Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Financial Assets And Liabilities Measured At Fair Value
Marketable securities	$ 34,166	$ 31,522
Interest rate cap (included in other assets)	17
Total assets	34,183
Liabilities measured at fair value	0	0
Carrying Reported Amount Fair Value Disclosure [Member]
Assets
Cash Equivalents	300,193	184,796
Liabilities
Mortgages Payable	1,033,541	1,049,959
Leasing commissions (included in amounts due to Vornado)	41,197	42,924
Total liabilities not measured at fair value	1,074,738	1,092,883
Estimate Of Fair Value Fair Value Disclosure [Member]
Assets
Cash Equivalents	300,193	184,796
Liabilities
Mortgages Payable	1,029,000	1,072,000
Leasing commissions (included in amounts due to Vornado)	41,000	43,000
Total liabilities not measured at fair value	1,070,000	1,115,000
Fair Value, Inputs, Level 1 [Member]
Financial Assets And Liabilities Measured At Fair Value
Marketable securities	34,166	31,522
Interest rate cap (included in other assets)	0
Total assets	34,166
Fair Value, Inputs, Level 2 [Member]
Financial Assets And Liabilities Measured At Fair Value
Marketable securities	0	0
Interest rate cap (included in other assets)	17
Total assets	17
Fair Value, Inputs, Level 3 [Member]
Financial Assets And Liabilities Measured At Fair Value
Marketable securities	0	0
Interest rate cap (included in other assets)	0
Total assets	$ 0