule of Equity Method Investments [Line Items]      
Investments in unconsolidated joint ventures 129,800,000    
Number of VIEs 9    
Office [Member] | Unconsolidated Joint Venture Land Parcels [Member]      
Schedule of Equity Method Investments [Line Items]      
Area of property (in square feet) 1,400,000    
South Pier At Harborside [Member]      
Schedule of Equity Method Investments [Line Items]      
Investments in unconsolidated joint ventures    [1]    
Number of units 350    
Percentage of interest in venture 50.00% [2]    
Letter of credit $ 4,100,000    
[1] The negative carrying amount for this venture of $1,937 and $1,854 as of March 31, 2015 and December 31, 2014, respectively, were included in accounts payable, accrued expenses and other liabilities.
[2] Company's effective ownership % represents the Company's entitlement to residual distributions after payments of priority returns, where applicable.