Quarterly report pursuant to Section 13 or 15(d)

Discontinued Operations (Narrative) (Details)

v3.20.2
Discontinued Operations (Narrative) (Details)
 1 Months Ended 3 Months Ended 9 Months Ended 21 Months Ended
Oct. 31, 2020
USD ($)
ft²
property
Sep. 30, 2020
USD ($)
ft²
property
Sep. 30, 2019
USD ($)
Sep. 30, 2020
USD ($)
ft²
item
property
Sep. 30, 2019
USD ($)
Sep. 30, 2020
USD ($)
ft²
property
Dec. 19, 2019
ft²
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]              
Unrealized losses on disposition of rental property     $ (10,063,000) $ (33,314,000) $ (15,865,000)    
Suburban Office Portfolio [Member]              
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]              
Area of property (in square feet) | ft²             6,600,000
Four Disposal Group [Member]              
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]              
Number of disposal groups | item       5      
Properties | property       10      
Unrealized losses on disposition of rental property   $ 0   $ 33,300,000      
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Suburban Office Portfolio [Member]              
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]              
Number of disposal groups | item       12      
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Properties Disposed One [Member] | Suburban Office Portfolio [Member]              
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]              
Number of real estate properties | property   21   21   21  
Area of property (in square feet) | ft²   4,000,000   4,000,000   4,000,000  
Disposal Group, Not Discontinued Operations [Member]              
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]              
Number of properties sold | item       14      
Sales proceeds       $ 242,645,000      
Gain (loss) on sale of property       $ 9,414,000      
Disposal Group, Not Discontinued Operations [Member] | Suburban Office Portfolio [Member]              
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]              
Number of properties sold | property           16  
Sales proceeds           $ 294,800,000  
Area of property (in square feet) | ft²   2,600,000   2,600,000   2,600,000  
Disposal Group, Not Discontinued Operations [Member] | Properties Disposed Two [Member] | Suburban Office Portfolio [Member]              
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]              
Number of real estate properties | property   10   10   10  
Area of property (in square feet) | ft²   1,900,000   1,900,000   1,900,000  
Gain (loss) on sale of property       $ 407,500,000      
Subsequent Event [Member] | Disposal Group, Not Discontinued Operations [Member] | Properties Disposed Three [Member] | Suburban Office Portfolio [Member]              
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]              
Number of properties sold | property 1            
Area of property (in square feet) | ft² 98,500            
Gain (loss) on sale of property $ 7,500,000