Fair Value Measurements (Financial Assets and Liabilities Not Measured at Fair Value) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Carrying Amount
Assets
Cash equivalents	$ 393,070	$ 263,688
Liabilities:
Mortgages payable (excluding deferred debt issuance costs, net)	1,164,544	974,836
Level 1 | Fair Value
Assets
Cash equivalents	393,070	263,688
Level 2 | Fair Value
Liabilities:
Mortgages payable (excluding deferred debt issuance costs, net)	$ 1,130,000	$ 974,000