Significant Accounting Policies (Schedule Of Rental Property Improvements) (Details) - USD ($) $ in Thousands |
6 Months Ended | 12 Months Ended |
|---|---|---|
Jun. 30, 2018 |
Dec. 31, 2017 |
|
| Property, Plant and Equipment [Line Items] | ||
| Land held for development (including pre-development costs, if any) | $ 498,701 | $ 483,432 |
| Development and construction in progress, including land | 506,117 | 535,971 |
| Total | 1,004,818 | 1,019,403 |
| Buildings and improvement | 204,000 | 188,100 |
| Development [Member] | ||
| Property, Plant and Equipment [Line Items] | ||
| Land | $ 71,700 | $ 77,000 |