Prepaid Expenses and Other Current Assets and Other Assets (Schedule of Prepaid Expense and Other Current Assets) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Prepaid Expenses and Other Current Assets and Other Assets [Abstract]
Prepaid ground rent	$ 31,257	$ 32,505
Other	19,659	17,211
Total prepaid expenses and other current assets	$ 50,916	$ 49,716