Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Financial Assets And Liabilities Measured At Fair Value
Marketable securities	$ 43,287	$ 43,191
Liabilities measured at fair value	0	0
Carrying Reported Amount Fair Value Disclosure [Member]
Assets
Cash Equivalents	224,600	226,476
Liabilities
Mortgages payable (excluding deferred debt issuance costs, net)	1,057,032	1,059,587
Fair Value, Inputs, Level 1 [Member]
Financial Assets And Liabilities Measured At Fair Value
Marketable securities	43,287	43,191
Fair Value, Inputs, Level 1 [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Assets
Cash Equivalents	224,600	226,476
Fair Value, Inputs, Level 2 [Member]
Financial Assets And Liabilities Measured At Fair Value
Marketable securities	0	0
Fair Value, Inputs, Level 2 [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Liabilities
Mortgages payable (excluding deferred debt issuance costs, net)	1,045,000	1,054,000
Fair Value, Inputs, Level 3 [Member]
Financial Assets And Liabilities Measured At Fair Value
Marketable securities	$ 0	$ 0