Annual report pursuant to Section 13 and 15(d)

Organization And Basis Of Presentation (Details)

v3.8.0.1
Organization And Basis Of Presentation (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2017
USD ($)
ft²
state
property
item
Dec. 31, 2016
USD ($)
Real Estate Properties [Line Items]    
Percentage of ownership interest 89.60% 89.50%
Number of properties owned or investment interests 157  
Aggregate square feet of the property owned or investment interest | ft² 17,700,000  
Number of states where properties are located | state 6  
Consolidated joint ventures, total real estate assets | $ $ 215.5 $ 201.9
Consolidated joint ventures, mortgages | $ 81.2 78.4
Consolidated joint ventures, other liabilities | $ $ 19.3 $ 19.2
Commercial Properties [Member]    
Real Estate Properties [Line Items]    
Number of tenants | item 900  
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 56  
Aggregate square feet of the property owned or investment interest | ft² 3,100,000  
Office [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 69  
Aggregate square feet of the property owned or investment interest | ft² 14,100,000  
Flex Properties [Member]    
Real Estate Properties [Line Items]    
Number of properties owned or investment interests 70  
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