Mortgages, Loans Payable And Other Obligations (Narrative) (Details)
12 Months Ended
Dec. 31, 2017
USD ($)
property
item
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Debt Instrument [Line Items]      
Cash paid for interest $ 103,559,000 $ 122,414,000 $ 115,123,000
Interest capitalized 20,240,000 19,316,000 16,217,000
Total indebtedness 2,809,568,000    
Adjusted total indebtedness $ 2,826,110,000 $ 2,357,055,000  
Total indebtedness, weighted average interest rate 3.93% 3.79%  
Projects Under Development And Developable Land [Member]      
Debt Instrument [Line Items]      
Number of projects with encumbered company mortgages | item 5    
Carrying value of encumbered properties $ 435,000,000    
Other Property [Member]      
Debt Instrument [Line Items]      
Number of properties with encumbered company mortgages | property 15    
Carrying value of encumbered properties $ 1,600,000,000    
Unconsolidated Joint Venture [Member]      
Debt Instrument [Line Items]      
Interest capitalized 1,056,000 $ 5,055,000 $ 5,325,000
Revolving Credit Facility Borrowing And Other Variable Rate Mortgage Debt [Member]      
Debt Instrument [Line Items]      
Total indebtedness $ 382,443,000 $ 481,282,000  
Total indebtedness, weighted average interest rate 3.63% 2.93%  
Fixed Rate Debt And Other Obligations [Member]      
Debt Instrument [Line Items]      
Total indebtedness $ 2,443,667,000 $ 1,875,773,000  
Total indebtedness, weighted average interest rate 3.98% 4.01%