Quarterly report pursuant to Section 13 or 15(d)

Recent Transactions (Impairments) (Narrative) (Details)

v3.19.3
Recent Transactions (Impairments) (Narrative) (Details)
$ in Thousands
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2019
USD ($)
ft²
property
Jun. 30, 2019
USD ($)
ft²
Sep. 30, 2019
USD ($)
ft²
property
Dec. 31, 2018
USD ($)
property
Real Estate Properties [Line Items]        
Property impairments $ 5,894   $ 11,696  
Land and other Impairments $ 6,345   8,844  
Property And Undeveloped Land [Member]        
Real Estate Properties [Line Items]        
Property impairments     5,900  
Land and other Impairments     $ 6,100  
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Parsippany [Member]        
Real Estate Properties [Line Items]        
Area of property (in square feet) | ft² 317,040 317,040 317,040  
Valuation impairment charge   $ 5,800    
Conshohocken And Bala Cynwyd, Pennsylvania [Member]        
Real Estate Properties [Line Items]        
Number of real estate properties | property 2   2 2
Land and other Impairments $ 200   $ 2,700  
Conshohocken And Bala Cynwyd, Pennsylvania [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]        
Real Estate Properties [Line Items]        
Land and other Impairments       $ 24,600