Significant Accounting Policies (Schedule Of Rental Property Improvements) (Details) - USD ($) $ in Thousands |
9 Months Ended | 12 Months Ended |
|---|---|---|
Sep. 30, 2020 |
Dec. 31, 2019 |
|
| Property, Plant and Equipment [Line Items] | ||
| Land held for development (including pre-development costs, if any) | $ 356,017 | $ 388,702 |
| Development and construction in progress, including land | 683,303 | 464,110 |
| Total | 1,039,320 | 852,812 |
| Buildings and improvement | 147,700 | 156,500 |
| Development [Member] | ||
| Property, Plant and Equipment [Line Items] | ||
| Land | 84,000 | $ 96,600 |
| Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | ||
| Property, Plant and Equipment [Line Items] | ||
| Buildings and improvement | 9,700 | |
| Land | 35,500 | |
| Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Development [Member] | ||
| Property, Plant and Equipment [Line Items] | ||
| Buildings and improvement | 1,000 | |
| Land | $ 500 |