Recent Transactions (Impairments) (Narrative) (Details) $ in Thousands |
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
|
|
| Real Estate Properties [Line Items] | |||
| Land impairments | $ 2,499 | $ 2,499 | |
| 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 | |
| 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 |
| Conshohocken And Bala Cynwyd, Pennsylvania [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | |||
| Real Estate Properties [Line Items] | |||
| Land impairments | $ 24,600 |