Investments In Unconsolidated Joint Ventures (Narrative) (Details)
$ in Thousands, ft² in Millions
 3 Months Ended
Mar. 31, 2016
USD ($)
ft²
property
item
Mar. 31, 2015
USD ($)
Dec. 31, 2015
USD ($)
Oct. 06, 2015
Schedule of Equity Method Investments [Line Items]        
Company's investments in unconsolidated joint ventures, net $ 303,647   $ 303,457  
Amount outstanding 90,000   155,000  
Management, leasing, development and other services fees 1,000 $ 1,600    
Accounts receivable due from unconsolidated joint ventures 700   $ 800  
Maximum exposure to loss 210,800      
Estimated future funding commitments 33,700      
Mortgage loan 1,823,311      
Proceeds from mortgages and loans payable $ 77,666 $ 1,150    
Unconsolidated Joint Venture Office Buildings [Member]        
Schedule of Equity Method Investments [Line Items]        
Number of properties | property 36      
Unconsolidated Joint Venture Office And Retail Buildings [Member]        
Schedule of Equity Method Investments [Line Items]        
Area of property (in square feet) | ft² 5.7      
Unconsolidated Joint Venture Retail Buildings [Member]        
Schedule of Equity Method Investments [Line Items]        
Number of properties | property 2      
Unconsolidated Joint Venture Multi-Family Properties [Member]        
Schedule of Equity Method Investments [Line Items]        
Number of properties | property 12      
Number of units | item 3,972      
Unconsolidated Joint Venture Hotel [Member]        
Schedule of Equity Method Investments [Line Items]        
Number of units | item 350      
Percentage of interest in venture       90.00%
Development costs $ 4,700      
Unconsolidated Joint Venture Development Projects [Member]        
Schedule of Equity Method Investments [Line Items]        
Number of units | item 1,074      
Unconsolidated Joint Venture Land Parcels [Member]        
Schedule of Equity Method Investments [Line Items]        
Number of units | item 2,910      
Unconsolidated Joint Ventures [Member] | Guarantee of Indebtedness of Others [Member]        
Schedule of Equity Method Investments [Line Items]        
Maximum borrowing capacity $ 492,100      
Amount outstanding 286,700      
Unconsolidated Joint Ventures [Member] | Parent Company [Member] | Guarantee of Indebtedness of Others [Member]        
Schedule of Equity Method Investments [Line Items]        
Maximum borrowing capacity 66,300      
Amount outstanding $ 44,800      
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]        
Company's investments in unconsolidated joint ventures, net $ 177,100      
Number of VIEs | property 5      
Office [Member] | Unconsolidated Joint Venture Land Parcels [Member]        
Schedule of Equity Method Investments [Line Items]        
Area of property (in square feet) | ft² 1.4      
South Pier At Harborside [Member]        
Schedule of Equity Method Investments [Line Items]        
Company's investments in unconsolidated joint ventures, net [1]      
Number of units | item 350      
Percentage of interest in venture [2] 50.00%      
Letter of credit $ 3,600      
Mortgage loan [3] $ 63,384      
[1] The negative carrying value for this venture of $4,235 and $3,317 as of March 31, 2016 and 2015, 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.
[3] Balance includes: (i) mortgage loan, collateralized by the hotel property, with a balance of $59,790, bears interest at 6.15 percent and matures in November 2016, and (ii) loan with a balance of $3,594, bears interest at fixed rates ranging from 6.09 percent to 6.62 percent and matures in August 1, 2020. The Company posted a $3.6 million letter of credit in support of this loan, half of which is indemnified by the partner.