Significant Accounting Policies (Schedule Of Rental Property Improvements) (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Property, Plant and Equipment [Line Items]    
Land held for development (including pre-development costs, if any) [1] $ 492,754 $ 483,432
Development and construction in progress, including land [2] 573,030 535,971
Total 1,065,784 1,019,403
Buildings and improvement 197,500 188,100
Land 784,619 786,789
Development [Member]    
Property, Plant and Equipment [Line Items]    
Land $ 72,600 $ 77,000
[1] Includes predevelopment and infrastructure costs included in buildings and improvements of $197.5 million and $188.1 million as of March 31, 2018 and December 31, 2017, respectively.
[2] Includes land of $72.6 million and $77.0 million as of March 31, 2018 and December 31, 2017, respectively.