Prepaid Expenses And Other Current Assets (Schedule Of Prepaid Expense And Other Current Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Prepaid Expenses And Other Current Assets [Abstract]
Prepaid ground rent	$ 32,505	$ 33,975
Other	17,211	18,230
Total prepaid expenses and other current assets	$ 49,716	$ 52,205