Quarterly report pursuant to Section 13 or 15(d)

Organization And Basis Of Presentation (Details)

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Organization And Basis Of Presentation (Details)
$ in Millions
 3 Months Ended
Mar. 31, 2018
USD ($)
ft²
state
property
item
Dec. 31, 2017
USD ($)
Real Estate Properties [Line Items]    
Percentage of ownership interest 89.80% 89.60%
Number of properties owned or investment interests 138  
Aggregate square feet of the property owned or investment interest | ft² 16,000,000  
Number of units | item 365  
Number of states where properties are located | state 6  
Consolidated joint ventures, total real estate assets | $ $ 229.1 $ 215.5
Consolidated joint ventures, mortgages | $ 88.4 81.2
Consolidated joint ventures, other liabilities | $ $ 25.2 $ 19.3
Commercial Properties [Member]    
Real Estate Properties [Line Items]    
Number of tenants | item 750  
Multi-Family Properties [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 18  
Number of units | item 5,826  
Office And Office/Flex Buildings [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 47  
Office [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 59  
Aggregate square feet of the property owned or investment interest | ft² 12,800,000  
Office Flex Buildings [Member]    
Real Estate Properties [Line Items]    
Aggregate square feet of the property owned or investment interest | ft² 2,700,000  
Flex Properties [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 61  
Unconsolidated Joint Venture Office Buildings [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 4  
Aggregate square feet of the property owned or investment interest | ft² 500,000  
Industrial/Warehouse Facilities [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 6  
Aggregate square feet of the property owned or investment interest | ft² 387,400  
Unconsolidated Joint Venture Multi-Family Properties [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 8  
Number of units | item 3,275  
Unconsolidated Joint Venture Office/Flex Buildings And Hotel [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 1  
Parking/Retail [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 6  
Aggregate square feet of the property owned or investment interest | ft² 137,100  
Unconsolidated Joint Venture Parking/Retail Buildings [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 2  
Aggregate square feet of the property owned or investment interest | ft² 81,700  
Land [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 1