Identified Intangible Assets and Liabilities (Schedule of Identified Intangible Assets and Intangible Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Gross amount	$ 112,534	$ 116,969
Accumulated amortization	(91,187)	(93,113)
Total, net	21,347	23,856
Identified intangible liabilities (included in deferred revenue):
Gross amount	237,388	273,902
Accumulated amortization	(207,941)	(238,541)
Total, net	$ 29,447	$ 35,361