Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Financial Assets And Liabilities Measured At Fair Value
Marketable securities	$ 43,191	$ 44,646
Short-term Investments	0	24,998
Interest rate cap (included in other assets)		11
Total assets	43,191	69,655
Liabilities measured at fair value	0	0
Carrying Reported Amount Fair Value Disclosure [Member]
Assets
Cash Equivalents	226,476	111,590
Liabilities
Mortgages payable (excluding deferred debt issuance costs, net)	1,059,587	1,032,780
Estimate Of Fair Value Fair Value Disclosure [Member]
Assets
Cash Equivalents	226,476	111,590
Liabilities
Mortgages payable (excluding deferred debt issuance costs, net)	1,054,000	1,025,000
Fair Value, Inputs, Level 1 [Member]
Financial Assets And Liabilities Measured At Fair Value
Marketable securities	43,191	44,646
Short-term Investments		24,998
Interest rate cap (included in other assets)		0
Total assets	43,191	69,644
Fair Value, Inputs, Level 2 [Member]
Financial Assets And Liabilities Measured At Fair Value
Marketable securities	0	0
Short-term Investments		0
Interest rate cap (included in other assets)		11
Total assets	0	11
Fair Value, Inputs, Level 3 [Member]
Financial Assets And Liabilities Measured At Fair Value
Marketable securities	0	0
Short-term Investments		0
Interest rate cap (included in other assets)		0
Total assets	$ 0	$ 0