Quarterly report pursuant to Section 13 or 15(d)

Disclosure Of Fair Value Of Assets And Liabilities (Narrative) (Details)

v3.19.2
Disclosure Of Fair Value Of Assets And Liabilities (Narrative) (Details)
 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2019
USD ($)
ft²
property
Jun. 30, 2019
USD ($)
ft²
property
Dec. 31, 2018
USD ($)
property
Fair Value Measurement Inputs and Valuation Techniques [Line Items]      
Fair value of Company's long-term debt $ 2,638,850,000 $ 2,638,850,000 $ 2,711,712,000
Principal balance outstanding 2,687,642,000 2,687,642,000 $ 2,792,651,000
Land impairments $ 2,499,000 $ 2,499,000  
Conshohocken And Bala Cynwyd, Pennsylvania [Member]      
Fair Value Measurement Inputs and Valuation Techniques [Line Items]      
Number of real estate properties | property 2 2 2
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Conshohocken And Bala Cynwyd, Pennsylvania [Member]      
Fair Value Measurement Inputs and Valuation Techniques [Line Items]      
Land impairments     $ 24,600,000
Parsippany [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]      
Fair Value Measurement Inputs and Valuation Techniques [Line Items]      
Area of property (in square feet) | ft² 317,040 317,040  
Valuation impairment charge $ 5,800,000